HP 8753D Option 011 Service Manual page 163

14 fractional-N digital
19 graphics processor (disconnect W14, 18W1, and W20)
4. Switch on the analyzer and observe the green LEDs on 8.
If any of the green LEDs are o or ashing, it is not likely that any of the assemblies
listed above is causing the problem. Continue to \Brie y Disable the Shutdown
Circuitry."
If all green LEDs are now on, one or more of the above assemblies may be faulty.
Continue to next step.
5. Switch o the analyzer.
6. Reconnect W14 and W20 to 19.
7. Switch on the analyzer and observe the LEDs.
If the LEDs are o or blinking, replace the 19 assembly.
If the LEDs are still on, continue to next step.
8. Switch o the analyzer.
9. Reconnect 18W1 to the 19 assembly.
10. Switch on the analyzer and observe the LEDs.
If the LEDs are o , replace the 18 display.
If the LEDs are still on, continue with the next step.
11. Switch o the analyzer.
12. Reinstall each assembly one at a time. Switch on the analyzer after each assembly is
installed. The assembly that causes the green LEDs to go o or ash could be faulty.
It is possible, however, that this condition is caused by the 8 post regulator
Note
not supplying enough current. To check this, reinstall the assemblies in a
di erent order to change the loading. If the same assembly appears to be
faulty, replace that assembly. If a di erent assembly appears faulty, 8 is most
likely faulty (unless both of the other assemblies are faulty).
Briefly Disable the Shutdown ircuitry
In this step, you shutdown the protective circuitry is disabled for a short time, and the
supplies are forced on (including shorted supplies) with a 100% duty cycle.
Damage to components or to circuit traces may occur if 8TP4 (SDIS) is
aution
shorted to chassis ground for more than a few seconds while supplies are
shorted.
1. Connect 8TP4 (SDIS) to chassis ground with a jumper wire.
2. Switch on the analyzer and note the signal mnemonics and test points of any LEDs that
are o . Immediately remove the jumper wire .
3. Refer to the block diagram (Figure 5-8) at the end of this chapter and do the following:
Note the mnemonics of any additional signals that may connect to any 8 test point that
showed a fault in the previous step.
5-12 Power Supply Troubleshooting
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