Power Supply Measurements; Signal Input Circuit - Fluke Victoreen 875 Operator's Manual

Victoreen 875
Operators Manual

5.4 Power Supply Measurements

Turn the 876A-1 on by turning the function switch to the ALL position.
Adjust the mechanical zero of the panel meter (use mirror scale to avoid parallax error) so that the needle
is centered on the first hash mark of the black expanded arc to within 0.50 needle width.
Verify the output voltage of the power supplies as follows (See drawings 876-1-78 and 876-1-89).
Mother Board (P/N 876-1-78, Schematic 876-1-3A)
1. Connect the negative lead of the DMM to TP102.
2. Probe TP101 with the positive lead of the DMM. The DMM should read +24 ± 3 VDC.
Power Supply Printed Circuit Board (P/N 876-1-89, Schematic 876-1-3C)
3. Probe TP5 (white) with the positive lead. The DMM should read -21 ± 2 VDC.
4. Probe TP4 with the positive lead. The DMM should read -10.00 ± 0.01 VDC. Adjust R4 as
necessary to correct this reading.
5. Probe TP2 with the positive lead. The DMM should read + 15.0 ± 0.2 VDC. Adjust R5 as required to
achieve correct readings.
6. Probe TP3 with the positive lead. The DMM should read +14.3 ± 0.4 VDC.
PreamplifierIMeter Board (P/N 876A-1-86, Schematic 876A-1-3E)
7. Probe TP401 on preamplifier meter board with the positive lead. The DMM should read +6.200 ±
0.001 VDC. Adjust R413 as necessary to correct this reading.
Rear Panel
8. Probe the back panel high voltage connector, J2. The DMM should read +506 ± 10 VDC.

5.5 Signal Input Circuit

(P/N 876A-1-35, Schematic 876A-1-92 & P/N 876A-1-75A, Schematic 876A-1-
3B)
The signal input circuit is partly on the preamplifier board, and partly on the relay driver board. It consists
of logarithmic amplifier U301 and its associated circuitry (preamplifier meter board) and amplifier U501
(relay driver board). The output of U501 provides the input for the meter circuit on the preamplifier meter
board and the high and alert alarm circuits on the relay driver board. The alarm circuits are covered in the
"Alarm Circuits" paragraph. The signal input circuit can be tested at two test points, using the CHANNEL
TEST push button to provide a convenient input signal. Voltages at these points should be measured with
no signal input.
1. Disconnect the cable connecting the readout module to the detector. Turn the function switch to
TEST.
2. Measure the voltages at TP501 and TP502 under two conditions: 1) with no signal input; 2) with a
signal input obtained by pressing the CHANNEL TEST push button.
The voltages should be:
5-4
Allow all equipment, including the readout module,
to warm up for at least 60 minutes before
attempting any calibration.
No Signal
(P/N 876-1-89 Schematic 876-1-3C)
CAUTION
Channel Test Signal