updated marshall jcm 800 amp help thread

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by yoyohomieg5432, Jan 31, 2008.

  1. yoyohomieg5432

    yoyohomieg5432 Member

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    alright, so im still looking for help on which type of pot to buy for an '83 jcm 800 2204. the presence pot is bad and needs changing.

    john philips also recommended to change the caps. if caps are the black things shown below then i think they have already been changed. blue colored ones are standard.

    here's the guts
    [​IMG]

    this is the knob that is making all the trouble. the presence knob.
    [​IMG]

    here is the black capacitors(i think?) i was talking about
    [​IMG]
     
  2. sliberty

    sliberty Member

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    I strongly recommend that you bring the amp to a tech. It sounds like you don't have any experience working inside of an amp (no offense meant), and that can be dangerous. Some of the components in an amp (filter caps in particular) carry leathal voltages, and you need to be at least somewhat experienced in working safely in that environment.

    If you do insist on changing the pot your self, I would recommend that you buy a pot from Metro Amps. Call them up and ask them for a recommendation of a pot that will best match what you are replacing from a size and feel point of view.

    As for the caps, don't do it without help. And besides, if the amp sounds great, they may not need it. The idea that the caps "should be replaced" is not wrong for an older amp, but it is also not a universal rule.
     
  3. yoyohomieg5432

    yoyohomieg5432 Member

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    well i want to atleast fix the pot myself. the pot is part of the problem because it makes a thunder-like sound every time i turn it. this could be a problem with the high input channel.

    the caps are the black things right? i have no idea how to fix those and would probably have to get a tech if those were the problem. it looks like they've already been replaced, so i dont know why they'd need it again
     
  4. phsyconoodler

    phsyconoodler Member

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    The original amp had blue colored F,& T filter caps and those may indeed have been changed.The presense pot often makes a scratchy sound when turned on those amps and thats not always the sign it need a new pot.It may have too much DC voltage on the pot meaning it may have a bad cap somewhere in the presense circuit,and installing a new pot won't fix the scratchy noise.
    Regardless,you need to get a book on how to work safely inside your amp before you even attempt to do any repairs yourself.Better yet,take it to a good tech and at least get him to assess the problem before you make guesses.
     
  5. yoyohomieg5432

    yoyohomieg5432 Member

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    is not like a sounod with the pot, i can hear it through the speakers. a loud thundery sound
     
  6. rockon1

    rockon1 Member

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    Good advice! You may replace the pot and have the same problem or worse if you dont discharge the caps(black things) you may get the shock of your life! :eek: Bob
     
  7. TheAmpNerd

    TheAmpNerd Member

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    You can lead a horse to water...

    ...sounds like the guy really want to replace the pot.

    No harm there. Replace it.

    ...then let us know if the problem is there or not.


    Okay Noodler...how is that verse ?


    Bets, the problem is there after pot replacement or not?



    For my money I'd clean and lube the pot first.

    If still messed up then replace it.

    if still messed up then replace the other components.

    If still messed up then take it to the tech you should have
    done with to begin with only know you will have a much higher
    bill because he'll have to fix your unclean mess that you left behind.

    Though funny thing, that pic you have already looks like
    the pot was fooled around with once already, look at the
    melted out plastic from the pot wiring.



     
  8. phsyconoodler

    phsyconoodler Member

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    This guy was already asking about pots in another post so I know he probably tried to clean the pots already.
    And I'm not a 'noodler,I'm a 'phsyconoodler' phsyco for short:crazyguy

    someone left the amp out in the rain
    I don't think that I can take it,cause it took so long to make it,
    and I'll never have those type of Drakes no more,
    oh no,oh no........
     
  9. yoyohomieg5432

    yoyohomieg5432 Member

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    whats going on, im confused now
     
  10. Groovey Records

    Groovey Records Member

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    Yo Yo Homie G

    waz up is they be ryme in about your equipment ....player.

    so dig this homey

    Chill

    you straight up asked our man John and you be totally dissing what he represented.

    that ain't cool

    but you keep asking the same question and someone who knows less then YoYo Mama will tell homie what choo wanna hear

    is that enough 411 or you still confused
     
  11. twinrider1

    twinrider1 Member

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    I'm thinking YoYo just didn't get Psycho's Beatle reference. I don't know that YoYo was dis'ing anyone.
     
  12. Groovey Records

    Groovey Records Member

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    YoYo didn't like the answers he got from John Phillips on another thread and started another asking the same question and getting the same advice on this second thread he started. The thing is he particularly asked for John's opinion by name.

    Oh and BTW it's Richard Harris "MacArthur's Park" not the Beatles.


    Best
    Groovey Records
     
  13. yoyohomieg5432

    yoyohomieg5432 Member

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    1) i was dissing on anybody, so i dont appreciate you smartassing.

    2) i tried to bring me previous thread back by adding pictures, etc, to get more opinions but no body was responding, so i made a new thread.
     
  14. Groovey Records

    Groovey Records Member

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    Gee G

    I didn't meen to offend just my sorry attempt at humour.

    hey you can count to 2
    bump to the top
     
  15. TheAmpNerd

    TheAmpNerd Member

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    Psych not there noodler. beueath such amp int he rain
    yet there may :rotflmaobe not such payne as w:munch eye, rather dien arsch//1

    Meinstensdu, many aschen hat schone gemACHT HAUTE BIE Dem
    dinks dort linkkkk.:p
     

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