GE Healthcare DPX-NT Troubleshooting

4 1112

Troubleshooting

Chapter 1:Troubleshooting

This chapter contains troubleshooting techniques for diagnostic
failures, failing quality assurance tests, mechanical failures and
imaging problems.

4.0 Diagnostic Failure Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-119

4.1 Transverse Motion failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-119

4.1.1 Operator Induced - switch closed during scan . . . . . . . . 4-119

4.1.2 Mechanical Failures - Unusual noise or irregular motion 4-119

4.1.3 Loss of OMI signal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-121

4.2 Longitudinal Motion failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-122

4.2.1 Limit Switch Tripped During a Scan . . . . . . . . . . . . . . . . 4-122

4.2.2 Longitudinal Binding . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-123

4.2.3 Loss of OMI Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-125

4.3 Failure of the 28V power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-126

4.4 Emergency Stop Button . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-127

4.5 Tube Head Thermostat. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-127

4.6 Communication Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-127

4.7 Other Diagnostic Failure Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-127

4.7.1 Reasons For Invalid Diagnostic Failures. . . . . . . . . . . . . 4-128

4.8 Failing Quality Assurance Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-128

4.8.1 Block Position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-128

4.8.2 Beam Stop Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-128

4.8.3 Mean% Spillover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-128

4.8.4 Reference Counts and Ratio . . . . . . . . . . . . . . . . . . . . . . 4-129

4.8.5 Ratio Fluctuations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-129

4.8.6 Transverse or Longitudinal Mechanics . . . . . . . . . . . . . . 4-129

4.8.7 Tissue Value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-130

4.8.8 Bone Mineral of the Standard Chambers . . . . . . . . . . . . 4-130

4.8.9 Symptoms of High and Low KV. . . . . . . . . . . . . . . . . . . . 4-131

4.9 Reference Counts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-131

4.10 Arcing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-134

4.10.1 Limit Switch Tripped During Scan . . . . . . . . . . . . . . . . . 4-135

4.11 Imaging Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-136

4.11.1 White, or Grey in the first or second scan line: . . . . . . . 4-136

4.11.2 Femur Scan Problems . . . . . . . . . . . . . . . . . . . . . . . . . . 4-136

4.11.3 AP-Spine Image Problems: Probable causes . . . . . . . . 4-137

DPX-NT Service Manual (Rev A- 1999) Troubleshooting4117

4.11.4 Broken Signal Cable . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-137

4.11.5 Loss of tube head current . . . . . . . . . . . . . . . . . . . . . . . 4-137

4.11.6 X-Ray Relay Failure. . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-137

4.11.7 Unstable AC Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-138

4.11.8 Arcing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-138

4.12 Failing Alignment Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-138

4.12.1 Image. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-138

4.13 Indicator Failures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-140

4.13.1 X-ray On LED Blinking. . . . . . . . . . . . . . . . . . . . . . . . . . 4-140

4.13.2 Shutter Open LED Blinking . . . . . . . . . . . . . . . . . . . . . . 4-140

4.13.3 Shutter Not Operating . . . . . . . . . . . . . . . . . . . . . . . . . . 4-141

4.13.4 End of Exposure Alarm During Scan . . . . . . . . . . . . . . . 4-141

4.14 Communications Failures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-142

4.15 Viewing Quality Assurance Trends . . . . . . . . . . . . . . . . . . . . . . . . 4-142

4.15.1 What to Look for in the QA History . . . . . . . . . . . . . . . . 4-143

4.16 MAX Board Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-143

4.17 FOINK Board Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-144

4.18 OMI Board Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-145

4.19 SBC Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-145

4.20 XORB Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-147

4.21 Detector Motherboard Troubleshooting . . . . . . . . . . . . . . . . . . . . 4-148

4.22 Detector Daughter Board Troubleshooting . . . . . . . . . . . . . . . . . . 4-149

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4.0 Diagnostic Failure Codes

The following conditions halt the operations of the scanner, and generate a
diagnostic failure message which is displayed on the monitor screen:

All of these interrupts are detected by the cSBC

• Transverse Mechanics Failure (4.1)

• Longitudinal Mechanics Failure (4.2)

• Emergency Stop Button activated (4.3)

• X-ray source over temperature (4.4)

• DC power supply failure (4.5)

4.1 Transverse Motion failure

Motion Detection

• cSBC / OMI fail to see transverse motion during a patient scan, an
interrupt signal is generated and the cSBC resets and closes the shutter.

• A slotted disk at the end of the arm rotates through an infrared beam
(OMI), and pulses are sent to the cSBC board when there is
transverse motion.

• The transverse and longitudinal motion detection system (on cSBC) is
operational during patient scans and the “find block” test of the daily
QA. If the problem occurs during a quality assurance, it may be high
voltage arcing or a problem with the OMI.

4.1.1 Operator Induced - switch closed during scan

• Cause: When scanning, a defect in the transverse mechanics or a mis­positioned patient may cause one of the transverse limit switches to
close when the scanner is acquiring data. Closure of a limit switch
prevents further operation of the motor. The shutter will close, the shutter
open lamp will go out and the end of exposure alarm will sound. Seconds
later the error message will appear on the screen.

Solution: If the patient is not centered on the table top or if the region
being scanned is too close to a limit in transverse travel, the limit switch
switch may be close while scanning. Re position the patient on the table,
further away from the limit.

4.1.2 Mechanical Failures - Unusual noise or irregular motion

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If the Detector / Tube Head motion is irregular, or scraping noises are heard,
the Transverse Mechanics may be binding. This symptom will typically be
detected as a failure by the daily QA Mechanics Test.

• Symptom: If the Detector Array / Tube Head is not moving when
scanning check:

• Mechanics are free to move

• Centent

• Stepper Motor

Troubleshooting Binding

Turn off the power to the scanner and move the affected parts by hand. Feel
the motion for spots where the carriages are more difficult to move. Listen for
unusual noises.

The following are common causes for Transverse Binding

• High Voltage Cable Routing

One of the most common problems is a failure of the Source and Detector to
reach the rear Limit Switch due to the Tube Head running into its own high
voltage cables. These cables must have a hump formed at the Rear
Longitudinal Carriage that allows the lower portion of the Tube Head to pass
under the cables.

The High Voltage Cables can also impede transverse motion toward the front
Limit Switch. This is caused when the cables have been tied down without
enough play for the Tube Head and Detector to move all the way forward.
These problems should be investigated by manually tripping both Limit
Switches while inspecting for cable conflicts, binding, or tension problems.

• Check to see that the bottom of the Tube Head is not hitting the
Transverse Centent

•Wiring

In rare instances, the wires from the Shutter Solenoid and/or Fans can snag
on the bolts that protrude through the frame on the foot end of the scanner.
This is solved by properly tying down these wires.

• Transverse Belt

The Transverse Belt should not be excessively tightened or this will cause
excessive binding in the transverse mechanism. It should be possible to
deflect the belt by 4 cm when it is properly tightened. Sometimes the spare
belt material near the clamp on the Tube Head Carriage comes into contact
with the forward gear and prevents the scanner from going all the way to
Home position.

