Cover Image

PART III
Fault diagnosis


and repair modules




E




MODULE 5.0


Common procedures for fault
diagnosis and repairs


a. Problem diagnosis, or trouble-shooting


Method
Trouble-shooting is a procedure of observation, then
making suitable tests to either eliminate, or confirm,
a suspect section of equipment. As the area under
examination is reduced by further tests, it becomes
easier to locate the actual problem.


Note. With any trouble-shooting technique, it is not
necessary to approach a problem from any specific
direction or set of rules. Rather, you should first
observe, consider a possibility and then devise a test
to check that assumption.


Consider which items are quick or easy to check.
This can save time if first carried out.When a problem
occurs, record how the equipment was used just before
the problem occurred. This allows a similar procedure
to be used as a test, in case the symptoms of the
recorded problem are not easily reproduced.


During the process of locating the cause of a
problem, record the tests or checks made, and the
results.This will provide a valuable record if it becomes
necessary to ask advice from the service department.


Typical problems
● Operator error.
● Equipment incorrectly calibrated.
● Faulty connecting plugs, sockets, or cables.
● A safety interlock is preventing equipment


operation.
● Electrical or electronic failure.
● High-tension cable or X-ray tube failure.
● Mechanical problems.
● Alignment adjustments.


Observation of a problem
This is important, especially at the time a problem
occurs. Possibilities that may be observed are:


● Is there an operator error?
● A burning smell? Where does it come from?
● Is there an increase in temperature? For example:


—The X-ray tube housing has become very hot to
touch.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


65


Aim


The aim is to provide information for common proce-
dures involved in diagnosing or repairing a problem.
Most of these procedures are applicable to all of the
fault diagnosis and repair modules.


Objectives


On completion of this module the student will be
able to:


● Adopt a systematic approach to fault diagnosis,as an
introduction to the modules for individual equipment.


● Be aware of methods for locating broken wires, and
faults in plugs and sockets.


● Test and replace a fuse with a suitable replacement.


Task 8, ‘Fuse identification’, should be attempted on
completion of this module.


Contents


a. Problem diagnosis, or trouble-shooting
i. Method.
ii. Typical problems.
iii. Observation of a problem.
iv. Equipment manuals.
v. Request for assistance.


b. Safety first
c. Locating bad connections


i. Typical areas.
ii. Locating a broken wire or bad connection.
iii. A plug or socket may have a fault.
iv. Power plug connections.


d. Is a fuse open-circuit?
i. Indications and tests.
ii. Fuse locations.
iii. Why has a fuse failed?
iv. Removing and replacing a fuse.
v. Common fuse types.
vi. Circuit breakers.
vii. Selecting a replacement fuse.
viii. Special fuses for high frequency generators.




—A lock coil, in the area where a burning smell is
observed, is very hot to touch.


● Unusual sound. What sort of sound? Where from?
● Absence of sound. For example:


—No anode rotation noise from the X-ray tube.
—Ventilation fans are quiet


● Wrong mechanical operation.Look for obstructions,
or loose sections. For example:
—An indicator knob on a control panel has slipped


into a wrong position.
—A film is jammed in the processor.


● Visual observation. For example:
—Appearance of the film immediately as it leaves


the processor.
—Smoke rising from equipment, or a HT cable end.


Equipment manuals
Should be referred to whenever there is a problem.The
operation manuals often include a section on fault or
problem symptoms, as do the installation or service
manuals.The spare parts illustrations can help find the
physical positions of parts, such as locating a fuse in
equipment.


If during maintenance or other events manuals
appear to be missing, replacements should be
obtained as soon as possible. Quite often, service engi-
neers attending your equipment will also require these
manuals. If not available, this could lead to delays in
correcting a problem.


Request for assistance
When requesting advice from the service department,
the following information may be required.


● Hospital name, address, fax, and phone number.
● Who to contact at the hospital when discussing


the problem. Include the department and phone
number.


● Department and room number for equipment
location.


● Make and model number of equipment.
● A description of the problem. Include any


symptoms.
● What tests have been made, and the results.
● Are you asking for advice, or is this a direct request


for a service call?
● If a request for a service call, is an order number


available?
● Any conclusions that were made regarding the


cause of the problem, or what will be needed to
correct the problem.


If the request is made via e-mail or by fax, then this
information should always be included. If the request


is made via a phone call, having the information avail-
able will save time.


A record should be kept of service department
address details.This should include the address, e-mail,
phone, and fax numbers. Where a service engineer is
assisting with advice, include the engineers name and
contact details.


A sample service request form is provided in appen-
dix ‘C’ page 177.


b. Safety first


Before investigating a possible fuse or wiring
problem, always ensure power is turned off and
unplugged from the power point. If the equip-
ment is part of a fixed installation, besides
switching the generator power off, ensure the
isolation power switch for the room is also
switched off.


With battery operated mobiles, ensure the
battery isolation switch is in the off position. If
this cannot be located, contact the service
department for advice before proceeding.


c. Locating bad connections


Typical areas
● The generator handswitch cable.
● The connecting cable to the collimator.
● The fluoroscopy footswitch for a fluoroscopy table.
● Plugs or sockets used with mobile or portable X-ray


equipment.
● Power plugs.
● Plugs or sockets for tomographic attachments.
● Cables, which are pulled or twisted.


Locating a broken wire or bad connection
● Remove the cover from the plug or socket, and


check if wires have broken away from the contact
pins.


● Wires can break inside a cable.This will occur where
there is a lot of twisting or stretching. For example,
a handswitch cable.


● Note. Some wires may seem intact, but can be
broken a short distance from a connection point.
This is difficult to see, as the wire is covered by the
plastic insulation.


● A simple test is to give a gentle to firm tug to a
suspect wire. If a particular wire appears to stretch,
compared to other wires, it is probably broken


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


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inside the insulation. However, this test is not reli-
able, as a break can occur in another position.


● A multimeter should be used to give an accurate
test of a suspect connection or broken wire.
i. Select the low ohms position of the multimeter.
ii. Connect the two probes together. The scale


should read less than 1.0ohm. If using an ana-
logue meter, adjust the zero-ohms knob on the
meter, so the meter needle is on the zero
position.


iii. Record the minimum value that was indicated
when the probes were touched together.


iv. Connect the meter probes at the two ends of
the wire being tested.The meter should indicate
less than 2.0ohms above the value previously
recorded with the probes connected together.


v. A broken wire in a cable may have a partial con-
nection, and cause an intermittent fault. Give
the cable under test a tug or twist while watch-
ing the meter. If the meter flickers or indicates
a changing value while the cable is moved, the
wire is faulty.


Check for a faulty handswitch, or handswitch cable.


Caution.
Ensure the generator is switched off, and the
room power isolation switch also turned off. If
this is a mobile or portable generator, ensure it
is switched off, and the power cable unplugged
from the power point.


● This test should be performed with the assistance
of an electrician or electronics technician.


● Make a diagram, so that when the handswitch is
disconnected or unplugged, it can be correctly
reconnected.


● A multimeter is required, set to the low ohms posi-
tion.Check that the meter indicates zero ohms with
the meter probes touching together.


● Open the hand switch assembly, and identify the
terminals of the suspect switch. With the meter
probes touching the switch terminals, operate the
switch.The meter should indicate zero ohms.Repeat
this test for other switches in the handswitch.


● Identify the connecting wires between the switch
terminals and the other end of the handswitch
cable.With the meter connected to each end of the
cable wires, the meter should indicate less than
2.0ohms. When making this last test, if at first
you have a good result, test again by tugging on the


connecting lead, and also move the cable in differ-
ent positions.


● If there is a broken wire in the handswitch cable,
this often occurs close to the handswitch, and
sometimes where the cable enters or is attached to
the control desk.


● To look for a broken wire, cut open the cable outer
insulation to expose the internal wires. Commence
where the cable enters the handswitch, and con-
tinue about 15cm down the cable. Test individual
conductors by giving a firm pull. If a broken wire
is found, shorten the cable past the bad section,
and reconnect to the handswitch. The entire cable
should be replaced as soon as possible, in case of
other partially broken wires.


● The above procedures should be repeated for all the
switches in a handswitch assembly.


A plug or socket may have a fault
This can occur due to:


● A pin or contact has moved out of position.
i. This is due to bad assembly during manufacture.


However, the plug or socket may have consider-
able use before this fault occurs.


ii. Remove the back of the plug or socket
assembly.


iii. Locate the wire attached to the pin or contact.
iv. Try pushing it firmly back into position. If it sets


in place and will not move with a gentle to firm
tug on the wire, all is well.


v. If the pin or contact is not firmly attached, then
remove it and look for bent ‘hooks’ on it.
Straighten these out, so that when reinserted
they will keep the pin or contact in position.


● The contacts of a socket may have become
enlarged,and not provide a reliable or good contact.
i. The contact can be adjusted by pushing the


sides of the contact closer together. A useful
tool is a large sewing needle.


ii. Care must be taken not to damage the contact.
iii. This problem may occur where plugs and


sockets have had a lot of use. For example, with
a portable X-ray generator.


Power plug connections
The wires connected to the power plug terminals can
become loose.This can cause arcing, and may cause a
fuse to become open circuit.


The wires must be held securely inside the plug. If
the cable is pulled, this should not pull the wires from
the plug terminals. If the plug does not have a suit-
able method to prevent this from happening, then
replace the plug with an improved type.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


67




If wires have pulled loose from a power plug, this
may be due to a previous incorrect assembly.
Have the connections checked by an electrician
or electronics technician. This is to ensure the
active and neutral wires are connected to the
correct positions on the power plug, and, most
important, correct connection of the earth or
ground wire.


While wire colours now conform to interna-
tional standards, older equipment may use non-
standard colours. If this is found, have the power
cord replaced by an electrician.


d. Is a fuse open-circuit?


Indications and tests
● Some glass fuses can visually show if they are open


circuit by metal deposited on the glass. If the failure
is a small break in the wire, this is not easy to see.


● Fuses may have fine wire, again not easy to see,
so it may appear open circuit, but still be in good
condition.


● A continuity test with a multimeter is the only reli-
able way of verifying if a fuse is good or open circuit.
The meter is set to the low ohms range. If the meter
shows no indication when the probes are attached
to the fuse, the fuse is open circuit.


● Do not try to test a fuse with a meter while it is
still connected in the equipment, this can give a
false result.


Fuse locations
The physical location of fuses will vary greatly depend-
ing on the manufacturer and model of equipment.
Electrical regulations in many countries require a fuse
to be protected from access without using a tool.
Where fingers may be able to unscrew the cap of a
fuse holder, a protective cover must first be removed.


Possible fuse locations are:


● X-ray generator, fixed installation. There will not be
any external access fuses. Most fuses will be located
in the control cabinet, and a panel will need to be
removed to gain access. In some cases, there may
be additional fuses under a cover at the HT
transformer.


● Note. In some installations miniature circuit break-
ers may be fitted instead of fuses.These have a reset
switch, or button, mounted on top of the device.


● Mobile or portable X-ray generators can have exter-
nal access fuses mounted on a rear panel. Other-
wise internal access to the equipment is required.


● The Bucky table may have an external access fuse
panel on one side, or else on the side of a small
control box. Otherwise, a panel may have to be
removed to gain access.


● The vertical Bucky and stand may have a small
power supply box for magnetic locks.This may have
external access to a fuse, or require removal of the
box cover.


● The fluoroscopy table may have external access
power fuses located at the table foot. There will be
additional fuses inside the control cabinet, or inside
electronic control boxes placed on the table body.


● A floor-ceiling tube stand can have a small power
supply box mounted at the top of the column. This
usually has external access to the fuses.


● A ceiling suspension tube support may have exter-
nal access to the fuses. In most cases a panel cover
will need to be removed.


● The operation or installation manuals often show
the location of fuses. The parts manual will also
indicate fuse positions, however the diagrams can
be very complex. Otherwise, contact the service
department for advice.


Why has a fuse failed?


● There is a fault. The fuse has blown to protect the
equipment.There will often be a heavy metal deposit
on the glass. On replacing the fuse, the new fuse will
also fail.


● There was a temporary fault caused by a power
surge.


● There is no fault. The fuse has become ‘fatigued’ or
‘tired’. This sometimes happens. If a glass fuse, the
wire may show a small broken section.


● An incorrect fuse was previously fitted. For example,
a 5A fuse fitted where a label indicates a 7.5A fuse.
This may have been a temporary replacement,
however first contact the service department for
advice.


● When a blown fuse is found, contact the service
department for advice. Give full details of the fault
symptoms, fuse number or identification, and posi-
tion in the equipment.


Removing and replacing a fuse
Never attempt to remove or replace a fuse unless all
power is switched off, and where applicable, unplugged
from the power point. In an X-ray room, also turn off
the main power isolation switch.


There are a large variety of fuse holders. Some types
are listed below.


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


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● The fuse is held between two spring clips.
i. Remove by pushing or lifting first at one end. If


trying to prise out by lifting in the middle, some
glass fuses may break.


ii. When re-inserting a fuse, the spring clips should
have a positive grip. If not, remove the fuse,bend
the clips inwards a little, and then reinsert the
fuse.


● The fuse is in a container, totally enclosing the fuse.
i. The front appears as a small square.There is no


screwdriver slot. In this case there should be a
small gap under the square front. Pushing a
small screwdriver into this gap will release the
catch, allowing an internal spring to push the
fuse out.


ii. There is a round cap, similar to a large version
of a toothpaste tube cap. Grip with the fingers,
and turn anticlockwise to undo.


iii. Two versions may have a screwdriver slot. One
version has a bayonet catch. To remove, first
push inwards with a screwdriver, then rotate
anticlockwise a quarter turn.This should unlatch
the top. In the second version, this is a simple
threaded type. Undo with a screwdriver, turning
anticlockwise.


Common fuse types
Fuses come in a great variety of styles, shapes
and sizes. Most common are the larger 3AG sizes,
6 ¥ 32mm, and the smaller M205 size, 5 ¥ 20mm.
The fuse may have a glass or ceramic body.


Of the above fuses, there are two main types.


● General-purpose fuse.
i. The element is normally a straight piece of wire,


or a thin metal strip.
ii. European fuses may have ‘MT’ marked on one


end.
● Slow blow or delay fuse.


i. These fuses are designed to allow a short high
surge current. This allows for the momentary
peak current demand from motors, transformers,
or power supplies, when first switched on.


ii. The element appears as a piece of wire,
attached to a spring.


iii. Another version has a wire, similar to a general-
purpose fuse. However, the wire has two small
metal beads spaced along the fuse wire.


iv. European fuses may have ‘T’marked on one end.


Circuit breakers
Circuit breakers may be fitted instead of fuses. In most
cases they are designed to handle large currents, such
as the main power supply to an X-ray generator. In
some cases, small circuit breakers are also fitted
instead of standard 5A or 10A fuses.


If a circuit breaker has tripped, the switch at the
front of the circuit breaker may be half way between
the ‘off’ and ‘on’ positions. To reset, push the switch to
the off position, then back to the on position.


Caution: Circuit breakers, like fuses, should only be
reset after the supply power is switched off.


Selecting a replacement fuse
Providing the fuse has the same rating and charac-
teristic, a ceramic fuse may be replaced with a glass
fuse.


If a fuse of the correct current rating is not avail-
able, then a smaller rated fuse might sometimes be
substituted as a temporary replacement, providing it
is close to the original value. Eg, a 2.5A fuse might
substitute for a 3A fuse. In case a delay fuse is not
available, a standard fuse of the same rating may be
tried as a temporary replacement. Do not substitute a
delay fuse for a standard fuse.


Special fuses for high-frequency generators
These are very large fuses, sometimes rated up to
200amps, for use in the inverter. The fuse may be a
long, large diameter cartridge fuse, seated in heavy-
duty brass clips; or else a large ceramic type, retained
by a nut and bolt. While inverter fuses can fail due to
fatigue, or a temporary problem due to X-ray tube
instability, there could be a semiconductor failure in
the inverter.


● Only an electrician or electronics technician should
attempt to test or replace an inverter fuse.


● Before replacing the fuse, a test for a possible short
circuit in the inverter should be made.


● Caution: High residual voltages can be present in
the power supply capacitors.


● Always consult the service department for advice
before attempting to test or replace an inverter
fuse. The service department may require specific
tests to be made before replacement, otherwise
further damage could occur.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


69




TASK 8


Fuse identification


You have been supplied with a mixed selection of fuses.


● What is the current and voltage rating of each fuse?
● Are any of these fuses a ‘delay’ or ‘slow blow’ version?


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


70


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Fuse No Voltage Current Delay fuse?


1


2


3


4


5


6


One or two of these fuses may be faulty. Test the fuses, using a multimeter. Use the instructions provided in
module 8.0


Were any of these fuses faulty? Indicate which fuse No.


Was there any difficulty in using the multimeter?


Tutor’s comments


Satisfactory/Unsatisfactory


Signed Date


Tutor




MODULE 6.0


X-ray generator:
Fixed installation


Task 9.‘No Preparation, Part 1’ and task10.‘No Prepa-
ration, Part 2’, should be attempted after section one
of this module.
Task 11. ‘No Exposure’, and task 12. ‘X-ray output lin-
earity’, should be attempted after section two of this
module.


Contents


Section 1: No preparation
Part 1. Nothing happens.
Part 2. Is there a bad connection or fuse?
Part 3. Warning signals due to a fault con-
dition.
Part 4. X-ray tube tests.
Part 5. Other tests.


Section 2: No radiographic exposure
Part 6. Operation tests.
Part 7. No mA or kV.
Part 8. High-tension problems.


(Note: Reference module page numbers refer to the
title page.)


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


71


Aim


The aim is to provide information and procedures for
diagnosing, or repairing, a problem with an X-ray gen-
erator.The generator is installed as a fixed installation
in an X-ray department. Flow charts are provided to
indicate logical steps, when diagnosing a problem.


Objectives


On completion of this module, the student will be able
to carry out a set of procedures to locate a problem
area in the generator. This will allow minor repairs to
be carried out. An electrician or electronics technician
may also provide assistance. Otherwise an accurate
description of the problem can be provided to the
service department, if requiring advice or direct
assistance.


This module is divided into two sections. The first
section looks at problems that occur during prepara-
tion for an exposure.The second section looks at prob-
lems affecting an exposure, after preparation for an
exposure has been completed.


Section 1: No preparation


This section examines a number of situations where
the generator prepares for an exposure. Before the
control system will permit preparation to begin,
the generator makes a number of safety tests. Once
the generator enters into the preparation mode, more
tests are made.When all tests are satisfied, the control
system signals ready for an exposure.There are a total
of five parts, each with an associated flow chart.
Study each flow chart first, and then read the text for
additional information.


Part 1. Nothing happens


Refer first to the flow chart, Fig 6–1 page 75, ‘Unable
to obtain preparation, part one’.


On attempting to have the control prepare for an
exposure, nothing happens. There is no sound of X-ray
tube anode rotation. At the end of the normal prepa-
ration time, there is no sign the generator is ready for
an exposure.


Are there any warning lights on
the control panel?
The warning light could indicate a fault in the gener-
ator, or else an operator error. In some systems there
may be two warning lights, one for incorrect setting
of the X-ray control, and the other for a fault in the
generator.


In the case of a warning light indicating wrong
exposure factors, this could be due to:




● The kV set for the exposure is above the maximum
X-ray tube rating. Reduce the kV setting.


● The kV is below the minimum kV specified by
radiation regulations. Increase the kV setting.


● The mA selection is too high for the required mAs.
Select a lower mA position, and a longer exposure
time.


● The combination of a high value of mA, and a low
value of kV. This could overheat the X-ray tube
filament. Either increase kV, or else select a lower
value of mA and increase the exposure time.


● With some generators, selecting a very short expo-
sure time combined with a low mA will prevent
operation. For example, if the limit is 0.5mAs, then
500mA at 0.001 second is accepted. However, if
250mA is selected, then the minimum exposure
time becomes 0.002 second.


● The X-ray control microprocessor has calculated
the amount of heat in the X-ray tube anode from
previous exposures. A further exposure would cause
the anode heat capacity to be exceeded.Wait a few
minutes for the anode to cool down.


● Note. Most X-ray controls, which calculate total
anode heat, display the result on the control panel.
This may take the form of a number, or a bar graph.
In other cases a small symbol indicates excessive
anode heat.


Does the control panel display a message,
instead of a warning light?
Modern microprocessor-controlled generators can
have special display modes to indicate problems or
operator error. Compared to a single indicator light,
these systems give increased information.For example:


● A direct message ‘Reduce mAs’ appears on the
control panel. This direct type of message might be
displayed with microprocessor-controlled genera-
tors, together with a plasma or liquid crystal display
panel.


● The kV display does not show the required kV.
Instead a code E2 appears in the kV display.This is
another way a microprocessor-controlled generator
may indicate an error.


● The operation manual has a list of the codes and
what they mean. In this case E2 could mean ‘Set
kV is too high’. Codes are used to also indicate fault
conditions. A code F3 could mean the generated
mA exceeded the calibration limit during the previ-
ous exposure. If a fault code appears, consult the
service department for advice.


● The actual code numbers, where they appear on the
control panel, and their meanings, depend on the


make and model of equipment. Only some X-ray
controls have these features.


Does resetting the exposure factors turn off
the warning light?
● If the warning light does not turn off, go to part


three.
● If the warning light is off, then test again for prepa-


ration. If preparation can now be obtained, all is
well. Otherwise continue with ‘Other basic checks’.


Other basic checks
● Is a suitable technique selected? For example, if the


fluoroscopy table is selected instead of the table
Bucky, handswitch operation may not be permitted.


● Is a suitable focal spot selected? If the exposure
factors were suitable for the large focal spot, select-
ing the small focal spot with the same exposure
factors could prevent operation.


● Check all other settings. If unsure of their correct
use or position, please refer to the operation
manual, or contact the service department for
information.


● Was an Automatic Exposure Control (AEC) in use for
the last exposure? The AEC may have generated an
inhibit signal. Disable the AEC and try again.


● Does the X-ray room have a door-open safety switch
or ‘interlock’? The operation of this switch may be
faulty.
i. When the door is closed,can you hear the switch


operate? In this case, it is probably ok.
ii. If no indication is heard, check the switch


operation with a multimeter.
iii. Ensure all power is turned off, including the


room power isolation switch.
iv. Set the multimeter to the low ohms position.


Connect the probes together. The meter should
indicate close to zero ohms.


v. With the probes connected to the switch con-
tacts, test the switch operation by opening and
closing the door.


Can preparation now be obtained?
If the answer is yes, the problem is solved. Otherwise
continue with part two.


Part 2. Is there a bad connection or fuse?


Refer first to the flow chart, Fig 6–2 page 76, ‘Unable
to obtain preparation, part two’. In this situation, the
tests indicated in part one have been completed. No
warning lights or error codes are displayed on the
control panel.


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Is there a fault with the handswitch?
● Listen at the X-ray tube while an assistant presses


the preparation button. Is there any sound of
anode rotation, or other noise, from the X-ray tube
when the button is pressed? If there is, then the
handswitch is ok. Proceed to part four.


● On pressing the preparation button, can you instead
hear a relay operate in the generator control
cabinet? If so, the hand switch is not at fault.
Proceed to part four.


Check for a faulty preparation switch,
or handswitch cable
● First ensure the generator is switched off, and the


room power isolation switch also switched off.
● This test should be performed with the assistance


of an electrician or electronics technician.
● To test the handswitch or cable, refer to module 5.0


page 65.
● If there was no problem found with the handswitch,


or handswitch cable, proceed to part 5.


Part 3.Warning signals due to a fault condition


Refer first to the flow chart, Fig 6–3 page 77, ‘Unable
to obtain preparation, part three’.


In this situation,a warning light or code may appear
immediately the generator is switched on, or else
during the last exposure. The checks indicated in part
one have been performed. Operator error or incorrect
exposure settings are not the cause of the problem.


A warning light or code appears when
switched on
This indicates a serious fault condition. If a code or
message is displayed, refer to the operation manual
for its meaning. If the code indicates an operator or
setting error, then recheck the tests carried out in
part one. Otherwise contact the service department.
Provide details of the fault code, and any other symp-
toms that were observed.


● A fuse may have failed, or a circuit breaker tripped.
i. Before opening any panels to check a fuse,


always ensure the equipment is switched off, and
the room power isolation switch also turned off.


ii. Procedures for testing or replacing a fuse, are
described in module 5.0, page 65.


iii. If a fuse is open circuit, or a circuit breaker
has tripped, consult the service department for
advice regarding the possible cause.


● Is the mains power supply voltage too low? Or is
one phase missing? This could happen after a storm
or power failure.
i. If the generator has a manual adjustment for


the mains voltage, check and make sure it is set
correctly.


ii. Other generator designs have automatic
compensation for changes in supply voltages.
Depending on the design, the mains voltage may
have changed outside the adjustment range of
the automatic compensation. Ask an electrician
to check or measure the supply voltage.


iii. A three-phase generator may still switch on with
only two phases of the mains supply available.
Some designs have a fault detector in case this
happens.Ask an electrician if there is a problem
with the hospital power.


A warning light or code appears
during preparation
If a code or message is displayed, refer to the opera-
tion manual for its meaning, or contact the service
department. Provide details of the fault code, and any
other symptoms that were observed.


● Does the warning light appear immediately on
pressing the preparation switch? This may indicate
a serious problem with the X-ray tube filament
control section of the generator.Contact the service
department before proceeding.


● In case the warning light occurs during or just at
the end of preparation, this may indicate a filament
connection problem, or failure to pass the anode
rotation safety test. Proceed to part four. Otherwise
contact the service department for advice.


● Did the warning light operate during the last expo-
sure? This can indicate an over current (mA) situa-
tion. Over-current may be caused by instability in
the X-ray tube, or else a fault in the HT cable or
cable end.
i. Try resetting the fault detection by switching


the X-ray control OFF then ON again. Then try
to obtain preparation.


ii. If preparation can now be obtained, go to
part 8.


iii. If preparation still cannot be obtained, proceed
to part four, or contact the service department
for advice.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


73




Part 4. X-ray tube tests


Refer first to the flow chart, Fig 6–4 page 78, ‘Unable
to obtain preparation, part four’. There are no warning
lights or message codes. On attempting preparation,
some sound was observed at the X-ray tube. This
indicates the preparation handswitch is ok. During
preparation the X-ray control applies a test for anode
rotation,and minimum filament current in the selected
focal spot. There may be a problem with anode rota-
tion, or else a poor connection to the X-ray tube
filament.


