HP 8562E Service Manual page 465

1. Connect the negative lead of the DVM to A6TP301 and verify the power supply voltages.
a. Check A6TP302 for +15 Vdc.
b. Check A6TP303 for -15 Vdc.
c. Check A6TP304 for +28 Vdc.
d. Check A6TP305 for -12.6 Vdc.
e. Check A6TP308 for i-5 Vdc.
f. Check A6TP307 for -5 Vdc.
2. If the voltages measured above are correct but the power supply LEDs on the A2 controller
assembly are not lit, check Wl.
3. If the voltages are low, disconnect Wl from A6Jl and measure the test point voltages
again. Unless a dummy load is connected to the A6 power supply, the voltages should
return to their nominal voltages but be unregulated.
4. If the voltages do not return to near their nominal range, the A6 power supply is probably
at fault.
Part of the buck regulator control circuitry is on the A6 power supply assembly and part of
it is on the A6A2 regulator board, that is part of the A6 power supply assembly. The control
circuitry can be checked as follows:
1. The voltage at E302 should be 6.8 V.
2. If not, check for a triangle wave on the regulator board at TP31, or a 35 V peak-to-peak
square wave at CR305 pin 3.
3. If these signals are not present, check the VBUCK signal for a voltage of about 110 V, and
check Q103 and Q104 for proper switching.
4. If the 6.8 V control loop is functioning properly TP33, on the regulator board, should be
about 0 V.
5. The feedback signal is pulse width modulated to drive the opto-isolator U206. Check for a
rectangular waveform at U206 pin 3, to verify its operation.
1. Set the m switch off, disconnect the power cord, and remove the power supply shield.
2. Connect the negative lead of the DVM 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
Display/Power Supply Section 13-15