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Sansui QRX-9001 With a Problematic CD-4 Demodulator

K

Kaleb Martin

Active Member
I have a problem with the CD-4 demodulator in my Sansui QRX-9001. It has been completely recapped and rebuilt (all transistors and diodes have been replaced). With all the work that has been done, I still have one issue with the demodulator. My left channels have no front-back separation, but the right side is working properly, I also have good left-right separation. I’m pretty sure one of the demod I.C.’s aren’t working properly, and was wondering if anyone has, or knows of someone who has one to spare? And if anyone thinks there could be another/different issue, I’m open ears!
 
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Those IC's - the supplier and part number escapes me now - were last generation CD-4 demod chips, probably had a very short lived production cycle as quad was already nearly dead as a commercially viable product when those hit the market. Very few products used them, making them tougher to find in something that can be cannibalized.

You might fond NOS by trawling ebay, the off shore semiconductor suppliers have had pretty remarkable record of turning up and selling obsolete devices like this. The Sansui QS chips have been available off and on for years from long sitting stockpiles. I've bought a supply tpf those and can confirm those were legit, not counterfeits. These types of chips aren't nearly as prone to fakes as output transistors are, as there is little to no profit incentive to do so.
 
Thanks for the info. I’ve tried eBay several times with no luck. Do you know of any demodulators that use the CD4-392 I.C., aside from the Sansui QRX-9001?
 
The Sansui QSD-2 did use the same cd-4 chips I'm pretty certain. That one is probably not a great choice as a parts donor however, as they fetch pretty high prices these days. I have no real familiarity with the JVC quad product lineup, so I can't really advise on interchangeability of the chips from any specific model of theirs.
 
Sansuiman said:
The Sansui QSD-2 did use the same cd-4 chips I'm pretty certain. That one is probably not a great choice as a parts donor however, as they fetch pretty high prices these days. I have no real familiarity with the JVC quad product lineup, so I can't really advise on interchangeability of the chips from any specific model of theirs.
Click to expand...
QSD-2 does not have CD-4, just QS and SQ.

IMG_0526.JPG
 
With the CD4-392 there is no need to adjust the carrier level, as it’s automatically adjusted properly with the I.C.’s and demodulator. I believe with the other I.C. models they all require an adjustment potentiometer for the carrier level, which is another issue with trying to substitute another CD-4 demod I.C. to the circuit.
 
@KeithD is correct. No CD-4 on QSD-2. My mistake. You might want to post this question at the quadrophnicquad forums, as they are not strictly Sansui-centric, amd CD-4 was specifically a JVC developed quad system. Likely to be some experts over there who can better answer tech queations on it.
 
I tried to sign up for quadraphonicquad, but was not approved. It said something along the lines of “contact an administrator to complete registration.” But I couldn’t find a way to contact anyone other than emailing, and I never got a response back.
 
KeithD said:
QSD-2 does not have CD-4, just QS and SQ.
]
Click to expand...

Yep, my mistake. Sorry, senior moment. I believe what I was thinking of was Technics' stand-alone CD4 unit (SH-400), not the QSD-2 - both of which I've owned. The SH-400 is kind of scarce these days, so your best route may very well be looking for the chip itself.
 
1. You need a CD4 capable table and cartridge.
2. That needs to be calibrated using a test record.

* You won't get proper CD4 decoding with any other source as the high freq control signals aren't present. Even a worn disk may be missing that, so good luck. Never really saw the sense in CD4 myself - waaaaaaay too much bs and expense for the results.
 
I have a Shibata stylus with a Dual 1229 tt. As well as the adjustment record supplied with the Sansui QRX-9001. I also get the carrier signal light on the 9001.
 
I personally prefer SQ over CD-4. My biggest reason for wanting to fix this issue is to have a fully operational 9001. Although I do have a few records in CD-4 that I enjoy listening to.
 
Gettin' all "gung ho" are we? <G>

Luck with the filters - most any are listed as "obsolete" or "non-stocked" if you can find them at all. In case you're not aware of what "non-stocked" means ... it means ... luck with the filters, eh. Lucky enuf, the filters tend to be quite stable over time.

I highly recommend adding a 25v regulator to the decoder chips power circuit. Instructions are available at QRXRestore, along with some other tasty tidbits, including complete alignment procedures. Here's mine ...

25v-regulator-007.jpg


Be extremely careful making voltage adjustments, as those are tweaky, and the slightest nudge can do serious damage to unobtanium chips.
 
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You guys are the ones that would know this answer...or know someone that knows the answer. I picked up a QRX 9001. It lights up. Seems like it should work...but the audio is not coming out. I checked everything I know to check...which is super limited. I'm out of my depth. I know what I have, but I'm not smart enough to fix it. I need someone in So Cal (preferably Orange County) that you trust that can bring this beast back to life. Thoughts?
 
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