Hi folks, strange problem here.
I'm working on bringing this receiver back to life. When I got it there were a bunch of physically broken and burned resistors on the left side of the power amp. I replaced those and the output transistors and biased the amp while I was at it. When I powered it on for a test the left channel still had a nasty distortion in it. Since I already had it torn apart I figured I would go ahead and recap it too - so that has been don as well. Didn't change the problem though. Next I cleaned all the pots and switches with deoxit - still no change.
Now here's the weird part. I tested the unit through headphones, and when no speaker set is selected it sounds fine through cans. If a speaker is not connected to the left side and I listen through headphones it sounds fine as well, regardless of whether or not I have a speaker selection switch engaged. But as soon as signal is sent to a left side speaker the sound gets really grungy, both in the speaker and my headphones. It seems that having a load on the left channel is what is causing this distortion to occur.
I think I have also eliminated the pre-amp as a cause of the issues by sending the left channel from the pre-amp to the right side of the power amp. No distortion in the right side under those conditions.
This one is starting to test my diagnostic ability, so it would be a huge help if any of you all could give me a hand figuring out what to look at next. Happy to answer any additional questions that might shed more light on the issue.
Thanks!
I'm working on bringing this receiver back to life. When I got it there were a bunch of physically broken and burned resistors on the left side of the power amp. I replaced those and the output transistors and biased the amp while I was at it. When I powered it on for a test the left channel still had a nasty distortion in it. Since I already had it torn apart I figured I would go ahead and recap it too - so that has been don as well. Didn't change the problem though. Next I cleaned all the pots and switches with deoxit - still no change.
Now here's the weird part. I tested the unit through headphones, and when no speaker set is selected it sounds fine through cans. If a speaker is not connected to the left side and I listen through headphones it sounds fine as well, regardless of whether or not I have a speaker selection switch engaged. But as soon as signal is sent to a left side speaker the sound gets really grungy, both in the speaker and my headphones. It seems that having a load on the left channel is what is causing this distortion to occur.
I think I have also eliminated the pre-amp as a cause of the issues by sending the left channel from the pre-amp to the right side of the power amp. No distortion in the right side under those conditions.
This one is starting to test my diagnostic ability, so it would be a huge help if any of you all could give me a hand figuring out what to look at next. Happy to answer any additional questions that might shed more light on the issue.
Thanks!