Replace Twinmax Potentiometer

Discussion in 'The Garage' started by pedalmike, Oct 16, 2013.

  1. pedalmike

    pedalmike Horizontally Opposed

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    Wondering if anybody on the forum has expertise or experience in replacing the zero adjust potentiometer on a Twinmax. I tried deoxit but I can't make the existing potentiometer work...it makes the scale needle jump wildly from one end to the other...i can't get it to zero.

    I think I could replace it myself if I could find the part. This one mounts to the PC Board with soldered lugs rather than the panel.

    Let me know if you have any ideas.

    Thanks.
    #1
  2. Terry

    Terry Long timer

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    I could certainly help you out. Getting the replacement part might be the hardest part, but pots are usually pretty available. Can you post a pic?

    Terry
    #2
  3. Guy Young

    Guy Young Long timer

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    I replaced both a couple of years ago. They were "dead" when I went to pull it out to use it.

    I selected some linear taper pots normally used in a guitar with the same ohmic value of the ones in the Max. I had to add a couple of short leads to connect the pots to the PC board, and IIRC, had to enlarge the holes slightly so the pots would fit in the box.

    I'll see if I can find the paperwork where I bought them.

    .
    #3
  4. pedalmike

    pedalmike Horizontally Opposed

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    Thanks Terry and Guy.

    Terry, I'll take a photo or two and post them first chance I get.


    Mike
    #4
  5. Guy Young

    Guy Young Long timer

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    I have looked, but can't find the paperwork from when I ordered them.

    You'll play hell trying to find the PCB mounted types that are in there, that's why I went with the panel mounted types. The ohmic value is stamped/printed on the body of the pot. You'll need to get a short, split shaft to accept the push-on knobs.

    My apologies; wish I could be of more help.

    .
    #5
  6. pedalmike

    pedalmike Horizontally Opposed

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    Here are a few photos of the pot


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    #6
  7. pedalmike

    pedalmike Horizontally Opposed

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    #7
  8. pedalmike

    pedalmike Horizontally Opposed

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    I don't think I'll be able to find one closer than this.

    http://www.mouser.com/ds/2/13/TW-700149-186104.pdf

    B100K, Linear taper, even the mounting lug dimensions and the three solder terminals are the same dimensions as the one in the twinmax. It is a 'D" shaft instead of a serrated shaft...who cares? $2.07 each at Mouser Electronics.

    Let me know what you think...looks like it's worth a try.
    #8
  9. VentusA

    VentusA Adventurer

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    3 years ago, Paul Weis at Cal-Moto (paul@calmoto.com) was kind enough to ship me (at my shipping cost, only) a dud twinmax, returned under warranty, so that I could pull a pot to replace one of mine that failed. He was impressed that anyone would bother to repair rather than replace. It worked. I thanked him. It might work for you.
    #9
  10. Guy Young

    Guy Young Long timer

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    Looks good. You can always find a knob to fit at Radio Shack.

    Good find! :thumb

    .
    #10
  11. Terry

    Terry Long timer

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    #11
  12. pedalmike

    pedalmike Horizontally Opposed

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    Thanks, Terry. That's a nice offer. I have a standard Weller electric soldering gun with two heat settings. Would that be OK to use to replace this pot?

    Mike
    #12
  13. Terry

    Terry Long timer

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    I'm not familiar with the Weller, but it will probably be fine. You will want to use solder-wick or a solder sucker to remove the old pot. It might make it easier if you just use a sharp wire cutter to clip out the old one and unsolder the remnants.

    Terry
    #13
  14. Guy Young

    Guy Young Long timer

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    I've been repairing PCB for years and also use a 2-heat range Weller as well as a couple of pencil irons. Never had too much luck with the solder wick so I've always used a solder sucker.

    Just be careful with your heat so you don't lift the pads and/or traces from the board. Good suggestion to clip the old one out and remove the remaining bits separately. Also, make sure you use a rosin core solder when installing the new pot.

    Best of luck with it and let us know how it works out.

    .
    #14
  15. pedalmike

    pedalmike Horizontally Opposed

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    Well, I took Ventusa's advice and called Paul Weis at Cal Moto. He had another non-functioning twinmax that he is sending me at no charge other than shipping.

    I'll let everybody know what happens.

    Thanks again.

    Mike
    #15
  16. Gripsteruser

    Gripsteruser Service Monkey

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    If the Weller gun is what I think it is (trigger finger switch, heated wire hanging out in the air) it could be overpowered for the connections to the PC board. It might be needed to remove the brackets but not to do the 3 leads from the pot. Start with the lower wattage pencils first.

    PM sent
    #16
  17. RidingAgin

    RidingAgin Been here awhile

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    I concur that the gun is way too much power. Use a small chisel tip 45 watt pencil tip.

    Too much heat will lift the trace from the pc board.

    Did you try spraying the pot with electrical contact cleaner? It might be just dirty. This is a low usage device and hard to believe it is worn out.
    #17
  18. pedalmike

    pedalmike Horizontally Opposed

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    Thanks for the suggestion.

    Trying to clean it with contact cleaner was the first thing I tried. Didn't help unfortunately.

    Mike
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  19. pedalmike

    pedalmike Horizontally Opposed

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    Ok, here's the rest of the story. The non-functioning twinmax arrived from Cal Moto. Just as Paul Weis said, when this unit powers up, the needle goes to the far right of the scale and cannot be zero'd. Both pots feel pretty good though.

    I got out my new 25w Weller pencil iron (I tinned the tip previously), Solder Sucker, and rosin core solder. I disassembled the Cal Moto Twinmax to prepare to harvest a good pot from that unit's PC board.

    While I had it apart on the bench, I decided to power it up one more time to see what would happen. Surprisingly, it works fine! I can now zero the needle on the scale at max sensitivity. I checked over all of the connections. They are all clean and tight. I reassembled the Cal Moto twinmax. Everything still worked! Took my GS out for a short ride to warm it up. Connected the twinmax and it shows perfect balance, just like the unit I borrowed from my buddy a few weeks ago displayed.

    So, I'm not sure what condition caused this unit to pin the needle to the right, but that condition was somehow remedied by my disassembly. Who would have guessed that?

    I want to give a big thank you to Terry, Guy, Gripsteruser, VentusA and RidingAgin for all of your advice and offers of assistance. This forum continues to delight and amaze me...it's a good community.

    So now I have a few new tools ready to take on the next project!

    Best, Mike

    [​IMG]
    #19
  20. Terry

    Terry Long timer

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    Nice,
    Now you can still repair the one with bad pots....

    terry
    #20