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69.125.143.12
In Reply to: RE: Sansui 331 issues. posted by sanman on October 06, 2020 at 13:36:48
Looking at the schematic from HiFiEngine FM,Phono preamps, and Aux all feed the volume and tone circuits through the source selector switch. Aux is a direct connection from the input jacks to that switch. Separately, Tape Monitor comes right after the source selector and switches in tape rather than the selected source.
One would expect that issues with Aux would be poor connection at the source selector switch while issues with Tape would be the tape monitor switch. Since FM and Phono work there are no amplifier issues such as a bad transistor. Aux and Tape share the same amplifier path. I would primarily suspect the tape monitor switch but clean them both again.
Gary
Follow Ups:
"sanman", what flavor of contact cleaner did you try on the controls?
I'd - strongly - recommend CAIG DeOxit D5... although, in full disclosure, it can be hazardous to some potentiometers (typically, as I understand it, the plastic film types). Switches, though... I'd go for it, were I you.
CAIG also sells a pot lubricant (oh wow, man!) that can help restore that smoooooooooooooooooooth feeling to pots cleaned with DeOxit and left feeling "cheap".
all the best,
mrh
"recommend CAIG DeOxit D5... although, in full disclosure, it can be hazardous to some potentiometers (typically, as I understand it, the plastic film types). "
When you clean a pot you are not cleaning the carbon going around it, you are cleaning the little metal ring where the wiper makes contact with the center terminal.
And what do you suggest he clean ? All sources go through all of them. The only way for it to be a switch is a mechanical failure of the selector. I have actually had that but usually when it does the symptom will change when the switch is worked a few times. Not all the time, but if nothing else it found it is worth a look with a scope or signal tracer. For a signal tracer just find anything with a line level input and wire it to test probes.
I bet fifty bucks cleaning will not work.
the pot contacts have probably lost their tension to the carbon track, in which case a disassembly to the pot is necessary to re-tension.
Just replace the pot.
"Leo 2.0!!"
"the pot contacts have probably lost their tension to the carbon track, in which case a disassembly to the pot is necessary to re-tension. "
Now how the hell could that only affect certain sources if all sources go through it ?
that would be different of course, random problem or what ever it is. My comment was mainly directed to use of F5, so please xcuse
"Leo 2.0!!"
With the information given I think it will be found to be a fault on the PC board or in the wiring, or possibly one side of a connector corroded.
All of these inputs including the ones that work go through all the same shit, volume and tone, then tape monitor. So if a channel is out only on tape or aux then the only possibility is the wiring from the jacks. Or the jacks themselves.
I looked up the manual but actually the engine only has service manuals. What I was looking for is where the phono inputs are. If they are above the rest then it could have been sitting in a food which wrecked the aux and tape input jacks.
The aux and tape inputs are going to go straight to the selector, phono has a preamp so it takes a slightly different path. That is what to look for, what is different here ? The FM is onboard somewhere and also will likely have a different path.
The manuals don't have much in the way of pictures so this is all I can say at this point without seeing it.
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