Possible problem with QRX-7001 CD-4 Circuit?

[macdude]

If I connect a signal generator to the phono input and inject a 30KHz sine wave, the CD-4 lamp should light, correct? I just re-capped my CD-4 boards (2086 and 2475) and it will only light when I get up around 40KHz. The carrier adjustment has an effect, but doesn't seem to go low enough to allow 30KHz to activate the circuit.

When I first bought it, I couldn't get it to light at all. I found some leaking caps and replaced them, at which time it did light up correctly at 30KHz. Since I finished re-capping the board, I'm getting this issue. I double checked all the caps. Everything is in correctly.

I have a Technics SA-8000X CD-4 receiver and it lights right up at 30KHz. I'd imagine a few things shifted value due to the recap, but I don't see anything in the service manual about an internal carrier adjustment. Actually, I don't see much of anything relating to CD-4 adjustments. Everything else on the 7001 works great.

Can anyone tell me what voltages I should be getting at these PCBs? Any thoughts on this are appreciated. I won't have a good CD-4 turntable setup until early next week, but I would think I should at least get an indication with the signal generator.

On a side note, the Technics activates the CD-4 circuit properly with the current turntable I have. The Sansui does not.

I've had an audiokarma post on my cd-4 woes here since 2008: http://www.audiokarma.org/forums/showthread.php?p=6447087#post6447087

 

[macdude]

Looks like I tackled the issue. Problem was a transistor in the carrier detection circuit. This transistor, TR603 on F-2475 (2SA733) comes just before the CD-4 lamp. It drives a few 2SC945's which are used to light the lamp and provide power to (or a ground for) the final stages in the demod circuit. The transistor must have become leaky or the gain drifted. I'm not a transistor expert. I used the KSA733CLTA (center conductor is collector in this version - ECB) from Mouser. I am now getting a VERY solid detection sweeping from 28KHz to about 40KHz with the carrier set at roughly 20%. Maybe a tech can chime in on this, but it might not be a bad idea to try replacing this transistor if you're getting flaky carrier lock with an otherwise good cart/cable/turntable setup.

Now we're on to turntable tweakage!