Does anode rotation appear normal?
This should be the normal sound of the anode accel-
erating to the required preparation speed. Instead it
may be just a buzzing or humming noise. The possibil-
ities are:


● One of the three conductors for the X-ray tube
stator is broken or has a bad connection.
i. Check the stator cable where it enters the X-ray


tube housing.
ii. Does the cable show signs of being pulled or


stretched? A wire may have been pulled away
from a terminal.


iii. Before checking any connections, always ensure
the equipment is switched off, and the room
power isolation switch also turned off.


iv. Some x-ray tube housings have a plug and
socket for the stator cable connection. Has this
become loose, or is there a bad connection to
the plug or socket terminals?


● The X-ray tube itself is faulty, either with seized
bearings, or else with broken glass. If the glass is
broken, the anode may appear to rotate slowly, and
very quickly come to a stop when the preparation
switch is released.


● Is there oil leaking from the X-ray tube housing? An
arc may have occurred during the last exposure,
causing internal damage.


● Is there an open circuit fuse, or tripped circuit
breaker, supplying power to the X-ray tube starter?
This can be a common problem with some high-
speed starters.
i. Before opening any panels to check a fuse,


always ensure the equipment is switched off,
and the room power isolation switch also turned
off.


ii. If unsure where such a fuse or circuit breaker
may be located, contact the service department
for advice.


iii. If the fuse is faulty, take care to replace with
the correct size and type. See module 5.0 page
65.


iv. Examine the stator cable where it enters the X-
ray tube housing. If there is a possibility the
cable has been pulled, remove the cover plate
and check the connections for a possible short
circuit.


v. If on restoring power, or attempting preparation
again, the fuse blows, then stop, and contact the
service dept.


Is the focal spot filament connected?
During preparation the X-ray control tests for a
minimum filament current. This test is only to
ensure the filament is intact, and is at a minimum
temperature.
Note. This test does not ensure the correct mA will be
generated. A poor HT cathode-cable connection can
cause a drop in the required filament current, but still
be above the minimum value for the filament current
test. See part seven, ‘No radiographic exposure’.


● The selected focal spot may be open circuit, or have
a bad connection. Try obtaining preparation with
the other focal spot.


● There may be a bad connection to that focal spot
due to a bad HT cathode-cable cable-end pin con-
nection. There are three pins on the cable end. If
there is a bad connection at the centre pin, this will
affect both focal spots.
i. Before proceeding, ensure all power is switched


off.
ii. To check, undo the cathode cable-end retaining


ring nut. Partly withdraw the cable end about
2~4mm, then reinsert the cable end. Replace
and firmly tighten the cable-end ring nut.


iii. Test for preparation. If moving the cable end
has cleared the preparation problem, the cable
end will require further attention. This involves
removal of the cable end, cleaning the cable-end
pins, and re-sealing. For this procedure, see
module 7.3 page 117.


iv. Caution. The cable end may have silicon grease
as insulation instead of anti-corona silicon pads.
Removal of the cable end by more than 2~4mm
can reduce the effectiveness of the insulating
grease. As a precaution, do not exceed 100kV
until the cable end is re-sealed with fresh silicon
grease, see module 7.3 page 117.


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


74


E




PART III. FAULT DIAGNOSIS AND REPAIR MODULES


75


Fig 6–1. Unable to obtain preparation, part one


Are there any
warning


indications?


Is this fault code
or a message?


Look in the operation manual
for the meaning of the


message code. If necessary,
contact the service


department.


Proceed to part three.
See text for other possible


areas to be checked.


Has the warning
light turned off?


Can preparation
be obtained now?


Has a suitable
technique been


selected?


Select a correct
technique


End


Proceed to part two for further
tests.


Is a suitable tube
or focal spot


selected?


Select a suitable
tube or focal spot.


On attempting to obtain
preparation, nothing at all


happens


End


End


Yes


No


Yes


Yes


Yes


Yes


No


No


No


No


No


YesIs there a 'door
open' safety
interlock?


End


No


No


Yes


Yes


Check the door-open safety
switch. Make sure it is operating
properly when the door is closed.
See the text for a test procedure.


Can preparation
now be obtained?


Check setting of exposure factors
for possible X-ray tube overload
protection. Include check of focal
spot selection, and minimum KV




X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


76


E


Fig 6–2. Unable to obtain preparation, part two


On attempting to obtain
preparation, nothing appears to
happen. There are no message


codes or warning lights.


End


On pressing the
prep' button, can
you hear a relay


operate?


Power off. Disconnect the
handswitch cable from the control


desk. With a meter, test for
brocken wires or a faulty switch.


Preparation IS being attempted.
Proceed to part four.
Refer also to the text.


No


Yes


Power off. Turn isolation switch
off. Remove control cabinet


cover, and check for a possible
blown fuse. Refer to module 9
first for precautions in testing


or replacing a fuse.


Is there a faulty
fuse, or tripped
circuit breaker?


Refer to module
9.0 to replace a


fuse.
Contact service


before attempting
replacement.


Proceed to part five.
(See text for other possible


areas to be checked)


Yes


Yes


No


No


No


Yes


Listen at the
X-ray tube. Is


there any sound
on prep'?


Is there a broken
wire or faulty


switch?


Repair the broken wire in the
handswitch cable, or replace the


faulty preparation switch.




PART III. FAULT DIAGNOSIS AND REPAIR MODULES


77


Fig 6–3. Unable to obtain preparation, part three


On attempting to obtain
preparation, nothing appears to
happen. There is a permanent


message code or warning light.
The procedure in part one has


been carried out. Operation error is
not the cause of the problem.


No


Yes


Yes


Did the warning
fault light operate


immediatly on
power up?


This may be a serious fault.
Contact service for advice before


proceeding. Provide details of
tests carried out.


Did the
warning light


operate immediatly
after or during the


last exposure?


No


Yes


Contact service. Give full details
of the problem, and conditions


when the warning light operates.


Proceed to 'No exposure part 7'
Reduce kV to 60kV before


attempting another test
exposure.


No


Did the warning
fault light operate
when attempting


preparation?


Yes


No


This may be a serious fault.
Contact service for advice before


proceeding. Provide details of
tests carried out.


See the text for possible causes


See the text for possible causes


Can preparation
now be


obtained?


There may have been a high
tension fault, or excessive mA.


Switch power OFF then ON
again. Test if preparation can


now be obtained


There may be a blown fuse or
tripped circuit breaker.
Contact service before


proceeding.




X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


78


E


Fig 6–4. Unable to obtain preparation, part four


On attempting to obtain
preparation, nothing appears to
happen. There are no warning


lights or message codes. However
some sound was observed at the


X-ray tube. This indicates the prep
handswitch is functioning.


No


Yes




Listen carefully at the X-ray tube
during preparation.


Contact service
before proceeding.


Try a test exposure with selection
of a different focal spot. (eg, if on


broad focus, try fine focus).


Was a broken
wire or bad
connection


found?


Contact service
before proceeding.


End


Undo the ring nut holding the
cathode cable in place. Withdraw


the cathode cable a few
millimeters only and re-insert.


NOTE, do not attempt if this is a
CD mobile.


The cathode cable end has a bad
pin connection. See module 11.3,


High tension cable.


Can preparation
now be obtained?


Contact service
before proceeding.


Can preparation
now be obtained?


There is a strong possibility that
the other focal spot is faulty. Do
not use that focal spot. Contact


service and ask for advice.


As the HT cable end has been
disturbed, refer module 11.3,


High tension cable, before
continuing to use the generator.


End


Yes


No


Yes


Yes


No


No


No


Yes


Are there any
signs of an oil


leak?


Does the X-ray
tube anode appear
to rotate normally?


Switch off. Turn the isolation
power switch off. Locate the stator
connection cable to the tube stand.
Check carefully for signs of a bad
connection or broken wire in the


cable to the X-ray tube.




Part 5. Other tests


Refer first to the flow chart, Fig 6–5 page 79, ‘Unable
to obtain preparation, part five’.


There remain two possibilities to be checked.


● The wiring to the X-ray tube stator or the housing
over-temperature switch is broken or has a bad
connection. This could occur where it enters the X-
ray tube, or where the cable has received a lot of
flexing or twisting. See module 7.1 page 104.


● There may be an internal fault or problem in the
generator, but the warning light is also faulty or
burnt out. Test the light by setting very high expo-
sure factors, which would normally cause a tube
overload condition. If no warning light illuminates,
then the globe or control circuit is faulty.


● Include the results of all tests, when requesting help
from the service department.


Section 2: No radiograph exposure


This section assumes you are able to obtain prepara-
tion, the control has indicated preparation is com-
pleted, and is ready for an exposure. On attempting
to obtain an exposure, nothing happens. Or else, the
control appears to expose, but the film is blank or very
light. Each part has an associated flow chart. Refer to
these flow charts before reading the text.


Part 6. Operation tests


Refer first to the flow chart, Fig 6–6 page 83, ‘No expo-
sure, part six’.


The control has indicated it is ready for an exposure.
On attempting to obtain an exposure, nothing appears
to happen.There is no sound from the Bucky.The expo-
sure light does not operate.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


79


Fig 6–5. Unable to obtain preparation, part five




No


YesWas a wiring break or bad
connection


found?


Check carefully all wiring to the
X-ray tube. Especially check for
a break in the stator cable, or to


the over-temperature safety
switch.


End


Can preparation
now be obtained?


Yes


No


Repair the break in wiring or
loose connection. If a faulty
temperature switch, make a
temporary bypass for testing


purposes.


Was there a
faulty


over-temperature
switch?


Yes


No


It is possible there is faulty or
burnt out warning light. Test by
selecting a very large mA, kV
and time setting. See if the
overload light does illuminate.
Advise the service department of
the results of this test, in addition
to all other tests and
observations.


On attempting to obtain
preparation, nothing appears to
happen. There are no warning


lights or message codes. No sound
was observed at the X-ray tube.


The hand switch and cable tests ok
There are no open circuit fuses or


circuit breakers.


Contact the service department
for advice, and to obtain a new


over-temperature switch or
sensor.


Continue to operate the system
with caution. Monitor the X-ray
tube housing, and stop using if


hot to touch.




Operation tests
● Check the technique selection to ensure a valid


operation. Look for selection buttons or switches
that are sticking, and may not have properly
operated or released.


● Is an Automatic Exposure Control (AEC) in
operation?
i. The warning light or signal with the AEC reset


button may have failed. Press reset and try
exposing again.


ii. Have you selected the correct AEC mode for the
particular Bucky or technique?


iii. Disable AEC operation, select suitable manual
exposure factors, and attempt another
exposure.


iv. If you can now expose, continue using the
system with AEC switched off. For AEC tests, see
module 10.0 page 140.


● Select the direct, or non-Bucky, handswitch tech-
nique.Try again to expose. If successful, consider the
following.
i. First ensure all power is turned off, including


the room power isolation switch.
ii. There is a possible open fuse or circuit breaker


suppling power to the Bucky. If found faulty,
check the wiring to both Bucky’s before replac-
ing the fuse. There may be loose connections,
causing a short circuit. A film marker may have
fallen onto electrical connections in the vertical
Bucky.


iii. Similar to the above, there may be a loose or
broken connection to a particular Bucky. This is
most likely to occur at either a plug or socket,
or else at the Bucky terminals on the side of the
Bucky.


iv. The grid may have become dislodged, stopping
operation of the grid drive motor. A common
cause is poor attachment of lead numerals to
the cassette. When the cassette and tray is
inserted, these catch on the grid, dislodging it.


v. Some older Bucky’s have small motor drive
gears.These gears may be damaged.As a result,
although the motor operates, the grid does not
oscillate or move to the expose position.


vi. In the case of a vertical Bucky, a lead numeral
may become dislodged, and fall into the drive
motor area. This could prevent operation, or
cause a short circuit.


vii. For other problems with the Bucky, refer to
module 8.0 page 121.


● Does the X-ray room have a safety ‘Door closed’
interlock? This may, depending on installation
methods, interrupt preparation if the door is


opened, or simply prevent an exposure. When the
door is closed, can you hear the switch operate? If
so, it is probably ok.
i. If no indication is heard, check the switch


operation with a multimeter.
ii. Ensure all power is turned off, including the


room power isolation switch.
iii. Set the multimeter to the low ohms position,


and check the meter shows minimum ohms with
the probes connected together.


iv. With the probes connected to the switch con-
tacts, test the switch operation by opening and
closing the door.


● Can you hear a relay operating on pressing the
expose switch? If so, the switch and connecting
cable are properly working.


● If the handswitch is suspect, then the switch and
connecting cable should be checked with a multi-
meter set to the low ohms scale.
i. Ensure all power is turned off, including the


room power isolation switch.
ii. If available, request an electrician or electronics


technician to assist.
iii. Use the method described in part two of this


module. ‘Check for a faulty preparation switch,
or handswitch cable’. See module 5.0, page 65.


Part 7. No mA or kV


Refer first to the flow chart, Fig 6–7 page 84 ‘No expo-
sure, part seven’.


On attempting to obtain an exposure, the film was
blank, or very under exposed. The control indicates
preparation is completed and ready for an exposure.
The exposure indication operates on pressing the
expose position of the handswitch.
There is no warning light or fault indication during the
attempted exposure.


Check the cathode cable connection
A bad cable-end connection in the X-ray tube cathode-
receptacle is a common cause of light or blank films.
This occurs where the cable-end pins fit into the recep-
tacle. For example: Sufficient current flows through
the filament to satisfy the generator tests during
preparation. However the filament temperature is too
low for the required mA. A test exposure should be
tried first on the other focal spot.However, if the cable-
end centre pin has a bad connection, this can affect
both focal spots.
Note. During an exposure, if there is low, or no mA,
then the actual kV can rise above the set value of kV.


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


80


E




As a result, a microprocessor-controlled generator may
display ‘kV too high’ as a fault message, instead of ‘low
mA’. Always select low mA and kV for test exposures.


● To check for a poor cable end connection.
i. Ensure all power is switched off, before any


adjustment is made to the HT cables.
ii. To check, undo the cathode cable-end retaining


ring nut. Partly withdraw the cable end about
2~4mm, then reinsert the cable end. Replace
and firmly tighten the cable-end ring nut.


iii. Caution. The cable end may have silicon grease
as insulation instead of anti-corona silicon pads.
Removal of the cable end by more than 2~4mm
can reduce the effectiveness of the insulating
grease. As a precaution, do not exceed 100kV
until the cable end is re-sealed with fresh silicon
grease. See module 7.3 page 117.


● Try a test exposure after adjusting the cathode
cable end. If the test exposure is OK, there was a
poor pin connection at the cable end.The cable-end
pins need to be cleaned and adjusted. See module
7.3 page 117.


● If the test exposure still fails after adjusting the
cathode cable-end, try exposing again on the other
focal spot. If the exposure is now OK, the first focal
spot may have a fault. This is caused by;
i. The filament has a short circuit to the focus cup.


Only part of the filament is heated.
ii. The filament is able to pass the ‘open circuit’


safety test in preparation, but the actual mA on
exposure is less than half the expected value. In
this case, the X-ray tube requires replacement.


iii. To inspect the filament, see module 7.1 page
104.


iv. Unfortunately, this type of fault is not uncom-
mon. The problem occurs when the filament
bends, and touches the focus cup during prep-
aration. This causes the filament to become
welded to the focus cup, shorting out a section
of the filament.


v. Contact the service department for advice.


Has an inverter fuse failed?
If a trial exposure on the other focal spot also fails,
this may be due to no high voltage. With high fre-
quency generator systems, a common cause is an open
circuit inverter fuse. This often fails due to fatigue, or
a temporary fault with the inverter. Depending on the
make or model of generator, there may be no warning
signal, or message, to indicate high-voltage failure.


● First ensure all power is turned off, including
the room power isolation switch.


● Before attempting to test or replace the fuse,
contact the service department for advice. As
well as the fuse location, special test precau-
tions can apply before and after replacement.


● Checking or replacing the fuse, should only be
performed by an electrician, or electronics
technician.


● See module 5.0 page 65.


i. Before attempting to test the fuse, measure the
primary power filter capacitors, and ensure the
residual voltage is at a safe level.


ii. If the fuse is open circuit, check the inverter
SCR or power transistors for a possible short
circuit, before replacing the fuse.


iii. After the fuse is replaced, examine the power
circuit for charging the capacitors on initial
power up. There is normally a resistor in series
with each phase to limit the charging current.
These resistors are shorted out by a contactor
after a few seconds time delay. This circuit
needs to be disabled so the resistors remain in
operation.


iv. On power up, monitor the voltage on the capac-
itors to ensure they are in fact charging nor-
mally.This ensures there is no undetected direct
short circuit in the inverter.


v. A short test exposure at low kV and mA should
be attempted. If OK, then switch off, and restore
the operation of the charge current-limit resis-
tors to normal operation.


Other possible causes for no exposure
● A faulty fuse or connector in the generator control


cabinet.
i. Ensure all power is turned off, including the


room power isolation switch.
ii. With the aid of an electrician or electronics


technician, look for an open circuit fuse, or
tripped circuit breaker.


iii. Look for loose plugs and sockets, or other
connectors.


● Look for damage caused by rats eating the wiring.
This can especially apply inside cable ducts, or
cables to the HT transformer. Some species of rats
can bite through cables, or a wiring harness, as if
their teeth were cutting pliers.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


81




Part 8. High-tension problems


Refer first to the flow chart, Fig 6–8 page 85, ‘No
exposure, part eight’.


On attempting to obtain an exposure, the film was
blank, or very under exposed. The control indicated
preparation was completed, and ready for an exposure.
The exposure indication operates on pressing the
expose position of the handswitch,but only a very short
exposure results.


A warning light or error message is generated
during, or at the end of exposure.


Record the exposure factors, focal spot, and tech-
nique in use. Include any fault codes or error messages.


Check for a high-tension fault
The cause of the problem may be due to:


● No kV was generated. The inverter fuse is open
circuit in a high frequency generator. See part
seven.


● A kV fault. Caused by a short circuit in the HT cable
or cable end.


● A high voltage arc in the high-tension generator,
cables, or X-ray tube housing.


● An unstable X-ray tube, due to gas. This can gener-
ate a kV or mA fault indication. Instability can occur
if a high kV exposure is made, after using the tube
for a long time at a medium or low kV output.


● A kV fault can be caused if mA is too low. For
example, due to a bad connection in the cathode
cable end, or a partial short circuit in the X-ray tube
filament.


● The mA output has exceeded the correct value.
For example, although 200mA was selected for an
exposure, the mA increased to over 300mA. This
could be due to a fault in the mA regulation circuit,
a high-tension fault, or an unstable X-ray tube.


Check for a HT cable fault
HT cable faults normally occur at the X-ray tube end,
due to the HT cable twisting as the tube is positioned.
Arcing can also occur where the cable ends plug into
the X-ray tube, due to a fault in the insulation grease.


● Was a ‘bang’ heard during the exposure?
● Check for a burning or acrid odour at the HT cable


ends. If not sure, undo the retaining ring nut,‘sniff’,
and then replace the ring nut.


● If at all uncertain of the condition of the HT cable
ends, refer to module 7.3 page 117.


● Caution. Do not make this test on a CD mobile,
unless the capacitor is fully discharged. See module
6.2 page 94.


● If the HT cable or cable ends appear OK, then
attempt a test exposure at low output.
i. Caution. If the fault occurred below 80kV, do


not test further without advice from the service
department.


ii. Select a low kV and mA output. A suggested
exposure is 60kV, 100mA, for 0.1 seconds. Close
the collimator and make a test exposure.


iii. If the control is fitted with an mA or mAs meter,
observe the meter carefully during the test
exposure.


iv. If the mA meter needle moves very quickly, or
the mAs meter indicates 20% more than the
expected value, this can indicate a high tension
fault.


v. Should the generator fail a test at 60kV, stop.
There is a possible fault at the HT cable ends,
these should now be removed and carefully
examined. See module 7.3 page 117.


vi. Caution. Before removing the cable ends,
contact the service department for advice.
Include the exposure factors, focal spot, and
any error codes or messages.


Test the X-ray tube high-tension stability
If the test exposure at 60kV is ok, then test the X-ray
tube at higher kV.


● Do this by applying the seasoning procedure,
described in module 2.1 page 48. When applying
this procedure, take care to observe the HT cable
at the X-ray tube, in case an arc occurs.


● Observe the mA meter (if available). An unstable
tube can indicate an increase of mA when test
exposures are first made, then return to the correct
value after a few exposures at the same kV. Then
when kV is increased, the first exposure may again
show an increase of mA, returning to the correct
value after the second or third exposure.


● In case any unusual occurrence takes place, im-
mediately stop. HT cable or cable-end faults will
become apparent at higher kV values. If not fully
checked before, do so now. See module 7.3 page
117.


● Caution. Before removing the cable ends, contact
the service department for advice. Include the
exposure factors, focal spot, and any error codes or
messages.


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


82


E




● If the HT cable ends have been fully checked, then
start the seasoning test again, starting at 10kV
below the level where a problem occurred. Should
the problem still occur, then stop. Consult the
service department for advice.


● Providing the X-ray tube passes the seasoning test,
all is well.


● Make an entry in the logbook. Include a description
of the problem, together with the tests and results.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


83


Fig 6–6. No exposure, part six


On attempting to obtain an
exposure, NOTHING happens.
The 'expose' indicator does not
operate. The control indicates
preparation is completed, and


ready for an exposure.


YesCan you now
obtain an
exposure?


The AEC has generated a
'Lockout' from a previous


exposure. Reselect AEC and
press 'Reset'. Try another


exposure.


Providing a definite relay 'click'
is heard inside the control, the


handswitch is OK. Otherwise still
test the handswitch.


Yes


No


No


Turn AEC (if in use) to 'OFF'
position. Then try exposing again


Can you now
obtain an
exposure?


The AEC had generated a
'Lockout'. Check for a faulty


'Reset' or 'Low Exposure'
warning light. Increase exposure
factors. (kV, mA ,or max' Time)


No


Yes


There is a problem with the AEC.
Refer to the text for further


information.
Select direct handswitch


operation. EG, Non-Bucky.
Try exposing.


Can you now
obtain an
exposure?


Yes
The Bucky failed to operate. or
return the exposure signal. See
the text for possible reasons.


(Bad connection? Grid is stuck?)




Can you hear any
relay 'click' on


trying to expose?


Is the expose
switch or cable


faulty?


Repair the cable, or replace the
switch. See the text for details.


EndEnd


Test the " Door Open" switch
for correct operation


Is the switch
faulty?


Replace the faulty switch.
If not available , connect a


temporary bypass to place out
of action.


Have the switch replaced as soon
as possible


Yes


No


No


No No


See text for other possibilities.
See also 'No exposure' part 7


Contact service.


Yes


Yes


Test the expose switch for faulty
operation, or broken wire to the


handswitch. Is there a 'Door Open'
safety switch for the X-ray


room ?




X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


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Fig 6–7. No exposure, part seven


On attempting to obtain an
exposure, the film is blank,


(or very under exposed.)
The exposure indicator operates.
The control indicated preparation


was completed, and
ready for an exposure.


No


YesDoes a warning fault light operate
when trying to


expose?


Can you now
obtain an
exposure?


Contact the service
department for advice


No


Undo the cathode cable end
retaining ring nut, withdraw the
cable end about 2~4mm, then


reinsert and tighten the retaining
nut.


Can you now
obtain an
exposure?


Yes
There may be a poor filament


connection for both focal spots.
Another possibility is a partially
shorted focal spot. See the text


for furthur suggestions.


No


See 'Unable to obtain exposure'.
Part eight.


The cable end will need to be
removed, have the contact pins
cleaned and adjusted. Refer to


module 11.3, high tension cables.


Try exposing on the other
focal spot.


Yes


There is probably a failure to
generate HT. If a high frequency


generator, the fuse for the
inverter may be open circuit.




PART III. FAULT DIAGNOSIS AND REPAIR MODULES


85


Fig 6–8. No exposure, part eight


On attempting to obtain an
exposure, the film is blank,


or very under exposed.
The exposure indicator operated.
The control indicated preparation


was completed, and
ready for an exposure.


Yes


Do the cable
ends appear


OK?


Refer to module 11.3
High tension cables.


No


Try the ageing procedure
described in module 5.1


for the X-ray tube.


Is the test
exposure OK?


Are the test
exposures OK?


The X-ray tube may have failed.
There may be arcing in the HT


cable receptacles. See the text for
other possibilities. Call the


service dept for advice.


End


No


Yes


No


Yes


In this situation, a light indicates
a fault. If a microprocessor


controlled system, there may be a
message or error code.


Select low kV (60kV or less)
and a low mA station.
Try a test exposure.


Observe the cable ends for
possible smoke or arcing noise.


This may indicate a high tension
fault, an unstable X-ray tube,


or excessive mA.
Before proceeding, check for a
burning smell at the X-ray tube


HT cable ends.




TASK 9


No preparation
Part 1


You have a patient on the table. After instructing him to ‘take a deep breath and hold it’, you press the prepara-
tion button. However, the ‘ready to expose’ signal does not occur.


What action should be taken first?


Make a list of your tests and observations.


What do you think is the cause of the problem?


What action may be taken to correct the problem?


Tutor’s comments


Satisfactory/Unsatisfactory


Signed Date


Tutor


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


86


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TASK 10


No preparation
Part 2


The X-ray control does not provide the ‘ready for exposure’ signal after pressing the preparation switch. You have
just completed a previous check for a similar report, and taken action that should have corrected the problem.
However, while there are now ‘signs of response’ when the preparation button is pressed, the ready for exposure
indication still cannot be obtained.


What was the previous observed problem, and action taken?


Make a list of your further tests and observations.


What do you think is the cause of this problem?


What possible actions may be taken to correct the problem?


Tutor’s comments


Satisfactory/Unsatisfactory


Signed Date


Tutor


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


87




TASK 11


No exposure


You have positioned a patient on the upright Bucky to take a chest exposure.You place the generator into prepa-
ration, and press the exposure switch when the control indicates ‘ready to expose’. However, no exposure occurs.
After removing the patient, you investigate for a possible cause of the problem.


Make a list of possible reasons for this problem.


Describe suitable tests to either confirm, or eliminate, possibilities from this list.


Carry out these tests. What were the results?


What action is needed to correct the problem?


Tutor’s comments


Satisfactory/Unsatisfactory


Signed Date


Tutor


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


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TASK 12


X-ray output linearity


You have a report of ‘light’ films occurring in room 2. This appears to happen only on selection of fine focus.
Devise a test, using the stepwedge, to check the exposure linearity between the fine and broad focus selections
of mA.


Which exposure factors will be used for your generator?