• Drive Wheels

4-120Troubleshooting DPX-NT Service Manual (Rev A- 1999)

The wheels that support the Tube Head and Detector Carriages must be
adjusted so that they come into perfect contact with the Transverse Rails.
These wheel are best inspected with the table top, front panel and arm covers
off so one can sight down the extrusions. However, it is possible to test the
wheels by preventing any wheel from turning and seeing if the carriage will
still move. By preventing any wheel from turning, you should be able to tell
that it slides along the extrusion while the others roll. This indicates that the
wheel has not been excessively tightened down. This is least likely to be the
source of transverse motion problems, as it is unlikely that the adjustment of
the wheels would have become any tighter over time. They would be more
likely to loosen over time and fail alignment tests (see Alignment Test, section

4.12). Adjustments can be made by loosening and rotating the eccentric
bearings of any of the lower wheels.

• Gear And Pulley Positioning

Check all appropriate gears and pulleys. Verify that the set screws are
tightened and the gears and pulleys are not out of position.

• Limit Switch Positioning

If the transverse motion seems to be acceptable, but the number of steps in
the Quality Assurance Test is failing, check the position of the Limit Switches.

On Total Body scans, a limit switch out of position could allow the Source/
Detector Carriages to hit the frame or panels before the Limit Switch is
actuated.

• Transverse Motor

Check the Transverse Motor for a broken wire in one of the internal coils, or a
bad electrical connection to its Centent Motor Controller.

• Transverse Centent

The Centent Motor Controller, if defective, will cause transverse motion
problems. Sometimes the controller works well enough to acquire some
scans, but it will not provide enough torque to complete every fast scan. The
CURRENT SET voltage at terminal 11 on a properly operating controller
should be 14 to 16 VDC (transverse motor wired in parallel).

The longitudinal and transverse Centents are identical, and can be
exchanged. If the problem remains, the Transverse Motor should be
replaced.

4.1.3 Loss of OMI signal

If the error occurs consistently on the first line of a patient scan or during the
find block portion of the daily QA, and the scanner is moving in the transverse
direction, then check the following:

Cause: The Interrupt signal is being lost.

DPX-NT Service Manual (Rev A- 1999) Troubleshooting 4-121

Solution 1: The pulses that normally enter the cSBC board at J14 (the
black wire at the center of the connector) may have stopped. These
pulses are necessary to keep the cSBC from resetting. These pulses can
be seen on a cSBC board LED.

Use the DPX-NT service software (Tools/Diagnostics/Scanner Motion /
Motion Commands Tab) to set the joystick speed to 50 steps, enable the
joystick and watch the LED. If the OMI is working the LIght will flash
when the Transverse Motor is run. If the LED flashes when the
mechanics are engaged, but the error still occurs, the interrupt was
invalid. Check for arcing in the high voltage system or replace the cSBC.

If the LED D9 (B in figure 4-1) does not flash,

• Verify that the slotted disk at the front of the lower arm rail is in the
middle of the slot between the photo diode and photo transistor.

• The slotted disk must be completely flat and remain in the center of
the sensor slot during its entire rotation.

• If the slotted disk has been in physical contact with the optical sensor,
the sensor may have debris on it, disassemble this mechanism, and
clean the sensor and the slots of the disk.

• Check the Cable running from the cSBC to the OMI for a cable break
by checking the individual wires for continuity.

4.2 Longitudinal Motion failure

• cSBC/ OMI fail to see longitudinal motion during a patient scan, an
interrupt signal is generated by the cSBC which resets and closes the
shutter.

• A slotted disk at the foot end of the table on the pulley for the
Longitudinal Drive Belt rotates through an infrared beam (OMI), and
pulses are sent to the cboard when there is transverse motion.

• The transverse and longitudinal motion detection system (on FOINK) is
operational during patient scans and the find block portion of the daily
QA. If the problem occurs during a quality assurance, for instance, it may
be the high voltage system is arcing or the OMI may be malfunctioning.

4.2.1 Limit Switch Tripped During a Scan

4-122Troubleshooting DPX-NT Service Manual (Rev A- 1999)

• Cause: When scanning, a defect in the longitudinal mechanics (binding)
or a mis-positioned patient may cause one of the longitudinal limit
switches to close when the scanner is acquiring data. Closure of a limit
switch prevents further operation of the motor. The shutter will close, the
shutter open lamp will go out and the end of exposure alarm will sound.
Seconds later the error message will appear on the screen.

Solution: If the patient is not centered on the table top (length wise) or if
the region being scanned is too close to a limit in longitudinal travel, the
limit switch may be close while scanning. Re position the patient on the
table, further away from the limit.

4.2.2 Longitudinal Binding

• If the scan arm fails to move when scanning check the stepper motor,
and Centent, if arm motion is irregular, check for binding.

Turn off the power to the scanner and move the affected parts by hand. Feel
the motion for spots where the arm is more difficult to move. Listen for unusual
noises.

When moving the arm longitudinally, only
push on the arm column. Pushing on the
forward parts of the arm can ruin Tube
Head/Detector alignment.

• Cable Track

The major impediment to longitudinal motion is the plastic Cable Track that
runs through the trough at the rear of the scanner.

This track is attached at two points: at the Rear Longitudinal Carriage and to
the scanner frame (low, rear and center) each spot by 4 bolts. Also, adequate
slack must be left in the cables inside the Cable Track or they will stop the arm
from moving fully to the foot end.

Should the Cable Track detach from the scanner frame, it will slide freely in
the trough and will eventually cause trouble. This can allow the Cable Track to
get in between the Rear Longitudinal Carriage and the scanner frame on the
foot end preventing the tripping of the limit switch.

• Front Longitudinal Carriage Dragging

Check the distance between the front longitudinal carriage and the
longitudinal rail with a go/nogo gauge (See installation Procedure DXAP2000
Chapter 5 appendices). The carriage should not rub the front rail, if necessary
insert shims behind the front longitudinal carriage.

• Tube Head Cable Routing

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Problems at the head end of the scanner can be caused by a limit switch
being out of position (thus the arm runs into the frame before the Limit Switch)
or because the High Voltage Cables are tied down incorrectly where they
snake around from the Rear Longitudinal Carriage to the panel under the
Tube Head (High Voltage Cable Trough). If the cables are tied down too far
toward the head end (at the point where the three tie downs are), they can run
into the Longitudinal Motor Assembly and hold the arm away from the head
end Limit Switch.

• Slip Clutch

A slip clutch is part of the longitudinal motion system to limit torque. This is a
feature to protect the patient should he/she pinch an arm or leg between the
back side of the scanner and the Arm Column. If the Slip Clutch is set too
loose, it will fail to move the belt and will just "slip" as the motor turns. This
may produce the following symptoms:

• failure of Quality Assurance scan Mechanics test

• compressed image in limited areas of the image

• a Longitudinal Mechanics diagnostic failure

• Gear and Pulley Positioning

Check all appropriate gears and pulleys. Verify that the set screws are
tightened and the gears and pulleys are not out of position.

• Limit Switch Positioning

If the longitudinal motion seems to be acceptable, but the number of steps in
the Quality Assurance Test is failing, check the position of the Limit Switches.

On Total Body scans, a limit switch out of position could allow the Source/
Detector Carriages to hit the frame or panels of the scanner before the Limit
Switch.

If the mechanical stop is reached before the Limit Switch is actuated, check
carefully to see which part of the Arm Assembly is in contact with the Table
Assembly. The front part of the Lower Transverse Extrusion is clamped to the
Longitudinal Drive Cable at the front of the scanner. If the Lower Transverse
Extrusion is not clamped in such a way that it forms a 90 degree angle with
the length of the table, the rollers at the front end of the Lower Transverse
Extrusion may strike the end of the scan table before the Limit Switch is
actuated.

• Longitudinal Motor

Check the motor for a broken wire in one of the internal coils, or a bad
electrical connection to the Centent Motor Controller.

