Sansui QR-6500 - dead channel problem

[P. S.]

Hi,

I recently bought a quad QR-6500 with a dead front-right channel. Rear works perfectly. Trying to figure out how to fix front and looking for help.

Here's what I've done already:
- checked and swapped speaker fuses between channels & amps (4 fuses) - the dead channel does not move with rotation of fuses so I assume all good here
- took out and wiggled/cleaned the pre-out/main hook connectors
- checked with headphones - same issue - only left plays
- cleaned all pots, inputs, terminals, offset trimmers etc. (had limited ability to reach out to the sliders with loudness/muting etc. but managed to squirt some deoxit in)
- checked all speaker terminals for front - same issue present on all speaker outputs

- checked and regulated the DC offset on rear and back. Found interesting thing. There's dc offset and voltage present on the dead channel even though no sound comes out. It's perfectly normal - just as other channels - 25mV
So - even though no sound comes out - there's still voltage in it. Which makes me suspect there may be an issue with the preamp.

- did not bother to trim the bias - might do that but want to avoid as this proved painful for me to do in the past ;-)

I am currently playing rear speakers in stereo and not using front at all. It's fine for me but I would like to bring this receiver to full operation and maybe try quad sound as I have dynaco a25/a35 combo which I think might be perfect for that ;-)

Has anybody experienced same issue? What have you done to fix?

-Peter

 

[Robisme]

Been a while since I had one of these. Do the amp driver boards unplug? You could swap them to see if the problem follows or remains the same.
This would let you know if the problem was with the driver board.

Also you could pull the pre/main jumpers and use a patch cable to run right out to left in and left out to right in and see if the problem remains the same. Only front jumpers.
If the problem moves to the other channel, the issue is in the preamp.


Rob

 

[P. S.]

I used your idea and cross-connected the preamp1 to power amp2 section and vice versa. The problem moved from the front to rear channel which indicates the problem is in the preamp section. I think it might be worth to do the deoxit of the buttons once again for the front section. I will also measure the output voltages from the preamp section to the power amp.