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

Sparkey ) 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

On Jun 26, 1:22 pm, (Michael Black) wrote:
Sparkey ) 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- Hide quoted text -

- Show quoted text -

Maybe some of the electrolytics in the power area are going west.
Check the power sully at all pointss. That would possibly explain the
variations in [erformance with varying audio.

H. R. (Bob) Hofmann

On Jun 26, 2:27 pm, "hr(bob) "
wrote:
On Jun 26, 1:22 pm, (Michael Black) wrote:



Sparkey ) 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- Hide quoted text -

- Show quoted text -

Maybe some of the electrolytics in the power area are going west.
Check the power sully at all pointss. That would possibly explain the
variations in [erformance with varying audio.

H. R. (Bob) Hofmann

I got to the bottom of this problem today!!

When I pulled the RX board out again yet another time, I did notice a
discoloration on a couple of the traces near the edge of the board.
I'll be damned, looks like the remnants of a liquid spill ! Looking at
the top side of the board it hardly showed but the spill must have
followed gravity to the underside of the pcb, where it dried. I chased
down the traces and sure enough ! It dried shorting pin 15 (loop
filter) to pin 2
(composite signal in) I scratched it off and cleaned it with acetone
I had to re-tune the 19khz VCO but I had beautiful and STABLE FM
stereo !
Thanks for the repies. write this one down guys, I was going nuts !

On Jun 27, 9:23 pm, Sparkey wrote:
On Jun 26, 2:27 pm, "hr(bob) "
wrote:



On Jun 26, 1:22 pm, (Michael Black) wrote:

Sparkey ) 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- Hide quoted text -

- Show quoted text -

Maybe some of the electrolytics in the power area are going west.
Check the power sully at all pointss. That would possibly explain the
variations in [erformance with varying audio.

H. R. (Bob) Hofmann

I got to the bottom of this problem today!!

When I pulled the RX board out again yet another time, I did notice a
discoloration on a couple of the traces near the edge of the board.
I'll be damned, looks like the remnants of a liquid spill ! Looking at
the top side of the board it hardly showed but the spill must have
followed gravity to the underside of the pcb, where it dried. I chased
down the traces and sure enough ! It dried shorting pin 15 (loop
filter) to pin 2
(composite signal in) I scratched it off and cleaned it with acetone
I had to re-tune the 19khz VCO but I had beautiful and STABLE FM
stereo !
Thanks for the repies. write this one down guys, I was going nuts !

That's 'cuz in the 70's everybody drank while listening to
"underground" rock stations so you had a high probability of spills...