JCM 800 2205

Discussion in 'Marshall Amps' started by WoodandBread1, Jul 15, 2019.

  1. WoodandBread1

    WoodandBread1 New Member

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    Good morning,

    Looking for a little help. I have a 1986 Marshall JCM 800 2205, the 50 watt head. I haven't played it in a few years and looking to sell it. But The gain/boost channel is not boosting or gaining at all. I've checked the pre amp tubes, and the power tubes and they look fine. I've also swapped them around to try different tube positions. But still the boost channel is producing nothing. Any clues as to what might be going on?

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    Last edited by a moderator: Jul 15, 2019
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  2. Adrian R

    Adrian R Well-Known Member

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    Not sure, but I'll give ya $100.00 for it right now as is! Lol Start swapping 'known good' preamp tubes. Just because their lit means really nothing. Guitar + amp no pedals. Eliminate foot switch and switch manually (if you can)...Start simple, look for the obvious.
     
  3. Gunner64

    Gunner64 Well-Known Member

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    Clean the pots and tube sockets with deoxit..if that doesn't do it reflow the pot to pcb solder connections. My 87 had a broken solder joint on one of the pots..not sure which one it was..but reflowing the joints where the pots attach to the board solved the problem. My boost channel was weak, had little or no overdrive..and the normal channel and boost channel controls changed the tone of both channels no matter which channel was selected..reflowed the pot connections and it roared again.
     
  4. Mitchell Pearrow

    Mitchell Pearrow Well-Known Member

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    First off:cheers: :welcome: To the forum
     
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  5. marshallmellowed

    marshallmellowed Well-Known Member

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    If I'm remembering correctly, the boost function can only be selected via footswitch. If this is the case, I'd look at the footswitch or the footswitch jack first. A faulty footswitch or dirty footswitch jack would prevent the boost function from engaging.
     
  6. Gunner64

    Gunner64 Well-Known Member

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    You are correct. And thats a good question. The boost channel on mine can only be engaged via the footswitch. As soon as you plug the footswitch in the boost channel engages and the led illuminates..so expanding on that, the op never really said that he even had the footswitch plugged in...no footswitch plugged in, no boost channel...it may be as simple as that.
     
    Last edited: Jul 15, 2019
  7. MarshallDog

    MarshallDog Well-Known Member

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    Welcome aboard new MF’r and good luck fixing and selling her!!
     
  8. WoodandBread1

    WoodandBread1 New Member

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    Sorry i forgot to mention i do have a footswitch to change between the channels. When it is plugged in the boost channel indicator is on. I ordered some deoxit from amazon today, to try that solution thanks to Gunner64 for that.

    But i have a Gibson V plugged straight into the head, and then the footswitch by itself connected to the input in the back of the head for the footswitch port. The clean channel works well, clean at low volume and then breaks up nice and dirty when the volume is cranked. Just low volume and no distortion on the boost channel.
     

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