After carrying out the above test, you find the 100mA station has reduced output. A comparison test of 50mA
and 200mA indicates correct results. What is the most likely cause?


What are two other possible reasons for light films on this 100mA station?


Give reasons why these possibilities are low, considering that 50mA and 200mA indicated normal results.


Make another series of stepwedge tests. This time remain on the mA station that produced a low output. Make
a series of four test strips, and increase kV by 2.0kV for each exposure. What increase of kV was required to
increase density by one step?


Your test was first carried out at 80kV.You find that if kV is increased by 4.0kV, the density steps on the 100mA
test strip are darker than the test trips for 50 or 200mA stations. In terms of a 5% permitted kV error, would
the test result be:


OK? Marginal? Outside acceptance?


Tutor’s comments


Satisfactory/Unsatisfactory


Signed Date


Tutor


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


89




MODULE 6.1


Mobile or portable X-ray
generators


a. General precautions


● Before removing any covers, or testing any wires or
connections:
i. Ensure the system is switched off, and un-


plugged from the power point.
ii. Mobile high-frequency generators may be bat-


tery operated. The batteries in these are con-
nected in series, and may have a total voltage
of up to 240V DC. Refer to the operating or
installation manuals for the position of the
battery isolation switch, and ensure this is
switched off before removing the covers or
testing wires and connectors.


iii. Do not attempt to replace the batteries if a
mobile has more then two 12V batteries. Ask
for assistance from an electrician or electronics
technician.


● If removing a collimator or X-ray tube on a mobile
generator.
i. Do not rely on the vertical lock system.
ii. Ensure the suspension system is at the limit of


its maximum vertical travel.
iii. Or, attach a rope so that the system cannot


move upwards, once the weight of the collima-
tor or X-ray tube is removed.


● When replacing a motor drive battery.
i. Remove your wristwatch if it has a metallic


band.The same precaution extends to any rings.
While 12 volts, or even 24 volts, is too low to
cause a serious shock, the battery can cause
serious burns if a short circuit occurs across a
watchband or ring.


ii. Disconnect first the battery terminal that con-
nects to the mobile body or framework.This pre-
vents the danger of accidentally shorting the
other battery terminal to the mobile body.


iii. In the case of multiple battery systems, refer
always to the operation or installation manuals.
In some cases, the batteries will have the centre
connections between two batteries connected to
the mobile body. These connections should be
removed first,and replaced last. It is advisable to


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


90


E


Aim


The aim is to provide information related to servicing
or repairing a mobile or portable X-ray generator. This
information is additional to that provided for a fixed
installation described in module 6.0 page 71.
Note. Capacitor discharge mobiles are discussed in
module 6.2 page 94. Reference module page numbers
refer to the title page.


Objectives


On completion of this module, the student will be
aware of common problems with mobile or portable
X-ray generators.When used together with the module
6.0 procedures, the student will be able locate a
problem area, and carry out minor repairs. An electri-
cian or electronics technician may provide added
assistance where indicated in this module.


Contents


a. General precautions
b. Transport problems
c. The generator will not switch on
d. No preparation or no exposure
e. The generator appears to expose, but film is blank
f. Collimator light-beam alignment keeps changing
g. The magnetic locks sometimes do not work, or are


weak in action
h. Problems with the motor drive




request the aid of an electrician. If in any doubt,
contact the service department for advice.


b.Transport problems


Mobile and portable equipment are subject to addi-
tional problems due to transport. Portable equipment
may be dropped, while mobile generators may pass
over severe bumps while travelling.There are also prob-
lems due to dust, or corrosion due to high humidity.
This last can occur if the system is used in an air-
conditioned area, then parked in a general area which
is not air conditioned.


c.The generator will not switch on


● Check the power cable.
i. Is the power point faulty? Check by plugging


a lamp or other suitable item into the power
point.


ii. Is there a broken connection at the power-
cable plug? Important, check also the earth
connection.


iii. The power cable may plug into a socket on a
portable generator. In this case check the gen-
erator socket connections as well as the cable.


iv. The power cable-reel for a mobile can have
broken wires or faulty contacts in the mecha-
nism. If faulty, have an electrician connect a
temporary power cable directly into the mobile,
while waiting for a replacement.


v. If there is a bad connection to a power plug or
socket, this should be checked and repaired by
an electrician.


vi. For information on locating bad connections,
see module 5.0 page 65.


vii. Moving the mobile while still plugged into a
power point is not recommended.


● Check for a blown or faulty fuse. See module 5.0
page 65.


● The power on/off switch is faulty. Check for loose
connections. Test the switch operation with a mul-
timeter set to the low ohms range. Ask an electri-
cian or electronics technician for assistance.


d. No preparation or no exposure


Note. The following checks are to be made with all
power disconnected. If a battery operated high fre-
quency system, ensure the battery circuit breaker or
switch is opened.


● Look for possible blown fuses. See module 5.0 page
65.


● Check the hand switch, and handswitch cable. See
module 5.0 page 65.


● Check all external plugs and sockets. See module
5.0 page 65.


● Look for dislodged components internally, or poor
connections.


● Plugs and sockets can develop poor connections
due to build up of oxides, or else slight corrosion of
the plating. Check by unplugging and reconnecting
the plugs and sockets.
i. This procedure should only be carried out by an


electrician or electronics technician.
ii. Printed circuit board edge connectors are


subject to corrosion and poor connections,
especially older types that are not gold plated.
Later model generators use plugs and sockets
for the printed circuit boards.


iii. Ensure the generator is unplugged from the
power point.


iv. Before removing a printed board, touch the
main metal framework of the generator. This is
to discharge any static electricity from the body.
This is very important if working in a carpeted
area, or there is low humidity.


v. Only remove and replace one board at a time.
Take careful note of its position, so the board is
not replaced the wrong way.


vi. On removal of the printed board, clean the edge
connectors with a cloth dampened with a little
alcohol, or methylated spirits. After cleaning, do
not touch the contacts with your fingers.


vii. Printed circuit boards may become cracked,
breaking some of the tracks. For example, if
equipment was dropped. Examine with a mag-
nifying glass for this possibility. If there are signs
of corrosion, it is possible some of the tracks on
the board have become open circuit.This can be
a problem near the sea.


● Have any relays become dislodged? Move them
slightly in their sockets in case of a bad socket
connection.


● Bad contacts on control switches etc.
i. A build up of dirt on switch contacts can cause


excessive wear, and poor contact operation. In
most cases, spraying with a suitable contact
cleaner will restore normal operation.


ii. An optimum spray is one designed to clean and
lubricate. CRC 2.26 is recommended. WD-40 is
less optimum, but may also be used. Your elec-
trician may have a suitable contact cleaner.


iii. Before spraying, cover adjacent areas with cloth
or tissues to protect from unwanted spray.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


91




iv. Note. Never use any spray on electrical equip-
ment while it is energized.


● The X-ray tube head, or housing. (An X-ray ‘tube
head’ combines the X-ray tube, and the high-tension
transformer, in one housing.)
i. Check all connections to the X-ray tube head.
ii. For mobiles with a conventional X-ray tube


housing, check the stator cable.
iii. The HT cable may have a poor connection to the


X-ray tube cathode. For test procedures, see
module 7.3 page 117.


e.The generator appears to expose,
but film is blank


● Ensure the collimator opened correctly. Look inside
the collimator for loose or disconnected parts, due
to vibration in transport.


● Was an unusual noise or arcing heard during the
attempted exposure?
i. With conventional X-ray tube housings, check


the HT cable ends for arcing. See module 7.3
page 117.


ii. If a rotating anode tube, does it slow down
quickly when preparation is released? The tube
may be broken, and the anode is now immersed
in oil.


iii. By rotating the X-ray tube head or housing, can
you hear oil moving inside the housing? This can
indicate a broken tube.


iv. See also module 7.1 page 104.


f. Collimator light-beam alignment
keeps changing


● Parts of the collimator may have become loose due
to transport vibration. Remove the collimator cover,
and check for loose sections.


● For adjustments to the collimator, see module 7.2
page 110.


g.The magnetic locks sometimes do not work,
or are weak in action


There are two types of electromagnetic locks. Older
types require power to operate. Later types have a
permanent magnet, and require power to remove, or
cancel, the magnetism.


● The lock sometimes operates, depending on the
tube stand movement.
i. There may be a poor connection to the lock coil


or the lock switch.


ii. The mechanical position of the lock coil has too
large an air gap.Adjust the position for a smaller
air gap, with the lock in the off position.


iii. There is a build up of dirt, or oil, on the lock-coil
pole-piece. A thin piece of cardboard soaked in
methylated spirits is a good cleaning aid. Place
the cardboard between the pole-piece and the
brake plate. Energise the lock, while slowly
pulling the cardboard out from between the
lock and the brake plate. Repeat this a number
of times, until fresh sections of cardboard show
no smudges of dirt from this wiping action.


● The lock does not energise. (Old type.) Or does not
release. (Permanent magnet type.) Check for the
following.
i. The lock switch may be faulty.
ii. Look for an open circuit fuse.
iii. A broken wire to the lock coil.
iv. The lock coil itself may be open circuit. Test by


disconnecting one wire, then with a multimeter
set to a medium or high ohms scale, check for
continuity of the lock coil. If necessary, request
assistance from an electrician.


h. Problems with the motor drive


Many mobiles are fitted with battery-powered motor
drives. A 12 volt car battery is most commonly fitted,
and in some cases two batteries to provide 24 volts.


Caution
Battery powered high-frequency generators operate
the motors from the same high voltage supply used to
power the high-frequency inverter. Due to the high
voltages that may be present, do not remove the
covers, or attempt any internal adjustment. This
should only be attempted by an electrician or elec-
tronics technician, under instructions from the service
department.


● There is no motor drive in either direction.
i. Units fitted with a drive control key switch.


The switch may be faulty, or have a loose
connection.


ii. The fuse for battery power is open circuit.
iii. The battery is discharged.
iv. There is a bad connection to the battery termi-


nal. Remove the battery terminals, and scrape
corrosion from the posts or terminal clamps.


v. Caution. See part a, general precautions, before
disconnecting a battery.


vi. The brake release bar on the handle operates a
microswitch. The microswitch may need adjust-
ment to operate correctly.


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


92


E




vii. Check the electrical cables for loose plugs or
sockets.


● There is no forward motor drive.
i. The anti-crash bumper may be stuck in the


operated position, or one of the switches oper-
ated by the bumper is damaged.


● There is only a low level of motor drive assistance.
i. The motor may be in bedside mode. A con-


trol switch selects the change between bedside
speed, and travel speed.The control switch could
be faulty, or the knob has slipped, and indicates
the wrong position.


ii. Other mobiles require the tube stand to be
placed in the travel position before permitting
full power. In which case a microswitch to sense
the tube stand position may need adjustment.
Ask an electrician or electronics technician to
check the switch, or microswitch operation.


iii. New mobiles have microcomputer control of the
motor power. Some systems allow the opera-
tor to change the amount of power assistance.
Refer to the operation manual to adjust the level
of motor power.


iv. There may be a poor battery connection due to
corrosion. Remove the battery terminal clamps,
scrape of any corrosion, and reassemble.


v. Caution. See part a, general precautions, before
disconnecting a battery.


● The battery is not charged up.
i. The battery was not charged overnight. Or the


power point used was faulty. Check the power
point with a lamp or similar item.


ii. The power cord used for battery charging has
a bad connection. Have an electrician repair
the connection. (Do not move the mobile while
plugged into a power point.)


iii. There is an open circuit fuse, in the battery
charge section of the mobile. To check a fuse,
see module 5.0 page 65.


iv. Caution. If this is a battery operated high-
frequency generator, this check should only
be performed by an electrician, or electronics
technician.


● After charging, the battery soon looses power.
i. Has the electrolyte level of the battery been


checked? (This may not be possible with sealed
or low maintenance batteries.)


ii. The battery may have a shorted cell, or the
cells are sulphated, in this case a new battery
is required. Before replacing the battery, have
the battery tested at a garage, or by an auto
electrician.


iii. Caution. See part a, general precautions, before
disconnecting a battery.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


93




MODULE 6.2


Capacitor discharge mobile


a. CD operation modes


Unlike the fixed installation, or standard mobile gen-
erator, the CD mobile has special modes of operation.
This list is provided as a reminder.


● High voltage is applied to the X-ray tube continu-
ously while the capacitor is charged. This includes
the kV remaining after the exposure.


● When not in preparation, the X-ray tube filament
has no pre-heating. There is also a high negative
voltage applied between the cathode cup or grid,
and the filament. Despite these precautions, a very
small electron emission does occur. This is called
‘dark current’.


● To prevent X-ray emission due to dark current,
the collimator has an additional lead shutter. This
shutter blocks all X-ray emission.The shutter moves
out only when the mobile begins preparation, or else
just before the X-ray exposure.


● When in preparation, the exposure is prevented by
the negative voltage applied to the X-ray tube grid.
During an exposure, this voltage is removed, allow-
ing full emission from the cathode. At the end of
the exposure, the negative voltage is again con-
nected to the grid.This shuts off the electron beam
to the anode, ending the exposure.


● Earlier CD mobiles set the exposure as a percent-
age of kV drop during an exposure. Later systems
have an mAs timer.


● The capacitor discharges during an exposure, at the
rate of 1kV per mAs. As a result, the X-ray output
of a CD mobile is not linear. A 20mAs exposure will
not give twice the output of a 10mAs exposure.


b. General precautions


● Before removing any covers, ensure the mobile is
switched off, and unplugged from the power point.


● If removing a collimator or X-ray tube.
i. Do not rely on the vertical lock system.
ii. Ensure the suspension system is at the limit of


its maximum vertical travel.


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


94


E


Aim


The aim is to provide information related to servicing
or repairing a capacitor discharge (CD) mobile. This
information is additional to that provided for a fixed
installation described in module 6.0 page 71, and
mobile generators described in module 6.1 page 90.
(Note: Reference module page numbers refer to the
title page.)


Objectives


On completion of this module, the student will be
aware of common problems with capacitor discharge
mobile generators. When used together with modules
6.0 and 6.1 procedures, the student will be able locate
a problem area, and carry out minor repairs. The
student will also be aware of special precautions when
dealing with the capacitor high-voltage system, where
repairs must only be attempted by an electrician or
electronics technician.


Contents


a. CD mobile operation modes
b. General precautions
c. High-tension cable precautions
d. The mobile does not switch on
e. Unable to charge the capacitor
f. On charging the capacitor, there is a loud ‘bang’
g. Unable to obtain preparation
h. On going into preparation, the capacitor discharges
i. No exposure
j. The kV does not adjust to a lower value
k. Apparently there is an exposure, but the film is


blank
l. On exposing, the exposure continues till the capac-


itor is fully discharged
m. Problems with the motor drive




iii. Or, attach a rope so that the system cannot
move upwards, once the weight of the collima-
tor or X-ray tube is removed.


● When replacing a motor drive battery.
i. Do not attempt to replace the batteries if a


mobile has more then two 12V batteries. Ask
for assistance from an electrician or electronics
technician.


ii. Remove your wristwatch if it has a metallic
band.The same precaution extends to any rings.
While 12 volts, or even 24 volts, is too low to
cause a serious shock, the battery can cause
serious burns if a short circuit occurs across a
watchband or ring.


iii. Disconnect first the battery terminal that con-
nects to the mobile body or framework.This pre-
vents the danger of accidentally shorting the
other battery terminal to the mobile body.


iv. If two batteries are fitted, refer always to
the operation or installation manuals. In some
cases, the batteries will have the centre con-
nection between the two batteries connected to
the mobile body. These connections should be
removed first, and replaced last. It is advisable
to request the aid of an electrician. If in any
doubt, contact the service department for
advice.


c. High-tension cable precautions


Special care is required due to dangerous high voltage
stored in the capacitors. Several of the tests described
involve removing or exchanging the high-tension
cables. This requires taking care to ensure the capac-
itor is fully discharged, before any attempt is made to
remove or adjust the cable ends. Only an electrician,
or electronics technician, should attempt this
procedure.


● If possible, make an exposure to fully discharge the
capacitor, or reset the kV to the minimum level
possible.


● Wait until the kV has dropped to below 5kV, as indi-
cated on the panel meter. If no indication of capac-
itor high-voltage by a panel meter, wait overnight
before proceeding.


● Switch off, and unplug the power cord.
● Open the control panel, and locate the two manual


capacitor-discharge control knobs. These may be
operated by lifting and rotating, and must stay in
the discharge position. If uncertain of their opera-
tion, refer to the installation or service manual for
the mobile. Otherwise contact the service depart-
ment for advice.


● Before operating the discharge knobs, you may
observe two neon lamps glowing. On operation of
the discharge knobs, both of these lamps should
turn off. If one lamp continues to glow, contact the
service department for advice before proceeding.
i. Undo the ring nut holding the cable end in posi-


tion at the X-ray tube receptacle.
ii. Do not remove the cable end, but first inspect


the safety-shield metal braid for damage.Twist-
ing of the cable may have caused it to break,
and become disconnected from the cable end.


iii. If the shield does not appear damaged, then
re-tighten the ring nut so the cable shield is
properly grounded.


iv. Undo the ring nut holding the high-tension cable
in the high-tension tank receptacle. On with-
drawing the cable end, do not touch the pins,
but first short them to the side of the recepta-
cle. This is to ensure any possible charge in the
high-tension cable is completely shorted out.


v. In case the high-tension cable shield appears
damaged at the X-ray tube end, then remove
the cable end from the X-ray tube first. Again,
touch the end pins to side of the receptacle to
discharge any residual high voltage. This will
include any charge in the capacitor as well as
the high-tension cable. Now undo the ring nut,
and remove the cable end from the high-tension
tank.


vi. The above precautions are in case the knobs for
discharging the capacitors have not operated
correctly. In part (iv) only a small spark will
occur if the capacitor was not discharged, but
in part (v) take care, as there may be a very big
spark. Normally, there should be no spark at all.
In case there is, then contact the service depart-
ment before proceeding further.


● When the high-tension cable is removed or re-
placed, the cable ends must be cleaned and re-
sealed. See module 7.3 page 117.


● After replacing or adjusting the high-tension cable,
return the discharge knobs to their normal position.


d.The mobile does not switch on


● Is the power cable faulty?
i. Is the power point faulty? Check by plugging a


lamp or other suitable item into the power
point.


ii. Is there a broken connection at the power-
cable plug? Important, check also the earth
connection.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


95




iii. The power cable-reel may have broken wires or
faulty contacts in the mechanism. If faulty, have
an electrician connect a temporary power cable
directly into the mobile, while waiting for a
replacement.


iv. If there is a bad connection to a power plug or
socket, this should be checked and repaired by
an electrician.


v. For information on locating bad connections,
see module 5.0 page 65.


vi. Moving the mobile while still plugged into a
power point is not recommended.


● Check for a blown or faulty fuse. See module 5.0
page 65.


● The power on/off switch is faulty. Check for loose
connections. Test the switch operation with a mul-
timeter set to the low ohms range. Ask an electri-
cian or electronics technician for assistance.


e. Unable to charge the capacitor


On pressing the charge button, nothing happens. Oth-
erwise all appears normal.


● With power switched off, and the mobile unplugged
from the power point, check the following;
i. Some CD mobiles have the capacitor charge


switch mounted on the hand switch. There may
be a broken wire or a faulty switch.


ii. To check the hand switch or cable, see module
5.0 page 65.


iii. Open the control panel, and check for an open
circuit fuse.At this time also check internally for
loose plugs or sockets, and or loose connections.


iv. Check the wiring to the collimator for broken or
loose connections.


v. Remove the collimator cover. Locate the dark-
current shutter mechanism. Check that the
shutter is in the correct position,and the shutter
microswitch operates correctly.


vi. Have the manual capacitor-discharge knobs
been left in the discharge position, after a
high-tension cable was adjusted? Or, is a micro-
switch, operated by these knobs, sticking? This
will indicate the manual discharger is still
operated, and prevent the capacitor charging.


f. On charging the capacitor, there is
a loud ‘bang’


This indicates a high-tension fault. This could be the
capacitor, but may instead be in a cable end, or
perhaps the X-ray tube.


These tests should only be performed by an elec-
trician or electronics technician.
Refer to (b), ‘High-tension precautions’, before
proceeding.


● Undo the ring-nuts retaining the high-tension
cable-ends in the X-ray tube receptacles. Is there a
strong odour from one of the cable ends?
i. If there is, either the cable end is faulty, or there


has been an arc-over in the receptacle.
ii. With the capacitor fully discharged and safe,


withdraw the suspect cable end. (See part b.
High-tension cable precautions.)


iii. After taking the precaution of shorting the pins
to ground, examine the cable end and recepta-
cle for traces of carbon.An easy way to find con-
tamination of grease etc is to wipe with a paper
tissue.


iv. If there is no indication of arcing inside the
receptacle, but there is a strong odour from the
high-tension cable as it enters the cable end,
the cable is faulty and requires replacement.


v. In case there are signs of arcing in the recep-
tacle, then the receptacle and cable end must
be carefully cleaned, and re-sealed. See module
7.3 page 117.


vi. After a cable end has been withdrawn, it will
need to be re-sealed with fresh grease, or have
new anti-corona pads fitted. See module 7.3
page 117.


● Do the high-tension cables or X-ray tube recepta-
cles appear OK? The capacitors or X-ray tube could
have a short circuit.Contact the service department
for assistance. Provide full details of the fault, tests
made, and the results.


g. Unable to obtain preparation


● Is the capacitor fully charged? Check by pressing
the charge button. Or else by increasing the preset
kV, in which case the charge mode should operate.


● There may be a faulty preparation switch, or a faulty
cable from the handswitch. To check the switch or
cable, see module 5.0 page 65.


● Check the wiring to the X-ray tube and collimator,
especially if it has been subject to pulling. This
includes;
i. Stator cable and connections.
ii. Connections to the thermal overload switch, in


the tube housing.


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● Check for a loose plug or socket. See module 5.0
page 65.


● Look for a loose or open circuit fuse. See module
5.0 page 65.


● Contact the service department for assistance.
Provide full details of the fault, tests made, and the
results.


h. On going into preparation, the capacitor
discharges


The negative control voltage applied to the X-ray tube
grid is missing. As the filament heats up, this results in
an uncontrolled exposure, and may fully discharge the
capacitor. A common cause is a faulty high-tension
cathode cable, with an internal short circuit between
the grid wire, and one of the filament wires. To check
for a possible fault in the high-tension cable, the cables
can be exchanged between anode and cathode. (Of
course, there is a possibility the cables were previously
exchanged, but no record kept of this event.)


This procedure should only be performed by an
electrician, or electronics technician.


Refer to (b), ‘High-tension precautions’,
before proceeding.


● Mark each cable end before removal, to ensure they
are correctly exchanged after being re-inserted.


● Ensure the capacitor is fully discharged, power is
disconnected, and the manual discharge knobs are
in position.


● Undo the ring nuts’ holding the cable ends in posi-
tion, and withdraw the cable ends from the high-
tension transformer. Take note, which receptacle
is positive, and which is negative. The X-ray tube
cathode must connect to the negative receptacle.


● Remove the high-tension cable ends from the X-ray
tube housing.


● For cleaning and resealing the cable ends on rein-
sertion, see module 7.3 page 117.


● Both high-tension cables have now been discon-
nected. Now reconnect the cables to the X-ray tube
and generator. The previous cathode cable is con-
nected to the anode, and the previous anode cable
is connected to the cathode.


● Take care to connect the anode cable to the posi-
tive receptacle, and the cathode cable to the neg-
ative receptacle of the high-tension transformer.


● Power up. Recharge the capacitor and make a test
exposure.


● If all is well, attach a label to the previous cathode
cable. This should indicate it has an internal short
circuit, and is suitable as an anode cable only.


● If the problem still occurs, contact the service
department for assistance. Provide full details of
the fault, tests made, and the results.


i. No exposure


● Does the mobile have a Bucky connection option?
Try exposing with the Bucky option switched off or
bypassed.


● Is the capacitor fully charged? In some designs, if
the capacitor is not fully charged to the required
value, this will prevent preparation. In other systems
it may instead prevent a radiographic exposure.


● Check the operation of the handswitch, or a possi-
ble broken wire in the handswitch cable. To check
the switch or cable, see module 5.0 page 65.


● Check the wiring and connections to the
collimator.
i. Remove the collimator cover and check for


correct operation of the dark-current shutter.
This should move out of the way, either during
preparation, or just before an exposure.


ii. Check the microswitch operated by this shutter.
If sticking, or not fully operated, this may be the
cause.


j.The kV does not adjust to a lower value


For example, after charging the capacitor, you decide
to use less kV for the exposure. However, on trying to
reset to a lower kV, nothing immediately happens,
although the capacitor voltage may very slowly drop
in value.


To reset the kV down to the new setting, the gen-
erator makes a low mA exposure. Radiation is pre-
vented from leaving the collimator by the dark-current
shutter.The shutter also operates a safety microswitch.
This prevents the low mA exposure if the shutter is not
closed.


● Switch the power off, and unplug the power cord
from the power point.


● Remove the collimator cover.
● Check the collimator dark-current shutter for cor-


rect operation.
● Check if the shutter microswitch has operated cor-


rectly, and there are no bad connections or broken
wires to the collimator.


● If the shutter and microswitch appear correct,
contact the service department for advice. Provide
full details of the fault, tests made, and the results.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


97




k. Apparently there is an exposure, but the
film is blank


On exposing, the capacitor voltage drops the expected
amount of kV. For example, the kV dropped by 10kV
after a 10 mAs exposure.


● In this situation, the dark-current shutter has failed
to open properly. Remove the collimator covers and
check the operation of the shutter, and its associ-
ated microswitch.


l. On exposing, the exposure continued till
the capacitor was fully discharged


● The X-ray tube may have become unstable.Try a test
exposure at a much lower kV setting. If successful,
then try the X-ray tube seasoning procedure. See
module 2.1 page 48.


● If a low kV test exposure shows the same fault,
contact the service department for assistance.
Provide full details of the fault, tests made, and the
results.


m. Problems with the motor drive


Some mobiles are fitted with battery-powered motor
drives. A 12 volt car battery is most commonly fitted.
In some cases two batteries are used, to provide 24
volts.


Whenever possible, refer first to the operation
or installation manual. If in doubt contact the
service department, or request the assistance of an
electrician.


● There is no motor drive in either direction.
i. Units fitted with a drive control key switch. The


switch may be faulty, or have a loose connec-
tion.


ii. The fuse for battery power is open circuit. See
module 5.0 page 65.


iii. The battery is discharged.
iv. There is a bad connection to the battery termi-


nal. Remove the battery terminals, and scrape
corrosion from the posts or terminal clamps.


v. Caution. See part b, general precautions, before
disconnecting a battery.


vi. The brake release bar on the handle operates a
microswitch. The microswitch may need adjust-
ment to operate correctly.


vii. Check the electrical cables for loose plugs or
sockets.


