Loss Of Omi Signal - GE Medical Systems PRODIGY Service Manual

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.
Check all appropriate gears and pulleys. Verify that the set screws are
tightened and the gears and pulleys are not out of position.
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.
Check the Transverse Motor for a broken wire in one of the internal coils, or a
bad electrical connection to its Centent Motor Controller.
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).

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:
DPX-NT Service Manual (Rev A- 1999)
• Gear And Pulley Positioning
• Limit Switch Positioning
• Transverse Motor
• Transverse Centent
The longitudinal and transverse Centents are identical, and can be
exchanged. If the problem remains, the Transverse Motor should be
replaced.
Cause: The Interrupt signal is being lost.
Troubleshooting 4-121