Marshall guitar amp pots cleaning

Discussion in 'General Electronics Chat' started by atomtm, Jan 3, 2015.

  1. atomtm

    Thread Starter New Member

    Aug 13, 2012
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    Hello!
    I have some trouble with my Marshall Valvestate (VS15r) and to be more specific with it's potentiometers . When I turn the gain pots , i get scratching sounds or no sound at all !
    It seems there is a lot of dirt inside them so I was wondering if there is a safe way to clean them (Contact cleaner?) . I ve seen videos cleaning guitar amp pots , but they are not of my type . I have attached what mine looks like.
    Is anybody familiar with this guitar amp , and if so could you give me a guideline on how to clean them or with what pots to replace them?

    Thank you in advance



    2.png 3.png 1.png
     
  2. #12

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    Last edited: Jan 3, 2015
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  3. ian field

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    Be wary of using switch cleaner spray - many components of this type have ABS plastics in their construction - it can fail spectacularly in contact with hydrocarbon solvent/lubricant.

    In my TV repair days, I remember spraying a VCR mode switch with switch cleaner - I watched in amazement as the plastic snail cam turned into tiny granules in front of my eyes!

    If you have the patience to carefully disassemble the pots and put them back together, an old trick is to polish the carbon track with a pencil - use a HB pencil (softer graphite - less clay).
     
  4. MrChips

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    Maybe drill a hole in the casing and squirt contact cleaner in. Just a thought.
     
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  5. #12

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    That mold mark on the top looks like the perfect place to put a 0.05 inch hole.
     
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  6. cmartinez

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  7. MrChips

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    I would have chosen a spot closer to a corner to avoid hitting the carbon track.
     
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  8. MrChips

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    I believe I haven't found a carbon volume control pot that does not eventually run into this problem. So you can either keep replacing the pot after every so many years or squirt contact cleaner every so many years.
     
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  9. Lectraplayer

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    Jan 2, 2015
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    You can try contact cleaner, and it probably will help big time, but I have also had luck with that PTFE oil Radioshack used to have. Some type of grease like that will also help. Other than that, you may have to replace the pot
     
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  10. #12

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    Sad, but true. I have some 1K wire wound pots from 1973 that are so good that I try to use them in new designs.
    Carbon pots? Can't get ten years out of them without maintenance. :(
     
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  11. cmartinez

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    I'd correct that last sentence to "So you can either keep replacing the pot after every so many years or squirt contact cleaner every so many weeks"
     
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  12. #12

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    Funny, but not true. My 1977 Onkyo audio amplifier is ready for its third squirt job at 38 years old.
     
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  13. ian field

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    Depends on the quality of the pot - in some; the carbon track is washed off by solvents in the switch cleaner, then the effect lasts forever.
     
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  14. cmartinez

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    Stupid me... I got confused and thought we were talking about an electric guitar... I was speaking from personal experience
     
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  15. atomtm

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    Aug 13, 2012
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  16. ian field

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    Google the name of the amp followed by "customer services" and find out whether they have a parts catalogue.
     
  17. #12

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    I have to give you the point on this one.
    Besides, 1977 carbon pots had not been, "improved" to today's standards. :rolleyes:
     
  18. atomtm

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    Aug 13, 2012
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    Seems it's out of production!
    Customer services didn't give products catalogue or something similar .
    Anything else I can do to find what potentiometers I have to buy?
    There is a label (shown also at the pictures I have attached ) , b200k . Would that mean 200kohm logarithmic?
     
  19. atomtm

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  20. ian field

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    A while back I acquired a Fender practice amp, unfortunately the previous owner hadn't treated it well - I was looking into buying replacement pots, and getting well into the realisation that it would be cheaper to buy another s/hand amp, when on the way to visit a relative, I found an amp just laying under the hedge alongside the footpath. Not as good as the fender could have been and even google had never heard of that brand, but all it needed was a squirt of switch cleaner on the input jack.
     
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