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Moving on. I need help with quad boards. QRX-5500A

crkeith65

crkeith65

Member
This is my first quad repair. I need to move on from my tuner problem that I have been struggling with. I have the FM functional but not happy yet. ( see this thread if interested:
http://audiokarma.org/forums/index.php?threads/qrx-5500a-fm-audio-problem.718021/ )

I have a Sansui QRX-5500A with F-2048 and F2084 quad boards. The amps are good and I have good sound whether I input to front rear or both as long as I have the function switch in 2-ch or discrete. All other function positions produce very weak audio with cracking and popping. With F-2048 pulled I get the same very faint audio but none of the cracking popping sound on all functions except 2-ch and discrete which sound great. I have read about noisy transistors on the F-2048 board. Would this be the case here? If so, any transistor in particular since there are I think 16 on this board? What else should I look for? All switches and pots have been de-oxed and all other functions seem to work OK.

Here is a link to my SM:
http://akdatabase.org/AKview/albums/userpics/10007/Sansui QRX-5500A, QRX-7500A Service Manual.pdf
 
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You really should be injecting in a signal and trace it through the circuits using a good DMM or scope. Check the supplies, check the bias on the amplifier stages.
 
I feel like I should help with this, but really, there's not much that can be done with these early quad processing boards. If you are getting noise, etc, from the boards about the only way to repair them is to check transistors one by one.

Sansui was extremely guarded about letting any information out about their quad boards, especially these early ones. It's my opinion that they purposely made the schematics impenetrable. It is almost impossible to trace signals on the schematic.

The signal processing offered by the early quad models is not much. That is why they are worth so little on the market. They are amazing receivers though, with very nice sound, and 4 output channels instead of two, ideal for driving speaker systems in different rooms at the same time.
 
Thanks for the advice. I am not sure if the fellow I'm working on this for really cares about the quad decoder. He has no real quad sources and since all four channel outputs are working, he may be happy like it is. Jim I was thinking about contacting you about this. You did an excellent job for me earlier this year when you brought a burned F-2624 back to life for my 8080DB. I will contact my friend that owns it and get his input. In the meantime is it OK just to leave the card pulled? It sounds great without it. Clean and powerful with no popping.
 
I think you can operate just fine with the boards out. I think there might be an adjustable voltage for running the preamp stages, that you might want to check. With the quad boards out, that'll be less load and that voltage might go up a bit.

I'm not sure without looking at a schematic, I may have your QRX5500 confused with a different model.
 
Trnsfmr said:
I think you can operate just fine with the boards out. I think there might be an adjustable voltage for running the preamp stages, that you might want to check. With the quad boards out, that'll be less load and that voltage might go up a bit.

I'm not sure without looking at a schematic, I may have your QRX5500 confused with a different model.
Click to expand...
The schematic link is posted above. It uses F2048 and F2084 quad boards unlike the earliest models which use F2048 and F2047 boards.
 
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crkeith65 said:
Thanks for the advice. I am not sure if the fellow I'm working on this for really cares about the quad decoder. He has no real quad sources and since all four channel outputs are working, he may be happy like it is. Jim I was thinking about contacting you about this. You did an excellent job for me earlier this year when you brought a burned F-2624 back to life for my 8080DB. I will contact my friend that owns it and get his input. In the meantime is it OK just to leave the card pulled? It sounds great without it. Clean and powerful with no popping.
Click to expand...
 
crkeith65 said:
Thanks for the advice. I am not sure if the fellow I'm working on this for really cares about the quad decoder. He has no real quad sources and since all four channel outputs are working, he may be happy like it is. Jim I was thinking about contacting you about this. You did an excellent job for me earlier this year when you brought a burned F-2624 back to life for my 8080DB. I will contact my friend that owns it and get his input. In the meantime is it OK just to leave the card pulled? It sounds great without it. Clean and powerful with no popping.
Click to expand...

I talked with the owner and after he heard it playing Steely Dan, he was perfectly happy running the receiver without the one quad board. I will continue looking for the F-2048 board or if I run out of other things to do, I will change out the 16 transistors on that board.
 
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