• Longitudinal Centent

4-124Troubleshooting DPX-NT Service Manual (Rev A- 1999)

The longitudinal Centent Motor Controller may be the cause of a failure. The
current set voltage should be roughly 9-11 volts at terminal 11 on a properly
operating controller. If this voltage is not correct, replace the Centent
Controller.

The longitudinal and transverse Centents are identical, and can be
exchanged. If the problem remains, the Longitudinal Motor should be
replaced.

• Longitudinal Belt

The Longitudinal Belt should not be tightened too much or this will cause the
brackets holding the gears to deform at either end of the scanner. When the
belt is properly tightened, it should be possible to deflect the upper and lower
sides of the belt so that they touch within 8 cm of the gears at either end.

• Drive Wheels

The rollers in front and the wheels in back that support the Arm must be
adjusted so that they come into perfect contact with the Longitudinal Rails.
Test them by preventing any wheel from turning and see if the carriage will still
move. By preventing any wheel from turning, it should be possible to slide the
carriage along the rail with one wheel dragging while the others roll. This
indicates that the wheel has not been excessively tightened down.
Adjustments can be made by loosening and rotating the eccentric bearings of
any of the lower wheels.

4.2.3 Loss of OMI Signal

• If the Scan Arm motion is irregular, or scraping noises are heard, the
Longitudinal Mechanics may be binding. This symptom will typically be
detected as a failure by the daily QA Mechanics Test.

If the error occurs consistently after the first line of a patient scan, and the
scanner is moving in the longitudinal direction, then check the following:

• Cause: The Interrupt signal is being lost.

Solution 1: The pulses that normally enter the FOINK board at J (the

black wire at the center of the connector) may have stopped. These
pulses are necessary to keep the FOINK board from sending an interrupt
to the SBC. These pulses can be seen on a FOINK board LED.

For LED location see figure 4-1. Use the DPX-NT service software
(Tools/Diagnostics/Scanner Motion / Motion Commands Tab) to set the
joystick speed to 50 steps, enable the joystick and watch the LED. If the
OMI / FOINK is working the LIght will flash when the Longitudinal Motor
is run. If the LED flashes when the mechanics are engaged, but the error
still occurs, the interrupt was invalid. Check for arcing in the high voltage
system or replace the FOINK and SBC.

If the LED does not flash,

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• Verify that the slotted disk at the foot end of the scan table is in the
middle of the slot between the photo diode and photo transistor.

• The slotted disk must be completely flat and remain in the center of
the sensor slot during its entire rotation.

• If the slotted disk has been in physical contact with the optical sensor,
the sensor may have debris on it, disassemble this mechanism, and
clean the sensor and the slots of the disk.

• Check the Cable running from the FOINK to the OMI for a cable
break by checking the individual wires for continuity.

4.3 Failure of the 28V power supply

The 28 VDC power supply is only enabled when the X-ray tube is ramped,
use the service software (Tools/Diagnostics/ Scanner X-ray) to attempt to
ramp the Tube Head.

When the Supply is ramping the Red and Green LED’s on the MAX board will
light.

If the LED’s illuminate and the go out:

• Measure the output of the 28VDC power supply, and verify that it remains
constant during the voltage ramping and scanning operations.

• Check the High voltage power supplies, insure they are not arcing (Error
Log - see section 3.2) and are ramping.

If the LED’s fail to light:

• This supply is turned on by the X-ray Relay, so verify that the Relay is
closing. If not, then either the Relay is bad or it is not receiving the signal
from the SBC via the FOINK.

• Check the continuity of the cathode, the filament may have broken, MAX
board TP 4, TP 5 and TP 13 should be continuous with the Tube Head
control cable connected.

• The Tube Head Thermostat is wired in series with the Relay, so if it has
opened, the Relay will not be able to close.

• The 28VDC should also be measured at the Terminal Block. If not, check
the continuity of the wiring and refasten all connections. Also, check the
wire tie-downs for excess tension they may be putting on the wires.

• It may be necessary to check the wiring from the Terminal Block to the
MAX board and to the High Voltage Power Supplies.

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4.4 Emergency Stop Button

The Emergency Stop button is a normally closed circuit, if it opens the
Emergency Stop interrupt will be sent from the FOINK to the SBC.

• Verify that the emergency stop button is out. If it has been pressed in,
press it again to release it.

• If 26VDC can be measured on both pins of FOINK connector J17, the
Emergency Stop Switch and the wires connecting it to the FOINK board
are good and the FOINK board should be replaced.

• If 26 VDC is missing, the Circuit is open between the FOINK and the
Switch.

• Insure the switch is functional

• Check the continuity of the wires from the switch to the FOINK board.

4.5 Tube Head Thermostat

There is a thermostat inside the Tube Head. This thermostat is normally
closed, but opens when the Tube Head temperature is too high.

• The thermostat will close again automatically after a cool down period of
usually less than 30 minutes. If 0 VDC is measured on both pins of
FOINK connector J15, the Thermostat and the wires connecting it to the
FOINK board are good and the FOINK board should be replaced.

4.6 Communication Error

The computer is not communicating with the SBC board.

Verify communications with the SBC in the service software (Tools/Service
Options Comm tab - Test Communications).

If this is unsuccessful, verify that the I/O cable from the computer to the SBC
Board is secure. Also, verify that the comm port is configured correctly (see
DXPC 2000 Chapter 5 appendices) and that all required drivers are present. If
all fails, the SBC or computer serial port is defective.

4.7 Other Diagnostic Failure Codes

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Multiple error codes are possible. These will be displayed one after the other,
but the first one displayed is probably the problem. The Error Log will always
show the failures in the correct order, the others are generated as a result of
the first failure.

4.7.1 Reasons For Invalid Diagnostic Failures

Arcing of the x-ray high voltage system releases a large amount of
electromagnetic energy. This energy creates noise in the electronic circuits
and may cause the SBC to do unpredictable things, such as give invalid
diagnostic errors. Arcing is usually accompanied by white, blue or black lines
across patient scans (See Arcing, section 4.10).

4.8 Failing Quality Assurance Test

See chapter 2 section 12, for explanations of the various tests that are
performed during the running of the Daily Quality Assurance.

If any of the QA test results fail, none of the results are considered valid. The
results will be stored in the Quality Assurance History file, but these values will
not be averaged with the other results for calibration purposes. In addition, the
software will prevent patient scans until a passing daily QA has been
completed. Recent valid QA's are necessary for accurate results.

4.8.1 Block Position

After starting a QA, the operator is prompted to place the QA standard n the
table, if the DPX-NT fails to detect the Block in the correct orientation the QA
will not progress.

• Check Block position and orientation

The scanner may not be finding the correct "Home" position. The correct
"Home" position aligns the center of the x-ray beam with the center of the
Brass Piece when the Standard is correctly positioned. The Air Counts must
be obtained outside of the QA standard, next to the Brass Piece. If the
Reference Counts are obtained with the x-ray beam passing through the
Brass Piece, the Quality Assurance Scan will fail.

• Verify that the scanner limit switches are set correctly with the DPX-NT
home position jig (see DXAP2000 - DPX-NT Installation Procedure
Chapter 5 appendices).

4.8.2 Beam Stop Action

The Beam Stop Action test verifies the ability of the lead shutter to attenuate
x-rays from the tube head by verifying that the Background counts when the
shutter is closed are lower than counts taken through the brass piece with the
shutter open.

