High Voltage Supplies - HP 8560A Service Manual

9. If the voltages do not return to near their nominal range, the A6 Power Supply is
probably at fault.
10. If the +5 V supply is low, suspect the feedback circuit. Measure the voltage of the +5 V
reference (U305 pin 5) and the f7.5 V references (U306B pin 7 and U306D pin 14).
11. Check output of U306A pin 1. If the feedback circuit is working properly, the output of
12. Check output of U302; its output should be high if the feedback circuit is working
properly.

High Voltage Supplies

1. Set the luNE) switch off, disconnect the power cord, and remove the power supply shield.
2. Connect a DVM's negative lead to A6TP401 and positive lead to A6TP405.
3. Set the (LINE) switch on.
4. If the voltage displayed on the DVM is approximately i-110 Vdc and the rear-panel CRT
Note
Ideally, the DVM should read the voltage written on the label of the A6Al
HV Module. If necessary, perform the High Voltage Power Supply adjustment
in Chapter 2.
5. If the DVM does not read approximately -l-110 Vdc, measure the voltage on A6U401 pin
10. This is the HV-SHUT-DOWN signal and should be near +5 Vdc.
6. If HV-SHUT-DOWN is low, suspect a bad connection along W8 between the A6 Power
Supply and the 17 CRT Driver.
7. If HV-SHUT-DOWN is correct, connect an oscilloscope to A6TP402. Connect the scope
probe's negative lead to TP401. Set the oscilloscope to the following settings:
Sweep time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 ps/div
Vertical Scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 V/div
8. A nearly-sinusoidal waveform, greater than 30 Vp-p, with an approximately i-18 Vdc
offset, should be observed.
9. If the waveform is a dc voltage near 0 Vdc with narrow, positive- and negative-going
pulses, the A6Al HV Module is faulty. If the waveform is a dc voltage near +18 Vdc with
narrow, positive- and negative-going pulses, connect the probe to TP403.
10. If the waveform at TP403 is a sawtooth waveform with a 1.8 V amplitude, the A6Al HV
Module is faulty.
11. If the TP403 waveform has pulses similar to those on TP402, the A6 Power Supply is
probably faulty.
12-14 Display/Power Supply Section