Symptoms Of High And Low Kv; Reference Counts - GE Medical Systems PRODIGY Service Manual

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