the left channel is cutting out. the power amp section tested fine. there is sound from the left channel but it's just high frequency and virtually no volume. i tried lubing the volume pot put it didn't fix anything. it was working fine earlier today. any suggestions what to do?
https://docs.google.com/file/d/0B5bsCCYZz1YhRTNoa2JHY2pQc0E/edit?usp=sharing
link to service manual above.
https://docs.google.com/file/d/0B5bsCCYZz1YhRTNoa2JHY2pQc0E/edit?usp=sharing
link to service manual above.
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Just high frequency suggests either a coupling cap is going faulty or perhaps even a break in the print or a poor connection somewhere and stray capacitance is allowing a little signal to get through.
Its the kind of problem a scope and test tone (from generator or CD etc) would find in minutes.
Its the kind of problem a scope and test tone (from generator or CD etc) would find in minutes.
Cold spray...
Use a squirt of cold spray (Maplin's) on the caps in the signal path and see if it makes the sound come back, if so, there's your culprit. Cold solder joints could also be an issue given the age of the unit, have a look at all solder joints. If the sound comes back after the cooling with cold spray, use your solder iron to simulate the spot you think is the problem to heat up. If then the sound disappears again, you have located the fault. Good luck.
Use a squirt of cold spray (Maplin's) on the caps in the signal path and see if it makes the sound come back, if so, there's your culprit. Cold solder joints could also be an issue given the age of the unit, have a look at all solder joints. If the sound comes back after the cooling with cold spray, use your solder iron to simulate the spot you think is the problem to heat up. If then the sound disappears again, you have located the fault. Good luck.
That's exactly how a hairline crack in a signal carrying conductor (such as PCB print) would behave. The stray capacitance between the break allows higher frequencies to pass.
If you can't find anything and haven't any test equipment then you need to try and eliminate various chunks of the circuitry, for example by applying the same signal to the "top" of the volume control and making sure the power amps and volume pot really are OK. On a stereo amp its relatively easy to isolate and cross couple various sections in the preamp to try and find where things are going amiss.
Make sure any speaker relays are OK... doesn't really sound like that kind of issue tbh but worth checking. Often if the contacts are poor then temporarily using higher volume can correct the problem by "punching through" any tarnish layer on the contacts. I don't think that is your problem though.
i think the problem is a really dirty speaker selector switch. i lubed it and it seems to have solved the problem.
another weird issue is when i connected the speakers to 'speaker A' terminals, opposite of what they were connected to before, there is lack of bass in the right channel. is still sounds okay, but def'n less bass in one side. what could cause that?
another weird issue is when i connected the speakers to 'speaker A' terminals, opposite of what they were connected to before, there is lack of bass in the right channel. is still sounds okay, but def'n less bass in one side. what could cause that?
That's most likely a physical problem... bad joint/cracked print. You are going to have to do some tests or follow the signal path visually looking for problems. If you can't just see anything obvious then reflow the whole PCB.
This is how some dry joints can look (last pictures in post #1),
http://www.diyaudio.com/forums/digital-source/226288-sony-cdp790-kss240-restoration-project.html
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