Maintenance
760A / 760D / 760N 4–11
Load the Low Volts Supply with the instrument, or with the 20 W resistor as
stated at the beginning of the Troubleshooting Procedure.
Table 4–4: High Volts Supply Fault Symptoms
Symptom Procedure
Unable to focus CRT using the front-panel
control Focus Amplifier Check
Unable to adjust CRT intensity using the
front-panel control Z-Axis Amplifier Check
Grid Drive Check
No CRT display High Voltage Oscillator Check
CRT Voltage Check
Focus Amplifier Check
HUnsolder and lift one end of R24.
HTurn on the power supply.
HUsing the digital multimeter, measure the voltage between TP1 and the
collector of Q1. It should be approximately –140 V.
HTurn off the power supply.
HReconnect the lifted end of R24.
Z-Axis Amplifier Check
HUnsolder and lift one end of R8.
HTurn on the power supply.
HUsing the digital multimeter, measure the voltage between TP1 and the
collector of Q4. It should be approximately +10 V.
HShort together the base and emitter of Q5. The collector of Q4 should be
approximately +100 V.
HTurn off the power supply.
HReconnect the lifted end of R8.
Grid Drive Check
HTurn off the power supply. Use the digital multimeter’s diode check to
test CR1, CR2, CR3, CR5, and CR6 for shorts.
HTurn on the power supply.