On/off volume pot replacement part 500c

Discussion in 'Fisher' started by fahfisher500, Mar 2, 2017.

  1. fahfisher500

    fahfisher500 New Member

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    My on/off volume pot is going bad (weak and intermittent left channel, better with high volume), I have read the forum and understand that this is a largely unobtainable part, is there a suitable replacement part that is readily available? I know almost nothing about electronics but would be game to try to replace this part myself if I had clear instructions on what to do. I own a soldering iron and a voltmeter but that is it when it comes to electronic repair equiptment. Thanks for all advice.
     
  2. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    Have you cleaned the pot with DeOxit yet? If not, Get a can of DeOxit (D-5) and a can of Faderlube (F-5). Read this Thread......The Idiot's Guide to using De-Oxit....Revisited! Then follow instructions and do all pots and switches on the 500c. If it goes up and down, in and out, or Round and round, it gets DeOxit. Clean them all and then use it. Compare results with before. The Volume pot may need more than one application.

    With DeOxit a little goes a long way. a little spurt is better than a long spray.
     
  3. notdigital

    notdigital AK Subscriber Subscriber

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  4. fahfisher500

    fahfisher500 New Member

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    I think I'll try the deoxit first. I had it worked on by Terry DeWick when I put it back into service several years ago and it has worked great until this week. I really don't know what I am doing with electronics, but if it is just a matter of unsoldering and resoldering a few wires I think I could handle that. My concern is that the replacement will not look like the original and I will not know which wire to solder to which pin.
     
  5. AlTinkster92

    AlTinkster92 AK Subscriber Subscriber

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    Take pictures before you unsolder anything, then you'll know where the wires go....good luck with it!
     
  6. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    fahfisher500; No need to unsolder anything to use De-Oxit. There will be two slots where the wires are all connected on the Volume pot. Spurt the DeOxit in there and work it in and around with the knob (make sure you are unplugged 1st) Work the knob back and forth about 50 times, vigourously. Then give it a shot of Faderlube and work it in the same. Wait an hour before plugging in and starting up.
     
  7. tube-a-lou

    tube-a-lou Super Member

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    4,276
    Or you could do what I did, purchased a Alps 500K blue velvet volume pot, and put a switch on the back of
    the Fisher. Unless you want to keep it original.
     
  8. notdigital

    notdigital AK Subscriber Subscriber

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    Voluminous pictures will address your re-construction concerns. Daunting at first but good pictures will really put you at ease.

    Also, I believe there is nothing like a complete teardown and cleaning out of the pot. Years of wear on the traces together with all sorts of liquids shot in there inevitably leaves a slurry of goo that hardens and negatively impacts the functioning of the control. I've attached a couple of shots of the the pot of my 500-c that I took apart when I got up enough guts after tiring of the scratchiness and intermittent sound. Notice the speckles of dirt that fell out and remain. Once I cleaned the entire control and lubed it, no more noise!

    DSCN2027.JPG DSCN2028.JPG
     
    Last edited: Mar 3, 2017
    AlTinkster92 likes this.
  9. njcanuck

    njcanuck aka: MacGyver Subscriber

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    There is also the option of sending it to Mark Oppat for a complete rebuild.
     
  10. fahfisher500

    fahfisher500 New Member

    Messages:
    35
    I think I will try to clean it first with the deoxit/faderlube and see how that does. Then I may try to repair it as shown above. I will put my full ignorance on display and ask about how to safely attempt this. I have read in many posts about the danger of working on tube equipment with very high voltage components which may be hazardous even when unplugged. Of course I will unplug it, but what else do I need to do to do this safely. Thanks for the help.
     
  11. notdigital

    notdigital AK Subscriber Subscriber

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    If you're going to remove the pot, then working with it unplugged will be 99.9999999999999999 % safe. The high voltage caps actually drain after a while if they were recently energized. You can put a (DC) meter on them and watch them drain. You can do it quickly by shorting them with, say, a screw driver but only if you're into drama. Otherwise, leaving it unplugged for a half hour should be enough.

    Since the pot is mounted on the front, just have that side of the unit closest to you when you work. That way they'll be little reason to reach over the chassis.

    Hopefully the sprays will correct your issue. If not, and you decide to take it apart, don't forget the pictures.
     
  12. fred soop

    fred soop Super Member

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    Use a resistor. Directly shorting, unless it is already close to discharged, results in a very high pulse current and can damage the capacitor.
     
  13. gadget73

    gadget73 junk junkie Subscriber

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    It can also melt the tip right off the screwdriver, leaving you with a reminder of why you aren't supposed to do that.
     
  14. tube-a-lou

    tube-a-lou Super Member

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    4,276
    I've done this for one of my Fisher amps and the treble control of the Eico Hf81, once you
    clean and lube a little it should be good unless the carbon is so worn it not any use. just watch
    those metal tabs when your putting it back together.
     
    bhamham likes this.
  15. fahfisher500

    fahfisher500 New Member

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    Follow up with resolution of the problem. I tried cleaning the pot with deoxit and fader lube and it actually seemed a little worse. Tried again and it was definitely worse. I called Mark Oppat and he helped me troubleshoot it to be sure it was the pot and it was. He built me a new pot with the on/off switch which I finally got around to installing yesterday and the problem is solved!. I'm thankful for all the advice given here and will post again if there are any changes. I highly recommend Mark, he was very helpful and patient with my very elementary questions and made the new part within 1 week.
     
    3l3ctron likes this.
  16. Csermonet47

    Csermonet47 New Member

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    Do you have pictures of the new pot? I just got a power switch from Mark for my original pot, but it is a bit scratchy and I am wondering if this is a good route to go.
     
  17. monkboughtlunch

    monkboughtlunch Super Member

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    Are you saying the new pot from Mark is scratchy? Did you try spraying some DeOxit in the new pot?
     
  18. Csermonet47

    Csermonet47 New Member

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    Location:
    Atlanta
    Sorry if that was confusing. My 500C came with the original volume pot but no power switch assembly. I got the power switch assembly from Mark to put on the back of my original volume pot, but the original volume pot is scratchy so I am considering getting a whole new power switch/volume pot assembly instead. A friend sprayed some Deoxit in my old pot and I disassembled/cleaned/reassembled and it is still scratchy.
     
  19. gadget73

    gadget73 junk junkie Subscriber

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    Make sure you don't have a bad coupling cap leaking some DC into the pot. That makes them very noisy. The pot itself might be OK.
     
  20. fahfisher500

    fahfisher500 New Member

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    View attachment 931921 IMG_4645.JPG View attachment 931921
     

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