Technics ST-S3 tuner problem

Discussion in 'Tuners' started by tmho, Dec 21, 2014.

  1. tmho

    tmho Member

    Messages:
    67
    Location:
    Richmond, BC, Canada
    I bought this tuner together with my first stereo system more than 30 years ago. It is still working but with a few problems. The memory (both AM and FM) is not working (Memory cannot be set). A few years ago, 2 of the 7 memories could still be set. Now all of them cannot be set. Also, for FM, no stereo reception, just mono (to be more exact, the stereo light won't turn on). Although it is an old tuner, it is quite a good memory to me. I do hope that someone can give me some suggestions on how to fix the problems. I have opened it but could not see any damaged components. I have some basic electronics knowledge and soldering skill.
     

     

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  2. ConradH

    ConradH Addicted Member

    Messages:
    7,707
    Location:
    Canandaigua, NY
    None of the usual suspects have a free service manual for this one, though they seem to be common enough on eBay and with independent manual sellers. Do you have a schematic for it?
     
  3. tmho

    tmho Member

    Messages:
    67
    Location:
    Richmond, BC, Canada
    Sorry, I do not have a schematic.
     
  4. 39cross

    39cross AK Subscriber Subscriber

    Messages:
    917
    Location:
    Beverly, MA
    According to this little blurb the memory presets are protected by batteries, have you replaced the batteries?

    [​IMG]
     

    Attached Files:

  5. dr*audio

    dr*audio Fish fingers and custard!

    Messages:
    18,548
    Location:
    Cleveland, Ohio
    The symptoms are not consistent with a bad memory backup battery. In that case you would be able to set the presets but you would lose all of them when you turn the power off. Being able to set a few of them but not all sounds like bad preset switches if you are lucky, or a bad microprocessor if you are not. The backup battery may be bad also but you should at least be able to set the presets and call them up while the power is on. You have to see if you can fix that first before bothering with the backup battery.
    Regarding the stereo lamp, listen and see if you are receiving stereo and maybe the lamp is just burned out. Switch from stereo to mono and see if you hear a difference. If not, the MPX PLL adjustment needs to be made. If you can find the service manual it will tell you which trim pot adjusts the PLL. You can just tune to a known good station and adjust it to the center of the region where the stereo comes on.
     
  6. 39cross

    39cross AK Subscriber Subscriber

    Messages:
    917
    Location:
    Beverly, MA
    tmho, you're in good hands with dr*audio.

    May I also recommend, if you find after the tests he describes that you're not getting stereo, please post some pics of the innards. There's a good chance the functions for the various pots are silk-screened on the board, and the pot he mentioned can be id'd for you. It's best not to fiddle with anything unless you have some proper direction.

    My two cents worth of advice, I hope you fix the problems and get back to enjoying your tuner.
     

     

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  7. tmho

    tmho Member

    Messages:
    67
    Location:
    Richmond, BC, Canada
    Thank you very much for everybody's reply and/or suggestion.
    Yes, I have replaced the batteries.
    As far as I remember, the memories/presets should work even if there is no battery when the power is on. Now the memories/presets do not work when the power is on and there is backup batteries.
    dr*audio, sorry, I do not understand what you want me to do in the first part of your suggestion. Regarding the stereo lamp, it is not burnt out because I can see that it flicker at some points when I tune the channels. For example, 96.1Mhz is one of our local radio stations. When I tune to 95.9Mhz, the stereo lamp flickers and the sound I receive is very noisy. But when I tune to 96.1Mhz, then the sound is without any noise but the stereo lamp is off. When I try to switch between stereo and mono, I cannot hear any different, so I think what I hear is just mono.
    Attached please find some photos of the inside of the tuner. If you need more or clearer photos, please advise and I will try my best to do so.
     

    Attached Files:

  8. dr*audio

    dr*audio Fish fingers and custard!

    Messages:
    18,548
    Location:
    Cleveland, Ohio
    In the first picture on the right hand side there is a trim pot with VCO next to it. Note the origintal postion of the pot; mark it with a sharpie or something. Tune to a known good station and using a small screwdriver, turn the pot slightly clockwise and counter clockwise 1/4 turn. See if the stereo light comes on. If so, keep turning the pot back and forth and note the 2 points where the lamp goes out. Set the pot midway between those 2 points.
     
  9. tmho

    tmho Member

    Messages:
    67
    Location:
    Richmond, BC, Canada
    Hi dr*audio, thank you very much for your advice. I followed your advice and the stereo light problem is fixed. Now the stereo light comes on solidly when it is tune to a good station and I can hear stereo sound instead of mono. Do you have any advice for me regarding the memories/presets problem?
     
  10. dr*audio

    dr*audio Fish fingers and custard!

    Messages:
    18,548
    Location:
    Cleveland, Ohio
    Glad that worked. For the presets you are going to have to replace the preset switches. You will have to remove the pc board behind the front panel and de-solder the switches using de-soldering braid. Digikey has switches. You probably need something like this, but measure what you have and make sure these fit.
    http://www.digikey.com/product-detail/en/1825910-6/450-1650-ND/1632536
     
  11. tmho

    tmho Member

    Messages:
    67
    Location:
    Richmond, BC, Canada
    dr*audio, thanks for your advice.
    I have not taken off the switches because it will take some time to remove the PCB. But I have tried to test the switches with a multi-meter. I tested the continuity of the leads of the switches by measuring the resistance between 2 of the leads. I got very low ohm (almost zero) between 2 of the leads when the switch was pressed down for all the same type of switches (including the preset switches and the tuning switches). Also, in the operation of setting the presets, when the switch is pressed, the corresponding lamp lights up as it should be (but just goes off instead of keeping on when the switch is released). Will these mean the preset switches are okay and something else cause the problem?
     

     

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  12. dr*audio

    dr*audio Fish fingers and custard!

    Messages:
    18,548
    Location:
    Cleveland, Ohio
    Yes, the switches are ok. I think you have a bad microprocessor, which will not be available.
     
  13. tmho

    tmho Member

    Messages:
    67
    Location:
    Richmond, BC, Canada
    dr*audio, thanks for the bad news that the microprocessor will not be available. Anyway, I can still enjoy the tuner manually.
    Is the microprocessor the larger IC marked "AN7001"? Hope I might get it from a defective tuner in the future.
    Merry Christmas!
     
  14. dr*audio

    dr*audio Fish fingers and custard!

    Messages:
    18,548
    Location:
    Cleveland, Ohio
    No, the AN7001 is part of the receiving circuitry. The micro should be a large multi pin part. Might be on the front panel.
     
  15. tmho

    tmho Member

    Messages:
    67
    Location:
    Richmond, BC, Canada
    dr*audio, the front panel is only with the "display" and switches. If possible, please kindly give me more hints on locating the microprocessor.
     
  16. dr*audio

    dr*audio Fish fingers and custard!

    Messages:
    18,548
    Location:
    Cleveland, Ohio
    I don't have the schematic so I really don't know. All I can tell you it is a large IC with usually 20 pins or more.
     

     

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  17. tmho

    tmho Member

    Messages:
    67
    Location:
    Richmond, BC, Canada
    Recently, I open up the tuner again and took out the pcb. I tried to see if there is any cold solder joint. Actually, I do not have much experience in that. My experience is just from internet. I found some suspected joints (but I was not sure), and so I just resoldered them. After that, I found 4 of the 7 preset memories are working now.
     

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