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SONY STR-6120 FM muting issue

spaghetti

spaghetti

Active Member
Hi, I was able to buy a rare Sony STR-6120 for a good price, but of course the good price didn't come for free. It has some cosmetic issues, and the FM section is not great. Still, I'd like to bring it back to its glory days.

The main issue is that when FM muting is on, only very few stations can be heard. I read the manual, and I was able to "fix" the issue by grounding R420 on the Muting board, which carries the static and interstation noise from Q304 (last transistor on IF board) to the Muting board.

So the muting circuit is fine, now what? I already recapped all the FM stages, checked the transistors, but I run out of ideas on how to troubleshoot/fix this noise issue. Any help is appreciated! If you need the schematics I can upload it, so please just ask!

Thanks,
Andrea
 
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Sorry, I'd have to look at the design to give better advise. I do not like using muting anyways. I just turn down the volume so I am not blasted by noise. when I tune to a station. depending on the muting threshold, you can miss many dx stations.
There are different means of muting, sig noise and deviation.
in the case of sig muting, the take off is the last bjt in the IF, from there it needs rectification, sometimes Ge diodes are used, once you have it held up on a cap, you need a comparator and the comparator usually is a schmitt trigger type of ckt with hysteresis. it drives the audio mute gate, could be a bjt, relay, transmission gate,fet.
 
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