4.8.3 Mean% Spillover

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An increase in the Spillover percentage over time is an indication that the
detector is losing resolution, even if the Spillover test does not fail. A large
change in the Spillover can be explained in some cases by standard
positioning (or a small change in the home position of the scanner). If the
beam is not fully eclipsed by the brass piece during the Spillover test, the
Spillover value increases dramatically.

Spillover stability is a test of detector bias drift. if the detector bias is drifting,
the mean spillover value will also drift.

4.8.4 Reference Counts and Ratio

During this test the baseline is established which will later be used for
comparing with the values obtained during the scan of the standard. Care
should be taken that the x-ray beam is not missing the standard, nor being
obstructed by the brass piece on the standard during the High and Low Air
Count test.

The Ratio value should remain fairly constant over time.

4.8.5 Ratio Fluctuations

The ratio of High to Low Channel Air Counts is the way the bone density
measurement is calculated by the changes in the ratio of High to Low Channel
counts. The Ratio should remain constant as long as the x-ray beam quality
and the resolution of the detector remain constant.

It is possible to view the Ratio trends in the Quality Assurance History. Check
both the 3mA Ratio and the 150 Ratio to determine if the either Ratio has
changed significantly.

The problems which could cause a change in air ratio are:

· deterioration of the resolution of the detector

· current leakage through the transorbs on the XORB board

· a faulty High Voltage Power Supply (kV unstable over time)

· changes to the x-ray tube insert

These are very difficult to diagnose by a method other than substitution of new
components until the Reference Counts Ratio returns to normal.

Detector deterioration or unstable High Voltage Power Supply, will usually
cause the Alignment Test Scan to fail.

The specification for XORB Board transorbs is that they must allow less than

0.5 micro amperes reverse bias current. At LUNAR, each transorb is
measured by applying a 5 Volt reverse bias to the transorb and a 100 kW 1%
resistor connected in series. The voltage measured across the 100 kW
resistor must then be less than 50 mV.

4.8.6 Transverse or Longitudinal Mechanics

Failure of this test is caused by one or more of the following:

DPX-NT Service Manual (Rev A- 1999) Troubleshooting 4-129

• Incorrect Limit Switch positioning

• Defective Limit Switch

• A mechanical constraint

• A defective Motor

• A defective Centent Motor Controller

The values recorded for these tests should remain fairly constant over time.
Variations between QA's of under 25 steps should not be a cause for concern
as 1 transverse step = 0.05 mm and 1 longitudinal step = 0.1 mm, so the
actual variation is only a few millimeters.

If the number of steps continually increases from QA to QA, this could indicate
an impediment to the scanner's motion and should be rectified (see 4.1
(Transverse) or 4.2 (Longitudinal)).

4.8.7 Tissue Value

The tissue value should not be the sole failing parameter. The failure of this
test is usually accompanied by problems with Bone Mineral values (see
below) or Reference Counts Ratio trends (see above). If this is failing alone it
is probably a problem with the counting system or high or low kV (4.8.9).

4.8.8 Bone Mineral of the Standard Chambers

The software contains values which it expects the scanner to measure for the
scan of each chamber. If the mean of the BM measurements made for the
chamber does not fall within the predefined software limits the QA will fail. If
the percent coefficient of variance is over 3%, the QA will fail.

These failures will always occur if the Reference Counts or Reference Ratio
test have deviated severely from normal results. However if the Reference
Count results look normal, and the values are approximately equal to the
numbers obtained during the scanner installation, then the counts may be
unstable.

Another cause of failing on the bone chamber measuremnts can be arcing
during the QA. This can be detected by examining the QA History graphically
and looking for variation of the Large BM values. Note the few data points that
vary. These are the early signs of arcing.

This will also be apparent (but not obvious) on the QA Results printout. The
arc occurred in the third standard scan and elevated the BM values. If a
customer reports a failing QA because of a bone chmaber measurement
being too high, be aware that this could be an early warning of arcing. Obtain
from the site the QA history file and error log for analysis. Look for variation of
the Large BM values.

It is very important to notice these early warning signs of arcing so that the
system can be re-greased before any damage is done to the high voltage
cable connectors or the tube head.

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4.8.9 Symptoms of High and Low KV

It has been noted in a small number of cases that defective high voltage
power supplies, or an arcing tube head may produce a voltage other than 76
kV. The DPX-NT monitors kV once per scan sweep.

Note: :It would be prudent in both of these cases to take a positive

and negative power supply, AND a tube head. Also, the XORB
test points may look normal (indicating 76 KV) in each case as
well. This usually occurs where the power supplies are
defective and so the monitor voltages returned to the XORB
may not show the true voltage. When the tube head arcs
causing the voltage to go too high, then the XORB test points
may indeed show the actual voltages.

4.9 Reference Counts

4.9.1 Unstable Counts

To examine the scanner's ability to count detector pulses consistently over
longer periods of time, run the Alignment Test option from the service software
program.

• If the "End of Exposure Alarm" rings during the time the Alignment Test
scan is running, see "Alarm Pings During Scan" in section 4.13.4. If the
Shutter Open or the X-ray On lamps on the front panel blink, during the
test, see section 4.13 also.

• While the Alignment Test scan is running, measure the voltage at test
points 1, 2, 5 and 6 of the XORB board. They should have approximately
the following values respectively: -0.150VDC, 3.8VDC, 0.150VDC, and

3.8VDC.

• A pure DC voltage on an oscilloscope at test point 1 and 5 of the XORB
will verify that there is constant current through the filament of the X-ray
Insert.

• If there is AC ripple in excess of 0.2 Vpp, the power supplies should be
replaced.

• Start and stop the x-rays several times while observing the voltage at
TP3 and TP7 of the XORB board. This is the programming voltage from
the SBC, and although this voltage is dependent on the feedback
information returned to the SBC, the voltages at the XORB board test
points should be approximately the same each time the x-rays are
produced. The AC ripple on this signal must be less than 0.2 Vpp.
Replace the SBC board if the proper control signal is not present.

DPX-NT Service Manual (Rev A- 1999) Troubleshooting 4-131

• When the x-rays are off between scans, verify that the shutter aperture
lines up with the aperture to the Tube Head beneath. Take some
alignment pictures and verify that the image is a bright, rectangular
image and the entire alignment box is visible. If the alignment box is not
visible, the shutter Tube Head and detector apertures are not aligned.

• Open and close the shutter to make sure that it returns to the same
position each time. Turn the x-rays back on, and make sure that you
obtain nearly the same count rate each time the shutter is opened.

4.9.2 No Counts

When the table to the right of the peak graph on the Quality Assurance
Results printout is entirely filled with zeros, use the Signal monitor program in
the Diagnostics (see section 5.1) to create x-rays at 76 kV and 150 uA and
open the Shutter for sampling. Then check the following items:

I.Is the amber X-ray On LED illuminated?

A.If it is, skip to part II.

B.If not, the voltage or current ramping has probably failed. Are both the red
and green LED's on the MAX Board illuminated?

1.Voltage or Current Ramping Failures

If not, is the red LED illuminated?

a.X-ray Relay or FOINK

If not, measure the output of the 28 Volt Power Supply. Check the operation of
the X-ray Relay or the FOINK Board which controls its operation. If all of the
above are working, the red LED may be defective.

b.MAX Board Fuse

If so, the fuse is blown on the MAX Board (see section 4.16).

