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I am just going to put this here in the hope that it helps someone else. I was given a really nice hi-fi amplifier, a Denon PMA-720. They were made in the 80's and it's hard to find much on them.
I came to me working, but one channel wasn't putting out as much volume as the other one and after playing for a while it would intermittently crackle. I checked the wires, the speakers, and so on. I tried different inputs, switching speakers left, right, A channel, B channel, defeating the tone stack. Plugging in headphones, I could hear the same problem in the headphones. So it seemed to me that something before the headphones was at fault. Good! Nothing wrong with the output transistors!
Since none of that worked out, I noticed some of of the RCA input jacks in the back were loose. I figured I'd reflow the solder on those. I also gave them a good deoxit treatment. That didn't help.
So I took the thing apart and gave all of the pots and switches on the front panel a good deoxit treatment. That seemed to get it. I suspect it was the balance pot since a symptom was unbalanced output. Have been listening to it for hours and no problems at all.
This troubleshooting process went on for many months, and I googled all over the place looking for help and didn't get too far. So I figured I'd put it here, since I visit this site regularly, it gets decent pagerank, and I wanted to put this somewhere findable in the hopes it'll help someone else.
Cheers
I came to me working, but one channel wasn't putting out as much volume as the other one and after playing for a while it would intermittently crackle. I checked the wires, the speakers, and so on. I tried different inputs, switching speakers left, right, A channel, B channel, defeating the tone stack. Plugging in headphones, I could hear the same problem in the headphones. So it seemed to me that something before the headphones was at fault. Good! Nothing wrong with the output transistors!
Since none of that worked out, I noticed some of of the RCA input jacks in the back were loose. I figured I'd reflow the solder on those. I also gave them a good deoxit treatment. That didn't help.
So I took the thing apart and gave all of the pots and switches on the front panel a good deoxit treatment. That seemed to get it. I suspect it was the balance pot since a symptom was unbalanced output. Have been listening to it for hours and no problems at all.
This troubleshooting process went on for many months, and I googled all over the place looking for help and didn't get too far. So I figured I'd put it here, since I visit this site regularly, it gets decent pagerank, and I wanted to put this somewhere findable in the hopes it'll help someone else.
Cheers
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