GE Medical Systems PRODIGY Service Manual page 118

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:
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
b.Voltage Ramping Failure
4-132Troubleshooting
• 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.
I.Is the amber X-ray On LED illuminated?
• 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.
• 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.
DPX-NT Service Manual (Rev A- 1999)