● There is no forward motor drive.
i. The anti-crash bumper may be stuck in the


operated position, or one of the switches oper-
ated by the bumper is damaged.


● There is only a low level of motor drive assistance.
i. The motor may be in bedside mode. A control


switch selects the change between bedside
speed, and travel speed.The control switch could
be faulty, or the knob has slipped, and indicates
the wrong position.


ii. Other mobiles require the tube stand to be
placed in the travel position before permitting
full power. In which case a microswitch to sense
the tube stand position may need adjustment.
Ask an electrician or electronics technician to
check the switch, or microswitch operation.


iii. There may be a poor battery connection due to
corrosion. Remove the battery terminal clamps,
scrape of any corrosion, and reassemble.


iv. Caution. See part b, general precautions, before
disconnecting a battery.


● The battery is not charged up.
i. The battery was not charged overnight. Or the


power point used was faulty. Check the power
point with a lamp or similar item.


ii. There is an open circuit fuse in the battery
charge section of the mobile. See module 5.0
page 65.


● After charging, the battery soon looses power.
i. Has the electrolyte level of the battery been


checked? (This may not be possible with sealed
or low maintenance batteries.)


ii. The battery may have a shorted cell, or the cells
are sulphated, in this case a new battery is
required. Before replacing the battery, have
the battery tested at a garage, or by an auto
electrician.


iii. Caution. See part b, ‘general precautions’, be-
fore disconnecting a battery.


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MODULE 7.0


X-ray tube stand


a. General precautions


● Electrical safety.
i. In most installations the tube-stand power will


come from the generator, but in some installa-
tions, switching off the generator does not
remove power from the tube stand.


ii. Before removing any covers, ensure the genera-
tor is switched off, and the room power isolation
switch is also turned off.


iii. This also applies if testing wiring connections, or
electrical components.


● If removing an X-ray tube, or collimator.
i. See module 7.1 page 104, and module 7.2 page


110.
ii. Ask an electrician or electronics technician for


assistance.
iii. Do not rely on the vertical lock system.
iv. Attach a rope so that the system cannot move


upwards, once the weight of the collimator or
X-ray tube is removed.


v. The X-ray tube is heavy. Removal or replacement
requires two people.


vi. Make a diagram of electrical connections.
Attach labels to wires or high-tension cables.
This is to ensure correct connection when an
X-ray tube or collimator is replaced.


vii. Place all screws or other small parts in a box,
so they are not lost.


● Do not place a ladder against a tube stand.The tube
stand may suddenly move.


● An adjustment to any tube-stand bearing requires
skill, and good mechanical knowledge. When a
problem is identified, request the service depart-
ment to make the required adjustments.


b.The vertical movement is not balanced


For example, with the vertical locks off, or if power is
turned off, the tube carriage tends to move down, or
up. This problem may have occurred after fitting a
replacement X-ray tube.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


99


Aim


The aim is to provide information for repairing or
adjusting the tube stand.This is additional information
to the maintenance procedures, provided in module
2.0 page 44. Procedures for electrical tests are pro-
vided in module 5.0 page 65.
(Note: Reference module page numbers refer to the
title page.)


Objectives


On completion of this module, the student will be
aware of common problems with the X-ray tube stand.
When used together with the module 5.0 procedures,
the student will be able identify a problem area, and
carry out minor repairs. An electrician or electronics
technician may provide added assistance where indi-
cated in this module.


Task 13. ‘Bucky tabletop and tube-stand centre’,
should be attempted on completion of this module.


Contents


a. General precautions
b. The vertical movement is not balanced
c. When power is turned off, the tube stand starts


moving
d. The tube stand is not centred to the vertical Bucky
e. Check the tube stand centre stop position
f. Mechanical centre-stop adjustments
g. Electrically operated centre-stop adjustments
h. An electromagnetic lock fails to operate
i. A group of locks fail to operate




● Most tube stands have a system of ‘trim weights’.
Adding or removing these weights balances the
vertical suspension.
i. With ceiling suspensions, these weights may be


positioned inside the cross arm.
ii. Floor ceiling tube stands allow for trim weights


to be attached to the main counterbalance
weight. To gain access, a panel is removed from
either behind the tube stand, or from one side
of the tube stand.


iii. If added trim weights are required, these may
be formed from lead sheet, available from a
builder’s hardware shop.


● Some ceiling mounted tube stands require a spring
to be added or removed to achieve balance. The
service department should make this adjustment.


● Floor ceiling tube stands may have a large spring
instead of a counterweight.The variable ratio pulley
at the top of the tube stand can identify this
method. Final counterbalance may still be achieved
using trim weights attached to the cross-arm.
Otherwise contact the service department.


c.When power is turned off, the tube stand
starts moving


● A common reason is the support method of the HT
cables. Providing the tube stand movement is not
restricted, arrange for added or more suitable HT
cable support.


● With a floor ceiling stand, this may be due to a floor
that is not level. It may be possible to improve by
adding shims under the floor rail. Check the floor
rails with a spirit level.


● With a ceiling mounted system, the ceiling rails may
not be level. This may be due to incorrect initial
installation.There is a possibility the ceiling attach-
ment points have shifted, or a problem with the
building. Check the rails with a spirit level. Depend-
ing on the age or style of construction, have the
installation checked by a building inspector.


d.The tube stand is not centred to
the vertical Bucky


In this situation, the x-ray tube may appear to be cor-
rectly centred to the table centre. However, when the
X-ray tube is rotated, it is not centred to the vertical
Bucky.


● The tube stand may not be vertical.
i. A floor-ceiling tube stand may be checked with


an accurate spirit level. A more accurate check
is to use a plumb bob.


ii. A ceiling mounted tube stand can only be
checked with a plumb bob. With the tube
stand first at lower, then at maximum height,
the plumb bob should deviate by only a few
millimetres.


iii. A ceiling mounted tube stand may need adjust-
ment of the gantry-rail bearings.


iv. The floor-ceiling tube stand has a ceiling or wall
mounted guide rail. Check the guide-rail bearing
assembly. This may be loose or incorrectly
adjusted.


● The cross arm may not be horizontal.
i. This can be a common fault with some floor


ceiling tube stands. Check the cross arm with a
spirit level.


ii. Look for broken or loose bearings, especially
with the cross-arm bearings inside the vertical
movement.


iii. Adjustments to any tube-stand bearings require
specialized knowledge.When a problem is iden-
tified, request the service department to make
the required adjustments.


● Is the light-field vertical alignment correct?
i. Bring the collimator down onto the tabletop. If


necessary adjust the X-ray tube rotation in the
trunnion rings, so it sits ‘flat’ on the tabletop.


ii. Raise the tube a small amount. With the colli-
mator light switched on, place a marker in the
centre of the light field.


iii. Raise the collimator to the normal operating
height. The centre of the light field should stay
on the marker. If not, rotate the tube a small
amount in the trunnion rings, and repeat this
test.


iv. Alignment is correct when the light field does
not shift, as the X-ray tube is raised or lowered.


After checking the first three items, now centre the
light field to the centre of the tabletop. Caution, do
not use the cross arm centre stop as a guide, as this
may also need adjustment.


● If the Bucky table has lateral movement of the
tabletop, the centre stop position of the tabletop
should first be checked.
i. Move the tabletop to the centre position.
ii. Place a cassette in the Bucky, with a marker


positioned on the centre of the cassette.
iii. Place another marker on the centre of the


tabletop.
iv. Make a low kV and mAs exposure. Process the


film.The markers should have the same position
on the film.


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v. If required, adjust the position of the tabletop
centring device. See module 8.0 page 121.


Rotate the X-ray tube to face the vertical Bucky.
Move the tube stand close to the Bucky.The light field
should be centred to the Bucky. Next, move the tube
stand away from the Bucky. Check the position of the
light field.


● Although the light field is not centred to the verti-
cal Bucky, it does not shift as the tube stand moves
away from the Bucky.
i. Was the vertical Bucky positioned correctly


during installation? Attach a string to the far
end of the tabletop, positioned at the centre.
Take the other end of the string to the centre
of the vertical Bucky.


ii. When the string is tightened, it should remain
centred along the full length of the tabletop.


iii. Is the tube stand movement parallel to the
tabletop? The light field should remain centred
while the tube stand is moved from the table
foot end to the table head end. If the light
moves off centre, this could indicate either the
tube stand or the Bucky table was incorrectly
installed


● The light beam shifts off centre, as the tube stand
is moved away from the vertical Bucky.
i. The tube stand cross-arm may not be horizon-


tal. Check with a spirit level.
ii. Many tube stands allow rotation of the cross


arm. (In some cases, the entire tube stand
rotates.) The rotation index-plate may be loose,
or not correctly centred.


iii. Common rotation angles are -90 degrees,
centre, and +90 degrees. A lock pin is inserted
into a slotted index-plate to hold the rotation
position.The index-plate and locking pin may be
worn, or incorrectly adjusted.


e. Check the tube stand centre-stop position


● If the Bucky table has lateral movement of the
tabletop, the centre stop position of the tabletop
should be checked.
i. Move the tabletop to the centre position.
ii. Place a cassette in the Bucky, with a marker


positioned on the centre of the cassette.
iii. Place another marker on the centre of the


tabletop.
iv. Make a low kV and mAs exposure. Process the


film.The markers should have the same position
on the film.


v. If required, adjust the position of the tabletop
centring device. See module 8.0 page 121.


● Is the tube stand centred to the Bucky table?
i. Make this test, after checking the light-field ver-


tical alignment described in part ‘d’.
ii. Move the Bucky tabletop to the centre position.
iii. Switch on the collimator lamp.
iv. Test the lateral centre-stop position of the tube


stand. With the cross-arm retracted, move the
X-ray tube out towards the centre stop posi-
tion. The light field should be centred to the
tabletop.


v. Repeat the test, start with the cross-arm
extended, then move inwards to the table
centre. The light field should again be centred
to the tabletop.


vi. The actual centre stop position can depend on
how quickly the X-ray tube is moved across the
table, and the method used to indicate the stop
position.Depending on the design,accurate cen-
tring may require moving the X-ray tube from
one direction only.


f. Mechanical centre-stop adjustments


● A steel ball, pushed by a spring, clicks into a slot
when the cross arm is centred. This holds the cross
arm in position.


● If the spring is weak, it is difficult to feel when the
centre position is reached.


● There is usually a screw provided, to adjust the
spring tension.Adjust this screw to provide the best
‘feel’ when centring the X-ray tube.


● The centre-stop position is adjusted by changing the
position of the mechanical system on the cross arm.


● To adjust the position, see the directions provided
in the installation manual. Otherwise contact the
service department for advice.


g. Electrically operated centre-stop adjustments


Caution: Before making any electrical tests, ensure the
generator is switched off, and the room power isola-
tion switch is also turned off. An electrician or elec-
tronics technician should carry out electrical tests or
adjustments. See module 5.0 page 65.


A number of different electrical centre-stop sensors
have been developed. These operate the lateral lock
when in position.


● A microswitch, operated by a cam. In normal oper-
ation, you may hear a small ‘click’ as the switch
passes over the cam. The position of the cam con-


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


101




trols the centre stop position. A problem may be
caused by:
i. The cam height is too small. As a result, there


is insufficient pressure on the microswitch for
reliable operation.


ii. The cam or microswitch has become loose, and
the microswitch does not operate.


iii. A broken wire or connection to the microswitch.
iv. A ceiling tube stand may have incorrect adjust-


ment of the lateral movement bearings.This may
cause the cam to move away from the switch,
so it does not operate. In some cases, it may
instead move too close, damaging the switch. A
close visual inspection can indicate if this is a
problem.


● A vane operated sensor. A vane passes through a
small slot in the sensor. The position of the vane
controls the centre stop position.A problem may be
caused by;
i. The vane is positioned too high, and does not


fully enter the sensor. This can cause unreliable
operation.


ii. The vane is missing.
iii. The vane or sensor is damaged. Check by visual


observation.
iv. A broken wire or connection to the sensor.


● An optical sensor, operated by reflected light. This
system requires a white or silvered reflector,
mounted opposite the sensor at the stop position.
A problem may be caused by;
i. The reflector is a small piece of foil, with a self-


adhesive backing.Due to poor adhesive, this may
have become dislodged.


ii. The sensor is not close enough to the reflector
for reliable operation.


iii. The reflector is dirty, or there is dirt on the
sensor.


iv. A broken wire or connection to the sensor.


h. An electromagnetic lock fails to operate


This may be due to a faulty lock coil. Other reasons
may be a faulty switch, or a broken connection due to
a cable being pulled. See module 5.0 page 65.


First ensure the generator is switched off, and the
room power isolation switch is also turned off.


● The lock may have too large an air gap.This can also
cause erratic or slow operation. Most locks have
slotted mounting plates. Adjust by undoing the
screws a small amount, adjust the lock position, and
retighten the screws.


● The lock may only partially release. In this case it
may be too close to the surface. Again, adjust its
position. In some cases, the lock has residual mag-
netism. This can be a design problem with some
tube stands. Contact the service department for
advice.


● Permanent magnet locks have become popular.
These ensure the locks remain on when power is
removed.


● Some ceiling suspended tube-stands use a solenoid
operated ‘piston’, attached via a lever to a brake
pad. A spring maintains brake operation, until the
solenoid operation pulls the pad away from the
surface. If the stroke is too long, the piston fails to
pull inside the solenoid, and the lock does not
release. Adjustment is by a screw thread fitted with
a locknut.


● In some cases, there is a fuse specific to the failed
lock. Before checking fuses, ensure all power is
turned off.


● See Module 5.0 page 65.


i. A group of locks fail to operate


First ensure the generator is switched off, and the
room power isolation switch is also turned off.


● Look for an open circuit fuse at the tube stand.
● In most installations, the tube stand obtains power


from the generator. This may involve several differ-
ent voltage supplies. Check at the generator and at
the high-tension transformer for an open circuit
fuse.


● See Module 5.0 page 65.
● Check where cables enter the tube stand or control


panel. If the cables are pulled during the tube stand
movements, a wire may have broken from a termi-
nal strip.


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


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TASK 13


Bucky tabletop and
tube-stand centre


A number of films have appeared which show incorrect lateral centring. You decide to verify the accuracy of the
X-ray tube and table centre-stop.


1. Design a method to verify the tabletop is accurately centred over the Bucky. Note: this should include possible
errors due to the film position in the cassette.


Carry out this test; include moving the tabletop to centre position from either direction.


Is the tabletop correctly centred to the cassette?


If not, is the cassette tray correctly centred in the Bucky?


Is the crosshair on the collimator faceplate correctly centred to the ‘closed’ position of the collimator leaves?


With the X-ray tube positioned close to the tabletop, is the crosshair aligned to the tabletop centre? Include moving
the X-ray tube to centre position from either direction.


As the X-ray tube is raised from the tabletop, does the crosshair move away from the centre mark?


What adjustment might be made so that the crosshair position does not move as the X-ray tube is raised from
the tabletop?


If this adjustment is performed, will it affect the centre-stop position of the X-ray tube cross-arm?


Tutor’s comments


Satisfactory/Unsatisfactory


Signed Date


Tutor


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


103




MODULE 7.1


X-ray tube


a. General precautions


● Before disconnecting any wires, or removing the
high-tension cables, always ensure power is turned
off and unplugged from the power point. If the
equipment is part of a fixed installation, besides
switching the generator power off, ensure the iso-
lation power switch for the room is also switched
off.


● Mobile high-frequency generators may be battery
operated. The batteries in these are connected in
series, and can have a total voltage of up to 240V
DC. Refer to the operating or installation manuals
for the position of the battery isolation switch, and
ensure this is switched off before removing the
covers, or testing wires and connectors.


● If removing a collimator or X-ray tube from a tube
stand.
i. Do not rely on the vertical lock system.
ii. An X-ray tube is heavy. Two people are required


for removal or installation.
iii. Use a rope to prevent the system moving


upwards, when a collimator or X-ray tube is
removed.


iv. Provide a container to hold all small parts, or
screws. Protect against loss.


● If removing an X-ray tube from a capacitor dis-
charge mobile, observe the high-tension precau-
tions described in module 7.3 page 117.


b. X-ray tube failure modes


● The X-ray tube is unstable. A common cause is gas,
which causes very high current to flow during an
exposure. Unstable operation is usually corrected by
‘seasoning’.This is described in module 2.1 page 48.


● Attempts to improve the performance by seasoning
are not successful. This can be due to;
i. The glass has developed micro-fine cracks.With


the collimator removed, this will be observed as
a fine ‘crazing’ effect on the output window, or
port. These cracks indicate the glass is punc-
tured. As a result, the tube is gassy.


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


104


E


Aim


The aim is to provide information for testing or replac-
ing the X-ray tube. Different failure modes are ex-
amined. This module is an extension of module 2.1
page 48. Reference should also be made to module 7.3
page 117.
(Note: Reference module page numbers refer to the
title page.)


Objectives


On completion of this module, the student will be
aware of common problems with the X-ray tube,
together with the test procedures. This includes
removal or replacement of the X-ray tube, together
with assistance from an electrician or electronics
technician.


Contents


a. General precautions
b. X-ray tube failure modes
c. Inspection of the anode or filament
d. Focal spot performance
e. Oil leaks
f. Removal of the X-ray tube
g. X-ray tube transport
h. Re-installation of the X-ray tube




ii. The bearings have seized, so X-ray exposures are
hitting a stationary anode.


iii. In both cases, the tube requires replacement.
● Arcing at the HT cable ends or in the receptacles.


i. You have may have observed smoke at one
receptacle. Or an actual spark.


ii. The X-ray control might generate ‘mA overload’
or ‘kV fault’ signals. This depends on the design
of the X-ray control and the severity of the
arcing.


iii. You have noticed there is a strong odour at the
suspect cable end or receptacle.


iv. High-tension cable problems are discussed in
module 7.3 page 117.


● The bearings have become very noisy. In many cases
a tube with noisy bearings can still have a useful
life. However, budget for a replacement if the anode
slows down quickly once preparation is released.
This can indicate a failure in the near future, and is
especially the case if the anode slows down while
still in preparation.


● Poor X-ray resolution.
i. The anode is badly worn.
ii. The anode is cracked or distorted, so that the


focal spot wobbles as the anode rotates.
iii. Heavy metal deposits on the output window.This


causes excessive hardening or filtration of the X-
ray output. In this case, it will not be possible to
observe the anode or cathode after removing
the collimator. Metal deposits can also lead to
a micro arc through the glass, causing the tube
to become unstable or gassy.


iv. See ‘inspection of the anode or filament’ in part
‘c’.


● A filament is open circuit. To test, use a multimeter
set to the low ohms scale. There should be a very
low resistance between any two pins in the cathode
receptacle. An exception is the X-ray tube for some
mobiles, which may have only one focal spot.


● A filament has a partial short circuit. This is due to
a section of the filament touching the cathode
focus cup, and then welding itself to the cup. Unfor-
tunately, this is not a rare occurrence.
i. The generator will indicate sudden low mA


output, while films will not only appear under-
exposed, but may also have poor contrast due
to an increase of kV. With high frequency, or
microprocessor-controlled generators, a kV fault
signal may be generated.


ii. Checking the other focal spot will indicate
normal operation.


iii. Attempting to re-calibrate mA output will indi-
cate a rapidly increasing filament drive current,


especially at higher mA output. In addition, cor-
rection of mA at medium to low kV calibration
points becomes very difficult. (Space charge
compensation).


iv. In some cases it is possible to see a faulty
filament, after the collimator is removed. See
‘inspection of the anode or filament’.


c. Inspection of the anode or filament


Note. This technique must not be attempted with
a capacitor discharge mobile, due to high voltage
that may be stored in the capacitor.


● Removing the collimator.
i. Where possible, refer first to the installation


manual of the collimator. If in doubt, contact
the service department for instruction. Two
people are recommended, to hold the assem-
bly in position as it is removed or replaced.


ii. Rotate the X-ray tube so it is aimed at the
ceiling. Adjust the height close to the tabletop.


iii. Secure the vertical movement of the tube
stand so it cannot move upwards once the col-
limator is removed. Do not rely on the magnetic
lock system, this can slip, or not operate when
power is switched off.


iv. Examine the connecting cables to the collima-
tor, and the tube-stand operation panel. Is
there sufficient length? Undo any cable ties if
required, to allow cables to hang freely.


v. Ensure all power is off. Turn of power at the
room isolation switch. Do not rely on the gen-
erator power switch, as some installations
allow direct power to the tube stand.


vi. To avoid pulling on cables once the collimator
is removed, place a box of a suitable height on
the tabletop.The collimator can rest on this box
when removed from the tube head. This may
include the tube-stand control panel.


vii. If the cables are short, disconnection is
required. Make a careful diagram of connec-
tion terminals before disconnecting,and ensure
the wires have a suitable label or mark. Ensure
any attached labels will not fall off.Any exposed
terminals attached to wires must be covered
with insulation tape. (Power may need to be
re-applied to see inside the X-ray tube.)


viii. Undo the retaining screws holding the collima-
tor to the tube housing, and place the colli-


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


105




mator on the tabletop, or box. Take care on
removal, as part of the collimator can extend
into the tube-housing port. In some cases, the
tube-stand control panel will be detached at
the same time. Assistance may be required to
hold or place components as they are removed.


ix. Have a container ready to receive screws etc.
These are easily lost.


x. The tube-housing port may have an aluminium
filter, and a lead ‘proximal’ diaphragm fitted.
The latter is often in the form of cone extend-
ing into the port, and the filter is then placed
under this lead diaphragm. The proximal
diaphragm is held in place by a spring clip, or
else by two or four very small screws. Before
removing the lead diaphragm, make a mark so
it can be replaced in the same position.


xi. Caution: do not remove the larger screws
holding the port assembly in place. Air will
enter the housing, or oil will leak out. If this
happens, the tube housing needs to be
reprocessed.


● Inspecting the anode.
ii. With the collimator, proximal diaphragm, and


any added filter removed, it should now be pos-
sible to see the anode and filament.


iii. Often observation of the anode may be made
using a torch. However, any metal evaporation
on the glass acts as a mirror, and prevents
observation.


iv. Most generators have a filament pre-heat
circuit, which will light up the filament, and
allow observation of the anode. Ensure any dis-
connected wires have their ends taped up, and
then switch on the generator.


v. Note. If the glass has heavy metal deposits, this
technique may only yield limited results. In this
case, the future reliability of the tube is not
good.


vi. To observe the anode for defects, the anode
needs to slowly rotate.


vii. To rotate the anode, press the preparation
button on the handswitch. This should be very
brief,so that the anode only just starts spinning.
Do not expose. As a safety precaution, preset
minimum kV and time, and a low mA station.


viii. As the anode slows down, carefully observe the
track area. Look for the following.
—Anode wobble, this indicates possible crack-


ing, and poor focal spot performance.
—Stationary hits.These appear as small melted


areas of the anode, as if hit by a small arc
welder.


—Worn anode. This appears as a fine crazed
pattern, like coarse sandpaper.


—Overloaded anode. This has a fine orange
peel pattern.


—Smudged areas. This often occurs during
manufacture. However, if the tube is unsta-
ble, this can be an indication of gas.


● Inspecting the filament.
ix. When the generator is switched on, the pre-


heat circuit will light up the selected focal spot.
x. Select fine focus, and then broad focus. The


broad focus will appear a little longer and
larger in diameter.


xi. (An exception to the above will occur with a
fluoroscopy table. In this case, the fine focus
remains selected at all times, unless in prepa-
ration for radiography).


xii. If there is a partial short in the broad focus,
then the broad focus will appear shorter in
length than the fine focus. Careful observation
can sometimes see a short length of filament
that is not heated.


● Are there fine cracks in the glass?
i. These can appear over the anode or cathode


area. A minor case may appear as a single fine
line, like a single strand of spider web. More
severe cases can appear as a fine crazed
pattern.


ii. These marks are due to high voltage discharge
through the glass. This condition occurs more
often with metal deposits on the glass, which
increases the possibility of arcing in this area.


iii. The presence of these marks, together with a
suspect unstable or arcing tube, means the tube
is gassy and will need replacement. In this case,
seasoning is not effective.


● Replacing the collimator.
i. Re-assembly is in the reverse order as the dis-


mantle process.
ii. Take care that any added aluminium filters are


returned to their previous position,and the prox-
imal diaphragm is correctly aligned.


iii. After reassembly the collimator will need
realignment. Please refer to module 7.2 page
110.


d. Focal spot performance


Focal spot performance can be tested using a ‘Star
pattern’ gauge.


In use, the gauge is positioned in the centre of the
X-ray beam, close to the focal spot. This gives a mag-
nified view of the star pattern. Part of this pattern is


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


106


E




blurred.The diameter of the blurred area is used to cal-
culate the size of the focal spot.


There are several versions of star patterns. Use the
directions enclosed with the pattern, which includes a
formula specific to the supplied star pattern.


A star test pattern may be obtained as a loan item
from the service department, or from the physics
department of a major hospital.


When measuring the focal spot, take the following
precautions.


● Use a low value of kV. (60~70kV)
● Use a medium value of mA suitable for the focal


spot under examination. Note. As mA is increased,
the focal spot will also increase in size.


● Use non-screened film.Or else a cassette with detail
screens.


● Exposure time should be more than 0.04 seconds.
This allows at least two rotations of the anode, in
case anode wobble is degrading the focal spot.


● If the test result is too light, increase the time or
mA station.


● If the result is too dark, consider increasing the FFD
or reducing kV.


● If the outer blurred area is too large in diameter to
measure easily, then reduce the magnification, and
adjust mA and kV to suit.


e. Oil leaks


Oil leaks should always be reported. Even a very slow
oil leak has the possibility of letting air into the
housing. An air bubble in the wrong position can lead
to arcing, and possible destruction of the X-ray tube.


● Oil leaks may be seen at either end of the tube
housing, or at the collimator, if a crack or faulty seal
occurs in the housing port.


● An X-ray tube with oil leaks will need to be repaired
by the service department. In some situations, the
service department may supply a loan unit, while
the faulty housing is repaired.


● To locate where the oil leak occurs, first thoroughly
wipe clean with a paper tissue. Leave overnight,
and then test by wiping with a fresh tissue next
morning. This will indicate the origin, and assist in
repairs when the tube is returned to the service
department.


