JCM 800 2210 strikes back

Discussion in 'The Workbench' started by Dre Oliveros, Oct 18, 2019.

  1. Dre Oliveros

    Dre Oliveros New Member

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    hello guys i have a question, as some might remember about a year ago i went ahead with multiple upgrades to my amp, with success the amp sounds awesome and fully eliminated the bleed problem, however some nights ago i turned the amp and notice 2 different things.

    1) the LED channel (in normal channel mode where its supposed to be no light at all) light turns on as you strum the guitar, as if it is detecting sound.

    2) channel bleed on boost channel, if you use or not the normal channel knobs the bleed its there, so you clearly hear a clean guitar over the boost channel. This does not happen in normal channel , theres no bleed at all.

    So after i notice this also did notice that as time goes by playing the bleed goes away and also the light slowly stop reacting to the strumming, so for the symptoms im guessing its a cap, or well might be the time to change the IC chip, so if anyone any ideas of where should i look would be awesome, thanks a lot.
     
  2. ampmadscientist

    ampmadscientist Well-Known Member

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    "So after i notice this also did notice that as time goes by playing the bleed goes away and also the light slowly stop reacting to the strumming,,,,"
    "the LED channel (in normal channel mode where its supposed to be no light at all) light turns on as you strum the guitar, as if it is detecting sound...."

    The first thing you do is test the low voltage power supplies. To do this you will need a DC volt meter.
    The channel switching appears to be 1/2 on, 1/2 off...stuck between normal and overdrive...

    If you don't have a meter you should probably take it to an amp tech.
     
  3. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    You should link the past thread so we may see what modifications were performed.
    It appears the bleed issue was not taken care of all that well.
     
  4. Dre Oliveros

    Dre Oliveros New Member

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    Yes i own a meter i performed all the things in this amp, also yes back when i finish it the amp was working great, it worked fine all this time until some days ago, when i notice this things, im pretty sure that its something recent. Thanks for replying ill keep waiting for more feedback, to maybe narrow down the problem.
     
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  5. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    It will be hard to narrow anything down if you do not provide information.

    You can start with what Ampmadscientist mentioned, test the LT supply.
     
  6. ampmadscientist

    ampmadscientist Well-Known Member

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    What you got here is an amp with a channel switching problem.
    But it was modified to fix the channel switching, because somebody did not understand how to troubleshoot and repair it the right way.

    Now you need to Un-modify it completely back to stock, before you really fix the real problem.....
    Sounds like a really bad start to an amp repair: modifying a broken amp to fix a problem that was misidentified to start with.

    I really would not want to do this on the internet. I would need to use test equipment to analyze the actual problem first.

    And what it might turn out to be caused by: a corroded footswitch jack. :lol:
     
  7. johan.b

    johan.b Well-Known Member

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    check the footswitch jack. it has a switch function ..those fail.
     
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  8. ampmadscientist

    ampmadscientist Well-Known Member

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    You need to Un-modify the amp, 100% back to stock.
    Then you can start working on the real problem.
     
  9. pedecamp

    pedecamp Well-Known Member

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    Retrace your steps, everything you did to it originally when you modded it. Check everything is good.
     
  10. Dre Oliveros

    Dre Oliveros New Member

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    http://www.marshallforum.com/threads/1986-jcm800-2210-important-info.105908/

    Sorry i forgot to put the link, i think we got a lot of assumption here, so ill try to explain real quick the situation, the amp was in bad shape due to the country i live here theres no amp tech or at least someone who is professional about it so thats why i started to do things myself ten years ago, so last year i went to california and took the amp with me, the guy at Advanced Music there put the amp back to stock and fully working (didnt have the time back then to work on it myself), then the only thing that was done was change some knobs and caps to Soso, also a few resistors from a basic photo/ schemes/ diagram that i followed step by step which also worked, the “mod” done to the bleed problem was something i read a lot even in this forum which was changing the value to C40, so as i repeat again the amp was done in January, used quite a lot all this months working flawesly, i notice this two things im commenting just some days ago that werent there before, to hope someone as usual give some pointers based on knowledge or experienced something similar, my bad i didnt give some backstory to this, but yeah thats my situation.
     
  11. South Park

    South Park Well-Known Member

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    The problem is a flimsy circuit board. If you can’t up grade the board replace the amp.do you really want to fix this and it go out again.i really hate say it.
     
  12. Gunner64

    Gunner64 Well-Known Member Premium Member

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    These amps have pcb mounted pots ect., and the pcb is partially mounted in the amp by the pots. Removing the pcb for modding ect risks compromising the solder connections were the pots and other things mount to the board. My 2205 did some weird shit when it had a broken solder joint at one of the pots. One day it worked, next day it didnt..I would reflow the connections, pots, led, any leads that could be compromised by past board removal.
     
  13. ampmadscientist

    ampmadscientist Well-Known Member

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    No guitar plugged in.
    No footswitch plugged in.
    Power on, standby set to warm-up position. Do not turn standby to operate position.
    Set meter for DC volts.
    Connect black probe to metal chassis.
    Connect red probe to R8.
    Test both sides of R8 with the red probe. What are the voltage readings from both leads of R8?

    2. Connect red probe to R40.
    Measure both sides of R40. What are the DC readings from both leads of R40?

    Report back w/ the DC readings.
     
  14. Dre Oliveros

    Dre Oliveros New Member

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    Hey ampmadscientist, this is what i got

    R8 side to red cable footswitch 1.6v / 1.55v

    R8 other side 3.6v / 3.50v


    C40 to normal volume center leg side =3.0v / 3.00v

    C40 to side IC chip leg =2.6v / 2.57v

    Note: my C40 is a 225K 400/cap that i put when i notice the symptoms thinking that might be and before was a .1uf 400 there which i put instead the stock one.

    Thanks for the steps mister, ill wait your thoughts.
     
  15. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    What makes anyone think that changing C40 will help a channel bleed issue?
    Please tell us the year of your amplifier manufacture so that everyon is on the same page.
     
  16. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Please note whether voltage measurements are AC or DC.
     
    Last edited: Oct 20, 2019
  17. Dre Oliveros

    Dre Oliveros New Member

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    Its a january of 86’
     
  18. ampmadscientist

    ampmadscientist Well-Known Member

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    Th
    There is something wrong.
    It appears that the jack switches are corroded (input jack and footswitch jack).

    With no guitar plugged in:
    There should be 0 volts on one side of each resistor, R40 and R8.

    2210FS.png

    And so it seems that you have been modifying your amp to try to compensate for corroded jack switches.
    Which seems to have been a mistake.

    Put the amp back to stock.
    Take out all modifications.
    Change the input jack and the footswitch jack.
    Make sure you are getting 0 volts on one side of R40 and R8, with no guitar plugged in.

    The switching circuit can't function unless the jack contacts are working.
     
    Last edited: Oct 20, 2019
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  19. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Ah, I had a look at your other thread. I see that you have a 1986 year transition model. It is similar to what Ampmadscientist posted, a bit different. I also understand the "C40 modification" now along with the other two added capacitors in the switching system.


    I am still reading. :)
     
  20. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    @ampmadscientist
    His voltages may be low at the switching system. Does that 220R really pull it down to 3.6VDC with a buggered jack leaving 1.6VDC instead of 0VDC?
    His voltage readings may be whacky at the C40 modification he put in there.
    I agree he should have those 0VDC readings with nothing plugged into the two jacks.

    @Dre Oliveros
    You need to discern for us whether you are taking DC or AC voltage measurements, please.
     
    Last edited: Oct 20, 2019

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