CD-4 demodulator repair?

[Colin Dunn]

Does anyone here know of someone who can repair broken CD-4 demodulator units?

I took one (a Harman Kardon 44+) to a local vintage audio guy. But he wasn't able to repair it - the caps were OK, but he didn't know how to troubleshoot more in-depth into the demodulator. This one has a serious hum and is not even usable as a stereo phono stage.

Then I have another one, a JVC 4DD5, which was new old stock. I can get the CD4 light to come on with three different cartridges (Denon DL-160, JVC 4MD-20X, Audio-Technica AT150MLX). But it outputs double stereo and doesn't extract the rear channels properly.

Is there anyone left in the USA who can work on these units, and has a track record for completing successful repairs?

 

[Disclord]

Does anyone here know of someone who can repair broken CD-4 demodulator units?

I took one (a Harman Kardon 44+) to a local vintage audio guy. But he wasn't able to repair it - the caps were OK, but he didn't know how to troubleshoot more in-depth into the demodulator. This one has a serious hum and is not even usable as a stereo phono stage.

Then I have another one, a JVC 4DD5, which was new old stock. I can get the CD4 light to come on with three different cartridges (Denon DL-160, JVC 4MD-20X, Audio-Technica AT150MLX). But it outputs double stereo and doesn't extract the rear channels properly.

Is there anyone left in the USA who can work on these units, and has a track record for completing successful repairs?

You need to find someone who is capable of repairing and aligning FM Stereo receivers, which is a complex procedure since FM Stereo receivers have all kinds of adjustments that interact plus matrix sections to derive the Left and Right channels. Both of your CD-4 units don't use any proprietary parts so should be repairable and a good repairman with FM knowledge would be your best bet,