● Occasionally, when a tube is returned after a repair,
an apparent oil leak might appear. This can be
caused by a small amount of spilt oil around such
areas as the external terminal strip etc. A few drips
may initially occur, and then no further symptoms
appear. If drips continue after a few days, then this


needs to be reported, and have the tube returned
for further attention.


f. Removal of the X-ray tube


Due to the presence of an oil leak, or to have a new
insert installed, the X-ray tube and housing is required
at the service department.


● Preparation for removal.
i. Where possible, refer first to the installation


manual of the tube stand. If in doubt, contact
the service department for instruction.


ii. Two people are recommended to assist in
removing or installing the X-ray tube assembly.
This is a heavy object.


iii. Rotate the X-ray tube so it is aimed at the
ceiling. Adjust the height close to the tabletop.


iv. Secure the vertical movement of the tube
stand so it cannot move upwards once the col-
limator is removed. Do NOT rely on the mag-
netic lock system, this can slip, or not operate
when power is switched off.


v. Examine the connecting cables to the collima-
tor, and the tube-stand operation panel. Undo
any cable ties or clamps, to allow cables to
hang freely.


vi. Carefully mark the anode and cathode cables.
vii. Hint. The stator cable normally enters at the


anode end of the housing. (In some cases, it
enters at the centre. Be careful in this situa-
tion)


viii. Ensure all power is off. Turn of power at the
room isolation switch. Do not rely on the gen-
erator power switch, as some installations
allow direct power to the tube stand.


xi. If removing an X-ray tube from a capacitor dis-
charge mobile, observe the high-tension pre-
cautions described in module 7.3 page 117.


x. Undo the ring nuts holding the HT cable ends,
and withdraw the cable ends from the housing.
As they are withdrawn touch the end pins to
the tube stand. This is to discharge any resid-
ual high-tension that may be present. When
they are withdrawn, wrap the cable ends in
cloth or paper towel to protect from damage.


xi. To avoid pulling on cables once the collimator
is removed, place a box of a suitable height on
the tabletop.The collimator can rest on this box
when removed from the tube head. This could
also include the tube-stand control panel.


xii. Disconnection of all wires to the tube housing
is required. Make a careful diagram of con-


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


107




nection positions before removing, and ensure
the wires have a suitable label or mark. Ensure
any attached labels will not fall off.Any exposed
terminals attached to wires must be covered
with insulation tape. (This is in case power is
turned back on)


xiii. Undo the retaining screws holding the collima-
tor to the tube housing, and place the colli-
mator on the tabletop, or box. Take care when
removing, as part of the collimator may extend
into the tube housing port. In some installa-
tions, the tube-stand control panel will be
detached at the same time. Assistance will be
required to hold or place components as they
are removed.


xiv. Have a container ready to receive screws etc.
These are easily lost.


● Removal of the X-ray tube housing from the tube
stand.
i. Check again, that vertical movement of the tube


stand is properly secured.
ii. After the collimator, high-tension cables, and


stator cables have been removed, examine care-
fully the shape of the trunnion mounting rings.
With the X-ray tube aimed at the ceiling, the
bottom section of the rings should be able to
hold the housing in place, after the top section
is removed. Sometimes the assembly is installed
in the reverse direction, so then the tube needs
to face the tabletop.


iii. With the housing in the required position, undo
the top half’s of the trunnion rings, taking
special note if any washers have been inserted
between where the trunnion rings are fastened
together. (These are sometimes fitted to adjust
the trunnion rings, in case they are too tight a
fit for the tube housing.)


iv. The tube housing may now be lifted up out of
the rings. This is a heavy object. Two people
should assist in this process.


g. X-ray tube transport


The X-ray tube housing offers no protection to the X-
ray tube if it is bumped or dropped. Incorrect pack-
aging for transport can easily result in a broken tube,
due to the weight of the anode.


● Before sending the tube to the service department,
take careful note of all housing and X-ray tube
details. Include serial numbers.


● Attach full documentation to the housing. This
should give a full description of the problem to be
rectified. There should also be full contact details,


such as hospital address, phone number, person to
contact, etc. Include an order number or other
authorisation if required.


● Include a request for suitable silicon grease, and or
anti-corona silicon pads to be supplied when the
tube is returned.


● Before looking for suitable boxes etc, contact the
service department.They may be able to send a suit-
able size box and packing material.


● Select a box size about twice that of the housing.
Pack the housing in the centre, using material to
cushion any bumps. For example, shredded poly-
styrene foam. Make a mark on the box to indicate
the anode end.


● Place this box in another box about twice the size
of the first box. Fill the space between the two
boxes with suitable cushion packing.


● Position the second box so that the X-ray tube is
vertical, and the anode end is towards the bottom
of the box.


● Attach very large labels with an arrow to indicate
‘This side up’ on the sides of the box.Attach another
label on the top to indicate ‘Top side’. Attach
‘Fragile, do not drop’ labels on all sides.


● Take care both the service department address and
the hospital return address is protected, eg, inside
a transparent plastic cover. If sending to another
country, be sure to provide suitable information for
customs etc.


● Ensure you have a full copy of the shipping details.
Also phone the service department and notify them
of the method of transport etc. If the X-ray tube
is sent to another country, enclose copies of the
required customs forms.


h. Reinstallation of the X-ray tube


Caution: If a new tube insert or assembly is supplied,
a complete mA re-calibration is required. This should
be performed by the service department.


The X-ray tube is re-installed in the reverse order of
the instructions for removal. Eg, first it is mounted in
the trunnion a ring, then the collimator is attached,
and finally the wiring and HT cables.These precautions
should be observed.


● Check the HT receptacles. If there is any grease
residue, this must all be removed, and the recepta-
cles left in a polished condition. Even if apparently
clean, still wipe them carefully with fresh paper
tissues. This is to remove any possible moisture. Do
not touch the inside with the fingers, or scrape the
sides with a metal object. (This may leave very slight
traces of metal behind).


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


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E




● If the housing has been repaired, or a new insert
fitted, check carefully for any areas of oil residue,
and wipe away with paper tissues.


● Before installing the collimator, ensure the proximal
diaphragm and aluminium filters are in place.


● Reconnect the wires, using the diagram previously
made when the tube was removed. If a new tube
and housing is supplied, and the connection points
appear different, contact the service department
before connecting any wires.


● When inserting the high-tension cable ends, use the
instructions provided in module 7.3 page 117.


● Important.After the cable ends have been inserted,
and the ring nut fully tightened, retighten a few
hours later, and again next day.


● The collimator will need re-alignment. Please refer
to module 7.2 page 110.


● Before making a test exposure, just enter prepara-
tion only. Listen carefully to the tube anode as it
rotates. Is this the normal anode rotation sound?


● Providing the original tube insert and housing has
been returned, then the mA calibration should be
the same. Select a low mA position, set 60kV, and
0.1 second exposure time. Make a test exposure. If
any problem occurs, STOP. Contact the service
department for advice.


● The X-ray tube should now be seasoned. Use the
technique described in module 2.1 page 48.


● Keep the boxes and packing the X-ray tube assem-
bly arrived in for future use.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


109




MODULE 7.2


X-ray collimator


Contents


a. General precautions
b. The light field has insufficient brightness
c. Changing the collimator globe
d. A wrong collimator globe
e. This collimator was not designed to rotate
f. Centring of the collimator lamp
g. Centring of the X-ray beam
h. The light field is larger than the X-ray field
i. The Bucky centre light
j. The X-ray field fades out on one side of the film
k. The collimator blades close, after adjusting the


field size
l. The collimator lamp fails to operate
m. The globe has failed, and there is no spare globe


Equipment required


■ Basic tool kit.
■ X-ray alignment template.*
■ 24/30 cm cassette.
■ Spare collimator globe.
■ Cloth, for cleaning.
■ Detergent.


* The template is described in appendix ‘B’ page 169.


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


110


E


Aim


The aim is to provide information and procedures
related to adjusting the X-ray collimator.This is in addi-
tion to the collimator maintenance,provided in module
2.2 page 50.
(Note: Reference module page numbers refer to the
title page.)


Objectives


On completion of this module, the student will be
aware of common problems with the collimator and
their solutions.Adjustments and repairs may be carried
out. Some tests for the collimator lamp can be
made with the help of an electrician, or electronics
technician.


Task 14. ‘Help! No spare globe for the collimator’,
should be attempted on completion of this module.


a. General precautions


● Before disconnecting any wires, or removing a
cover, always ensure power is turned off and
unplugged from the power point. If the equipment
is part of a fixed installation, besides switching the
generator power off, ensure the isolation power
switch for the room is also switched off.


● Whenever changing a collimator lamp, ensure all
power is turned off.


● If removing a cover, position the collimator close to
the tabletop. Secure the tube stand so it cannot
move upwards once the cover is removed.


● The timer switch may be fastened to the cover.
Place a small box or pillow within reach to support


the cover when removed, so the connecting wires
are not pulled.


b.The light field has insufficient brightness


This may be due to several causes, some of which can
combine to give an overall drop in light level.


● Dirt or dust builds up on the inside of the trans-
parent exit cover of the collimator.
i. To clean, it will be necessary to include removal


of the collimator outer cover. Before removal,
ensure all power is turned off.


ii. Clean with a soft rag and mild detergent. Wipe
off any residual detergent.




iii. The above also applies if cleaning the mirror.
Take care not to scratch the surface, or change
the position of the mirror.


● The globe has metal evaporation on the inside of
the globe. Fit a new globe.


● The voltage supply to the lamp is too low.This is due
to a supply voltage that has not allowed for voltage
drop, due to wiring resistance. As an example, when
the lamp is switched on, the voltage can drop by
2~5 volts.This is a common problem when installed
with long connecting cables.
i. Ask an electrician, or electronics technician, to


measure and adjust the lamp voltage.
ii. Check if the lamp has the correct voltage. To


do this, set the multimeter to a convenient AC
voltage range. For example, 25V or 100V AC.
Remove the lamp covers, and place the meter
probes on the lamp terminals. Look away from
the lamp while switching the light on, and then
measure the operating voltage. This might be
only 7~8V for a 12V lamp, or perhaps 17~20
V for a 24V lamp.


iii. A number of systems have a transformer, with
a selection of output voltages. The required
voltage is selected by changing a connection
on a terminal strip.


iv. During installation this may be set at the lamp
voltage. For example, set at 12V output for a
12V lamp.This is incorrect, as it does not allow
for voltage loss in the connecting cable.


v. A correct installation may even set the voltage
as high as 16V for a 12V lamp. This compen-
sates for voltage drop due to cable resistance,
when the lamp is switched on.


vi. If the test voltage is low, eg, below 10V for a
12V lamp, then contact the service depart-
ment for instructions to adjust the voltage
supply. Include the make and model of the col-
limator and the generator.


vii. In some other situations, there may be spare
conductors in the cable. These may be placed
in parallel with the existing wires for the lamp,
to reduce the voltage drop. This is best left to
a technician from the service department to
carry out.


viii. Note. While an 8V operating voltage for a
12V lamp is too low, increasing to the full
12V will give a shorter lamp life.A compromise
between brightness and life for a 12V lamp is
10~11V.


c. Changing the collimator globe


Before attempting to replace a collimator globe,
ensure all power is turned off.


When replacing the globe, take care not to touch
the glass with the fingers. This especially applies to
quartz iodide globes, as slight oil or perspiration from
the fingers will cause premature failure. Use a paper
tissue to hold the globe.


d. A wrong collimator globe


Two versions of a quartz iodide globe appear very
similar. If the wrong version is installed, there is a large
error between the light field, and the X-ray field.


● The correct globe has longer connecting pins. OR,
the filament is placed further towards the tip of the
lamp. Both are correct, in that the filament is the
same distance from the rear end of the pins.


● The incorrect version has shorter pins, so that the
distance between the filament and the rear end of
the pins is smaller.


● In an emergency, the short pin version may be used.
Insert the lamp sufficiently to make good contact
in the socket, however do not push it all the way in.
There will still be an error in the light beam to X-
ray alignment, so obtain the correct version as soon
as possible.


e.This collimator was not designed to rotate


Older installations may have a collimator of European
origin. With this collimator, four adjustable metal
‘fingers’ attach the collimator to a circular flange, or
plate. There is no other adjustment. Correct adjust-
ment is with the fingers tightened, so the collimator
does not rotate.


However, in some installations these fingers are not
tightened, allowing the collimator to be rotated.


● The collimator can only be aligned correctly to the
focal spot in one position.When it is rotated, correct
alignment to the light beam may be lost, especially
if the light beam has also been adjusted. See ‘Cen-
tring of the X-ray beam’, part ‘g’.


● Rotating the collimator can cause wear to the
metal fingers. As the wear increases, the collimator
may ‘wobble’ when pointed at a wall Bucky. In a
severe wear case, the top of the metal finger breaks
off. Replacement metal fingers are difficult to
obtain.


● As the adjusting screws were not tightened, these
can vibrate to a more open position.This will cause


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


111




erratic collimation. In a severe situation, the colli-
mator may even detach from the flange, and fall off.


● Assuming the collimator must rotate, please take
the following precautions.
i. Apply a very thin layer of oil to the upper surface


of the mounting ring, to reduce wear.
ii. After the metal fingers have been adjusted,


apply a dab of nail polish to the outer threads
of the adjusting screws. This will help prevent
them from unwinding.


f. Centring of the collimator lamp


There are two methods of aligning the light beam to
the X-ray field. One is to move the position of the lamp,
and the other is to adjust the position of the collima-
tor relative to the X-ray beam.


With a collimator that can rotate, it is essential to
adjust in the correct sequence, otherwise alignment is
correct only in one position.


● Bring the collimator down until it touches the table-
top, and adjust the tube rotation so the collimator
face is flat against the tabletop. Now raise the col-
limator to its normal working height.


● Rotate the collimator clockwise 90 degrees.
● Place a used X-ray film on the table top as a tem-


plate. A suggested size is 24 ¥ 30cm. Switch the
collimator lamp on, and adjust the collimator so the
light field just covers the film.


● Next, rotate the collimator anti-clockwise 180
degrees. With the lamp switched on, look for any
error in alignment. This should be less than 2.0mm
in any direction.


● Before making any adjustment, check to see the
correct lamp is fitted. If in doubt, contact the
service department to obtain positive identification.


● If adjusting the lamp position, adjust so the error
is reduced by 50%.Then adjust the film position to
the light, and test again with the collimator rotated
180 degrees to the previous position.


● Can the mirror be adjusted?
i. With most collimators, the mirror is fixed in


position. Attempting to move the mirror against
the clamping screws can distort or break it,
requiring a replacement. (If the mirror is dis-
torted, the sides of the light field are at an
angle, and not parallel).


ii. The exception is where there is a spring-ten-
sioned adjustment screw. This may be found on
some mobiles or portable units. In this case, the
lamp may be adjusted sideways, and the mirror
rotation replaces the vertical adjustment of the
lamp.


g. Centring of the X-ray beam


Attempting to adjust the collimator to the X-ray beam
should only be attempted after checking that the light
beam is correctly centred.This especially applies when
the collimator can rotate.


● An X-ray alignment template is required. A suitable
design is shown in appendix B page 169.


● Place the X-ray alignment template on a 24/30cm
cassette.


● Collimate the light beam to the outer 20 by 26cm
rectangle.


● Make a low kV and mAs exposure.
● Develop the film.
● Does the alignment meet the required compliance?


Two versions are provided as an example only. The
actual compliance requirement will depend on indi-
vidual country regulations.
i. The X-ray field edges should not deviate by more


than 2% of the distance between the plane of
the light field and the focal spot.
[a1] + [a2] £ 0.02 ¥ S.
[b1] + [b2] £ 0.02 ¥ S.
Where S is the distance from the focal spot, a1
and a2 are the two sides on one axis, and b1
and b2 are the two sides of the other axis.
For example; at a FFD of 100cm, if the two ver-
tical edges of the light field were displaced by
10mm, this would be at the limit of acceptance.
If only one edge was displaced, then 2.0cm is
at the limit of acceptance.


ii. Another version has a different requirement.
The total misalignment of any edge of the light
field with the respective edge of the irradiated
field must not exceed 1% of the distance
between the plane of the light field and the
focal spot.
For example; at a FFD of 100cm, the maximum
displacement of any edge should be less than
10cm.


● In case the X-ray field is off-centre by more than
the permitted amount, re-centring is required.


● To adjust a non-rotating collimator.
i. Refer where possible to the installation or


operation manuals for the collimator. If neces-
sary, contact the service department for infor-
mation specific to your version of collimator.


ii. Locate the adjusting screws for the metal
fingers. These usually require an Allen key for
adjustment.


iii. By slackening off one finger, then tightening
the opposite finger, the collimator will move rel-
ative to the X-ray field.Only a small adjustment,


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


112


E




of about one turn of the screw, is sufficient to
move the X-ray field several millimetres.


iv. Adjust the collimator to move in the same
direction you require the X-ray field to move.


v. After adjusting, make another test film and
compare the results.


vi. If necessary, make further adjustments until
compliance is achieved.


vii. Tighten carefully all four fingers, ensuring the
collimator position does not change.


viii. Make a final test film for verification.
● To adjust a rotating collimator.


i. Refer where possible to the installation or oper-
ation manuals for the collimator. If necessary,
contact the service department for information
specific to your version of collimator.


ii. With a true rotating collimator, the ring or
bearing on which it rotates is repositioned rel-
ative to the X-ray beam. (Unfortunately some
simplified systems may not have this facility,
and so can only be correct in one position).


iii. It is necessary to locate the screws that clamp
this ring in position. These may require a small
spanner. Undo these screws a small amount, so
the ring can just be moved.


iv. With some rotating collimators, once the rota-
tion ring is free to move, adjusting screws
similar to the fixed-collimator, are used for
alignment. Otherwise gently tap the collimator
into position, moving it only a part of a mil-
limetre at a time.


v. Adjust the position and test in the same fashion
as the fixed-collimator.


vi. Repeat the above test, with the collimator
rotated 90 degrees clockwise, and 90 degrees
counter clockwise.


vii. Ensure the ring clamping screws are correctly
tightened when alignment is satisfied. Make a
final test film for verification.


h.The light field is larger than the X-ray field


Most collimators depend on a standard distance
between the X-ray tube housing and focal spot. If a
manufacturer supplies non-standard tube housing, this
distance may be incorrect.


● The collimator is required to be positioned at a spe-
cific distance from the focal spot. Some collimators
are supplied with shims.These can be added or sub-
tracted to make the required adjustment. Check
with the service department for this possibility.


● A common reason is the method of installation.


i. The bracket for the tube-stand command panel
is placed between the collimator and the X-ray
tube port. This increases the collimator to focal
spot distance.As a result the X-ray field becomes
smaller.


ii. In some cases it may be possible to have a
mounting block machined to reduce this added
distance, or have shims removed. Otherwise the
mounting method of the control panel will need
to be changed to correct the situation.


i.The Bucky centre light


Collimators have been fitted with a number of
methods to indicate Bucky centre. Two versions are
discussed here.


● One method is a fixed slot, immediately below the
collimator lamp. If the lamp is not correctly
adjusted, then the light shines at an angle through
this slot, creating an error. This is usually corrected
by re-alignment of the collimator. See ‘Centring of
the collimator lamp’, part ‘f’.


● Other versions may have a small focussing lens,
attached to a slit in the collimator cover. Adjusting
the lens can shift the position of the light beam.


j.The X-ray field fades out on one side of
the film


If the fade out occurs towards the anode side of the
film,when selecting a large format, this is probably due
to the ‘heel affect’ of the X-ray tube anode.


Otherwise, it may be due to the following.


● The collimator is not centred to the focal spot, and
the lamp has been adjusted to align the light beam
to the X-ray field.Test by making sure the light field
remains centred as the collimator is rotated. See
‘Centring of the collimator lamp’.


● The collimator primary-beam shutter, or blade, is
touching the side of the X-ray tube port, or ‘throat’.
The cause is due to incorrect centring of the
collimator.
(This problem depends on the collimator design, and
how the collimator is attached to the X-ray tube.)


● The lead proximal-diaphragm has been incorrectly
fitted inside the tube port. For example, after
replacement of the X-ray tube.


● The collimator lead-shutters, or blades, are out of
adjustment.This may be either the middle blade, or
the bottom blade.
i. The shutters are coupled to the field size knob


by a thin stainless-steel cable.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


113




ii. The cable may be loose, or has slipped where it
attaches to the shutters. To check, remove the
collimator cover, and make a careful compari-
son of both sets of collimator blades. The lead
strip, on the bottom blades, can be adjusted in
most collimators.


● In some cases there may be a slow fade off towards
the cathode side of the film.This is more noticeable
at lower kV levels. If this is an older, or hard worked
X-ray tube, then it might be due to metal deposits
on the glass. To check, you will need to remove the
collimator. See module 7.1 page 104.


k.The collimator blades close, after adjusting
the field size


A collimator has an internal ‘brake’ or ‘clutch’. If this
becomes loose, the springs, fitted between the colli-
mator blades, cause the blades to close.


Two common methods are described here.
To adjust, it is necessary to remove the collimator


cover. Ensure power is turned off, and the tube stand
is prevented from moving vertically.


● Japanese origin.
i. The shutter control knob is attached to a round


shaft. This shaft, which controls the opening of
the blades, passes through a cylinder attached
to the inside front of the collimator.


ii. A small nylon pad forms the brake action. This
is pressed firmly against the shaft that passes
through the cylinder.


iii. A screw, attached to the cylinder, controls the
amount of pressure. As the screw is turned
clockwise, the pressure of the nylon pad against
the shaft increases.


iv. To adjust, first undo the locknut on the screw.
Then turn the adjusting screw about a quarter
turn clockwise. Retighten the locknut, and test
the feel of the control knob.


v. Repeat the above action so the knob is firm to
turn, without being over tight.


vi. Check and adjust the other shutter control knob.
vii. Replace the cover.


● European origin.
i. The shutter control knob is attached to a round


shaft. This shaft, which controls the opening of
the blades, passes through to the rear of the
collimator.


ii. At the rear of the collimator, a circular disc is
attached to the end of the shaft.


iii. There are two screws on the outer side of this
disc. These adjust the pressure of a wide spring
washer on the disc.


iv. The screws are adjusted so the control knob is
firm to adjust, but not over tight.


v. These screws tend to become loose. After they
are adjusted, clean around the screw heads
with alcohol. Then paint the immediate area
with nail polish. This will help retain the screws
in position.


● For other collimators, contact the service depart-
ment for advice regarding adjustment of the brake
and its location.


l.The collimator lamp fails to operate


The most common cause of failure is, of course, a burnt
out globe. In case this is not the reason, then check
the following. Ask an electrician, or electronics techni-
cian, for assistance.


● The lamp timer switch. Mechanical types are prone
to failure, and to a lesser degree, electronic versions.
i. Ensure all power is switched off, while removing


the cover to gain access to the timer.
Note. Some tests for the timer will require
power after the cover is removed.


ii. Check the internal wiring, looking for loose
connections.


iii. Mechanical timers have only two terminals.
Operate the timer, and with a multimeter set to
low ohms range, check the timer-switch con-
tacts for continuity. See module 5.0 page 65.


iv. An alternate test is to set the multimeter to AC
volts, and look for voltage across the terminals.
This should be 12~15V for a 12V lamp. When
the timer is operated, there should be no voltage
across the terminals.


v. Electronic timers have several connections. It is
necessary to trace out the wiring and locate the
two terminals that switch the power to the
lamp. Look for voltage across these terminals.
This should be 12~15V for a 12V lamp. When
the timer is operated, there should be no voltage
across the terminals.


vi. In case the timer is faulty, a temporary repair is
to remove the timer and replace it with a stan-
dard on-off switch. Order a new timer and
replace the temporary switch at the first
opportunity.


● No power to the collimator. Check the connecting
cable for broken connections, especially if the col-
limator is a rotating version.


● There may be a faulty fuse in the collimator power
circuit. Contact the service department for the
location of this fuse.


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m.The globe has failed, and there is
no spare globe


● The collimator should have a scale on the front.This
indicates the field aperture as the blades are
opened. The accuracy of this scale has, hopefully,
been checked at the last routine service. However,
let us assume this has not happened.
i. Lower the collimator so it is touching the table-


top.Adjust any angulation or rotation, so it sits
flat on the tabletop.


ii. Adjust the tube stand so the collimator is at
the table centre.


iii. Place a ruler on the tabletop, end-on against
the centre of the collimator. Use this as a
guide to assist in centring the Bucky to the
collimator.


iv. Raise the tube to the normal working height.
Adjust the X-ray control for a low kV and mAs
exposure.


v. Place a 24 ¥ 30cm cassette in the Bucky.
Adjust the collimator to the film size using the
scale on the collimator. Make a test exposure.


vi. If the test exposure shows all the film was
exposed, then repeat the above test, this time
reducing the collimator aperture a small
amount. If all is well, the film should now have
a border around all four sides.


vii. Continue the above test with the most com-
monly used sizes of films and orientation.
Adjust the position of the control knob on the
collimator shaft to obtain a correct indication.
Or, place a mark on the collimator front to indi-
cate the required opening for the different
films.


viii. A similar test to the above is required for the
wall Bucky.


● To estimate the position of the anatomy under
examination. AP view.
i. With the patient on the tabletop, bring the col-


limator close to the area under examination.
View the position both from the head, or foot,
end of the table, as well as the side of the table.


ii. To estimate the area to be covered, place a
sheet of film on the patient, centred directly
under the collimator.This is to simulate the pre-
vious appearance with the light beam. The
actual area will be about 10% less.


iii. Where possible, protect other immediate areas
of the patient by masking with lead rubber
strips.


iv. Raise the X-ray tube to its normal height, and
set the aperture size using the scale on the front
of the collimator.


● To assist in Bucky centring during an examination.
i. Attach a length of string to the front of the col-


limator side, positioned at the centre. Attach a
small weight at the end to act as a plumb bob.


ii. Move the X-ray tube across the table, so the
plumb bob is over the Bucky tray. Centre the
Bucky to the X-ray tube, and then return the X-
ray tube back to the table centre position.


iii. Coil up the string etc on the X-ray tube when
not in use.


