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Technics SL220 Turntable Circuit Board Repair

Discussion in 'Troubleshooting and Repair' started by winnard, Aug 29, 2012.

  1. winnard

    winnard

    3
    0
    Aug 28, 2012
    I have an FSU student Rebecca that works for me (I am retired engineer) performing investment property repairs. She came to me with the subject circa 1978 (33 /45 rpm) turntable. I oiled the motor and it restored the turntable function but at a lower speed than the standard 33 rpm. Inspection of speed circuit board shows a variable resistor (see attached PFD; left pot is 33 rpm) missing its slider. Any recommendations for repair would be appreciated. I have a soldering iron and electrical solder but the specifics on the resister and where to obtain would be helpful. Thank you in advance for your help.
     

    Attached Files:

  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    You need to determine the value of that trimpot. It may be marked with a number like "203" (that would mean 20 kilohms - a 2, a 0, then 3 more zeros, with the result in ohms). If not, remove it from the board and measure its end-to-end resistance with a multimeter. Then measure its dimensions and try to find a suitable replacement on a site like Digikey or whatever is local. (You don't say where you're located so I can't be more specific.)
     
  3. winnard

    winnard

    3
    0
    Aug 28, 2012
    Thank you - I am located in Tallahassee, Florida, USA - I have a multimeter - between the 33 and 45 directly below the two trimpots (on backside of board) is 6731V - nothing is visible on the trimpots
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    OK. The marking on the board doesn't relate to the value of the trimpots. You will need to desolder the broken trimpot and measure the resistance between the two end terminals, that is the two terminals on the same end.

    The value you measure will not be exactly the rated resistance of the trimpot, because they typically have a tolerance of at least +/- 10%, often 20%, but you should be able to guess the rated resistance of the trimpot. They usually follow the 1-2-5 series - that is, 1, 2, 5, 10, 20, 50, 100, 200, 500, 1000, 2000, 5000 and so on. So if you measure 12,434 ohms, for example, it's probably a 10,000 ohm (10 kilohm) part.

    Also while you have the trimpot out of the board, have a close look for number markings on it that would tell you the value.

    Here is the page for a 10 kilohm trimpot from a Florida mail order company.
    http://www.westfloridacomponents.co...+Potentiometer+Trimpot+PT15NV02-103A1111.html

    You will need to search for the actual resistance that you need. Go to http://www.westfloridacomponents.com and choose the "potentiometers" category, then the "trimmer pots" category, and look for a part that has the right resistance and seems to be physically compatible. In this case, I think the "Piher" brand trimpots may be a good fit. Choose the one you think is closest and check the dimensions in the data sheet to make sure it will fit. Good luck!
     
  5. winnard

    winnard

    3
    0
    Aug 28, 2012
    Thank you - I cut the damaged trimmer (33) out with ss toe nail clippers - its resistance was 18.6K. The resistance of the adjacent (45) trimmer was 22.4K. The marking on it (barely visible) appears to be 203 - so I believe I should purchase the component you identified in a 20K version.

    The next problems are skill and tools. The use of the soldering iron I own on this circuit board with my skill level and eyesight would be like a medical school student doing surgery with a kitchen knife. I am attempting to contact technicians locally (TV repair shops, etc.) that may be willing but without much luck. I am thinking that there must be some hobbyist or other electronics buff locally that would be interested. The other route would be to obtain better quality soldering equipment to complete the repair; practice on some discarded circuit board. Thank you again for your thoughtful advice.
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
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    Nov 28, 2011
    Yes. That was a lucky guess!
    Yes, that sounds like a good idea. See if there are any electronics hobbyist groups in your area. Someone there should be happy to do that for you for free. There are probably a lot of young students who would do it for a small fee but I don't know how you could get in touch with them. Ask all your friends whether they have youngsters who are into electronics and have a small soldering iron. Lots of young people are, nowadays, and it's not a difficult job provided that you have good eyesight.
    I wouldn't spend a lot of money on tools unless you plan to get into electronics. You're welcome :)
     
    Last edited: Aug 30, 2012
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