Testing a CD-4 demodulator with a signal generator?

[BeoProf]

Hi Everyone, I have found here and on AudioKarma indications that it is possible to set up or test a CD-4 demodulator without a test record but with a signal generator. I am interested in this for the purpose of testing a Sansui QRX 7001 I am planning to buy, I am going to see it tomorrow in person so I need to be able to decide if the CD-4 demodulator is shot or not.

As I understand, the first step would be to feed 30kHz into PHONO and see if the CD-4 beacon lights up. But if this happens what would be the next steps? This should mimic the test record somehow, so if any of the experts here know how to do it I would be very grateful.

Are there similar tricks that one can do with the VarioMatrix/QS/SQ demodulators? I will take with me a couple of SQ records, and some quadrophonic headphones (I don't think I'll have access to 4 speakers there to test it) but if there is an easy trick to test the quad functionality this would be very helpful.

Thanks in advance!

 

[krkier]

Hi Everyone, I have found here and on AudioKarma indications that it is possible to set up or test a CD-4 demodulator without a test record but with a signal generator. I am interested in this for the purpose of testing a Sansui QRX 7001 I am planning to buy, I am going to see it tomorrow in person so I need to be able to decide if the CD-4 demodulator is shot or not.

Yes, it is possible. But you need a signal generator with the ability to perform a FM modulation at 30kHz with, say 400Hz, to check the output of the demodulator part in your circuit, and of course the ANRS. And it should be able to output this voltage in the 500µV range (for check of the "lock range"), so output noise can be an issue for the right choice of your generator.

The best advise I can give you is to get a service manual for your receiver, which hopefully describes the functionality and test procedures for the demodulator. Try hifi engine. You may also look for the bigger units (8001, 9001), since the demodulator boards may be the same, and so the check and repair.

Now a tip for all the 4DD-5 users and repair buffs: Use the service manual of the Marantz CD-400, it is a clone of the JVC. The service manual is way more sophisticated and detailed than JVC's own!

-Kristian

 

[BeoProf]

Thanks! The guy selling the receiver is a tech and has professional equipment, so it might be possible to do this. The manual for the QRX 7001 of course has instructions, but for the CD-4 test record -- it came with the receiver when it was new. I know for a fact there is no CD-4 turntable setup available, so the signal generator might just give an indication if the demodulator works at all...