● To estimate the position of the anatomy under
examination. Oblique view.
i. A simple method is to use a long ruler, or


similar object, resting against the upper or
lower side of the collimator. This is extended
towards the patient. By alternating the ruler on
the upper and lower side of the collimator, a
reasonably accurate positioning of the X-ray
field may be made.


ii. A torch may be used. The torch should be the
type that has a focussed spotlight, and a flat
bottom end.


iii. Hold the torch bottom end against the centre
of the collimator faceplate. Switch the torch
on, and place a marker in the centre of the
light beam on the tabletop.


iv. Rotate the torch, and check that the light
beam stays in position. This test indicates the
torch is suitable for use.


v. Now place the patient on the table. Adjust the
X-ray tube to the required angle. Place the
torch on the collimator front as before, and
use the torch light to indicate the X-ray beam
centre.


vi. As before, a sheet of film may be used to esti-
mate the area to be covered.


vii. Set the collimator aperture, using the scale on
the front of the collimator.


viii. Use lead rubber strips to protect the patient.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


115




TASK 14


Help! No spare globe for
the collimator


The collimator globe has failed. On checking supplies, there is no spare globe. You are required to continue pro-
cessing patients, while waiting for a new globe.
Please refer to module 11.2 for an outline of suggested techniques.
Note; for this exercise, the collimator lamp must not be used.


Using a 24/30cm film, test the accuracy of the collimator scales. Is the accuracy adequate? Does the scale need
to be reset?


Make a suggestion for other methods to achieve patient positioning, with an AP view.


Can this method be adapted for a wall Bucky?


With a water phantom to simulate the patient, try the methods suggested for an oblique view. Will this give the
required accuracy?


Discuss other problems that may arise if the lamp fails. Suggest a technique that may be used.


Tutor’s comments


Satisfactory/Unsatisfactory


Signed Date


Tutor


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MODULE 7.3


HT cable


a. Safety precautions


● Do not attempt repairs or replacement of the HT
cables by yourself. Ask an electrician, or an elec-
tronics technician, for assistance.


● Before disconnecting any wires, or removing the HT
cables, always ensure power is turned off and
unplugged from the power point. If the equipment
is part of a fixed installation, besides switching
the generator power off, ensure the isolation power
switch for the room is also switched off.


● Mobile high-frequency generators may be battery
operated. The batteries in these are connected in
series, and can have a total voltage of up to 240V
DC. Refer to the operating or installation manuals
for the position of the battery isolation switch, and
ensure this is switched off, before removing the
covers, or testing wires and connectors.


● If removing a HT cable from a capacitor discharge
mobile, observe the high-tension precautions
described in module 6.2 page 94.


● Whenever a HT cable is removed from a receptacle,
immediately short the cable-end pins to ground.
This is to remove any residual high voltage in the
cable. The same precaution applies before applying
grease or any other handling of the cable end.
Failure to take this precaution could cause a severe
electrical shock.


b. High-tension failure of the HT cable


The HT cable tends to fail at the cable ends.This is due
to the added flexing, or twisting, as the X-ray tube is
rotated and repositioned. This is often due to poor
support of the HT cable. Failure is usually accompa-
nied with a pungent, or acrid, smell.


● A metal ‘cuff’ often hides the actual failure point.
This cuff helps support the cable end where it enters
the tube housing. If suspicious of the HT cable, then
undo the retaining ring nut, and slide the cuff out
of the way.Then inspect again for an unusual smell.
Make a comparison with the other cable end.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


117


Aim


The aim is to provide information related to the high-
tension (HT) cable. This includes repairing common
faults, and procedures for replacing the HT cable.
Information in this module also applies to module 7.1
page 104.
(Note: Reference module page numbers refer to the
title page.)


Objectives


On completion of this module, the student will be
aware of common problems with the high-tension
cable, and their symptoms. With the assistance of an
electrician or electronics technician, a number of cor-
rective actions can be carried out.


This includes:


● Repairs to eliminate high-tension arcing.
● Correcting bad cathode cable connections to the


X-ray tube filament.
● Removal and reinsertion of the cable ends,when the


X-ray tube is replaced.
● Replacement of the HT cable.


Contents


a. Safety precautions
b. High-tension failure of the HT cable
c. Damage to the cable electrical safety shield
d. Arcing in the X-ray tube receptacle
e. Burnt pins on the cathode cable end
f. Caution on removing HT cable ends
g. HT cable replacement
h. HT cable fault with CD mobiles
i. Preparation prior to inserting the HT cable end
j. Inserting the HT cable end
k. Need for re-calibration




● If a HT cable is suspect, test by replacing the cable.
i. This may be a spare cable from an old installa-


tion, or else a loan cable sent from the service
department.


ii. Observe carefully the procedures and precau-
tions in this module, before replacing a cable.


● See ‘Arcing in the X-ray tube receptacle’, part ‘d’.


c. Damage to the cable electrical safety shield


The HT cable is fitted with a wire mesh safety shield.
This is just below the outer insulation. If there is a
failure of the cable insulation, the shield conducts the
high-voltage spark to ground. The safety shield is sol-
dered to the metal flange of the cable end.Twisting of
the HT cable can cause the wire strands to break.


In some cases, the shield is found completely dis-
connected. This can be very dangerous. See ‘Caution
on removing high-tension cable ends’, part ‘f’.


● To inspect, undo the cable-end retaining ring-nut.
Slide back the cable support cuff. Check for broken
strands.


● In some cases, the shield connection is wrapped in
insulation tape. This form of construction is weak,
and is prone to have damage to the shield. Unwrap
the tape to inspect for broken strands. If ok, then
re-wrap using fresh tape.


● If there are broken strands, and especially if this is
extensive, a repair should be attempted. An electri-
cian or electronics technician should perform this
repair, after obtaining advice from the service
department.
i. A soldering iron is required. 75~100 watt is


optimum.This is to allow quick soldering to the
cable end without spreading excessive heat.


ii. You will need some fine multi-strand ‘hook up’
wire. (The type needed for general electronics
wiring). Or if possible, the braided shield from a
length of co-axial cable. If using hook-up wire,
remove the insulation from the wire.


iii. Gather the broken strands of the shield wire. If
necessary, remove a little of the cable outer
insulating sheath. Twist together to make four
bunches, spaced around the cable end.


iv. Solder to one end of the hook-up wire.Take the
hook-up wire a full turn clockwise around the
cable end, then solder to the cable end.


v. Repeat this with the other three bunches, alter-
nating the direction around the cable end. Eg,
anticlockwise, then clockwise, and finally
anticlockwise.


vi. Use insulation tape to cover the repaired shield
connection.


● Please note. In some cases it may be claimed that
the system is safe, providing the shield is connected
to ground at the transformer end. This is not
correct. Besides possible danger, this can upset the
performance of high-frequency X-ray generators,
and create interference in other equipment.


d. Arcing in the X-ray tube receptacle


This is a common cause of failure. Arcing can be
caused by a number of reasons. There may be poor
quality or dried-out insulating grease. The grease may
have been incorrectly applied. If the cable end is loose,
this will create air gaps, and eventual arcing. Later
systems use silicon rubber anti-corona insulating pads.
Unless care is taken installing these pads, arcing will
occur. Finally, a fault can occur inside the cable end
itself. In affect, a fault in the HT cable, but not exter-
nally apparent until the cable end is removed.


● See ‘Caution on removing HT cable ends’, and
‘Preparation prior to inserting the cable end’.


● With the cable end withdrawn, look for possible
carbon tracks on the cable end, or in the
receptacle.


● Where there is grease in the receptacle, wipe the
grease with a fresh paper tissue. If arcing occurs in
the grease, this will show up as carbon deposits on
the paper. Old grease may have a yellow colour, but
this does not indicate arcing.


● Examine the cable end carefully for signs of swelling
or cracking. This would indicate arcing. In this case
a replacement HT cable is required.


● Wipe out all grease from the receptacle and the
cable end. With a torch examine the receptacle
carefully for signs of arcing.


● If silicon rubber anti-corona pads are fitted, these
may remain attached to the cable end. More often
they will remain in the receptacle.
i. Pads are often used without grease. However,


wipe the inside of the receptacle and the cable-
end with a fresh paper tissue. If it appears dirty,
this is a sign of arcing.


ii. Examine the pads for possible hairline black
marks, which indicate arcing.


iii. The pads should be replaced after being dis-
turbed.


iv. In case a replacement pad is not immediately
available, then they may be returned to service.
Take care not to touch them directly with the
fingers. (Use a paper tissue.) Have the pads
replaced at the first opportunity.


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e. Burnt pins on the cathode cable end


The cathode filament current may be between 4.0~
5.5amps. If the pins on the cable end do not make
good contact inside the receptacle, they will become
burnt. This produces added resistance to the filament
circuit, and reduced filament heating.


In the case where light or no exposures occur, this
may be due to poor contact of the cathode cable-end
pins.


Do not make the following test with a capacitor dis-
charge mobile. Please refer to ‘High tension precau-
tions’ in module 6.2 page 94.


Undo the ring nut sufficiently to withdraw the cable
end about 2~4mm. Then reinsert the cable end and
tighten the ring nut. If this action restores or improves
the X-ray output, then the cable-end pins are suspect.


The cable end should now be fully withdrawn and
examined.


● See ‘Caution on removing HT cable ends’, and
‘Preparation prior to inserting the cable end’.


● Examine the cable-end pins. Look for a pin that
shows burn marks, or pitting.


● Clean the pin with fine emery cloth or sand paper.
● If the cable-end pins are burnt, then the pin sockets


of the housing receptacle will also need cleaning.
One method is to use a wire coat hanger, with one
end filed flat. This can be used to scrape the sides
of the socket into which the cable-end pins fit.


● Most HT cable-end pins are solid brass, split in two
halves.These tend to close together, and make a less
secure fit in the receptacle. The pins may be care-
fully spread apart, so the air gap in the middle is
parallel.


● Caution; these pins are brittle. Do not try to spread
them apart using a screwdriver. The best tool is a
utility knife with a retractable blade. This blade is
just slightly thicker than the required gap. Push
the blade into the gap very carefully, so the gap
becomes almost, or just, parallel.


● Help. A pin is broken. All is not lost. However, you
will need to exchange the anode and cathode cables.
(At the HT transformer as well as the X-ray tube)


● Before attempting to reinsert the cable end, ensure
it is thoroughly cleaned.This is especially important
after handling the end, as small traces of perspira-
tion or fingerprints etc may be left behind. See
‘Inserting the HT cable end’.


f. Caution on removing HT cable ends


● If in a capacitor discharge mobile, please refer to
‘High tension precautions’ in module 6.2 page 94.


● When replacing a cable, remove the cable-end first
at the X-ray tube, and then at the high-tension
transformer. This especially applies if the safety
earth shield is damaged at the X-ray tube end.


● As the cable end is withdrawn, touch the endpins to
the screw-thread side of the housing receptacle.
This is to short out any residual high voltage in the
HT cable. This especially applies if high voltage was
generated, but with no mA.


● The cable end may be a very tight fit. Do not try
tugging on the HT cable to remove it. Instead, use
two screwdrivers, one on each side of the cable-end
flange, to lift, or ease, the cable end from the
receptacle.


g. HT cable replacement


● If the anode HT cable is replaced with a different
type or length, in most cases this makes little dif-
ference to the performance, especially if the differ-
ence in length is less than 10~15%.


● An exception may be with some medium frequency
inverter systems, which have an adjustment for dif-
ferent lengths of HT cables. Check with the service
department for this possibility.


● In the case of the cathode cable, a different length
or type can change the mA calibration. Providing
the anode cable is the same type and length as
the failed cathode cable, then exchange cables, so
the replacement is used for the anode side. This
will avoid the requirement for immediate mA
recalibration.


h. HT cable fault with capacitor
discharge mobiles


The CD mobile cathode-cable can develop a short
circuit between the internal control-grid wire, and the
filament wires. In most cases, the anode cable will be
in good condition, and can be exchanged for the
cathode cable. mA calibration is not critical, and will
not need to be adjusted. If exchanging cables, attach
an internal notice to indicate a change has been made.
This will avoid future frustration in case another
change is attempted.


Before attempting to remove or replace a CD mobile
cable, please refer to ‘High tension precautions’ in
module 6.2 page 94. Otherwise replacement is the
same as for a standard system.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


119




i. Preparation prior to inserting the HT
cable end


● Old grease on the cable end, and in the receptacle,
should be removed.


● Thoroughly clean the receptacle and cable end.
When cleaning the receptacle, use paper tissues
wrapped around a wood or plastic rod.


● If necessary, a hydrocarbon cleaning solvent may be
used. Be sure to remove all residues.When cleaning
a cable-end, avoid touching with your hand, this can
leave unwanted perspiration or skin oil. After clean-
ing, the cable end or receptacle should have a high
polished appearance.


● Examine the cable-end pins of the cathode cable.
If of the split pin version, check the pins are
not bent together, and the gap is parallel. See
‘Burnt pins on the cathode cable end’, for tips on
adjusting.


● Most HT cable ends have a rubber sealing-ring.This
is placed over the cable end, up against the flange.
Ensure this is fitted correctly before applying
grease.


● Fresh insulating grease is now required, or a silicon
anti-corona disk.
i. Grease is applied using a wooden or plastic


spatula. For example, a tongue depressor.Do not
apply or smooth the grease with a finger. First
wrap a paper tissue around the finger, to avoid
directly touching the grease.


ii. Apply the grease to about 70% of the length of
the cable-end, starting at the pin end.The depth
of grease at the pin end should be about 2~
3mm, tapering off at the 70% point. The appli-
cation of grease is not critical, as any irregular
area will flow around the sides of the cable end,
as it is inserted.


iii. A layer of about 1~2mm may also be applied to
the front of the pin end, between the pins.


● If a silicon rubber anti-corona disk is used.
i. The disk should be supplied in a sealed package.


Handle the disk with a pair of clean tweezers,
or else by a paper tissue.


ii. Place the disk in position on the cable end, with
the pins passing through the disk.


iii. A small layer of silicon grease may be placed
around the sides of the cable end. This is an
option. If in doubt, check with the service
department for advice.


j. Inserting the HT cable end


● The cable end has a ‘key’ at the flange end.This fits
into a ‘notch’ in the receptacle. Before inserting the
cable end, check the rotational position, so these
two areas will be aligned on insertion.


● On inserting the cable end, try to keep it aligned in
the centre of the receptacle. This ensures an even
distribution of the grease.


● As it becomes fully inserted, rotate the end a little
to align the cable-end pins into the receptacle
sockets.


● A very firm continuous pressure is often required.
This is due to pockets of air in front of the grease,
as well as the viscosity of the grease itself.


● Once the cable-end pins are properly inserted into
the receptacle sockets, it should now be possible to
attach the cable-end retaining ring-nut and cable
support cuff.


● Tighten the ring nut fully. Then check again every
few minutes until it can no longer be even partially
rotated.This should be checked again over the next
few days.


● Attach cable ties to support the HT cable in
position.


k. Need for recalibration


Note. Replacement of the cathode cable can alter the
mA calibration. While replacement with an identical
type and length may have very little affect on the cal-
ibration, this should still be checked.


In case the cathode cable is a different length or
type, this may have a large affect on the mA calibra-
tion, depending on the design of the generator. Before
attempting any calibration, check first with the service
department for the recommended procedure.


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MODULE 8.0


Bucky and Bucky table


a. General precautions


Please take the following precautions.


● Before testing any fuses, or removing a cover,
always switch the generator power off, and ensure
the isolation power switch for the room is also
switched off.


● Test procedures for fuses or wiring, are described in
module 5.0 page 65.


● When removing the cover from a vertical Bucky,
make sure the Bucky cannot move upwards when
the cover is removed. For example, attach a rope to
hold it in position, or remove the cover with the
Bucky set to maximum height.


● In most cases removal of the Bucky cover is a
simple operation. However, where possible refer to
an installation manual. This will indicate if there is
any special procedure for removing or installing the
cover.


● In the case of a Bucky table, removal of the table-
top may be required. The method used depends on
the table design.
i. Most tabletops may be removed once the screws


holding the ‘profile rails’ in position are removed.
Before attempting to remove these screws,
make sure the screw slots are not blocked with
dirt, and use a screwdriver that has a good fit
and is not blunt.


ii. In other cases, removal of the tabletop end-
stops will allow the tabletop to extend to over
one end. As the tabletop is moved past the end-
stop position, the tabletop will disengage from
the far-end bearings. Have a chair or other suit-
able object ready to support the tabletop.


iii. In some cases, power will need to be switched
on to release the table locks.


iv. To avoid unexpected problems, make sure at
least one person is available to assist.


v. On replacement of the tabletop, check and
manually reseat the locks to allow the tabletop
to pass over them.


vi. Ensure the end stops are securely replaced.
● Keep all screws, or other small parts in a container,


to avoid loss.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


121


Aim


The aim is to provide information and procedures
related to problems with the Bucky and Bucky table.
This is an addition to the maintenance procedures,
provided in module 3.0 page 53.
(Note: Reference module page numbers refer to the
title page.)


Objectives


On completion of this module, the student will be
aware of common problems with the Bucky and Bucky
table, together with their solutions. Adjustments and
repairs may be carried out. Some tests or repairs will
require the assistance of an electrician or electronics
technician.


Task 15.‘A film exhibits grid lines’, should be attempted
on completion of this module.


Contents


a. General precautions
b. Grid lines sometimes appear on the film
c. Grid lines appear on all films
d. The film is dark in the centre, but fades out to either


side
e. No exposure on a selected Bucky
f. The cassette tray does not hold the cassette prop-


erly in the vertical Bucky
g. The Bucky lock does not operate
h. The table magnetic locks slip, or are unreliable
i. The table auto-centre does not operate, or is not


accurate
j. Noisy tabletop movement
k. Elevating Bucky-table problems




b. Grid lines sometimes appear on the film


There are several possibilities.


● The grid starts oscillating as soon as the X-ray
control is placed in preparation.
i. This form of operation does not synchronise the


exposure to the grid position. As a result, an
exposure can commence when the grid has
reached the end of travel, and is reversing
direction.


ii. Test by looking for grid movement when in
preparation, before an exposure. If this is the
cause of the problem, re-installation of the
Bucky wiring is required. Consult the service
department for advice.


● The Bucky has a slow moving grid. In this case, there
is insufficient grid movement when performing
short exposure times. A replacement Bucky of a
later design is required.


● Some Bucky’s have a rotating cam to operate the
grid.
i. The grid moves quickly at first, then slower until


the full ‘in and out’ cycle is completed. This is
repeated till the exposure is completed.


ii. The Bucky has an adjustment to ensure the
exposure commences at the point of maximum
speed. If incorrectly adjusted, then the exposure
could commence before that point, when the
grid is at minimum speed.


iii. This is indicated if grid lines occur on short
exposure times. If adjustment is required,
request the service department to adjust the
Bucky.


● In the case of mammography, many Bucky’s have a
speed adjustment.
i. Optimum adjustment is for the grid to reach


75% of its stroke during an average exposure.
If grid lines occur on short exposures, then
increase the speed. Or, if grid lines occur during
long exposures, then reduce the speed.


ii. This may be a screwdriver adjustment at the
back of the Bucky, or it may be an internal
adjustment. In that case, the service depart-
ment must make the adjustment.


● The grid movement may be hitting an obstruction,
and while moving far enough to permit an exposure,
then stops moving. Or, in some cases, the grid drive
may be sticking.This can be indicated if short expo-
sure times are ok, but long exposure times have grid
lines.
i. Close the collimator, and direct the X-ray tube


away from the Bucky.


ii. Select minimum kV, the lowest mA station, and
a long exposure time.


iii. Remove the cassette tray, so the grid may be
clearly observed.


iv. Have an assistant make an exposure, using the
Bucky under test. Observe the grid movement,
looking for signs of hesitation. Does it tend to
stop before reversing?


v. If a problem is indicated, then remove the
Bucky cover, or tabletop, and examine the
mechanism while it is moving. Look for film
markers causing an obstruction.


vi. Some motors can have damaged gears, with
missing teeth. In this case, repair kits may be
available.


vii. Apply a small amount of oil to moving surfaces.


c. Grid lines appear on all films


● The wrong Bucky was selected. Is the selection
switch correctly labelled?


● Listen for a Bucky sound during a test exposure.
Does the selected Bucky operate? Does it sound
normal?


● A common cause is a dislodged grid. For example,
the grid has fallen from the grid frame, or holder.
In this situation, although the frame moves, per-
mitting an exposure, the grid itself does not move.
To remount the grid in the frame, removal of the
Bucky cover, or tabletop, may be required.


d.The film is dark in the centre, but fades out
to either side


● The grid was removed, and then reinserted upside
down.


● Is the grid focal distance within the range you are
using?
i. Can the grid be removed? Look for a label that


provides the focal length of the grid.
ii. If it is difficult to remove the grid, try a test


exposure after changing the FFD. Make a direct
low kV and mAs exposure, without a patient.


● Is the vertical Bucky correctly aligned to the X-ray
tube?
i. For example, is the Bucky at an angle to the


x-ray beam?
ii. This can occur if the vertical Bucky is not cor-


rectly installed. The Bucky may be mounted
against a wall, which is not at an angle of ninety
degrees to the tube-stand.


● Image fade off to one side may be a problem due
to the X-ray tube or collimator. To check, make a
direct exposure to a cassette on the tabletop.


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i. A direct exposure at low kV will exhibit some
fade off towards the cathode side of the tube.
On large films, a larger fade-off can occur
towards the anode side of the film, due to the
anode heel-affect.


ii. To test at the kV values normally used, a suit-
able filter is necessary. For example, 1.0mm of
copper in front of the collimator. Or else 10cm
of water in a plastic container.


iii. Set a similar kV to that used when observing
the problem. Adjust the mAs to achieve a suit-
able density.


iv. If the fade off is still present, the collimator may
be out of alignment. For example, the collima-
tor is incorrectly centred to the X-ray tube, and
the light beam was adjusted to compensate.See
module 7.2 page 110.


v. There may be excessive metal deposits on the
X-ray tube glass. You will need to remove the
collimator to check. Contact the service depart-
ment for advice before attempting removal.
See module 7.1 page 104.


e. No exposure on a selected Bucky


In this situation, a test exposure using direct non-
Bucky radiography is successful.


● Close the collimator, and move the tube away from
the Bucky.


● Select minimum kV, a low mA station, and a
medium time setting.


● When trying to make a Bucky exposure;
i. Listen carefully at the Bucky for any sound.With


the cassette tray removed, see if the grid moves.
ii. If no sign of any grid movement, check the


Bucky cable for a possible loose connection or
broken wire. See module 5.0 page 65.


iii. Check for a possible blown fuse. To locate the
fuse, see module 5.0 page 65, or consult the
service department.


● When trying to make a Bucky exposure, the Bucky
starts to operate, but there is no exposure.
i. Check the Bucky cable for a possible loose or


broken connection. See module 5.0 page 65.
ii. Remove the Bucky cover, or the tabletop.
iii. Look for any object that could be blocking the


grid movement, such as a lost film marker. This
can happen with a wall Bucky, or a Bucky with
a fluoroscopy table.


iv. On attempting an exposure, does the grid drive
motor operate? Look for damaged fibre gears,
or a broken drive cord.


v. Does the grid manage a full ‘stroke’? As the grid
moves from the ‘rest’ to the ‘expose’ position,
a microswitch is operated. This microswitch
allows the exposure to commence. Check the
microswitch for correct operation. See module
5.0 page 65.


f.The cassette tray does not hold the cassette
properly in the vertical Bucky


● In some cassette tray designs, the amount of ‘grip’
is insufficient.To prevent the cassette slipping down,
the manufacturer supplies small wood blocks with
an attached magnet. In other designs, a metal
support is provided, which fits into a series of holes.


● The rubber grips attached to the tray jaws become
smooth, allowing the cassette to slip. The rubber
grips can be improved by cleaning with lighter fluid,
or a similar hydrocarbon.


● The jaws may not be closing fully. Check and adjust
the position of the clamping knob on the shaft.


g.The Bucky lock does not operate


● Look for a faulty switch, or broken connection,
either to the switch or the magnetic lock coil. The
lock coil may be open circuit. Test with a multi-
meter set to medium ‘ohms’ scale. See module 5.0
page 65.


● The lock coil may have too large an air gap. Adjust
it closer to the operating surface.


h.The table magnetic-locks slip, or are
unreliable


● Before testing any fuses, or removing a cover,
always switch the generator power off, and ensure
the isolation power switch for the room is also
switched off.


● Test procedures for fuses or wiring, are described in
module 5.0 page 65.


● No locks operate.
i. A fuse could be open circuit. Before replacing,


check the wiring to the lock coils or switches,
and look for possible damaged insulation.


ii. A foot switch is faulty, or has a bad cable
connection.


● A specific lock fails to operate.
i. If other locks are operating, it is unlikely to be


an open circuit fuse. However, still check, as the
lock may not be the same type, and has a
separate fuse.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


123




ii. There may be an open circuit lock coil, or
winding.


iii. To check the lock coil, first ensure all power is
switched off.Disconnect the lock from the table.
Use a multimeter set on a medium ohms scale to
check the resistance of the lock coil. This may
measure around 500 to 2000ohms depending on
design.If unsure,check against a similar lock coil
in the table,or contact the service department.


iv. Check the wiring for possible loose or broken
connections.


v. Check the control switch.
● The table lateral-movement lock is weak.


i. Check the number of locks installed for lateral
operation. Some tables were supplied with only
one lock. In this case, apart from cleaning the
front of the lock, little improvement can be made.


ii. Where there are two locks, one of the lock coils
may have failed.Watch the locks when they are
switched on and off. If only one lock moves, the
other lock might have an open circuit winding.
In some cases, you may find the suspect lock
cool to touch.


iii. Note. Locks may be positioned either at one
end, or at both ends of the table.


iv. To check the lock coil, first ensure all power is
switched off.Disconnect the lock from the table.
Use a multimeter set on a medium ohms scale
to check the resistance of the lock coil.This may
measure around 500 to 2000ohms depending
on design. If unsure, check against a similar
lock coil in the table, or contact the service
department.


v. Check the wiring for possible loose or broken
connections to the suspect lock coil.


● The locks make a rattling or buzzing noise. Check
the mounting of the locks. Is the lock parallel to the
operating surface? Is there a large air gap when not
switched on? Another possibility is dirt on the top,
or face, of the lock.


i.The table auto-centre does not operate,
or is not accurate


● To test the table lateral centre-position.
i. Place a cassette in the Bucky, with a marker


positioned on the centre of the cassette.
ii. Place another marker on the centre of the


tabletop.
iii. Move the tabletop to the lateral centre-position.
iv. Make a low kV and mAs exposure. Process the


film and check if both markers are in the same
position.


● Some tables have a mechanical centre stop. A
spring tensioned steel ball clicks into a slot when
the table is centred.
i. The spring can have a tension adjustment screw.


Tighten the screw to obtain a firm stopping
action.


ii. Are the screws holding the mechanical centre
stop loose?


iii. To adjust the stop position, undo the screws a
small amount, and push the centre stop to the
required position. Tighten the screws to prevent
movement.Make a test film to confirm the table
is centred.


