Here’s an interesting one; would anyone be able to advise why this might happen?
I just repaired this Sansui 9090DB that was stuck in protection because of the amplifier card’s fuse resistors that went open. I ended up replacing all the suspect components, caps and trim pots. Also recapped the power supply, cleaned all controls and adjusted the dc offset and bias.
From a listening standpoint, the receiver works. When I went to check the channels on my dummy load however, I was presented with this nice squashed waveform on the left channel. I am not that familiar with what causes the half-wave in this situation. The only extreme thing I had to do with this one was ultrasonically-clean the volume pot assembly because the balance was nearly frozen, but I can’t imagine that had anything to do with it.
I’m going to start probing around and see if I can find where the wave starts to diminish, but I would be betting this would lie solely on the driver board / card, right? I haven’t replaced any transistors yet.
I just repaired this Sansui 9090DB that was stuck in protection because of the amplifier card’s fuse resistors that went open. I ended up replacing all the suspect components, caps and trim pots. Also recapped the power supply, cleaned all controls and adjusted the dc offset and bias.
From a listening standpoint, the receiver works. When I went to check the channels on my dummy load however, I was presented with this nice squashed waveform on the left channel. I am not that familiar with what causes the half-wave in this situation. The only extreme thing I had to do with this one was ultrasonically-clean the volume pot assembly because the balance was nearly frozen, but I can’t imagine that had anything to do with it.
I’m going to start probing around and see if I can find where the wave starts to diminish, but I would be betting this would lie solely on the driver board / card, right? I haven’t replaced any transistors yet.
If you got sound at the output, it seems the power stage is working, but some part of the pre stage is defective. Look at the schematic, backwards from the output transistors, until you find a coupling cap. The fault should be easy to find if you compare both channels.