2.If the red and green MAX Board LED's are illuminated, verify the following
test point voltages:

a.Current Ramping Failure

• XORB TP1 is approximately 0.150 VDC. If incorrect, go to step d. If this
test point is correct, verify that XORB TP5 is also approximately 0.150
VDC. If this voltage is incorrect, substitute a new Positive High Voltage
Power Supply.

b.Voltage Ramping Failure

• XORB TP2 and XORB TP6 are approximately 3.8 VDC. If these voltages
are incorrect, verify that the voltages on XORB TP3 and XORB TP7 are
approximately 3.8 VDC. If TP3 and TP7 are not equal the XORB jumper
at J26 is set in the wrong position. If they are equal but incorrect, test the
cable from the SBC to XORB, or substitute a new SBC Board.

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c.X-ray On LED

Test the X-Ray On LED by inserting it into the Power On receptacle. Replace
if defective.

d.High Voltage System

• Current ramping has failed. If TP1 and TP5 are zero and do not change,
check the polarity of the High Voltage Cables. The X-ray Insert is
essentially a diode, and will not conduct current from the anode to the
cathode.

• If either of the test points is at 1.0 VDC, the High Voltage Power Supply is
delivering as much current as it possibly can, and has automatically
limited the voltage.

• Check TP2 and TP6. If the voltage is approximately 3.8 VDC, the voltage
has been set properly.

Feel the heat sinks on the back of the High Voltage Power Supplies. If one of
the power supplies is cold, this is usually the defective one. If one is warm and
the other is hot, replace the hot one. The best troubleshooting technique may
be to substitute power supplies.

• If either TP2 or TP6 are incorrect, the possibility exists that one of the
High Voltage Cables or the Tube Head is shorted. The short may be
possible to find with an ohm meter, but often it takes several kV to break
down the defective component. It will be difficult to troubleshoot this
problem by any method other than part substitution.

Do not attempt to ramp the power supply above 50
kv without a cable connected, or arcing will occur
near the connector.

• Ramping between 40 and 50 kV is a good way to determine whether the
power supplies are able to increase voltage from 0 to 50 kV.

4.9.3 Decreasing Reference Counts

A long term, continuous decrease in the Reference Counts unaccompanied
by a change in Reference Ratio is a serious problem. A count rate of at least
500,000 Low Channel Reference Counts is necessary to maintain precision of
results when scanning thick patients. Reference Count values should change
by less than 10% from the day of installation. The possible causes are:

I.Lead Filings - Shutter Wear

DPX-NT Service Manual (Rev A- 1999) Troubleshooting 4-133

A rough edge around the shutter aperture may be wearing away on the tube
head below. The lead filings fall off the shutter aperture and gather on the filter
below, causing a reduction in x-rays over time. Any wear should be easily
visible on the underside of the shutter paddle. If there is visible wear, the lead
dust must be removed from the top of the filter. The Collimator assembly must
be removed, the filter cleaned, and then the Collimator assembly reinstalled
and realigned.

II.A Change in Current Control Settings

Use the Signal monitor option of the service software program to produce x­rays (Tools/Diagnostics? Scanner X-Ray). Select 76 kV and 750 µA operation.

• Verify that the SBC is properly controlling the current. TP11 of the MAX
board should be approximately 0.75 volts. This voltage is dependent on
feedback information from the power supplies, which makes it difficult to
troubleshoot by any means other than SBC substitution.

• Check the current through the X-ray Insert. The absolute value of the
voltage at test points 1 and 5 on the XORB board is proportional to the
current through the X-ray Insert. 1 millivolt is equal to 1 micro-ampere of
current. A current setting of 750 µA should give a reading of 0.750 VDC
at test points 1 and 5. If either of these voltages vary from the expected
by more than 10 millivolts, the MAX board could be at fault. If TP1 and
TP5 are more than 15 millivolts apart, substitute new high voltage power
supplies.

4.10 Arcing

The X-ray Tube Head Insert is an evacuated glass enclosure. An AC current
is applied to the filament inside the insert. It glows like the filament in a light
bulb, and electrons are boiled off into the evacuated space. A high voltage is
applied between the anode and the cathode causing electrons to rush toward
the anode, striking it and creating x-rays. As long as the insert is properly
evacuated, there can be no internal arc. However, no insert can be totally
evacuated and impurities can be ionized creating a lightning like effect; arcing.
During the arc the resistance of the insert is dramatically decreased and a
large amount of current flows.

• The significant amounts of electromagnetic energy released inside the
scanner can cause problems with the electronics of the scanner system
and may result in abnormal operations of the scanner. An arcing scanner
will have one or more of the following symptoms:

• complete lock up of the system

• a diagnostic error code message which is undefined or inappropriate

• a vertical stripe or artifact in the image of the patient's scan (effects all 16
detectors at once)

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• Transverse Motion Failure message.

To specifically locate the source of an arc, it is necessary to find out which
high voltage power supply provides the excessive current. This may be done
by recording the power supply current monitors at TP1 and TP5 of the XORB
board with a storage oscilloscope. An arc typically draws 1.5 mA from the
power supply for about 1 ms. The trigger voltage should therefore be set at

1.5V for TP1 and for TP5.

• Arcing can also occur inside the high voltage connectors. This will
usually result in a plainly visible black or brown carbon track through the
grease on the connector. In any case, once the high voltage connectors
have been removed from the Tube Head and the power supplies, they
should not be re-connected without first being cleaned and regreased
(see procedure DXSE0002 in the chapter 5 appendices).

• After cleaning the old grease off of the connectors, they should be
carefully inspected for carbon tracks. Look for these tracks on both the
rubber cable connectors and on the phenolic sockets of the Tube Head.
If such tracks are found after cleaning, the following are the options for
returning the scanner to service:

• If carbon tracks are found on the rubber cable connectors, they can be
removed by excising the damaged section with a sharp blade. Severe
tracks can burn quite deep into the rubber, so care must taken to remove
all the damaged rubber. After the carbon tracks have been removed,
additional grease must be used when repacking the connection to fill in
the volume of the removed rubber.

• If the above procedure requires too much rubber to be removed, or the
carbon track looks very severe, another option is to replace the high
voltage cable.

• Arc tracks will be impossible to see on the sockets in the Tube Head.
Therefore, if arc tracks are seen on the rubber cable connectors, the
sockets should be sanded with emory cloth as a precaution. After
sanding the socket, remember to flush the socket with cleaning solution
to remove any particles.

• If the tracking inside the socket is too severe or the carbon track cannot
be removed, another option is to replace the Tube Head.

Note: IT IS VERY IMPORTANT TO REMOVE ANY CARBON

TRACKS ON THESE SURFACES! Carbon tracks that are
simply covered by grease or not completely removed will still
provide a path for arcs to follow.

4.10.1 Limit Switch Tripped During Scan

If a Limit Switch is tripped during an install test, verify the Limit Switches'
location with the Service Software (Tools/Diagnostics/Scanner Motion). If this
problem occurs any time after install, see the problem description below.

DPX-NT Service Manual (Rev A- 1999) Troubleshooting 4-135

If the transverse mechanics of the scanner become imprecise, it may cause a
Limit Switch to be tripped during a scan. This will usually only happen during a
total body scan or during an Alignment Test test since both of these scans
involve full-width scanning. Once the switch is closed, the motors stop, the
End-of-Exposure Alarm sounds, the amber SHUTTER OPEN lamp turns off
and after a few seconds a Diagnostic Failure appears on the screen.

• During full-width scanning, the Detector Carriage comes very close to the
Limit Switches, so any imprecision will cause a Limit Switch to be tripped
and the scan will be aborted with a Diagnostic Failure message for
Transverse Motion Failure.

