6. TROUBLESHOOTING page 26
Model PRM-470B
6.2.1. Batteries and Charger:
If the instrument fails to operate properly, check the condition of the batteries. For example, if
the instrument does not pass the self-test procedure, fails to count down, etc., the cause is often
low battery charge. Check the condition of the batteries by measuring the voltage to confirm that
it is 5.75 volts or greater. If the voltage is low, install a fresh set of alkaline batteries before
continuing.
Do not go on to step 6.2.2. until the battery voltage is at least 5.75 volts.
NOTE:
Many apparent problems can be traced to a low battery condition, which can cause the
instrument to behave erratically.
6.2.2. High Voltage:
If the problem persists with proper dc voltage present, check the high voltage board by
connecting the high voltage probe to J2-1 on the HHV-454 board. The ground end of the probe
may be connected to any convenient ground. The voltage should be at least 600 VDC. If it is
not possible to adjust the level (R5 on the HHV 454 board), replace the board.
Do not go on to step 6.2.3. until the correct voltage range is present.
6.2.3. Detector:
Remove the three-pin Molex signal connector from the PRCB-001 board and attach an
oscilloscope probe to it. The coax is the signal and the black #22 AWG wire is the ground.
Set the oscilloscope for negative edge triggering. The pulses should be negative and about 50
millivolts peak amplitude. If present, the detector assembly is working. If not, then either the
detector or voltage divider assembly must be replaced.
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