SX-780 losing left channel

[Germ_nation]

I acquired this receiver about a month ago and immediately opened it up and did a deoxit cleaning. The past couple days I have started to lose the left channel. At first I thought it was just happening through the phono but now it's starting to happen on the aux also. It sounds like static or a blown speaker and comes and goes. I've swapped speakers and it keeps happening so it has to be the receiver. Does anyone know what may be causing this? Should I just reclean all the pots with deoxit? Any and all suggestions are welcome.

 

[blhagstrom]

It may be bad relay contacts.
It may be tired relay circuit.
It may be monitor switch.
It may be function switch.
It may be tired driver or pre driver or pre pre driver transister.
It may be bad RCA cord.
It may be bad solder joint.
It may be cracked board.
It may be dirty speaker switc.
It may be bad capacitor.

Intermittent problems are the worst.

 

[Germ_nation]

Wow! Thanks for the optimistic reply! Haha.

 

[Germ_nation]

Just out of curiosity, could any of those issues ruin my speakers? I wouldn't want to continue using it if that's the case.

 

[elnaldo]

Are you hearing random crackling noises, like pop-corn or fried bacon? If so, I'd point to this parts: I see you have 4 of those in your unit>> 2SC2291 double transistor.

Also, switches were reported many times as cause of noises.

BTW, I wouldn't risk any speaker with a problematic unit. Until proper diagnose, I'd disconnect them, or at least, connect a line fuse, a 1 or 2 A fuse in series with the speakers. It will protect them from any DC or failure at the output.

You can isolate a bad transistor using a freeze spray, or replace all of them and see what happens. The fact is the freeze spray will cost more than the transistors, but the proper way to face a problem is to diagnose first, and just replace the parts you know or suspect are bad.

 

[blhagstrom]

Wow! Thanks for the optimistic reply! Haha.

Sorry, the SX-780 has a lot of known weak points and some not-so-well known ones and in general the other things in my list can cause those issues.

Welcome to Vintage.

 

[Germ_nation]

Thank you so much for your input! I actually decided to reconnect with an old friend that builds and repairs guitar amps and he is going to help me fix it! Once we figure it out I'll post what the culprit(s) was/were.