[Kenwood] Removing AVR board from TS-940 for troubleshooting

[David Feldman]

Thank you, Clif,

Here are details:

TS940SAT S/N 7 million, no prior service issues

Press power button, getting a rattle/buzz sound (~20 Hz) from near/below the main power transformer (didn't remove bottom cover to investigate further), no lights/LEDs, no control panel response, no audio from speaker, meter in any select position displaying ~S5 with bit of vibration.

Q103 (2SD1266 regulator pass device) Emitter should be 23.2, measure 8.7
Q103 (2SD1266 regulator pass device) Base should be 23.8, measure 21.3
Q103 (2SD1266 regulator pass device) Collector should be 30.0, measure 33.0

Q104 (2SD1406 regulator pass device) Emitter should be 8.0, measure 2.1
Q104 (2SD1406 regulator pass device) Base should be 8.7, measure 2.8
Q104 (2SD1406 regulator pass device) Collector should be 11.6, measure 17.0

7805 regulator device input should be 8V, measure 2.18V
7805 regulator device common should be 0V, measure 0V
7805 regulator device output should be 5V, measure 0.6V

No smoke/heating symptoms
No visual damage

Collector pass regulator seems normal 28.3V out

Radio was on loan to a friend when it failed, he indicated the buzzing symptom came on intermittently at first, then permanently.

Thanks!

Dave


------------------------------
On Tue, Apr 15, 2014 11:10 AM MDT Clif wrote:

>Describe your problem.
>
>
>On Tue, Apr 15, 2014 at 12:01 PM, David Feldman <wb0gaz at yahoo.com> wrote:
>
>>
>> I am preparing to troubleshoot/fix TS-940 which appears to have developed
>> problem in low voltage rectifier/filter/regulator section of AVR board. Can
>> I unscrew the four screws holding the AVR board to chassis and prop the
>> board up so I can access PC traces to take measurements? Does the TS-940
>> AVR board rely on the screws/standoffs for ground?
>>
>> Thanks,
>>
>> 73 Dave WB0GAZ wb0gaz at yahoo.com
>>
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>
>
>
>-- 
>Clif Holland KA5IPF
>www.avvid.com