A cause of this problem is a loosening of the first drive Reduction Belt which
connects the Transverse Motor to the first Reduction Pulley. This loosening
causes the belt to "walk" on the pulleys causing enough imprecision in the
motion to trip a switch. To tighten the belt, first remove the Pulley Shroud and
loosen all four nuts that hold the motor in place. Then, while holding the motor
such that the belt is pulled taught, tighten the nuts to secure the motor in
place. Replace the shroud and test the scanner (an Alignment Test test works
well).

If the Tube Head cables come into contact with the cable bundle entering the
cable track, it may be impossible for the scanner to complete all of the
necessary transverse steps away from the operator. Consequently, on each
scan line the detector will move closer to the front transverse limit switch, and
the switch may be eventually closed. Form the cable bundle exiting from the
cable track into an arch such that the Tube Head cables will move under the
arch rather than running into the bundle. This arch must not be too high. If it is,
there will not be sufficient slack in the Tube Head cable bundle to allow the
Tube Head to move to the front transverse limit switch. Also, if the arch is too
small, it may cause too much slack when the Tube Head is at the forward side
of the table. This causes the Tube Head cable bundle to rub against the inside
of the front panel causing a scraping noise to be heard. If the above does not
solve the problem then check the other mechanical components. Electrical
components that could cause such a failure are the Centent Motor Controller,
the Transverse Motor, the FOINK board or the SBC board.

4.11 Imaging Problems

4.11.1 White, or Grey in the first or second scan line:

The software is not perfect in its ability to determine the correct grey level of
the entire scan based on the first line of data. Sometimes the grey levels will
be set incorrectly during acquisition. During analysis the grey level is easily
adjusted to give a good image, and the results are not affected by this imaging
problem. This problem is most often found on very thin patients. Adding extra
tissue equivalent material (rice bag or saline solution) to a very thin patient
may be all that is necessary to cure the symptom.

4.11.2 Femur Scan Problems

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Most image discontinuity problems occur in femur images performed at 3 mA
on thin or osteoporotic subjects. These lines usually occur in the trochanter
area where the x-ray beam is least attenuated by tissue.

These lines are caused by Automatic Gain Stabilizer (AGS) trying to adjust
the input signal which is at an excessively high count rate. However, the AGS
is not at fault, and the correct action is for the customer to attenuate the x-ray
beam. Lunar normally recommends placing a rice bag (on its side to create 12
cm of patient thickness in the x-ray beam) along the side of the patient's thigh
for thin or osteoporotic patients.

4.11.3 AP-Spine Image Problems: Probable causes

• the shutter closes (causes the shutter open lamp to go out, and the End
of Exposure Alarm to sound).

• increase or reduction of high voltage to the detector (causes horizontal
artifacts in the image).

• loss of the signal from the detector (this effects all 16 detectors at once)

• loss of current to the x-ray insert filament (28 volt power supply error
message, the orange lamp to go out, and the End of Exposure Alarm to
sound).

• bad x-ray relay contacts (providing power to tube head power supplies)

• reduction in AC Line voltage

• loss of proper high voltage on the x-ray tube

• faulty operation of the AGS system (white lines are short and found only
where scan lines move from air into tissue).

• arcing (may cause vertical artifacts in the image)

4.11.4 Broken Signal Cable

The cables which carry the voltage to the detector and return the signal from
the detector array are part of the upper and lower cable bundle assemblies.
Any break or significant pinch of the cable can cause reduction in counts in
either or both channels. This could result in horizontal artifacts which effect all
16 detectors at once.

4.11.5 Loss of tube head current

The tube head control cable contains the wires which provide power to the
filament transformer. If the wire to the transformer center tap breaks, the x­rays will stop, the orange lamp will go off, and the end-of-exposure alarm will
sound. If either of the other two wires break, the MAX board fuse will blow.
Always ask the operator if a "ping" sound (the end of exposure alarm) is
heard, and whether the Shutter Open or X-Ray On lamp turns off. In the case
of a tube head current problem, the X-Ray On light will turn off.

4.11.6 X-Ray Relay Failure

DPX-NT Service Manual (Rev A- 1999) Troubleshooting 4-137

See section 4.16.

4.11.7 Unstable AC Line

If the customer's AC line conditions are unstable, voltages 11% below the
scaners AC input configuration will begin to drop the high voltage on the x-ray
tube. The counts will drop significantly with only a change of a few kV.
However, this normally causes black or dark grey lines in the scan image.

4.11.8 Arcing

If the tube head is arcing, the arcs will be more likely to occur at the higher
current settings. Arcing generally also causes other strange symptoms such
as:

• Scanner stops in the middle of a patient or QA scan with no error
message or with transverse mechanics fail

• The QA scan fails intermittently on bone chamber measurements

• The scanner periodically leaves the message on the screen "Starting X­rays Please Wait" for a longer than normal period of time (more than 10
seconds)

If you see arcing symptoms, try the following service action:

1.View the Quality Assurance History (see section 4.15). In particular note the
trend in BM Values as discussed in the Failing QA's section of this chapter.

If there is evidence of failures in the mean BM value:

2.Repack the high voltage connections as described in the chapter 5
appendices. Note if an arc track is visible in the insulation compound.

3.Replacement of the tube head if no arc tracks are discovered, or if the
repacking of the connectors does not eliminate all arcing symptoms.

Summary

Except for the x-ray relay, the cause of the problem will be difficult to find. Try
to obtain some additional information. If the customer is hearing the end-of­exposure alarm, or seeing the yellow x-ray on lamp flickering, you can deduce
the tube head control cable is bad. Likewise, it is possible to decide on the
shutter/collimator/fan cable. In the case of no alarm or lamp indications, or in
the case where large deviations occur in the peak, the upper and lower cable
bundles should be replaced, as problems with the coaxial cable will be too
expensive to troubleshoot.

4.12 Failing Alignment Test Results

4.12.1 Image

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The Image is a graphic illustration of the counts recorded during the
Alignment Test. A good image has a black field with evenly distributed grey
dots and perhaps a few randomly distributed dots of various colors (green or
blue usually).

Figure 4-6. Failing Ailigment Test

A poor Deviation Image will have lines, streaks or spots (indicating counts
higher or lower than expected). When the image is analized, click first on
points and then back to results, this will typically point type failing points (they
will have a yellow box around them).

• The information tab (see figure 4-2) will show the test outcome (pass /
fail).

• Lines or streaks going longitudinally in the image indicate an alignment
problem. Recheck the alignment of the scanner including the levelness of
the scanner. Also, check the scanner frame for any bending that may
have occurred at the site or during shipment.

DPX-NT Service Manual (Rev A- 1999) Troubleshooting 4-139

• Lines or streaks going transversely across the Alignment Test image
indicate a problem with the AGS, on the Detector Daughter Board in the
detector array. Again, replace parts until a passing Alignment Test is
obtained.

• Troubleshooting tip: if the Alignment test can be run with the Alignment
Aperture on, this will make the test more sensitive as the beam will be
further collimated to the exact size of the detector. Any failures (beam
straying off the detector) will be exaggerated.

4.13 Indicator Failures

4.13.1 X-ray On LED Blinking

The amber X-RAY ON LED should glow steadily once it is illuminated, until
the x-rays are turned off. If the X-RAY ON LED blinks while the shutter is open
for a patient scan, the End of Exposure Alarm should sound.

