I had a similar problem with a 1970's Onkyo T9, and fixed it by adjusting the VCO pot while using a multimeter that measured frequency to set it to 19 kHz across the test points. I think this is VR203 on yours; look for the 19kHz test point on the circuit board and test the frequency between pin 12 (I think it is) and the test point on the board and adjust to 19kHz. I did mine ten years ago and it's still fine.
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Sure. You just need to probe between Pin 12 of the IC shown on your earlier picture of the circuit board (a3350) and the test point on the board (see the '19kHz' marked on the board - I can't quite see where the actual point is, but there will be a painted spot or arrow). Then adjust the pot mentioned in my last post so the output is at 19 kHz with the tuner switched on of course. The pot number is shown on that extract of the service manual.
Below is a DIP 16 footprint so you can work out which is Pin 12 is on that chip. Look for the indent at the 1 and 16 end.
I hope that works; I know of a few people that it has worked for, preventing them having to have the tuner realigned. The latter would be preferable, but would cost.
You may wish to measure the resistance across the trim pot before you move it so you have a base line in case the adjustment doesn't work, so you can return it to that point.
Below is a DIP 16 footprint so you can work out which is Pin 12 is on that chip. Look for the indent at the 1 and 16 end.
I hope that works; I know of a few people that it has worked for, preventing them having to have the tuner realigned. The latter would be preferable, but would cost.
You may wish to measure the resistance across the trim pot before you move it so you have a base line in case the adjustment doesn't work, so you can return it to that point.
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Neither of those has a frequency function.
You could try just tweaking the pot to see if you can make stereo break out: if it does, set it to the midpoint between the two extremes where it cuts out.
But this may not yield anything, in which case put it back where it was and find a tuner guy.
You could try just tweaking the pot to see if you can make stereo break out: if it does, set it to the midpoint between the two extremes where it cuts out.
But this may not yield anything, in which case put it back where it was and find a tuner guy.
@ejp
I agree.
Messing around with the critical adjustments and alignments of tuners is something that's caused a LOT of aggrevation to me in the repair shop over the years.
Particularly since the internet has created hoardes of do-it-yourselfers that increased the amount of "Golden Screwdriver" putzers that made my job much more difficult.
Yes, my mouth spewed tons of unflattering words at the service bench at times.
All the years of my professional training in the service industry were slowed down and caused a backlog at times to other work that was waiting for me.
Sometimes it caused annoyed customers, both of the destoyed units, and the other customers having to wait longer, due to me having to figure out the mess that someone caused by listening to what some self-proclaimed internet guru or youtube video told them to do.
I'm not fond of having to dig out cracked and broken ferrite tuning slugs in I.F. cans.
And 6, 8, or more slugs ALL turned in an attempt to "fix things".
In some ways, the internet blogs are not well-liked by us technicians... for the above reasons.
I agree.
Messing around with the critical adjustments and alignments of tuners is something that's caused a LOT of aggrevation to me in the repair shop over the years.
Particularly since the internet has created hoardes of do-it-yourselfers that increased the amount of "Golden Screwdriver" putzers that made my job much more difficult.
Yes, my mouth spewed tons of unflattering words at the service bench at times.
All the years of my professional training in the service industry were slowed down and caused a backlog at times to other work that was waiting for me.
Sometimes it caused annoyed customers, both of the destoyed units, and the other customers having to wait longer, due to me having to figure out the mess that someone caused by listening to what some self-proclaimed internet guru or youtube video told them to do.
I'm not fond of having to dig out cracked and broken ferrite tuning slugs in I.F. cans.
And 6, 8, or more slugs ALL turned in an attempt to "fix things".
In some ways, the internet blogs are not well-liked by us technicians... for the above reasons.
The Finisher, as indicated above, you need a multimeter that can measure frequency.
I still think it's worth a shot if you can borrow a meter with frequency. Turning this pot, if you take the precaution of measuring the resistance across it before moving it, can have no detrimental effect.
