Help with Sony SQR-8750, SQ boards repair?

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gvl_guy

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This was one of the receivers I purchased at an estate sale and, since I'm having so much trouble with my Sansui QRX-9001 these days, I really need a backup.

Although all the amps work just fine when playing through the discrete mode, albums are another issue. Different channels cut out in the SQ and "R-MTX" modes. I've done some investigating and apparently the SQ boards, the most advanced for the time, have been an issue with these. I'm guessing that's the problem. :cry:

Does anyone know a repair person/shop that might be able to look at this one? Not sure who deals with SQ boards anymore. :confused: I doubt a local shop near me would have a clue. I'll ship it anywhere in the USA if needed. This one is too beautiful to toss aside.

IMG_20220523_195726_952.jpg
 

Soundfield

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This was one of the receivers I purchased at an estate sale and, since I'm having so much trouble with my Sansui QRX-9001 these days, I really need a backup.

Although all the amps work just fine when playing through the discrete mode, albums are another issue. Different channels cut out in the SQ and "R-MTX" modes. I've done some investigating and apparently the SQ boards, the most advanced for the time, have been an issue with these. I'm guessing that's the problem. :cry:

Does anyone know a repair person/shop that might be able to look at this one? Not sure who deals with SQ boards anymore. :confused: I doubt a local shop near me would have a clue. I'll ship it anywhere in the USA if needed. This one is too beautiful to toss aside.

Good luck, but unfortunately that series of receivers used the Sony SQ chips for the decoder. If any of those are at fault they are all but unobtainable.
Sony gave this rather strange explanation of the circuit in the service manual which rather admits it wasn't as good as it could have been...
sony rec.JPG
 

gvl_guy

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Good luck, but unfortunately that series of receivers used the Sony SQ chips for the decoder. If any of those are at fault they are all but unobtainable.
Sony gave this rather strange explanation of the circuit in the service manual which rather admits it wasn't as good as it could have been...
View attachment 79726 :)
Well, that sucks. I understand doing it the "cheap" way and cutting back on performance a little. But now I guess the only way to fix this is buy a Surround Master.
 

Sonik Wiz

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Well, that sucks. I understand doing it the "cheap" way and cutting back on performance a little. But now I guess the only way to fix this is buy a Surround Master.
Yup, that will fix it! At least you didn't buy it at crazy inflated prices on Ebay. Keep in mind the SM doesn't have Hall or stereo Synthesis modes like your Sansui receiver does. Sorry to hear you say it spends more time in the shop than at home. Sounds like a Triumph TR6.
 
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furui_suterioo

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Both my Kenwood quad receivers have the same problem as you, works fine in discrete mode and cd-4 but matrix board is noisy. Luckily I now have a collection of super-decoders + Involve. I set up my two stereo Sonys yesterday so I can clean up the Kenwoods, the Sonys actually have a little bit better sound but now two volume controls.
20220603_193741.jpg
 

gvl_guy

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Yup, that will fix it! At least you didn't buy it at crazy inflated prices on Ebay. Keep in mind the SM doesn't have Hall or stereo Synthesis modes like your Sansui receiver does. Sorry to hear you say it spends more time in the shop than at home. Sounds like a Triumph TR6.
I guess like anything, including people, after 45+ years or so, things go wrong. I bought the 9001 from the QRX Restore and, in less than a year, it was back with an issue. Now, one of the channels seems to crap out in the matrix modes. We narrowed it down to either a problem with one of the drivers or the CD-4 board. (When you flipped the drivers, the problem moved from left front to right front.) But they couldn't find anything. So the parts are on their way home with no changes. 😫

Not to badmouth anyone, but they are SO SLOW there. It's been 2 months with those parts. Not big communicators. A little email every so often would be helpful. 😕 I'd look for another shop, but wouldn't know where to start.

I'd kill for a modern amp with analog inputs/outputs so I could add a Surround Master and CD-4 demodulator!!
 

Sonik Wiz

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I guess like anything, including people, after 45+ years or so, things go wrong. I bought the 9001 from the QRX Restore and, in less than a year, it was back with an issue. Now, one of the channels seems to crap out in the matrix modes. We narrowed it down to either a problem with one of the drivers or the CD-4 board. (When you flipped the drivers, the problem moved from left front to right front.) But they couldn't find anything. So the parts are on their way home with no changes. 😫

Not to badmouth anyone, but they are SO SLOW there. It's been 2 months with those parts. Not big communicators. A little email every so often would be helpful. 😕 I'd look for another shop, but wouldn't know where to start.

I'd kill for a modern amp with analog inputs/outputs so I could add a Surround Master and CD-4 demodulator!!

The Marantz SR6014 was mentioned elsewhere in the forum as having analog MCH inputs. I just checked the owners manual & it does indeed have 7ch analog inputs as well as all the other moderny stuff. I imagine it's a bit expensive but so is buying/maintaining vintage quad gear.

