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whit3rd whit3rd is offline
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Default Kenwood DVR-5070

On Saturday, May 8, 2021 at 7:30:57 AM UTC-7, legg wrote:
On Fri, 7 May 2021 15:18:01 -0700 (PDT), whit3rd
wrote:
My favorite stereo... developed a buzz, which didn't affect any of the
digital (like blue-ray) sound inputs, only the analog ones.
Sounded like 120 Hz, so I checked the regulators for that
bunch of op amps, and sure enough, a capacitor had bulged...
an hour to disassemble, five minutes to replace the thing, and now it works
fine again (except for the DVR parts)...

But, the capacitors I replaced were the OUTPUT filters on 7815/7915
regulators.


I'd check other caps in the chain, before the regulator. Most common
age-related failure is high z with no physical signs - just high
ripple voltage, where there shouldn't be any.


The preregulated supply is, I now see, well-enough documented (a printed wiring image) that
it's possible to look at ripple under bias; it takes a lot less than hours to get to the TOP surface
of that board, so next time I get curious, I can check that out (but those input capacitors
aren't ones that I can grab from my stock; instead of hours, it'd take a few days to order
replacements). I did check the diodes, and of course transformers rarely fail.

The replaced items included one tested-faulty capacitor, and it sounds OK now.