Tektronix 071-1143-01 Car Video System User Manual


 
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 Ripple
+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.