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Replacing Slide Potentiometer on radio

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Discussion in 'Troubleshooting and Repair' started by PtrkLnk, Feb 13, 2014.

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  1. Feb 13, 2014 #1
    PtrkLnk

    PtrkLnk

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    Jan 20, 2012
    So I have this Vector Research VMC-100 radio receiver/amplifier that is having issues. The problem is some of the channels on the Graphic Equalizer only work on once side or not at all. When I opened up the case a few bits of metal fell out that I identified to be contacts from the 7 slide potentiometers.

    Does anyone know what kind of potentiometer I should replace them with?

    Here are pictures:
    The radio:
    [​IMG]
    Graphic Equalizer assembly:
    [​IMG]
     
  2. Feb 13, 2014 #2
    PtrkLnk

    PtrkLnk

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    Jan 20, 2012
    If you need any more pictures I can get them.
     
  3. Feb 13, 2014 #3
    (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Look for a part number on the pots. If you're really lucky they are available and you can replace them.

    That would be my third thing to do.

    The first thing would be to run some basic tests to see if the pots are really busted.

    The second thing would be to document where every wire connected to that board connects.
     
  4. Feb 14, 2014 #4
    PtrkLnk

    PtrkLnk

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    Jan 20, 2012
    I tested them and there are three that don't work but I will probably just replace them all if I can find the replacement parts.I already drew a diagram of what wire goes to what, and took a couple of pictures. I will look for numbers tomorrow.

    Update: the numbers on the bottom of the pots are hard to see without desoldering them, but it appears to say "20KBX2". The radio its self is rare, so I am not sure these will be easy to find.
     
    Last edited: Feb 14, 2014
  5. Feb 14, 2014 #5
    (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    They sound like 20k stereo linear (maybe) pots.

    They'll be easy to get, but you need to make sure that they're the right size and shape -- that may be harder.

    Measure a working one from one end to the wiper with the wiper 0%, 25%, 50$, 75%, and 100% of its travel.

    You should read 0k, 5k, 10k, 15k, and 20k if the pots are linear.

    If they're log pots (unlikely) the readings will be bunched up.
     
  6. Feb 14, 2014 #6
    PtrkLnk

    PtrkLnk

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    Jan 20, 2012
    I confirmed they are 20k 2 channel linear pots. I can't really find any that are the right size.
     
  7. Feb 15, 2014 #7
    (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Describe the size.

    Saying you can't find any of that size won't help us help you unless we know exactly what you're trying to find.

    The important dimensions are the length, width, and height of the body, the distance between the mounting screws (if they are used) and the distance the slider moves.

    After that, it would be good if the connections were the same, but let's cross one hurdle at a time.
     
  8. Feb 17, 2014 #8
    PtrkLnk

    PtrkLnk

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    Jan 20, 2012
    The total length of the pot is 45mm, width is 10mm. The distance between screw holes is about 41mm. The travel of the slider is about 37mm. The length of the slider post is about 5mm. The width of the slider post is about 2mm.
     
  9. Feb 17, 2014 #9
    (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Yeah, I've had a brief look and stereo slider pots seem about as common as rocking horse manure.

    Have you tried cleaning the pots?
     
  10. Feb 17, 2014 #10
    PtrkLnk

    PtrkLnk

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    Jan 20, 2012
    They are too far gone to just be cleaned. The contacts inside broke off and the tracks are falling off.
     
  11. Feb 17, 2014 #11
    (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    It might be a sad story.

    See what slide pots are available and see if you can jury rig something.

    Alternatively, replace them with fixed resistors to simulate the pots being in the centre
     
  12. Feb 21, 2014 #12
    JerryG

    JerryG

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    Dec 17, 2013
    Just wondering if you had any success finding replacement pots yet? I was looking and found pots that looked like they might work. 45mm long, 41mm between mounting holes, 8mm wide, 30 mm slide. Are you sure that your slide travel is 37mm? Remember that the slide distance is from the center of the slider post at both ends of the travel. http://www.alps.com/WebObjects/cata...r/SlidePotentiometers/RS__1/RS3011114A02.html
     
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