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642 Chapter12

Display/Power Supply Section

A6 Power Supply Assembly

HP 8560E and 8560EC spectrum analyzers uses a switching power

supply operating at 40 kHz to supply the low voltages for most of the

analyzer hardware. In the 8560E, the power supply also provides a 30

kHz switching supply (CRT supply) for the high voltages used by the

CRT display used in E-series instruments. The CRT supply will be

treated as a separate supply since the remainder of A6 must be

operating for the CRT supply to operate.

Kick starting occurs when there is a fault either on the power supply or

on one of the other assemblies. The power supply will try to start by

generating a 200 ms pulse ("kick") every 1.5 seconds. A kick-starting

power supply often appears to be dead, but the fan will make one or two

revolutions and stop every 1.5 seconds.

Dead Power Supply

1. Use an isolation transformer and connect a jumper between

A6TP101 and A6TP301.

2. Connect the negative lead of a DVM to A6TP301.

3. Check TP308 for +5 V.

4. Check TP302 for +15 V.

5. Check TP303 for −15 V.

6. Check TP304 for +28 V.

7. Check TP305 for −12.6 V.

8. Measure the voltage at TP108 to verify the output of the input

rectiﬁer. The voltage should be between +215 Vdc and +350 Vdc.

9. If it is not within this range, check the rear panel fuse, input

rectiﬁer, input ﬁlter, and the rear panel line voltage selector switch.

10.Measure the voltage at TP206 to verify the output of the kick-

start/bias-circuitry. The voltage should be approximately +14 Vdc.

Test point 206 is on pin 1 of U203.

11.If there is no voltage at TP206, check TP210 for pulses 200 ms wide

with an amplitude of 14.7 V. If there are no pulses present, the

kick-start circuitry is probably defective. If the pulses are low in

amplitude (about 1 V), Q201 is probably shorted.

12.If there are pulses at TP206, or there are pulses at TP210, but not at

TP206, the buck regulator control circuitry is probably faulty.

13.Disconnect the power cord from the HP 8560E spectrum analyzer.

14.Connect the positive output of a current-limited dc power supply to

HP 8560E Service Manual

Questions and Answers: