I'm working on a Sansui 441 for a friend. He picked it up somewhere untested. The problem it has is that the right channel is (almost) dead. I say almost because there is a tiny bit of output if the volume is cranked to max. The problem occurs regardless of input and happens on both A and B speaker outputs. All controls (treble, bass, balance, function selector, volume) have been cleaned with DeOxit and appear to be functioning properly.
When I opened it up and saw STK-016 outputs I suspected one of them had gone bad. With fingers crossed hoping I wouldn't blow up the good one I swapped them. The problem stayed with the right channel. I found a function generator app for my Android phone and have been troubleshooting with an oscilloscope. I can see where the signal gets lost, I'm just at a loss as to why. I can see a good sine wave from the signal generator from the input all the way to pin 6 of both STK-016's. At pin 6 the amplitude varies with volume adjustments and is pretty even between left and fight channels. Looking at the schematic, it looks like pin 2 is the output and goes pretty much directly to the speaker output connectors. On the right (good) channel I see a good sine wave with significantly increased amplitude compared to pin 6 that varies with volume adjustment as would be expected. On the left (bad) channel I see no sine wave except for a very small amplitude signal with the volume at max.
Just to verify I swapped the STKs again and still have the same symptom. Regardless of STK placement the left channel is bad. I'm stumped on this and cant figure out what might be killing the left output other than the STK itself. Any suggestions as to how I can further troubleshoot this would be greatly appreciated. I tried to attach the schematic but it's too large to attach. It's available on Hifi Engine.
Thanks,
Joe
When I opened it up and saw STK-016 outputs I suspected one of them had gone bad. With fingers crossed hoping I wouldn't blow up the good one I swapped them. The problem stayed with the right channel. I found a function generator app for my Android phone and have been troubleshooting with an oscilloscope. I can see where the signal gets lost, I'm just at a loss as to why. I can see a good sine wave from the signal generator from the input all the way to pin 6 of both STK-016's. At pin 6 the amplitude varies with volume adjustments and is pretty even between left and fight channels. Looking at the schematic, it looks like pin 2 is the output and goes pretty much directly to the speaker output connectors. On the right (good) channel I see a good sine wave with significantly increased amplitude compared to pin 6 that varies with volume adjustment as would be expected. On the left (bad) channel I see no sine wave except for a very small amplitude signal with the volume at max.
Just to verify I swapped the STKs again and still have the same symptom. Regardless of STK placement the left channel is bad. I'm stumped on this and cant figure out what might be killing the left output other than the STK itself. Any suggestions as to how I can further troubleshoot this would be greatly appreciated. I tried to attach the schematic but it's too large to attach. It's available on Hifi Engine.
Thanks,
Joe
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Same point different color.