● Other tables may switch on the electromagnetic
locks when in the centre position. This is usually
by a cam passing over a microswitch. (Later
designs may use electronic sensors, such as
optoelectronics.)
i. If the microswitch is positioned away from the


cam, unreliable operation can result. If posi-
tioned too close, then poor centring action
results. For example, the stopping position
becomes wide.


ii. Centre position is adjusted by moving the cam,
or else the microswitch.


● The centre microswitch, or the auto-centre selec-
tion switch can have faulty contacts. Ensure power
is turned off. Check with a multimeter set to low
ohms scale to test the switch.


● For other possibilities, contact the service depart-
ment for advice.


j. Noisy tabletop movement


A ‘clunking’ noise is heard as the tabletop is moved.


● This may be due to a faulty bearing, or it may be
caused by dirt in the bearing tracks, or on the rim
of the bearings. Spray the bearings and bearing
track with light aerosol oil, and wipe down with a
rag.


● Watch the bearings as the tabletop is moved. A
faulty bearing may have a cracked or missing rim.
In some cases, the bearing does not rotate, and the
table is stiff to move.


● Contact the service department for a replacement
bearing, plus advice for replacing the bearing.


k. Elevating Bucky-table problems


● The tabletop will rise up, but not move down.
i. Many tables have been damaged after being


brought down onto a chair or patient stool.Two
common safety devices are now used.


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ii. A pressure-pad is installed on the floor, posi-
tioned at both ends of the table. Pressure on
these pads activates a relay, which stops the
downward movement of the table. Is there an
object pushing on the pad, or has the pad
become damaged?


iii. A sensitive microswitch is installed in the middle
of the longitudinal bearing tracks. This may
require adjustment. Contact the service depart-
ment for advice.


● The table does not stop at the operating height.
i. A cam-operated microswitch is used to switch


off the motor once the operating height is
reached.


ii. The position of the cam or microswitch may
require adjustment.


● The motor does not operate.
i. On some tables, occasional failure of the motor


power fuse occurs. Before attempting to replace
the fuse, ensure all power is turned off.


ii. When replacing the fuse, use a delay or slow-
blow type. See module 5.0 page 65.


iii. For location of the fuse, refer to the parts or
installation manuals.


iv. If the fuse continues to fail, contact the service
department for advice.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


125




TASK 15


A film exhibits grid lines


After taking a chest X-ray, you notice prominent grid lines on the film.


Make a list of possible reasons for this problem.


Describe suitable tests to either confirm, or eliminate, possibilities from this list.


Carry out these tests. What were the results?


What action is needed to correct the problem?


Tutor’s comments


Satisfactory/Unsatisfactory


Signed Date


Tutor


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MODULE 8.1


Tomography attachment


a. General precautions


Please take the following precautions.


● Before testing any fuses, or removing a cover,
always switch the generator power off, and ensure
the isolation power switch for the room is also
switched off.


● When investigating a possible bad connection, open
circuit fuse, or faulty switch, refer to the procedures
in module 5.0 page 65.


● Older tomography attachments have either limited,
or no safety interlocks. Do not operate the motor
without the fulcrum pole.


b. Failure to operate


This may be due to incorrect set-up, operation of a
safety interlock, or an open circuit fuse to the motor.
Where sections of the attachment are connected via
plugs and sockets, these need to be checked.


● Incorrect set-up may cause operation of a safety
interlock. This helps guard against operator error.
When all else fails, then read the operation manual.


● Current tomography attachments can have a
number of safety interlocks, depending on the
design, and integration with the tube stand.


● Older systems depend more on correct set-up, such
as ensuring the rotation and longitudinal tube-
stand locks, and Bucky lock, is off.This requires care
by the operator before using the system.


● Typical interlocks for a tomography attachment can
include:
i. The fulcrum pole interlock. If the fulcrum pole


is not attached, the tomography system does
not ‘know’ the stop or start positions. If ener-
gized, the motor would drive the tube-stand to
the end of the tube-stand track. The interlock
usually consists of a microswitch. This is oper-
ated when the fulcrum pole is attached to the
tube-stand cross-arm. The actuating lever for
this microswitch may be damaged, or out of
adjustment. Listen for a small ‘click’ as the
fulcrum pole is placed in position.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


127


Aim


The aim is to provide information and procedures
related to problems with a tomography system. This
may be a tomography attachment, fitted to a standard
tube-stand, or integrated with a Bucky table.This is an
addition to the maintenance procedures, provided in
module 3.1 page 55.
(Note: Reference module page numbers refer to the
title page.)


Objectives


On completion of this module, the student will be
aware of common problems with the tomography
attachment, including operator error, or problems with
a safety interlock. Adjustments and repairs may be
carried out.Some tests or repairs will require the assis-
tance of an electrician or electronics technician.


Contents


a. General precautions
b. Failure to operate
c. The tomography image has poor definition
d. The required exposure time is difficult to estimate




ii. An exception to the above is where the motor
has an arm that engages with a floor, or ceiling,
slotted guide plate.This system can only operate
over the distance controlled by rotation of the
arm. However, later systems do have an interlock
to check if the fulcrum pole is fitted. This pre-
vents a wrong exposure.


iii. X-ray tube height. If not correct, then tomogra-
phy calibration is incorrect. This is measured by
a cam-operated microswitch, or in some cases
by an optoelectronic sensor and reflective strip.
Operation of the height sensor occurs only over
a narrow distance.Try moving the tube-stand up
or down a small amount.


iv. Tube-stand and Bucky locks are often automat-
ically turned off or on by selection of tomogra-
phy operation. However, in some systems this
is not the case, and failure to switch off the
longitudinal lock can prevent the motor from
moving the tube stand.


● The tomography motor has a high ‘inrush’ current
on start up. An open circuit fuse is not uncommon.
i. Before testing or replacing a fuse, ensure all


power is turned off. See module 5.0 page 65.
ii. Look for any cables that might be damaged,


causing a short circuit.
iii. The fuse could be positioned close to the motor


system, or else in the tomography control
cabinet. Use a delay, or slow-blow, fuse as a
replacement.


iv. If the fuse fails shortly after replacement,
contact the service department for advice.


● The fulcrum tower has a number of contacts con-
trolled by rotation of the fulcrum.These may be cam
operated switches, or else a metal-strip with a
sliding contact, or ‘commutator’. Selection of the
appropriate section controls the start-stop position
of the motor, and the tomographic angle.
i. There may be broken connections in the cable


plug and socket. Another possibility is a broken
microswitch, or commutator brush, inside the
fulcrum tower. Before investigating, ensure all
power is turned off.


ii. An exception is where the tomographic angle
and start-stop position is controlled by a series
of cams coupled directly to the drive motor. In
this case, the tower will only have a motor and
light for setting the fulcrum height.


c.The tomography image has poor definition


During a tomographic scan, the film in Bucky must
retain the correct alignment with the X-ray tube focal


spot.This requires a smooth movement when travelling
through the actual exposure area.


● To evaluate the actual performance, the tomo-
graphic resolution test piece described in appendix
B page 169, section is recommended. When oper-
ated at the correct height, a clear image of the
central paper clips should be obtained.
i. To avoid over exposing the film, use a low mA


station, and low kV. If the film is still too dark,
then insert a sheet of paper between one inten-
sifying screen and the film.


ii. Repeat this test for different combinations of
speeds and angles.


● If a good image is not obtained with the test piece,
then check the following.
i. Uncouple the fulcrum pole. Otherwise remain


in tomographic set-up mode.
ii. Check that the tube rotation lock is off. The


tube should be able to rotate smoothly, and
remain balanced as it is rotated.


iii. Check the Bucky movement. The Bucky lock
should be fully off, and the Bucky should move
smoothly in the table.


iv. Is the longitudinal lock released? With some
systems, it will be necessary to exit tomo-
graphic mode, and then check the lock releases
correctly.


v. Is the fulcrum tower securely mounted?
vi. Is the fulcrum pole in good condition? The


fulcrum pole should not bend or twist.
vii. With the fulcrum pole in position, but not in


tomographic mode,push the tube-stand across
the floor. Look for any sudden stiffness, or
jerking. Look for dirt in the guide rails.


viii. A wire cable is used to pull some systems. Is
the cable firm, and not slipping on the motor
drive pulley?


ix. The same applies to units with a belt drive. A
loose belt can stretch, and give an uneven start
to the movement.


x. Some motors have a drive wheel pressed
against the floor. Depending on the floor
surface, the wheel slips and drives unevenly. To
stop the wheel slipping, glue a strip of mate-
rial that has a rough surface, to the floor. For
example, the type that is fitted to the steps of
a staircase.


d.The required exposure time is difficult
to estimate


● A microprocessor controlled tomography unit, inte-
grated with the X-ray control, may directly set the


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


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exposure time. Otherwise the operator must select
a minimum exposure time, called the ‘backup’ time.


● The backup time must be longer than the actual
exposure time, which is controlled by the combina-
tion of tomography speed and angle.The tomograph
operation manual should indicate the actual expo-
sure times. A minimum backup time of 5~10%
longer is recommended.


● If the operation manual indicates times for 60hz
operation only, a correction factor is needed for
50hz operation. Multiply the 60hz tomographic
times by the conversion factor of 1.20.


● If no information is available, contact the service
department. They may need to measure the actual
exposure times, and then make a suitable reference
chart.


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129




MODULE 9.0


Fluoroscopy table


including operator error, or problems with a safety
interlock.Adjustments and repairs may be carried out.
If assistance is required from the service department,
an accurate description of the problem can be
provided.


Note: Some tests or repairs will require the assis-
tance of an electrician or electronics technician.


Contents


a. General precautions
b. No fluoroscopy exposure, X-ray control checks
c. No fluoroscopy exposure, table interlock checks
d. No fluoroscopy exposure, table electrical checks
e. The X-ray control indicates fluoroscopy is operating,


but no image
f. No radiography exposure
g. Artefacts on the film
h. Manual collimation has unwanted beam limitation
i. X-ray beam alignment is incorrect
j. Table movements do not operate
k. Table locks do not operate


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130


Aim


A fluoroscopy table can range from the most basic
version to a highly sophisticated remote control micro-
processor system. Many problems are caused when
‘standard’ operating procedures are changed. For
example, switches and selections may be set to a dif-
ferent position.


The fluoroscopy table has a large number of safety
interlocks. These can be activated by operator error.
Other possibilities are problems with the X-ray tube,
the X-ray control, and the TV imaging system.


The information and procedures provided in this
module are for basic tables fitted with an under-table
tube. Some suggestions will however be common to all
versions.
(Note: Reference module page numbers refer to the
title page.)


Objectives


On completion of this module, the student will be
aware of common problems with the fluoroscopy table,


a. General precautions


Please take the following precautions.


● Before testing any fuses, or removing a cover, always
switch the generator power off, and ensure the iso-
lation power switch for the room is also switched off.


● Test procedures for fuses, switches, or wiring; are
described in module 5.0 page 65.


● Any dismantling of the table to test connections,
switches, or broken wires; should be performed by
an electrician, or electronics technician.


● If removing a cover, or dismantling any section,
place the screws in a container to avoid loss.


b. No fluoroscopy exposure, X-ray
control checks


● Has a correct technique been selected?
● Check the fluoroscopy timer. Has it timed out?


● Does the X-ray control have automatic regulation of
fluoroscopy output? If so, turn this off, and try a
manual setting of mA and kV.


● Is there a fault indication at the control on trying
an exposure?
i. In some cases, if actual fluoroscopy mA is too


high, the exposure immediately stops. A fault
condition may only illuminate while attempting
an exposure, but disappear once the exposure
attempt is released. In other cases, it may be
necessary to switch ‘off’ then ‘on’ again to reset
the safety interlock.


ii. Reduce the fluoroscopic mA and kV setting,
close the table collimator, and try another fluo-
roscopy exposure.


iii. If at a lower mA setting, fluoroscopy is now ok,
then try slowly advancing the mA knob during a
test exposure. Watch the mA meter. Look for




instability, as this could indicate a gassy tube, or
perhaps a high-tension fault. An ‘over mA’ fault
may occur when mA reaches 6.0mA, but in
some cases be as low as 4.0mA, depending on
equipment design.


iv. Some controls have no manual selection of mA;
instead the value of mA is controlled by fluo-
roscopy kV. In this case, advance the kV control,
as in part (v). Observe the mA meter for exces-
sive mA or instability.


v. If excessive mA is not the cause of the problem,
then slowly advance the kV control.Again, watch
the mA meter, looking for instability. Should a
problem occur as kV is increased, this could indi-
cate gas in the X-ray tube, or an arc where the
high-tension cable-end enters the X-ray-tube
receptacle. See module 7.1 page 104, and
module 7.3 page 117.


c. No fluoroscopy exposure table,
interlock checks


The fluoroscopy table can have a number of interlocks
for radiation safety. Some of the possibilities discussed
depend on individual table design, and may not be
present in your table.


● Is the correct technique selected at the table?
i. For example, a remote controlled table may be


in tomographic mode, or a collimator key switch
may have been turned to manual operation.


ii. The table may have a separate fluoroscopic
timer. Has this timed out?


iii. Some designs have a fluoroscopy-preparation
switch. This must be pressed to place the table
in operation, after selecting fluoroscopy opera-
tion at the X-ray control. (The switch has a flu-
oroscopy symbol.) With this system, the table is
automatically deselected if the technique is
changed at the control, and must be reselected
each time prior to use.


● Are there any warning lights or fault codes displayed
on the table? Refer to the operating manual, or con-
tact the service department for further information.


● Is the image intensifier, or fluorescent screen cor-
rectly mounted, and not loose?
i. This especially applies if the image system is


removed from the table, to park the serial-
changer out of the way.


ii. The safety interlock is a small microswitch. The
microswitch actuator may have become bent,
or out of adjustment, when the image system
was repositioned, or not operated if the image
system clamps are loose.


● Is the serial-changer fully positioned in the operat-
ing position?
i. When the serial-changer is brought forward


from the parked position to the operating posi-
tion, a microswitch is operated, permitting flu-
oroscopy operation.


ii. Locate the position of this microswitch, and
check if it has operated correctly. It may be pos-
sible to hear a small ‘click’ as the serial-changer
is moved into position.


iii. Some designs uncouple the undertable tube
carriage to allow parking of the serial-changer.
As the serial-changer is brought forward, the
tube carriage should lock back in position.
Check to make sure this has happened. Again, a
safety interlock microswitch needs to be oper-
ated. This microswitch may need adjustment.


● Is there a cassette incorrectly positioned?
i. For example, in the ‘load/unload’ position.
ii. Manually operated serial-changers have a


microswitch, which prevents fluoroscopy unless
the cassette carriage is fully retracted. For
example, when the cassette carriage is brought
to the radiography position, fluoroscopy is
immediately switched off. Further movement
operates another microswitch, which sends the
preparation request to the X-ray control. Check
the operation of these microswitches.


● Is the Bucky parked at the foot-end of the table?
i. This can apply to tables where a radiation shield


covers the Bucky-slot when the Bucky is parked.
Check the safety microswitch operated by this
shield. It may be possible to hear a small ‘click’
as the shield is opened and closed.


● Some older tables were designed to enable the
undertable tube to be used with a wall Bucky.These
have a microswitch to ensure the tube is correctly
positioned for fluoroscopy.This rarely has a problem,
but should be checked.


d. No fluoroscopy exposure, table electrical
checks


Note. Test procedures for fuses, switches, or wiring; are
described in module 5.0 page 65.


● The footswitch is a common cause of failure. The
connecting cable can have broken connections,
either at the footswitch, or where it connects to the
table. In addition, the cable itself may have a broken
internal wire.
i. Before removing any covers, or make any meas-


urements, ensure all power is disconnected.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


131




ii. With a multimeter set to the low ohms position,
test the continuity of the cable and footswitch
contacts. This test should be made where the
cable enters the table.


iii. With the footswitch operated, a low resistance
reading of less than five ohms should be
obtained.


● The connecting cables from the serial-changer to
the table foot, or to the table serial-changer ‘tower’,
may have broken or loose connections. This espe-
cially applies if the cables are pulled or stretched
during operation.Broken internal wires in the cables
can also occur. If suspect, the individual wires can
be checked by measuring across both ends, in a
similar fashion to the footswitch. This procedure
must only be attempted by an electrician or elec-
tronics technician.


● Have there been any indications of rats? Some rats
enjoy biting wires. This especially applies to the
internal wiring of a table. Damage can appear
similar to cutting wires with a pair of scissors.


e.The X-ray control indicates fluoroscopy is
operating, but no image


On attempting fluoroscopy, the X-ray control indicates
a fluoroscopic exposure is operating,and the mA meter
indicates a normal value of mA.


● Has the TV been properly switched on and adjusted?
See module 9.1 page 135.


● Is the collimator closed?
i. Try operating the collimator controls to the half


open position.
ii. To ensure the collimator is in fact open, place a


cassette face down on the tabletop. Make a one
or two second fluoroscopy exposure,and process
the film.


iii. If the film is blank, there can be a problem with
the collimation control. Contact the service
department for advice.


iv. If the film is exposed, there is a problem with
the TV image system. See module 9.1 page 135.


● If operating under automatic regulation, change to
manual operation.Check that a suitable value of mA
and kV can be obtained. If mA is too low, there may
be a poor filament connection at the cathode cable
end into the X-ray receptacle. See module 7.3 page
117.


f. No radiography exposure


The safety interlocks and conditions that prevent
fluoroscopy will also prevent radiography. So pro-


viding fluoroscopy operates correctly, we can con-
sider the requirements of most interlocks satisfied.
However, there are some additional requirements for
radiography.


● Has the cassette has already been exposed? Try
another cassette.


● Has a cassette of the correct size for the required
format been inserted?
i. Try a different size cassette or format selection.
ii. If a different size cassette allows operation,


there is either a problem with the internal
recognition of the cassette size, or else the cas-
sette is not compatible with the table. For
example, trying to use an imperial dimension
cassette, in a table designed for metric sized
cassettes.


iii. Contact the service department for advice.
● Does the cassette move forward into the expose


position? (This assumes a motor drive cassette
carriage.)
i. Try ejecting and reinserting the cassette. If the


cassette does not eject, it may have been incor-
rectly inserted, and fallen out of position. This
can cause the carriage to become jammed.


ii. In case of a cassette jam, try lifting the cassette
using a long wooden or plastic ruler. This may
then allow the cassette to be driven out. Other-
wise it will be necessary to gain access by either
removing the serial-changer cover, or removing
the image intensifier. Make sure all power is
switched off before removing the cover.


● As the cassette moves forward into the expose
position, does the X-ray control go into preparation
mode, and then indicate ‘ready for exposure’?
i. Check for normal operation of the X-ray control


by a test exposure on the over-table tube.
ii. A hand operated cassette carriage operates a


microswitch when it moves towards the expose
position. This microswitch produces the prepa-
ration request for the X-ray control. There may
be two microswitches close together.As the car-
riage moves forward, listen carefully for a ‘click’
from each microswitch.A small adjustment may
be required to obtain correct actuation.


ii. Listen to the X-ray tube. Can you hear anode
rotation on the preparation request? If not,
check the stator cable for possible damage. For
example, it may have been caught up in the
undertable mechanism, or have a broken inter-
nal wire where it enters the serial-changer
longitudinal carriage. Ask an electrician or elec-
tronics technician for assistance.


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


132




iv. There may be a problem with the large focus.
Try radiography on the fine focus. If preparation
is now OK, there could be a poor filament con-
nection with the cathode cable-end, in the X-ray
tube receptacle. In this case affecting the large
focus only. See module 7.3 page 117.


● The cassette has moved into the ‘expose’ position.
The X-ray control indicates ‘ready for exposure’
however, an exposure cannot be made.
i. Check for normal operation of the X-ray control


by a test exposure on the over-table tube.
ii. Some table designs prevent an exposure if the


motorized cassette carriage has stopped out-
side the correct expose position. Try either a
‘full format’ exposure, or else a ‘split’ format
exposure. If the change of format allows an
exposure, the carriage drive requires adjust-
ment. Contact the service department for
advice.


iii. The serial-changer has additional ‘close to film’
shutters that are operated when selecting split
formats. If these shutters are not in their
correct position, this can cause prevent an expo-
sure. This problem can occur with motor driven
shutters after a cassette jam occurs, or due to
lack of maintenance. Track lubrication is
required.


iv. With a manually operated cassette carriage, a
microswitch is operated when the carriage
reaches the ‘stop’ position. On some tables this
assembly can become loose and require adjust-
ment. Before attempting any disassembly,
contact the service department for advice.


v. See also ‘No fluoroscopy exposure, table electri-
cal checks’ regarding the possibility of broken
wires and rat damage etc.


g. Artefacts on the film


Film artefacts are due to several possibilities.


● The cassettes were incorrectly stored in the room,
and have been subject to scattered radiation.
Remember, one minute of fluoroscopy at 2.0mA
and 110kV is equal to four 30mAs exposures at
110kV.


● Poor calibration of the automatic collimation can
mean the X-ray field is much wider than the size
required for fluoroscopy.This can allow radiation to
penetrate the lead shield, designed to protect the
film while the cassette is waiting in its ‘garage’ or
parked position. This can cause intermittent bar
patterns on the film, depending on the type of


examination, fluoroscopy kV levels, and exposure
duration.
i. To test, attach a 35 ¥ 35cm directly beneath


the serial-changer. Apply a few seconds of fluo-
roscopy, then process the film


ii. The fluoroscopy pattern on the film should be
about 5~10% less than the stated diameter of
the image intensifier.


iii. A problem was experienced similar to the above
with some earlier designs of remote controlled
tables. In this case, it was possible to obtain flu-
oroscopy with the collimator key switch in the
manual position. The problems disappeared
after a design change, so that fluoroscopy
was only permitted under automatic beam
limitation.


iv. Some models of fluoroscopy tables, although
collimation was correct, still required additional
lead shielding. For example, the problem was
due to scatter. Discuss this possibility with the
service department.


● Radio-opaque contrast solutions find their way into
unusual places. Barium deposits are easy to see.
Media used for an IVP is less easy to see. If in doubt
clean all surfaces, including under the serial
changer. Look also under the tabletop, and on top
of the undertable tube collimator.


● Another cause can be wiring cables moved out of
position under the tabletop.A frequent cause is due
to the Bucky not parked fully at the table end.


h. Manual collimation has unwanted
beam limitation


In many examinations, such as a barium swallow, the
radiologist will desire to cone in horizontally to opti-
mize the image.When the film is developed, it is found
the top and bottom areas of the film are not exposed.
This affect is due to the collimator field size required
for fluoroscopy. For example, the X-ray field must not
exceed the diameter of the image intensifier field of
view.


Many later designs of tables have an added facility,
called ‘semi automatic collimation’. In this mode the
lateral collimation remains in the position set during
fluoroscopy, while the vertical collimation opens to the
film size during radiography.


It is sometimes possible to convert an older table,
depending on make and model, to also have semiau-
tomatic collimation. Discuss this with your service
department.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


133




i. X-ray beam alignment is incorrect


● Remove the bottom table cover.
● Check if the collimator is loose on the X-ray tube.
● The X-ray beam is shifted to one side of the image.


Lateral shift of the image.
i. In most cases, the tube may have shifted in the


trunnion mounting rings.
ii. Release the trunnion ring clamp, rotate the tube


position only a small amount and test again.
iii. The most critical position is with the spot filmer


at maximum height from the tabletop.
iv. Check with the table horizontal and vertical. If


necessary, a small adjustment between the two
positions may be needed.


● The X-ray beam has shifted vertically.
i. In many cases the tube and trunnion assembly


is mounted to the table via a ‘spigot’. A bump
or vibration of the table can cause this to rotate
slightly.


ii. Locate the clamping screws for the spigot, undo
them just a small amount. Then rotate the
assembly so the beam is realigned. Tighten the
screws, and re-check the alignment.


iii. Small changes in alignment are easily seen with
the spot filmer at maximum height from the
tabletop.


iv. Check with the table horizontal and vertical. If
necessary, a compromise adjustment for the two
positions may be required.


● If not able to adjust the X-ray tube position, or if
not sure of the procedure to suit your table, contact
the service department for advice.


j.Table movements do not operate


● Has an emergency stop switch been activated? The
warning lamp may have failed.Some switch designs,
once pushed in, require the knob to be rotated to
release. Remote controlled tables can have two
switches, one at the control desk, and the other at
the table body. Check both switches.


● Is the vertical compression lock activated? As a
safety precaution this can disable tabletop move-
ments. In some alternate designs, the compression
lock is automatically released when moving the
tabletop.


● Has a patient protection device been operated? In
some tables this is a light beam. Collisions with a
patient trolley can cause this to be misaligned, or
else there is dirt on the optical system. Look also
for table drapes in the wrong position, which can
block the light beam.


● The tabletop will only move in one direction. This
usually means a limit switch has been operated. A
common cause is a faulty microswitch. See also
‘No fluoroscopy exposure, table electrical checks’
in case of broken wires, or rat damage.


● Is there an open circuit fuse? Depending on table
design, this may only affect one motor, or else a
group of motors. Always ensure power is turned off
before checking or attempting a replacement. See
module 5.0 page 65. If unsure, contact the service
department for the fuse location, and to verify the
correct rating and type.


● The table will not tilt vertically.
i. If the table will not tilt in either direction, there


may be an open circuit fuse. Always ensure
power is turned off, before checking or attempt-
ing to replace a fuse. See module 5.0 page 65.


ii. The table may have reached its maximum angle
in one direction, and be unable to return.
(Perhaps it is in Trendelenburg position) This
could be caused by operation of the anti-crash
safety interlock.This may be a bar, or metal flap
at the table end.This can be damaged and stick
in the operated position. Some systems use a
pressure mat on the floor. Look for an object
trapped between the table base and the mat.


k.Table locks do not operate


● Has the compression lock been activated? Depend-
ing on the table design, this will release the serial-
changer longitudinal and lateral locks.


● Is there a problem with the wiring? See ‘No fluo-
roscopy exposure, table electrical checks’ for possi-
ble broken wires and rat damage.


● The lock may have too large an air gap. With the
power switched off, adjust the lock so this gap is at
a minimum.


● A lock coil, or winding, may be open circuit.
i. An electrician, or electronics technician, should


test the lock coil.
ii. Before testing, first ensure the lock activation


switch is off.Then ensure all power is turned off.
iii. Disconnect one of the lock coil connections.
iv. With a multimeter set to medium ohms posi-


tion, test the lock coil for continuity.
v. Depending on design, the lock coil should


measure well below 20,000ohms. If unsure of
the typical value to expect, contact the service
department.