Note there are a few things that can cause the symptoms you describe. For example, there is commonly a transistor connected to the stereo decoding IC which is switched by the mono stereo switch, grounding a pin on the IC (where the unit has a mono switch!) and causing mono reception. This may also be automatically switched by the signal strength going below a set level. However, you indicated the signal strength was high, so this seems unlikely. While there could be something wrong with this circuit, in my view it is more likely the 19kHz frequency has drifted slightly for whatever reason. I found the frequency only has to drift a tiny bit off 19kHz and stereo operation drops out. From memory, mine dropped out when the meter showed 18.98 kHz.
There are many other things in the chain that can ultimately cause the frequency at the chip to be wrong, but I can't see what you have to lose, as long as you don't start tweaking other adjustments, but I agree with WOT that you shouldn't just randomly poke around turning things if you value the unit and intend to take it to a tech for a proper alignment....but you might just get your stereo signal back and that might be good enough. Mine is still fine well over ten years later and it's my main tuner.
Cheers
Stuey
I still think it's worth a shot if you can borrow a meter with frequency. Turning this pot, if you take the precaution of measuring the resistance across it before moving it, can have no detrimental effect.
Note there are a few things that can cause the symptoms you describe. For example, there is commonly a transistor connected to the stereo decoding IC which is switched by the mono stereo switch, grounding a pin on the IC (where the unit has a mono switch!) and causing mono reception. This may also be automatically switched by the signal strength going below a set level. However, you indicated the signal strength was high, so this seems unlikely. While there could be something wrong with this circuit, in my view it is more likely the 19kHz frequency has drifted slightly for whatever reason. I found the frequency only has to drift a tiny bit off 19kHz and stereo operation drops out. From memory, mine dropped out when the meter showed 18.98 kHz.
There are many other things in the chain that can ultimately cause the frequency at the chip to be wrong, but I can't see what you have to lose, as long as you don't start tweaking other adjustments, but I agree with WOT that you shouldn't just randomly poke around turning things if you value the unit and intend to take it to a tech for a proper alignment....but you might just get your stereo signal back and that might be good enough. Mine is still fine well over ten years later and it's my main tuner.
Cheers
Stuey
Stuey you are a legend 😁
I couldn’t get it to rest at 19k but 18.99k seems close enough…..
Thank you very much mate
I couldn’t get it to rest at 19k but 18.99k seems close enough…..
Thank you very much mate
In that case there is still something wrong with it upstream. I set it to 19.00kHz so as to minimise phase shift and therefore distortion, and maximise separation, but it should lock in to stereo anywhere from say 18.80-19.20kHz.
The best I can get is either the 18.99 or 19.01 , but more than happy that I’m getting stereo.
I may recap it at sometime.
I may recap it at sometime.
Hi. Check la3350 pin6 connection , as i remember , many older stereo decoder ic require load from positive supply on this pin. Led diode through diode or even small incandescent lamp. If there's no voltage on this pin , stereo mode didn't works. Maybe it's the case here too. Try to connect led diode , any color , in series with 1k resistor , from 6 pin(lamp drive) to pin 1 (+supply voltage).
Got intrigued and looked around for a datasheet for The Sanyo LA3350 but that wasn't easy, found only a Japanese version (Did anyone found an English version?), however, looking at LA3361 it appears to be an identical revised version of LA3350 with an available datasheet in English with some good info at the end of the datasheet on how to apply the IC, a worthwhile read.
@TheFinisher may have already solved the problem, but I will attach both datasheets here for whomever it may interest.
@TheFinisher may have already solved the problem, but I will attach both datasheets here for whomever it may interest.
No worries mate, excellent result! Geez those Yamahas look good!
EJP, my memory could be wrong on that frequency, it was about 15 years ago. The tuner (Onkyo T9) also has a capacitive tuning dial which may affect it.
EJP, my memory could be wrong on that frequency, it was about 15 years ago. The tuner (Onkyo T9) also has a capacitive tuning dial which may affect it.
The PLL circuit will lock it to the 19khz signal if the local oscillator is close enough to 19khz. I would replace the osc adjust pot with a sealed one.