The amber LED is controlled by a comparator on the FOINK Board. This LED
illuminates when approximately 40µA (or greater) of current is passing
through the X-ray Insert. On Spellman system scanners the amber light may
appear to fade out slowly when x-rays are ramped down. This due to the
Spellman power supplies bleeding off current and is not a problem.

If the voltage ramping fails, the High Voltage Power Supplies must be shut
completely off before a second ramping attempt is made. If the amber X-RAY
ON LED turns on momentarily, then turns off for a few seconds before coming
on steadily, the system is having difficulty ramping the high voltage. One of the
High Voltage Power Supplies may be defective.

The SBC does not monitor the Insert current once the proper level has been
reached. Therefore, if the current to the Insert is interrupted, the SBC will not
recognize the problem and will not alert the computer, or terminate the
exposure.

If the X-RAY ON LED blinks once the x-ray high voltage has been set, there
must be a problem in one of the following areas:

• Tube Head Control Cable-The most likely cause of an intermittent
problem in this circuit is a broken wire in the Tube Head Control Cable.
The Red wire is most likely the broken one, as a broken blue or black
wire should blow the MAX Board Fuse. Turn the scanner off and test for
continuity between MAX Board test points TP4, TP5, and TP13.

• MAX Board-The MAX Board may be operating intermittently. Substitute a
replacement MAX Board.

4.13.2 Shutter Open LED Blinking

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The amber Shutter Open LED is controlled by the Limit Switch on the Shutter/
Collimator Assembly. If the Limit Switch is defective or improperly adjusted,
the Shutter Open LED may be switched on and off. This will usually be
accompanied by the sound of the End of Exposure Alarm if an exposure is
underway.

If the Shutter is actually opening and closing intermittently and uncontrollably,
the problem is either on the FOINK, or a broken wire between the FOINK and
the Shutter/Collimator Assembly. Remove connector J11 from the FOINK
Board and measure the resistance between pin 5 and pin 6. This will be a
measurement of the resistance of the Shutter Solenoid and the cable through
the Cable Track. If the problem occurs on every scan, run a scan while
making this continuity check. If the cable and solenoid seem to be working
properly, substitute a new FOINK Board.

4.13.3 Shutter Not Operating

If the Shutter Solenoid will not open, the problem may be caused by one of the
following:

• The Shutter Open LED-If the Shutter Open LED fails, a properly
operating FOINK board will prevent operation of the Shutter Solenoid.
Check the LED for continuity, replace it, or substitute a working amber
LED temporarily.

• Solenoid Cable-Remove J11 from the FOINK Board and check continuity
between pin 5 and 6 (see Shutter Open LED Blinking above).

• FOINK Board-Replace the FOINK Board.

4.13.4 End of Exposure Alarm During Scan

If the sharp "Ping" sound of the End of Exposure Alarm is heard during a
scan, look at the computer display to see if a Diagnostic Failure Code is being
reported. If so, see section 4.1.

If no Diagnostic Failure Code is reported, the scanner may still be in motion
continuing with the scan. Abort the scan and remove the patient from the
table. In any case, note the status of the SHUTTER OPEN light and the X­RAY ON light.

• Both the SHUTTER OPEN light and the X-RAY ON light are on and
steady. This would indicate a faulty FOINK board. Replace it

The SHUTTER OPEN light is off. This could indicate the following:

• The LED becomes defective during the scan and since the shutter
solenoid and this light are wired in series, the Shutter closed and the
Alarm sounded.

• The cable to the amber Shutter Open light broke during the scan with the
same result as above.

• The shutter solenoid failed and the Shutter closed followed by the Alarm
sounding.

DPX-NT Service Manual (Rev A- 1999) Troubleshooting 4-141

• The FOINK is faulty.

• The SBC is faulty.

The X-RAY ON light is off. This could indicate the following:

• X-ray production has halted. This turns off the X-ray On light and sounds
the Alarm.

4.14 Communications Failures

Should the scanner, host computer and or Detector Mother Board lose
communications with each other, there are a number of things to check:

A good troubleshooting tool is the COMM test in Tools/Service Options ­COMM tab.

Check

• the I/O cable connections at the serial port on the back of the Host
computer and at the SBC. Be sure both connections are tight and that
the thumb screws are used to hold the connectors firmly together.

• inspect the connector on the SBC. This connector is very fragile and may
have been damaged. Be very careful when connecting the I/O cables to
the SBC.

• Check and inspect the Signal Cable input at the SBC

• Check the Connection at the Detector Mother Board and the Bulkhead,
where the two halves of the signal cable meet.

• Verify the power LED’s on the SBC are lit (See section 4.19)

• Verify that the Power LED’s and PLD programming LED’s are lit on the
DMB (see section 4.21)

If the ports are properly configured and all power is present, and
communication still fails, then the probable causes are:

• A faulty I/O cable.

• A faulty SBC.

• A faulty serial port / serial port card.

Replacement of these parts is the best troubleshooting method.

4.15 Viewing Quality Assurance Trends

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DPX-NT software includes the capability to view, print or graph data contained
in the Quality Assurance database. View and print display selected results of
many of the tests run during the Daily Quality Assurance in tabular form. The
graph feature will graph the results of only one of the Quality Assurance
parameters. All features allow for the user to select the time period to be
examined.

4.15.1 What to Look for in the QA History

All categories should remain steady over time. Check the PASSED column for
failed QA’s. If a failing QA is found, try to determine the cause, including
operator error.

The limit for % Spillover is 13%.

If any sudden jumps are noticed in the values of any of the categories,
determine first if these are due to service work such as a Tube Head
replacement. If service work causes a shift in the QA values, then compare
present values to those obtained only after the service.

4.16 MAX Board Troubleshooting

The MAX board controls the current through the X-ray Insert in the Tube
Head. DPX-NT scanners use MAX version 02B currently.

The current at a given kV across the insert is a function of insert filament
temperature. The MAX board adjusts the current by regulating the filament
temperature to provide the proper current as set by the SBC. The relationship
is Insert µA X 1000 = SBC input (in volts DC), so for an SBC input of 5VDC,
Insert µA = 5000.

The Positive High Voltage Power Supply has a current monitor output (mA
MONITOR); the voltage at this output is proportional to the current passing
through the X-ray Insert. This monitor voltage is connected to the MAX board
as feedback (mA FEEDBACK).

What to look for

• Make sure that all connectors are fully seated.

• Check Lemo connectors for loose parts.

• Check for loose wires on the insulation displacement connectors.

• Check the position of the shorting jumpers on pin headers JB1, JB2, and
JB3 for: Be sure pins 1 and 2 are connected as indicated by silk screen.

When the X-ray Relay is on, both the red and green LED's on the MAX board
should be illuminated. If both are out, no power is getting to the MAX board. If
only the red LED is lit, then the MAX board fuse is burned out or missing.

Electrical tests

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When the board is powered up, and x-rays are being generated, the following
measurements may be performed:

With a VOM set on 200 VDC, you should measure about 18 to 21 VDC on
TP's 4, 13 and 5 referenced to TP3 (GND).

Note: If an oscilloscope is available, you should see about 18 to 21

VDC on TP13. However, TP 4 & 5 should have a 36 to 42 volt
peak square wave. A VOM will show the average value of the
square wave, i.e. 18 to 21 VDC.

4.17 FOINK Board Troubleshooting

The FOINK is a multipurpose interface board designed for use with the DPX­NT. Operation is both analog and digital.

Optical isolation is used to isolate the +26VDC supply from the +5VDC and
+12VDC (logic) supplies, and eliminate interference between the motor
circuits and the event (detector) signals.

