Hi
I have a Technics FM tuner from the 90's - pxs caps (don't have model number on me but will let you know when I get home) which switches from FM stereo to Mono and the quartz lock signal shifts to the beat of the music!
It spent many years in storage. Could it be a failed capacitor related to the tuning or line level output? If so which one? When I opened it up a few weeks ago it looked pristine inside.
It has various adjustment pots and the service manual is available from hifiengine but you need lots of test equipment to make adjustments.
Any ideas.
Thanks
I have a Technics FM tuner from the 90's - pxs caps (don't have model number on me but will let you know when I get home) which switches from FM stereo to Mono and the quartz lock signal shifts to the beat of the music!
It spent many years in storage. Could it be a failed capacitor related to the tuning or line level output? If so which one? When I opened it up a few weeks ago it looked pristine inside.
It has various adjustment pots and the service manual is available from hifiengine but you need lots of test equipment to make adjustments.
Any ideas.
Thanks
Most common cause of 'stereo to mono' on tuners is simply the 38kHz sub carrier oscillator needs a tweak... tweak as in whizz it end to end a few times and then set in the centre of the pull in range on a weak signal.
The preset will typically be hung off the stereo decoder chip.
Don't even look at the opamps 😉
The preset will typically be hung off the stereo decoder chip.
Don't even look at the opamps 😉
Hi
Will check the the service manual for the model concerned when I get home this evening and get back to you. I may ask your advice on exactly which pot this might be.
I will not be going anywhere near the op amps!
Thanks
Will check the the service manual for the model concerned when I get home this evening and get back to you. I may ask your advice on exactly which pot this might be.
I will not be going anywhere near the op amps!
Thanks
Hi
Just an additional bit of info. The tuner is connected to an external fm aerial located in the loft. Radio 1 - 4 are 56db signal strength.
Regards
Just an additional bit of info. The tuner is connected to an external fm aerial located in the loft. Radio 1 - 4 are 56db signal strength.
Regards
Hi
The unit is a Technics ST - G470 Quartz Synthesizer AM/FM Stereo Tuner (1990-93).
There are adjustments for:
1. FM Mono Distortion
2. MPX VCO
3. Separation
4. FM Stereo Distortion
5. FM Signal Strength Level
Which one(s) do I need to tweak?
Thanks
The unit is a Technics ST - G470 Quartz Synthesizer AM/FM Stereo Tuner (1990-93).
There are adjustments for:
1. FM Mono Distortion
2. MPX VCO
3. Separation
4. FM Stereo Distortion
5. FM Signal Strength Level
Which one(s) do I need to tweak?
Thanks
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The one to try is MPX VCO (Multiplex voltage controlled oscillator). Note and mark the preset position, then try adjusting. If it doesn't fix things then set it back to where it was.
Hi
Tried it and it did not make any difference. Not to worry - recovered from my father - in laws loft. Will have another go later.
Thanks
Tried it and it did not make any difference. Not to worry - recovered from my father - in laws loft. Will have another go later.
Thanks
Pity 🙁
Don't alter or adjust anything else though. I assume the aerial is good (outside FM aerial)
Don't alter or adjust anything else though. I assume the aerial is good (outside FM aerial)
My first tuner was an old but nice Sony i bought new in 1981.
In 2007, I used it for a few months and it had behavior similar to as described by the original poster. Mine added the symptom that the display lights dimmed with the music also. As background info, the regulators in the design were not well heat-sinked, so the interior was kinda' toasty with no ventilation holes. That suggested power problems and I suspected old or dried electrolytics.
I fixed it by replacing all the electrolytic caps that were not used as coupling caps. It wasn't as many as you might think. I also "vented" the top above the regulators (can you say Dremmel? 🙂 ).
A year or so later, I gave the tuner to a friend who tells me he happily uses it to this day
YMMV ...
mlloyd1
In 2007, I used it for a few months and it had behavior similar to as described by the original poster. Mine added the symptom that the display lights dimmed with the music also. As background info, the regulators in the design were not well heat-sinked, so the interior was kinda' toasty with no ventilation holes. That suggested power problems and I suspected old or dried electrolytics.
I fixed it by replacing all the electrolytic caps that were not used as coupling caps. It wasn't as many as you might think. I also "vented" the top above the regulators (can you say Dremmel? 🙂 ).
A year or so later, I gave the tuner to a friend who tells me he happily uses it to this day
YMMV ...
mlloyd1
None of these, it's T101 for centre tuning. Use TP101 and TP102 for checking the center alignment. Tune to strong station, use a digital voltmeter. The polarity does not matter when measuring TP101 and TP102, all you care about is adjust T101 until you get as close as possible to zero volts between the 2 test points.
Check the AC ripple across C708 100uF/35V, it should only be about 10mV or less. It is possible that C713 100uF/35 that is part of the voltage doubler is dried up. C713 can be increased safely to 470uF/35. This capacitor has a hard life due to the amount of AC voltage across it. Increasing the capacitance will make it last longer.
Replace C705, C706 and C707 too.
Don't even think of installing boutique capacitors into this tuner, it is not worth it.
Check the AC ripple across C708 100uF/35V, it should only be about 10mV or less. It is possible that C713 100uF/35 that is part of the voltage doubler is dried up. C713 can be increased safely to 470uF/35. This capacitor has a hard life due to the amount of AC voltage across it. Increasing the capacitance will make it last longer.
