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Maintenance
4–12
760A / 760D / 760N
H Using the digital multimeter, measure the voltage between TP1 and the
cathode of CR5. It should vary between approximately +75 and +200 V
as R58 (CRT Bias) is adjusted.
H Connect the oscilloscope probe to the anode of CR5 and the probe
ground to TP1. The signal should be a clipped sine wave of +75 to +200
V
p-p
.
High Voltage Oscillator Check
H Connect the oscilloscope probe to T1 pin 3 (Q6 collector) and the probe
ground to TP1. Turn on the power supply. The signal should be a +60
V
p-p
, 22 kHz sine wave.
H Check the following voltages using the digital multimeter:
Table 4–5: High Voltage Oscillator Test Points
Circuit Location Voltage
T1, pin 4 Approximately +40 V.
T1, pin 13 Less than +2 V.
U2, pin 2 Approximately +4.8 V.
U2, pin 6 +4 to +11 V.
CR9, cathode Approximately +100 V.
CRT Voltage Check
NOTE. This check requires a high voltage probe having an input resistance of
1 GW or more.
H Connect the high voltage probe ground to TP1.
H Load the Low Volts supply with the instrument, or with a 20W, 2 watt
resistor loading the 5 V supply.
H Turn on the power supply.
H Use the high voltage probe to measure the voltage at the anode of CR4.
It should be approximately –2530 V.
H Measure the voltage at the anode end of CR3. It should be 50-150 V
more negative than the reading from the anode of CR4.