Monroe Electronics Electrostatic Voltmeter - Isoprobe® - model 279L - Manual (Page 18)

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C. Detailed Troubleshooting – Initial Setup:
1. Follow instructions given in Section 6-C; Initial Setup and Adjustments leaving out Step 3
(potentiometer adjustments). NOTE: The following steps are done with the front panel
OPER/STBY switch in STBY.
D. Low Voltage Power Supplies:
1. With a DVM, check between chassis ground and TP-16 and TP-15 for plus and minus 15
volts. These are the ground referenced (non-floating) supplies for some of the output
circuitry. Incorrect readings could indicate trouble at A-1 or A-2 or their associated circuitry or
trouble with the supplies themselves, A-9 and A-10 and their associated circuitry.
2. With a DVM, check for plus and minus 15 volts at TP-18 and TP-20. These are the floating
supplies for the signal and reference circuits and are supplied from PS300 on the 279L/71
card.
E. Reference and Signal Section:
1. With floating common still tied to ground with JP-8 (Section 6-C-6), connect an oscilloscope
probe to TP-5. There should be a 6V p-p sine wave of about 1kHz present. The amplitude
should be adjustable with R-53. Trouble here usually indicates a defective probe.
2. Move the oscilloscope probe to TP-3. Turn the front panel GAIN pot (R-107) clockwise and
zero the display with ZERO 1 pot (R-108). Apply +100 volts to the test plate and the
oscilloscope should display a negative-going half wave rectified signal of about 1V p-p. Minus
10 volts on the test plate should produce a positive-going half wave rectified signal of about
1V p-p.
3. If the demodulator signal is incorrect, check for a +15 volt square wave at TP-4 and a 15 volt
p-p sine wave at the carrier signal test point TP-2 when 100VDC is applied to the test plate.