Monitor Audio Vector Service Manual download pdf (Page 142)

Troubleshooting Procedures

6-42

WFM90D and WFM91D Service Manual

Low -Voltage Power Supply

Use the following procedure to check that the low-voltage power supplies are

operating properly before proceeding to Fault Symptom Table.

1. Disconnect the AC adapter from the WFM90D or WFM91D.

2. Remove any installed batteries. S ee Batteries on page 6--28.

3. Remove the top cover. See Top Cover on page 6--5.

4. Connect the AC adapter and turn on the instrument.

5. Check that the low-voltage power supplies are operating properly, as

indicated by the supply voltages listed in Table 6--4:

Table 6- 4: Low-voltage power supplies

Supply Test Point Output Rippl e

+8 V J9, pin 13 40 mV 30 mV

-- 8 V J9, pin 14 40 mV 30 mV

+5 V J9, pin 15 25 mV 60 mV

6. If the low-voltage power supplies are operating properly, proceed to Fault

Symptom Table.

7. If any of the voltages are out of specification, check the two fuses on the

Bottom board.

CAUTION. Do not use a soldering iron larger than 18 W. To do so may damage

the circuit board and the surrounding circuitry.

8. If a fuse is bad, remove the AC adapter and replace the fuse before you retest

the low-voltage power supplies.

9. If both of the fuses are good, replace the Bottom board.

NOTE. Be sure to remove all modules one at a time, to isolate the Bottom board

in a supply is excessively loaded.

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Monitor Audio Vector Service Manual Page 142