Hello everyone!
I may need some advice!
Left channel works good, sounds good.
Right channel has noticeable noise and very low volume - music comes trough. But the volume of the noise and the music is the same regardless of the volume knob.
Speakers A or B - same result
What i did so far:
I visual checked the boards for any visible damage - nothing
Replaced The STK3102 chip, and idling adjustment to 7mV on both channels - This one didnt help. The status of the amp is exactly the same as before.
Without any source or speaker connected, I measured the 7mV on the left channel and ~55mV on the right channel.
I measured every resistor and capacitor (except the selector board) - I found a few not matching the service manual, i will make a list later.
According to the symptoms what should i check next?
I may need some advice!
Left channel works good, sounds good.
Right channel has noticeable noise and very low volume - music comes trough. But the volume of the noise and the music is the same regardless of the volume knob.
Speakers A or B - same result
What i did so far:
I visual checked the boards for any visible damage - nothing
Replaced The STK3102 chip, and idling adjustment to 7mV on both channels - This one didnt help. The status of the amp is exactly the same as before.
Without any source or speaker connected, I measured the 7mV on the left channel and ~55mV on the right channel.
I measured every resistor and capacitor (except the selector board) - I found a few not matching the service manual, i will make a list later.
According to the symptoms what should i check next?
I've attached a service manual.
Do you have any test equipment beyond a voltmeter?
Your measurements sound encouraging at least, but some fault isolation would be very helpful to narrow search. Do you have a scope or any signal tracing equipment? I suggest signal tracing from right channel input toward volume pot, through wiper and associated passives, eventually to pin 1 of IC301. Be sure to use DC block caps to avoid disturbing bias on IC301. See if that reveals anything. You might be able to use the working channel for signal tracer if no other test amp is available, but that's a bit more tricky.
Good luck.
Do you have any test equipment beyond a voltmeter?
Your measurements sound encouraging at least, but some fault isolation would be very helpful to narrow search. Do you have a scope or any signal tracing equipment? I suggest signal tracing from right channel input toward volume pot, through wiper and associated passives, eventually to pin 1 of IC301. Be sure to use DC block caps to avoid disturbing bias on IC301. See if that reveals anything. You might be able to use the working channel for signal tracer if no other test amp is available, but that's a bit more tricky.
Good luck.
Rock the Mono-stereo switch some tens of times (right channel signal passes straight through that while left channel volume pot is connected (excluding the optional filter) straight to the input socket).
Check the connector board contacts, clean these if necessary.
Check the connector board connectors' soldering (also soldering on other boards).
Bridge the input signal connector on STK board (i.e. vol pot wipers "at the end of the cable") and check if the problem persists (put the amp in mono mode for that).
Just to "eliminate the obvious".
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