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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
4.1.3 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
4.3 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
4-118Troubleshooting DPX-NT Service Manual (Rev A- 1999)

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

DPX-NT Service Manual (Rev A- 1999) Troubleshooting 4-119
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
DPX-NT Service Manual (Rev A- 1999) Troubleshooting 4-123
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,
DPX-NT Service Manual (Rev A- 1999) Troubleshooting 4-125
• 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.
4-126Troubleshooting DPX-NT Service Manual (Rev A- 1999)

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

DPX-NT Service Manual (Rev A- 1999) Troubleshooting 4-127
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