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JVC RS-33 Sound Cuts Out - Need Help for Design Flaw

Hi Bill! Thanks for your kind offer to help :rflmao:. I have some (primary) studies on circuit boards, but I haven't been able to find where is the speaker protection circuit.

Here you can find the service manual of my RX-805V: LINK. I think (just a guess) that the relevant schematic is on page 66.
I also found the service manual for your R-S77. If it helps you, here you can download it for free: LINK
 
I looked at your schematics and, yes, the protection circuit for the speaker output is on that sheet. Unfortunately, your design appears to use more ICs than they used in '81. Without a Service Bulletin to identify the right component values and location, it's going to take some physical analysis with diagnostic equipment. Unless there is a specific fix identified online for your receiver series, it will require sending to an audio tech familiar with the old JVC designs to find & correct the issue. Or you can do what I did and keep the unit with hope that someone will identify the fix.
 
A R_S33 was my first HFI purchase back in high school so I had to pick one up off of Ebay. Cleaned it up and it sounds great works well with the annoying exception of speaker protection cutting off now and them mostly when cold. I researched the service bulletine mentioned above. The fix is to replace R909 68K with a 39K 1/4 Watt resistor and to install a external ground wire from Post 702 to the nearest ground screw. Haven't done the repair yet but intend to in the future.
 
George Darcy said:
A R_S33 was my first HFI purchase back in high school so I had to pick one up off of Ebay. Cleaned it up and it sounds great works well with the annoying exception of speaker protection cutting off now and them mostly when cold. I researched the service bulletine mentioned above. The fix is to replace R909 68K with a 39K 1/4 Watt resistor and to install a external ground wire from Post 702 to the nearest ground screw. Haven't done the repair yet but intend to in the future.
Click to expand...
Brilliant. Mine has been cutting out when cold for decades. Is R909 and Post 702 easy to find?
Other issue I have. Right channel isn't working. The Balance slider is very dodgy, I suspect this. Both channels working fine when in Mono setting.
 
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