What to look for

Figure 4-7. FOINK Diagnostic LED’s

FOINK LED’s:

• A - (D10) Longitudinal OMI, when this LED flashes, the Longitudinal OMI
infrared beam is

• B - (D9) Transverse OMI, when this LED flashes, the Longitudinal OMI
infrared beam is

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• C- (D8) X-ray on (28 VDC supply), when this LED is lit when the +28
VDC power supply is on

• D - (D7) Mechanics engage, when LED is out the motor(s) are enabled

• E - (D6) - Errors Clear, must be lit - out when FOINK detects an error
(failsafe)

• F - (D5) Reset when this LED is lit the SBC is in Reset

4.18 OMI Board Troubleshooting

The OMI board, being a rather uncomplicated device, has little in the way of
things to watch for in installation and use. There are three such boards, one
on the Front Longitudinal Carriage (transverse), at the foot of the scanner on
the longitudinal idler shaft (longitudinal), and on the collimator (shutter open
detect).

What to look for

• Check the connector to each board for proper seating.

• Examine the area where the wires attach to the board itself; it is possible
the may fray or break.

• Insure that the interrupter disk does not rub against the plastic detector
housing. If it does, adjust by loosening the two machine screws that
attach the plastic detector, reposition the detector and re-tighten the
screws.

Electrical tests

The signal from the OMI board is nominally rectangular in shape. The signal is
generated when the Interrupter Disk alternately passes and occludes a light
beam between the two posts on the photo-transducer. With the beam
occluded by the disk, the output signal should be about 5 VDC (close counts).
When the beam is allowed to pass through a slot in the disk, the signal output
is near ground potential (see FOINK troubleshooting 4.17).

Symptoms of possible OMI failure

• Scanner shuts down at the beginning of a patient scan.

• Scanner shuts down unexpectedly during a scan.

• Either condition above should be accompanied by a Diagnostic Failure
Transverse or Longitudinal (see section 4.0).

4.19 SBC Troubleshooting

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The SBC consists of a single circuit board that uses the 8032 microprocessor
with a RS-422 interface to the Host PC and a RS-422 interface to the Detector
Motherboard (DMB)

The SBC is located on the electronics pan in the front center.

Figure 4-8. DPX-NT SBC highlight indicates the location of the diagnostic

LED’s

Figure 4-9. DPX-NT SBC Diagnostic LED’s

What to look for

• Green LED (C in figure 4-5) is on then you have +5VDC to the board.

• Red LED (A in figure 4-5) is on then you have +12VDC to the board.

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• Amber LED (B in figure 4-5) is on then you have -12VDC to the board.

• Red LED (E in figure 4-5) is the DTR reset line, when this LED is lit, the
Detector, FOINK, or SBC are detecting an error.

When the DTR Reset Line is lit:

• Check the LED’s on the DMB (see section 4.21)

• Check the FOINK LED’s

• Check the Signal Cable

The Service Software can be used to verify communications between the
Host / SBC and the DMB.

Go to Tools - Service Options - Communications Tab - test
communications

• Red LED (D in figure 4-5) the scanner Reset, when this LED is lit, the
communications with the Host PC are in Reset.

• Verify port settings on the Host PC (See DXPC 2000, chapter 5
Appendices)

• Verify communications cable

• Green LEDs (G and H in figure 4-5) flash when data is being received by
the SBC

• Green LED (F in figure 4-5) is not assigned a function at this time.

The reset button near the communications cable connector causes a reset
signal at the SBC microprocessor. Also, disconnecting the serial cable will
cause a reset state until the cable is re-attached and communications
reinstated.

4.20 XORB Troubleshooting

The XORB board routes a number of important signals to the rest of the
system and protects the system from transients by shunting them to ground
with transorbs.

What to look for

• All connectors firmly seated.

• Check to see that all wires and cables are firmly affixed to their
respective connectors. Pay particular attention to Lemo connectors,
since the jam nuts on the connectors are prone to be loose.

DPX-NT Service Manual (Rev A- 1999) Troubleshooting 4-147

• Check and tighten, if necessary, all mounting screws for the XORB
board.

Electrical Tests

• Measure impedance between XORB ground plane and the electrical
pan. It should be less than an ohm.

• There should be no low impedance (less than 10 ohms) reading between
any signal or signal ground and chassis ground on the XORB when the
as-associated signal connectors are disconnected.

The following test points should have the following readings:

Table 4-12. XORB Test Points

Test Point kV mA Limits

TP 1 76 .750 0.74 - 0.76

TP 5 76 .750 0.74 - 0.76

TP 1 76 3.00 2.97 - 3.03

TP 5 76 3.00 2.97 - 3.03

TP 2 76 .750 3.76 - 3.84

TP 6 76 .750 3.76 - 3.84

4.21 Detector Motherboard Troubleshooting

Figure 4-10. DMB Diagnostic LED’s

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Diagnostic LED’s in figure 4-6

• A - (Green) Power +12 VDC Present

• B - (Green) Power - 12 VDC Present

• If the 12 VDC power LED’s are not illuminated power down the
scanner, wait 30 seconds and power back up (see section Chapter

2.1.2)

• Check +5, +/-12 VDC Power Supply 1

• C - (Green) DMB PLD Programmed and ready

• If the DMB PLD LED is not lit verify FIRMWARE version with the
Service Software (Tools/Set Download Parameters / Query), if
necessary download to the DMB.

• D - (Green) DDB 1 PLD Programmed

• Verify the DDB card is seated in its socket

• E - (Green) DDB 2 PLD Programmed

• F - (Green) DDB 3 PLD Programmed

• G - (Green) DDB 4 PLD Programmed

• H - (Red) Data Sent to SBC (should flash when acquiring data)

• I - (Red) Data Sent to SBC (should flash when acquiring data)

• J - (Green) Detector Reset

• Verify Communications with the SBC

• Verify All DC voltages are Present on the DMB

• K - (Green) +5 VDC present

• Check +5, +/-12 VDC Power Supply 1

• L - Detector Mother Board Reset Button

4.22 Detector Daughter Board Troubleshooting

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Figure 4-11. Test Point Board

The Test point board gives the service engineer access to all of the signals for
the individual Detector Daughter Boards

The Test Point Board is broken into 2 areas:

Analog Signals

DMB Controlled Programming Information (same data to all DDB PLD’s

FIRMWARE from DMB Flash RAM)

• DCA REF - DCA Reference Levels - High and Low Energy Reference
Levels for event counting windows

LEL = 1.19 VDC

LEH = 1.66 VDC

HEL = 1.96 VDC

HEH = 2.79 VDC

• AGS REF AGS Reference Levels - High and low Energy

CENTER = 2.35 VDC

LOWER = 2.00 VDC

• Detector Bias Setting (BIAS =.450VDC)

• +5 VDC Ref (+5.00 VDC)

• - 5 VDC Ref (-5.00 VDC)

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Individual Detector Signals (Stored in DMB Flash RAM)

• GAIN - combination of Peak and AGS signal gain - setting for Shaping
Amplifier - visible only with Oscilloscope

• AGS - AGS amplify or Attenuate signal - visible only with Oscilloscope

• BiPolar - Bipolar signal out of the shaping Amplifier

Digital Signals

• AGS ROLL - logic signal for AGS rollover - this signal is not currently
utilized by the software

• LE - Low Energy Event detected and counted

• HE - High Energy Event detected and counted

• SAMPLE - Sample clock signal

• AGS ENABLE - Operate Calibrate signal - locks out AGS for Peaking
operation

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