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From: Sparkey on 26 Jun 2007 13:03
I'm restoring a vintage Kenwood Model Nine GX receiver
(cir. 1970's)no schematic.

I have gotten the FM working finally and receiving stereo but the
stereo indicator lamp thumps on and off with the modulated signal.
If it's tuned to a station with a dead carrier, it holds stereo. The
audio does "garble" a little when the thing is flopping in and out of
stereo lock.

So far, I've replaced the LA3350 MPX chip, the 1500 pico cap
associated with the oscillator, Adjusted the VCO for 19Khz(which it
does),
I Aligned the IF stages and tuned the front end coils with a scope
(At first the tuner could not receive stereo until I did that !)

When I scope the VCO output, it's a stable square wave but it does
shift a bit in step with the audio.

There are 2 adjustable coils in the area on it's own small board.
I'm assuming maybe they are quadrature coils. I have tried swinging
them a bit but there's no effect. I snapped a pic of this board
http://members.aol.com/ta7205/MVC-110f.jpg
if anyone is interested in viewing it.

This is starting to frustrate me and I could use some advice.
TIA
Sparkey

From: Michael Black on 26 Jun 2007 14:22
Sparkey (wwspage(a)aol.com) writes:
> I'm restoring a vintage Kenwood Model Nine GX receiver
> (cir. 1970's)no schematic.
>
> I have gotten the FM working finally and receiving stereo but the
> stereo indicator lamp thumps on and off with the modulated signal.
> If it's tuned to a station with a dead carrier, it holds stereo. The
> audio does "garble" a little when the thing is flopping in and out of
> stereo lock.
>
> So far, I've replaced the LA3350 MPX chip, the 1500 pico cap
> associated with the oscillator, Adjusted the VCO for 19Khz(which it
> does),
> I Aligned the IF stages and tuned the front end coils with a scope
> (At first the tuner could not receive stereo until I did that !)
>
> When I scope the VCO output, it's a stable square wave but it does
> shift a bit in step with the audio.
>
> There are 2 adjustable coils in the area on it's own small board.
> I'm assuming maybe they are quadrature coils. I have tried swinging
> them a bit but there's no effect. I snapped a pic of this board
> http://members.aol.com/ta7205/MVC-110f.jpg
> if anyone is interested in viewing it.
>
> This is starting to frustrate me and I could use some advice.

I don't have a clue, but when I saw the subject header, my first
thought was "the signal is too weak". That doesn't seem the case,
but your focus on the stereo decoder may be false. What if the decoder
is fine, but something in the FM demodulator is bad or misadjusted?
If the decoder doesn't get a good signal, it won't work.

Michael


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