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


134




MODULE 9.1


Fluoroscopy TV


a. General precautions


Please take the following precautions.


● Before testing any fuses, or removing a cover,
always switch the generator power off, and ensure
the isolation power switch for the room is also
switched off.


● Do not attempt any internal adjustment of a TV
monitor. Ask an electronics technician to assist if
internal adjustment of a TV monitor is required.
Dangerous voltages can exist for some time after
the monitor is switched off.


● The TV monitor may not use a standard power
voltage. Damage to the monitor will occur, if con-
nected to the wrong voltage.


● Test procedures for fuses, switches, or wiring; are
described in module 5.0 page 65.


● If removing a cover, or dismantling any section,
place the screws in a container to avoid loss.


● Current TV cameras now use a ‘charge coupled
device’ (CCD) instead of a camera tube. CCD
cameras have very good stability and reliability.
Adjustments to a CCD camera are complex, and
should only be attempted by a qualified technician.


● If in doubt of any adjustment described in this
module, contact the service department before
proceeding.


b. No image on the TV monitor


This most common help request to the service depart-
ment can have a large variety of causes. Many are due
to operator error. Whenever a request is made to the
service department, accurate reporting of the problem
will save time.


● Has the TV been properly turned on and adjusted?
i. Check the position of the brightness and con-


trast controls. Adjust the brightness control and
check if the picture tube lights up.


ii. Some monitors have two video inputs. Check
that the selection switch is in the right position.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


135


Aim


The aim is to provide information and adjustment pro-
cedures, related to problems with a TV imaging system.


The basic TV imaging system consists of the image
intensifier (II), the TV camera and monitor, with pos-
sibly a videocassette recorder (VCR). Systems with
greater complexity, such as DSA and electronic radi-
ography, are not included.


Older TV cameras use camera tubes such as
‘Vidicon’, ‘Chalnicon’, or similar device. Some adjust-
ments for these cameras are included in this module.
(Note: Reference module page numbers refer to the
title page.)


Objectives


On completion of this module, the student will be
aware of common problems with the TV imaging
system. This includes adjustments to the monitor, and
tests to locate the cause of poor image quality. The
VCR is included in these objectives.


Contents


a. General precautions
b. No image on the TV monitor
c. The image is not sharp
d. The picture has no detail in bright areas
e. Is it possible to connect a VCR
f. The VCR recording is the wrong shape on another


monitor
g. Is the image intensifier faulty
h. The image rotates as the fluoroscopy table is tilted




iii. Is a VCR fitted? This may not be switched on.
Or, the video connecting cables have been
wrongly connected. This occurs if the VCR was
used at another location, and then returned.


iv. If a VCR is fitted, this may be incorrectly set up.
Check the input settings. To make a positive
check, disconnect the VCR, and connect the
video cable from the TV camera directly into the
monitor.


● Is the image intensifier receiving a correct fluoro-
scopic exposure? For tests of the collimator, table
interlocks, foot switch and generator, please see
module 9.0 page 130.


● Check the video cable from the TV camera to the
monitor.This cable is sometimes pulled partway out
of its connector, disconnecting the centre wire, or
else causing the connecting pin to pull out.
i. A quick test is to disconnect the video cable. In


most cases, this will cause a change in the
monitor brightness level.


ii. The above test can also indicate if a video signal
is coming from the TV camera. For example, has
the camera been switched on?


● For further tests, see ‘Is the image intensifier
faulty?’


c.The image is not sharp


Besides the possibility of poor ‘system focus’, this can
also be caused by problems with the video cable, or a
faulty picture tube.


System focus includes electronic focus of the image
intensifier and TV camera, and optical focus of the TV
camera. (A CCD camera does not have an electronic
focus adjustment.)


Focus adjustments are sometimes attempted
without checking for other reasons first.They are
also attempted without a focus test tool, which
makes it difficult to find the optimum position.
Unfortunately, the focus adjustment is often the
first adjustment that is ‘fiddled’ with.


Many image intensifiers have multiple adjustments;
these must be carried out in the right sequence. For
these reasons, always consult the service department
first, before attempting any focus adjustments.


● Is the picture tube, or monitor, faulty?
i. The simplest test, if available, is to try another


monitor in the same position.


ii. Adjust the brightness control for a medium
setting. Examine the picture tube closely. The
scanning lines, or raster, should be clearly visible.
In some monitor designs, a focus control may
be available either from the front panel, or the
rear of the monitor.


iii. Does the monitor focus become blurred at
medium brightness levels, but appears ok at a
minimal brightness setting? This indicates a
worn picture tube. Replacement is required.


iv. Does the monitor take a long time to ‘warm up’?
For example, at first the available brightness is
low, and brighter areas of an image merge
together. This is an indication of low electron
emission, from the picture tube cathode. Picture
tube replacement is required.


● Is the 75ohm video-cable termination switch set
correctly?
i. This is a common error. It is often found that if


this switch is turned ‘off’, or unterminated; the
picture appears brighter and has more contrast.
However, in many cases this will cause a loss of
fine detail. The correct position is ‘on’, or termi-
nated; except when there are two or more mon-
itors. In this case, monitors in the middle should
have the termination switch turned off,while the
last, or end, monitor has the termination switch
turned on. (The final monitor will have only one
video cable connection.)


ii. Has a ‘T’connector been used to connect another
monitor or VCR? This is incorrect, as proper ter-
mination of the video cable cannot be obtained,
together with possible loss of fine detail.


● The video, or coaxial, cable has a woven metal shield
under the first layer of insulation. This is connected
to ground by the video connector. Is the shield
pulled out from the connector? This can also give
rise to interference patterns on the monitor, as well
as a loss of picture sharpness.


● Is the TV camera electronic focus correct?
i. This does not apply to CCD cameras, and only


to some cameras that have an accessible focus
control. This adjustment is normally very stable.


ii. Contact the service department to locate the
position of the focus adjustment.


iii. Tape a line-pair gauge directly under the serial
changer, as close as possible to the image inten-
sifier. If the gauge is not available, then use the
‘focus aid’ described in appendix B page 169.


iv. Set a minimum fluoroscopic kV and mA level,
just sufficient to obtain a good image.


v. With fluoroscopy ‘on’, adjust the focus control
for best results. This should be better than 12


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


136




LP/mm for a 9≤ image intensifier. (A typical
result might be 14LP/mm with a CCD camera,
and 16LP/mm with a vidicon camera.)


● Is the TV camera optical focus correct?
i. Optical focus is normally very stable, however


sometimes the image intensifier moves a slight
amount in the housing, or the camera tube and
deflection assembly moves a small amount in
the TV camera head.


ii. Older cameras may have a screwdriver operated
focus control at the rear of the camera head.
(This is sometimes ‘fiddled’ with.) In other cases
it is necessary to remove a cover plate to obtain
access to the lens.


ii. If directly adjusting the lens, first make a mark
on the adjustment ring so the lens can be
returned, if needed, to its previous position. In
most cases, it is necessary to undo a ‘locking’
screw before an adjustment is possible. Some
lenses also have an adjustable ‘iris’ Take care
not to accidentally adjust this instead of the
focus.


iv. Tape a line-pair gauge directly under the serial
changer, as close as possible to the image inten-
sifier. If the gauge is not available, then use the
focus aid described in appendix B, page 169.


v. Set a minimum fluoroscopic kV and mA level,
just sufficient to obtain a good image.


vi. With fluoroscopy ‘on’, adjust the lens focus for
best results. Or adjust the focus control at the
rear of the camera head with a screwdriver.


vii. This should be better than 12LP/mm for a 9≤
image intensifier. (A typical result might be 14
LP/mm with a CCD camera, and 16LP/mm with
a vidicon camera.)


● Is the image intensifier focus correct?
i. Current image intensifiers have very stable focus


adjustments. Older systems may occasionally
require adjustment.


ii. If you have a multi-field, or dual-field image
intensifier, check the resolution first on all fields.
If all fields indicate poor resolution, this will
indicate the problem is elsewhere, or else a com-
ponent failure in the intensifier power supply.


iii. Older designs have a single external focus
adjustment. This is a screwdriver adjustment,
positioned towards the top of the image inten-
sifier. Do not attempt adjustment of the image
intensifier focus, if there is more than one
adjustment. In this case, contact the service
department for advice.


iv. Tape a line-pair gauge directly under the serial
changer, as close as possible to the image inten-


sifier. If the gauge is not available, then use the
focus aid described in appendix B page 169.


v. Set a minimum fluoroscopic kV and mA level,
just sufficient to obtain a good image.


vi. With fluoroscopy ‘on’, adjust the image intensi-
fier for best focus.


vii. The combined TV and II focus should be better
than 12LP/mm for a 9≤ image intensifier. (A
typical result might be 14LP/mm with a CCD
camera, and 16LP/mm with a ‘vidicon’ camera.)


d.The picture has no detail in bright areas


● Is the automatic fluoroscopy system set at too high
a level?
i. Change over to manual operation, select a lower


kV or mA and observe if this corrects the
problem.


ii. If there is now a good image, remain on manual
operation, and contact the service department
to have the automatic fluoroscopy system
adjusted.


● Is the TV monitor correctly adjusted? If the monitor
contrast is set too high, in some monitors this will
cause bright parts of the image to merge together,
or to appear ‘flat’. In other cases, an overbright
image will appear smeared, or wiped, horizontally
across the picture tube.


● Does the monitor take a long time to ‘warm up’?
For example, at first the available brightness is low,
and brighter areas of an image merge together.This
is an indication of low electron emission. Picture
tube replacement is required.


● TV cameras that use a camera tube instead of a
CCD have a ‘beam current adjustment’.
i. If beam current is low, bright areas of the image


lack contrast and merge together. If beam
current is too low, the image will just appear
white,with no detail. In this case, the image may
become clear for a very short time, immediately
after fluoroscopy is switched off.


ii. If beam current is too high, this will result in
poor image quality and reduced focus.


iii. Beam current is a common adjustment for older
TV cameras. Contact the service department to
locate the position of this adjustment, and any
required precautions before adjusting. Ask an
electronics technician to make this adjustment.


e. Is it possible to connect a VCR?


● The videocassette recorder (VCR) must operate to
the same scanning format as your imaging system.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


137




In most cases, the X-ray TV system will use the same
standard as domestic TV, allowing a domestic VCR
to be used.
i. A 525 line, 60hz system requires a NTSC com-


patible VCR
ii. A 625 line, 50hz system requires a PAL com-


patible VCR.
● In case your imaging system operates at a higher


line rate, such as 1049 or 1249 lines, then con-
necting a VCR is not possible, unless there is an
alternate output from the TV camera, at the stan-
dard line rate.


● Playback of a recording will be the same aspect
ratio used by the X-ray TV camera and monitor.
The standard aspect ratio is 4 :3, however, some
systems, including CCD cameras, use a 1 :1 aspect
ratio. If a recording is played back on a monitor
adjusted for a 4 :3 aspect ratio, the image will be
stretched horizontally, and appear ‘egg shaped’


● The VCR must have direct video input and output
connections. A simple installation connects the
video lead from the TV camera to the video input
of the VCR, and the VCR video output to the
monitor. In most cases, this will require the VCR to
be always switched on during fluoroscopy.


f.The VCR recording is the wrong shape on
another monitor


This is a common complaint when the recording is
made from an X-ray TV using a 1 :1 aspect ratio,
instead of the domestic 4 :3 aspect ratio.


● To see if the system is adjusted for a 1 :1 aspect
ratio, adjust the monitor brightness so the scanning
lines, or raster, is clearly visible. A 4 :3 aspect ratio
will show scanning lines extended fully across the
screen, while a 1 :1 aspect ratio will show a small
blank area at both sides of the picture tube.


● Apart from systems deliberately set to a 1 :1 aspect
ratio for a CCD TV camera, it is possible the TV
camera and monitor is incorrectly adjusted.
i. For example, if the original size and shape of


the image from the camera was incorrectly
adjusted, and then the monitor was adjusted to
give the required size and shape.


ii. This is an incorrect set-up,as the monitor should
first be adjusted to the required aspect ratio
and size, then finally the TV camera adjusted to
suit the monitor.


iii. Fortunately, in most cases the TV camera and
monitor can be realigned for use with other
monitors. This possibility should be discussed
with your service department.


iv. Note. This adjustment is not available if a CCD
camera is used.


g. Is the image intensifier faulty?


There is no X-ray image on the monitor. The monitor
adjustments appear correct,and the X-ray control indi-
cates a normal fluoroscopic exposure.


● Is radiation entering the image intensifier?
i. Is the collimator closed? The collimator may


have a fault.
ii. Place a cassette on the table, underneath the


image intensifier.
iii. Make a 2~3 second fluoroscopy exposure, and


develop the film.
iv. The film should be very dark.
v. If the film is unexposed, the collimator could


have a fault. Contact the service department for
advice.


● Is the TV camera faulty?
i. Check the camera is switched on, and the video


cable is not disconnected or damaged.
ii. The following test should only be performed on


advice from the service department.
iii. Remove the TV camera from the image intensi-


fier. Switch on the camera power. Point the
camera around the room, but do not aim the
camera at any bright light. An ‘off focus’ image
should be obtained of objects in the room.


iv. Some systems, especially those with ‘last image
hold’, will require fluoroscopy to be ‘on’ during
the above test. First ensure the collimator is
closed, and the fluoroscopy kV is adjusted to its
lowest setting.


● There is a flickering background illumination, even
without fluoroscopy.
i. This is a possible electrical discharge or insta-


bility in the image intensifier.
ii. With a dual or multi-field intensifier, selecting


another field size can alter the appearance of
this illumination. This indicates a fault in the
image intensifier, or image intensifier power
supply. If the image intensifier loses focus on
selecting a different field size, the power supply
is faulty.


iii. The following test should only be performed on
advice, and instructions, from the service
department.


iv. Remove the TV camera. Cover the camera lens.
v. Switch the power back on.
vi. Close the fluoroscopy collimator. Do not make


a fluoroscopy exposure.


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138




vii. Turn off the room lights. Now look directly into
the image intensifier lens.


viii. If any ‘glow’ pattern is observed, the image
intensifier is faulty.


ix. Repeat this test for each image intensifier field
size.


● The image has a bright central area during fluo-
roscopy.
i. This is an indication of ‘gas’ inside the image


intensifier. This may occur if the image intensi-
fier has not been used for some time. In this
case, leave the system switched on overnight,
and test again next day.


ii. To test, place a piece of lead, of about one third
of the image intensifier diameter, up against the
serial changer. Position the lead test piece in the
middle of the image. This prevents radiation
entering the centre of the image intensifier.


iii. With fluoroscopy ‘on’, the area covered by the
lead should show very little illumination. If there
is gas, this will be seen as a bright area in the
centre, where radiation is blocked by the lead
test piece. The Image intensifier will need
replacement.


● Is the image intensifier ‘worn out’? This is a
common question with older systems, especially if
there is poor penetration with a ‘noisy’ or ‘snowy’
image.
i. The conversion gain of an image intensifier


drops with age as well as use. However in most
cases, adjusting the lens aperture on the TV
camera can compensate for reduced brightness.


ii. A measurement is made of the radiation value,
required to produce a standard video level, from
the TV camera.


iii. The radiation is set to the required value, and
the lens iris is adjusted to obtain the required
video level. If the required video level is not
obtained, then the image intensifier may need
replacement.


iv. Before replacing the image intensifier, the TV
camera should also be checked.


v. This applies if the TV camera uses a ‘Vidicon’
camera tube. The ‘target’ voltage may need
adjustment.


vi. The above test and adjustment should be
requested from your service department before
considering a replacement system.


h.The image rotates as the fluoroscopy table
is tilted


This affect is caused by an interaction with the earth’s
magnetic field. It depends not only on the local field
strength inside the hospital, but also the orientation
as the table is tilted.


Standard image intensifiers have a magnetic shield
in the housing to reduce this effect. However they are
not shielded at the entrance plane. (This is where the
X-ray radiation enters the II.)


Image intensifiers intended for high performance
digital image systems might be fitted with a ‘Mu-
Metal’ magnetic shield, to cover the entrance plane
into the II. While this virtually eliminates the rotation
problem, the added filtration reduces the conversion
efficiency of the image intensifier.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


139




MODULE 10.0


Automatic exposure control
(AEC)


a. AEC operation precautions


● Incorrect selection of a technique not covered by
AEC operation.
For example:
The wall Bucky may be fitted with a selection of
three separate measuring fields or chambers, while
the table Bucky has a central field only. Good design
of an AEC should prevent selection of an incorrect
field. Unfortunately, some AEC systems, in par-
ticular those fitted outside the X-ray control as an
accessory, may allow selection of an invalid field
position.


● Some AEC systems have a ‘film sensitivity’ control
in addition to the film density control. While this
gives greater flexibility, the film sensitivity control is
often never used. Instead it is left at a standard
setting.
i. The use of the film sensitivity selection control


can be forgotten. This includes the original
setting. If the setting position is accidentally
changed, then a sudden large change in film
density occurs. This results in an unnecessary
service call.


ii. In some cases, due to bad calibration, the film
sensitivity control may need to be reset when
changing from the table Bucky to the vertical
Bucky. This can easily result in operator error,
and should be corrected wherever possible.


● X-ray output for the exposure is too low. For
example, too low a kV, or insufficient mAs. In this
situation, the generator timer terminates the expo-
sure, and not the AEC. A light film results.
i. The AEC system, depending on design, may


prevent further exposures until a ‘reset’ button
is pressed. There may be only a small indicator
lamp to indicate this condition, which is some-
times overlooked.


ii. Other AEC systems may provide a short audible
signal. In some cases this is for only a few
seconds, and is easily ignored. As a result
another radiograph is made without adjusting


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


140


Aim


The aim is to provide a series of tests for an automatic
exposure control (AEC).These tests are aimed at deter-
mining whether there is a problem due to the AEC, or
caused by other reasons.


Objectives


A correctly installed and adjusted AEC can produce
excellent results. However, correct use of the system is
still required to obtain the desired performance. On
completion of this module, the student will be aware
of AEC operation requirements, and will be able
to perform basic tests for the AEC performance.
These tests will provide important information when
requesting advice, or else attendance by the service
department.


Contents


a. AEC operation precautions
b. AEC film density test
c. AEC incorrect operation
d. When a request is made for service




the exposure setting.A complaint is made about
‘occasional light films’


● X-ray output is too high. As a result the AEC cannot
terminate the exposure quickly enough.
i. The ‘minimum switch-off time’ is more of a


problem on older single or three-phase genera-
tors; especially those fitted with mechanical
exposure contactors. This can cause unreliable
results if AEC exposure times below 0.02~0.03
seconds are attempted.


ii. Modern high-frequency systems are able to
respond quickly to the AEC exposure-stop
signal, so this is not a problem. However it is still
good practise to keep exposure times above
0.005 seconds. This is due to the energy stored
in the HT cable, which will slightly extend the
actual exposure time.


iii. If AEC exposure times are close to the minimum
switch-off time, reduce kV or mA for the next
exposure.


● Selection of a less optimum chamber. For example,
use of a chamber centred behind the spine, instead
of the left or right chambers for a chest or lung
exposure.


● Combining two or more chambers.This depends on
the method of AEC operation. While the systems
appear similar, they can deliver different results.
i. In one system, the chambers are combined


together, and the average output of the cham-
bers controls the exposure.


ii. In the other system, each chamber has separate
control of the exposure. When chambers are
combined, only the chamber receiving the
higher level of radiation controls the exposure.
(This is called the ‘OR’ technique by one
manufacturer)


● Incorrect collimation. If collimating to a smaller
area, part of the measuring chamber is also coned
off. A dark exposure results.


● Bad patient positioning. In this case, radiation
passes through a relatively thin portion of the
anatomy, compared to the main item of interest. In
some cases, the measuring chamber may receive a
portion of direct radiation. In either case a light
exposure will result.


● The AEC chambers are sensitive to soft, or scat-
tered, radiation.
Although the grid removes most of this radiation,
the remainder still has an effect on the exposure.
In addition, with the chamber in front of the cas-
sette, this soft radiation is filtered from entering the
cassette.


i. The AEC is calibrated for a patient to be posi-
tioned against the Bucky. If there is an air gap,
this reduces the amount of soft radiation enter-
ing the chamber, and the film becomes darker.


ii. The above problem is much greater if there is
no grid in front of the AEC chamber.


iii. An extreme example is found on older fluoro-
scopic tables that have the chamber mounted
in front, instead of behind the grid. In this case,
an air gap of only about 6cm may double the
exposure time. The doctor should keep the spot
filmer close to the patient at all times, while
using the AEC.


● In case the cassettes, film, or intensifying screens
are changed, the AEC will need recalibration.


b. AEC film density test


The AEC calibration may require calibration, or there
may be a fault.


This test allows the performance to be verified, and
indicate if an individual chamber has a problem.


● A test phantom is required. This can be a plastic
bucket with water, or else a large flat-sided plastic
bottle. An empty plastic container used for bulk
detergent is ideal.


● Place a plastic bucket filled with water to a height
of 18cm on the tabletop,positioned over the middle
of the Bucky.


● Place a 24/30cm cassette in the Bucky. Set X-ray
tube height to 100cm.


● Select exposure factors of 90kV, 100~250mA, and
backup time of 0.5 sec. (Some X-ray controls allow
kV adjustment only, mA and backup time is auto-
matically set by the AEC)


● Select the AEC central chamber only. Set the
density control to the middle, or ‘0’ position.


● Make a radiographic exposure. Note the actual
exposure time, or alternately the mAs value. This
depends on the meter indications provided.


● In case a warning signal indicates an incorrect
exposure, reduce the level of water to about 10cm.
If the next exposure still indicates a problem, stop
testing that chamber. Contact the service depart-
ment for advice.


● Process the film. Film density should be in the
region of 1.4 to 1.6. If a densitometer is not avail-
able, compare the film density to a previously
exposed reference film. (The actual value of film
density often depends on individual doctor
preferences.)


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


141




● For under-table Bucky’s fitted with three fields,
repeat the above test for each chamber. Adjust
the phantom so it is positioned above the selected
chamber.


● A similar exposure time and film density should be
obtained with each chamber. In case there is a dif-
ference, expose another film, after adjusting the
density control by one step. If more than one step
is required to obtain a similar density, then calibra-
tion of individual chambers is out of tolerance.


● If any chambers fail this test, do not use that
chamber until the problem is corrected.Contact the
service department; advise them of the problem,
and the tests carried out


A similar test can be applied to the vertical Bucky. A
flat-sided plastic container with water is required.
If an empty bulk detergent container is not available,
then two empty fixer or processor bottles can be used,
placing them side by side. Rinse the bottles before
filling with water.


c. AEC incorrect operation


These tests are only provided as a general guide. This
is due to the great variety of AEC systems in use, most
of which require specialized instructions and test
equipment for calibration or service.


● The AEC exposures produce light films, and are not
consistent.
i. The AEC can be affected by humidity,or by light


leaking into a photomultiplier system. This is a
test for stability during a long exposure time.


ii. Set exposure factors for minimum mA and kV.
Set the backup exposure time to 5.0 seconds.
For those systems that provide adjustment of
kV only, set kV to minimum,and select fine focus.


iii. Set the density control to minimum density.
Select the centre chamber.


iv. Close the collimator, and aim the X-ray tube
away from the Bucky under test.


v. Leave all room lights fully ON.
vi. Perform a radiographic exposure. The AEC


should indicate the maximum exposure time
was reached, and the exposure was not termi-
nated by the AEC.


vii. Repeat this test for each chamber in the Bucky
or spot filmer under test. Caution; as these
are large test exposures, allow cooling time
between exposures.


viii. Does a chamber fail this test?
ix. Test again, this time with the room lights


turned off. If the AEC now gives a longer test


exposure, this is a system using photomultipli-
ers, and external light is leaking into the AEC
chamber or photomultiplier assembly.


x. Examine the front edge of the chamber assem-
bly carefully. Cassettes may have hit it, when
they were placed in the Bucky.This can damage
the chamber, allowing external light to enter.
Cover the damaged area with metal foil, and
test the chamber again.


xi. Many AEC systems use ionization chambers to
measure radiation. Older versions were sensi-
tive to humidity. Design changes overcame this
problem. Contact the manufacturers service
department, in case there is a design modifi-
cation to upgrade your unit.


xii. If any chambers fail this test, do not use that
chamber until the problem is corrected. Con-
tact the service department; advise them of
the problem, and the tests carried out.


● One or more chambers have stopped working.
i. Check the condition of the connecting cable.


This especially applies in fixed installations
where the cable passes through ducts etc. Some
varieties of rats appear to like chewing on small
wires.


ii. On a mobile system, check inside the connect-
ing plug for possible broken connections.


● The film density has changed. It is necessary
to adjust the density control several steps to
compensate.
i. Is a similar change of density setting required


for both the wall Bucky and the table Bucky?
This may be due to the processor instead of the
AEC. Check the processor for possible problems
with chemicals or temperature.


ii. Has the problem occurred after a new batch of
film? The new film may have a different sensi-
tivity. The AEC will require recalibration.


iii. Were the intensifying screens changed? The AEC
will require recalibration.


● For further assistance, contact the service depart-
ment. If an electronics technician is available, the
technician can carry out further tests after obtain-
ing advice from the service department. This would
be specific to the make and model of the AEC
requiring attention.


d.When a request is made for service


● After carrying out the maintenance tests for the
AEC, problem areas may be located.
i. Retain all test films, and document the condi-


tions of test. This includes mA station, kV, FFD,


X-RAY EQUIPMENT MAINTENANCE AND REPAIRS WORKBOOK


142




depth of water phantom, and indicated expo-
sure time.


ii. Test films made with anatomical test objects
may be very interesting. However, testing with a
water phantom produces the most consistent
results, and allows direct comparison with pre-
vious tests.


● When an AEC system has been in use for a while, it
may be found that the density control has to be
adjusted for different examinations. While it is a
simple matter to have service recalibrate the system
to “0” density setting, the following information can
indicate if attention is also required to kV tracking,
or short time compensation.
i. The type of patient examination.


ii. The chamber in use, and the density setting in
use for that chamber.


iii. Does density setting have to be changed on
chamber selection?


iv. Does density have to be changed depending on
kV used?


v. The kV and mA values used. Or kV and focal spot
if mA is not selected manually.


vi. The indicated exposure time obtained after an
exposure.


● Be aware that some apparent AEC problems are due
instead to film processor drift. Before requesting
service for the AEC, ensure the processor perform-
ance has been checked.


PART III. FAULT DIAGNOSIS AND REPAIR MODULES


143






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