I believe some of the current line of Emotiva & Anthem stuff has analog inputs. I'm not really a receiver kind of guy so I admit I'm not to up on that kind of product.

Speaking of Anthem, I have an older AVM pre-pro that has no HDMI but certainly has analog & SPDIF ins & out galore. It has worked flawlessly for me. And very good prices on Ebay. Might consider that but you will need power amps between that & the speakers. Stiil great flexibility in choosing these separate components & a good deal if you don't need 144 chs of ATMOS.

FWIW, even tho it has no HDMI on my Anthem AVM 30, that is not a limitation at least for me. My projector has 2 HDMI inputs & the Oppo & my desktop PC plugs into that. Modern high res audio is handled by the Oppo & sent to Anthem via analog mch.

Edit: I see that Marantz model is from 2019 & discontinued. But there are some on Ebay at reasonable prices:

 
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audiomaster

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My Marantz SR7013 also has analog inputs which get a feed from my Bose 4401 with SQ and CD-4 decoder boards in it.
 

par4ken

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Good luck, but unfortunately that series of receivers used the Sony SQ chips for the decoder. If any of those are at fault they are all but unobtainable.
Sony gave this rather strange explanation of the circuit in the service manual which rather admits it wasn't as good as it could have been...
View attachment 79726
You can still find chips on eBay. The only unobtainable chips are the Tate ones.
 

par4ken

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Although all the amps work just fine when playing through the discrete mode, albums are another issue. Different channels cut out in the SQ and "R-MTX" modes. I've done some investigating and apparently the SQ boards, the most advanced for the time, have been an issue with these. I'm guessing that's the problem. :cry:
I had a similar problem with a Sony SQD-2010. I ended up replacing a couple of the chips but then latter found that the board has a couple of hairline cracks in it. I forget if my problem was a complete loss of output or if the decoder logic just wasn't working. I still don't have that decoder adjusted exactly right (too much pumping). Sony's instructions are rather hard to follow. I much prefer the Motorola chipped decoders.
The problem that you describe is usually with the selector switches.
 

gvl_guy

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You can still find chips on eBay. The only unobtainable chips are the Tate ones.
Curious, do you have any idea what chips are in this that I might need? Or where I can find out? If I can find a shop or person who can fix this, (and that's probably a big IF,) it would be great if I could already have the right parts.
 

gvl_guy

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I had a similar problem with a Sony SQD-2010. I ended up replacing a couple of the chips but then latter found that the board has a couple of hairline cracks in it. I forget if my problem was a complete loss of output or if the decoder logic just wasn't working. I still don't have that decoder adjusted exactly right (too much pumping). Sony's instructions are rather hard to follow. I much prefer the Motorola chipped decoders.
The problem that you describe is usually with the selector switches.
It's the craziest thing. When using the Phone 1 or 2, 2 channel works fine. It's just the two front speakers. In the 2->4 mode, the volume drops to an incredibly low level in all 4 speakers. In SQ, it's exactly the same, all really low volume. In the R-MTX mode, the front speakers are really low, but the rears are nice and loud. Discrete is dead in the phono mode. But that could be by design. All is fine when using the AUX or 4 channel tape monitor positions. So it's definitely not the amps.
 

Sonik Wiz

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It's the craziest thing. When using the Phone 1 or 2, 2 channel works fine. It's just the two front speakers. In the 2->4 mode, the volume drops to an incredibly low level in all 4 speakers. In SQ, it's exactly the same, all really low volume. In the R-MTX mode, the front speakers are really low, but the rears are nice and loud. Discrete is dead in the phono mode. But that could be by design. All is fine when using the AUX or 4 channel tape monitor positions. So it's definitely not the amps.

I found a bit of interesting stuff about the Sony IC's here:


The only one I could quickly find was on Ebay, the CX-050 basic decoder chip for $15.62.
 

par4ken

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The Sony CX-718 is also available on eBay. The CX-049 was available not long ago, I think that is the chip that I replaced in mine, I should still have the original I kept it as it was not blown.
The CX-049 is the important one that is the logic circuit.

Low levels on RM as well points away from the Sony chips, the chips are only used for SQ. I would suspect bad coupling capacitors.
 

MidiMagic

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The biggest cause of dropouts in most quad receivers I worked on was bad rotary switch contacts.

DeOxIt worked on many of them but some actually had pitted switch contacts or loss of spring pressure on the wafer contacts.
 

quadsearcher

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The biggest cause of dropouts in most quad receivers I worked on was bad rotary switch contacts.

DeOxIt worked on many of them but some actually had pitted switch contacts or loss of spring pressure on the wafer contacts.

Agreed. I was going to post this too.
Some Sansuis have poor connections between contacts and traces on the small PCB also. It would explain why a servicer would find no problems with the PCB assemblies themselves.
 
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