Maintenance
4–12 760A / 760D / 760N
HUsing 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.
HConnect 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
Vp-p.
High Voltage Oscillator Check
HConnect 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
Vp-p, 22 kHz sine wave.
HCheck 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.
HConnect the high voltage probe ground to TP1.
HLoad the Low Volts supply with the instrument, or with a 20W, 2 watt
resistor loading the 5 V supply.
HTurn on the power supply.
HUse the high voltage probe to measure the voltage at the anode of CR4.
It should be approximately –2530 V.
HMeasure the voltage at the anode end of CR3. It should be 50-150 V
more negative than the reading from the anode of CR4.