Replace C705, C706 and C707 too.
Don't even think of installing boutique capacitors into this tuner, it is not worth it.
I would advise caution on altering any of the tuned circuits, once you do you will never be able to bring them back again without correct test equipment.
If you feel want to explore the possibility of misalignment then first try simply placing a suitable phosphor bronze twiddle stick 😀 into the coil. That alone may well pull the tuning enough for you to gauge the effect. Ferrite dust cores need the correct tool to tweak them and they can also crack amazingly easily. A plastic or ceramic trimmer should be used for final adjustment but I really would caution against twiddling in hope.
And it would be great if it could be tweaked into submission 🙂 but remember that if it doesn't work then you have altered the fundamental alignment and its downhill all the way from there.
Are you using a good outdoor aerial ?
If you feel want to explore the possibility of misalignment then first try simply placing a suitable phosphor bronze twiddle stick 😀 into the coil. That alone may well pull the tuning enough for you to gauge the effect. Ferrite dust cores need the correct tool to tweak them and they can also crack amazingly easily. A plastic or ceramic trimmer should be used for final adjustment but I really would caution against twiddling in hope.
And it would be great if it could be tweaked into submission 🙂 but remember that if it doesn't work then you have altered the fundamental alignment and its downhill all the way from there.
Are you using a good outdoor aerial ?
Please take heed of these wise words of excellent advice from Mooly:
The "mystic arts" of audiophile sound pale in comparison to those involved in RF circuitry., let alone trying to tweak it without instruments!
😱
mlloyd1
The "mystic arts" of audiophile sound pale in comparison to those involved in RF circuitry., let alone trying to tweak it without instruments!
😱
mlloyd1
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Hi
I have a cheap dipole fm aerial in the loft which works very well with my Denon tu260L and Tag McLaren T20. This technics tuner was a tip rescue as my in laws were about to chuck it in the bin so it is worth having a go at a fix. Also the days of FM in the UK are apparently numbered as it may be DAB only within the next decade (they keep shifting the timetable).
I must admit DAB sounds good in the car - better then FM. (side issue)
I have a cheap dipole fm aerial in the loft which works very well with my Denon tu260L and Tag McLaren T20. This technics tuner was a tip rescue as my in laws were about to chuck it in the bin so it is worth having a go at a fix. Also the days of FM in the UK are apparently numbered as it may be DAB only within the next decade (they keep shifting the timetable).
I must admit DAB sounds good in the car - better then FM. (side issue)
The tuner is already misaligned based on the symptoms given of the stereo lamps and quartz lock going in and out. This is a classic misalignment case.
You can't break what is already broken.
Re-centering the quad discriminator requires just a DVM and a strong signal.
To the original poster, I forgot to add that you can fashion an alignment tool off a bamboo chopstick. Use this to align the T101 core.
You can't break what is already broken.
Re-centering the quad discriminator requires just a DVM and a strong signal.
To the original poster, I forgot to add that you can fashion an alignment tool off a bamboo chopstick. Use this to align the T101 core.
Hi
I will have a go at the weekend. Any further tips / advice would be appreciated. I will need to have a look at the service manual to see what T101 is.
Thanks
I will have a go at the weekend. Any further tips / advice would be appreciated. I will need to have a look at the service manual to see what T101 is.
Thanks
Hi Folks
I have fixed it! It is obviously not technically calibrated which I cannot do as I do not have the instrumentation but to the ear it sounds good enough. I may use it in the garage with the first amp I ever bought new as a teen in 1987, a JVC AX220 and a pair of Wharefedale Diamond II's.
What I did was adjusted T101/2 (FM Detect) and VR302 (FM VCO) and VR301 (FM SEP) using a screw drive and a pair of headphones. The signal and stereo indicator are now stable and it sounds pretty good. Will test over a few days to see if it remains stable.
Will report back
Thanks
I have fixed it! It is obviously not technically calibrated which I cannot do as I do not have the instrumentation but to the ear it sounds good enough. I may use it in the garage with the first amp I ever bought new as a teen in 1987, a JVC AX220 and a pair of Wharefedale Diamond II's.
What I did was adjusted T101/2 (FM Detect) and VR302 (FM VCO) and VR301 (FM SEP) using a screw drive and a pair of headphones. The signal and stereo indicator are now stable and it sounds pretty good. Will test over a few days to see if it remains stable.
Will report back
Thanks
Well done 
You can set VR302 on a weak signal. Just hold the aerial plug out a little and then adjust so that the preset is in the midpoint between the extremes at which the light goes out.
You can set VR302 on a weak signal. Just hold the aerial plug out a little and then adjust so that the preset is in the midpoint between the extremes at which the light goes out.
Hi
Just for info: T101/2 (FM Detect) and VR302 (FM VCO) were the most critical adjustments. VR302 to get the general signal and T101/2 to stabalise it. As mentioned by Mooly above I went for the middle ground in making the adjustments. I am happy I could rescue it.
Thanks
Just for info: T101/2 (FM Detect) and VR302 (FM VCO) were the most critical adjustments. VR302 to get the general signal and T101/2 to stabalise it. As mentioned by Mooly above I went for the middle ground in making the adjustments. I am happy I could rescue it.
Thanks
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