JCM2000 TSL122 Burnt Circuit Board Track

Discussion in 'Marshall Amps' started by Parsonic, May 20, 2019.

  1. Parsonic

    Parsonic New Member

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    Quick story. Acquired the JCM2000 TSL122 after it was in storage for 11years.(a friends back bedroom).
    Tested it for about 3 hours, seemed fine, no crackles or scratchy pots or switches. The last Marshall service was in 2008. Tested again following day for about 2 hours same result, all good.
    Speakers wired as 16ohms into 16ohm socket.
    Another friend heard it running and asked to try it out at rehearsal with a view to buy it. At rehearsal it faded off a couple of times then died with a burning smell. He returned it, next day, dead as a dodo. First thing I noticed was the speaker jack was in one of the other 8/4ohm sockets and the impedance switch was on 4ohms. Probably, in panic to get it working, every socket and switch combination was tried.:(
    Yes the HT fuse was blown, a replacement slow blow T1A was also blown. Stripped the amp down looking for internal damage. (caps all discharged first).
    Here's what I found.
    Burnt-Trac-k.jpg
    So why was this 22J 6kV tantalum cap stuck on pins 3&4 ? Looking a the tracks it should have been on C46.
    Further examination of this board showed some minor damage to C12 and signs of a leaky C19 and that's all that's visible.
    So can anyone extrapolate what went wrong and give some pointers to a repair strategy ?
     
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  2. Mitchell Pearrow

    Mitchell Pearrow Well-Known Member

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    :welcome: To the forum I am no tech and can’t help you, but others here can be patient they will be by soon.
     
  3. neikeel

    neikeel Well-Known Member

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    The schem I can see shows C19 as a small mica in the PI (across the plate resistors R45 and R46 - anti-fizz) and C12 also 500v mica across R12 the plate resistor of V1a (ie to reduce high end on that stage and to limit oscillation). I cannot even see C46 on the schem (JCM2-60-60 on Ampwares site).
    http://www.ampwares.com/schematics/marshall/jcm2000_100w_dsl100.pdf
    Wonder if this is the correct version?
     
  4. ampmadscientist

    ampmadscientist Well-Known Member

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    It's difficult to repair because the insulation of the board is defective.
    You would need to cut out the fiberglass between the traces on the board, and eliminate all the carbon tracks that have formed in the fiberglass. Then you would need to mount a new socket that is isolated...
    In other-words it's basically a paperweight. It would take a lot of effort to make it work again.

    Maybe you can get a new board which is the only practical solution.

    Once the carbon tracks have formed, it will keep burning.
    The carbon cannot be cleaned off, it has to be cut out of the fiberglass and removed completely.
     
  5. neikeel

    neikeel Well-Known Member

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    Agree you need latest board iteration as well - just to be sure.
     
  6. ampmadscientist

    ampmadscientist Well-Known Member

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    Do you know where to order one?
    It's the EL84 power tubes...
     
  7. ampmadscientist

    ampmadscientist Well-Known Member

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    And welcome to the Marshall Forum Parsonic :cheers:.
     
  8. ampmadscientist

    ampmadscientist Well-Known Member

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    I found a board, $236.00
    https://www.tubesandmore.com/products/pcb-marshall-valve-pcb-tsl100tsl122-rev-20

    MarshallTSL122boardRev20.png
     
  9. Parsonic

    Parsonic New Member

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    Thanks for the welcome guys.

    Even though the tantalum wasn't on the specs Neikeel kindly showed me, I spot it peaking out from behind the square 1k resistor, top right, on the photo you've posted. Looks like it's sitting in the white box and not soldered directly to the socket pins.

    Going to experiment for now before going the route of a new board. Can you tell me what the latest version is so I can order one going forward? Have they changed the output tubes from EL34's? You mentioned EL84's?

    Have plenty of time to try a fix, being retired. Let you know how I get on.
     
  10. ampmadscientist

    ampmadscientist Well-Known Member

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    Try to get a new board.
     
  11. neikeel

    neikeel Well-Known Member

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    Last one I bought for a DSL100 was direct from Marshall. Very simple and iirc not that expensive.
     
  12. Sapphire Sounds

    Sapphire Sounds Member

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    Man I hope that shit doesnt happen to mine... I love it.. Just got a new multimeter to help with troubleshooting my 1999 TSL 122 here. The plan is to make sure it wont ruin a brand new set of tubes I bought for it... Because of bias drift, which it has for now...

    http://www.hotroxuk.com/marshall-tsl100-main-board.html

    Even though that store isnt USA based it is the most affordable updated replacement board in dollars. The output tubes are EL34 still, I bet the phone autocorrect feature switched the numbers on AMS, he is quite educated on these JCM2000 TSL/DSL circuit boards, aswell as a slew of other members who have kept up with any broken amp threads on here lol
     
  13. Jon C

    Jon C Well-Known Member

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    I was gonna chime in on the 84/34 thing but I was busy adding a small cooling unit to a Headphone amp……
     
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  14. neikeel

    neikeel Well-Known Member

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    I’m sure it was a typo/slip of finger on keyboard.

    That Hotrox one looks ok (v 20) and is about the same price I paid for the DSL100. A little over £100 or so.
     
    Last edited: May 21, 2019
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  15. Parsonic

    Parsonic New Member

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    Thanks everyone, yes will be ordering a new board soon, as the new valves EL34's matched quads arrived today.
    Cleaned track.JPG UvResin insulation.JPG Wired soldered and tantalum in correct place.JPG
    The devil in me still wants to resurrect the old board, if only to see this wandering bias issue for myself. So today I cleaned up the burnt track treated the insulation under the burnt track with UV curing resin and soldered a single cored wire between the cleaned up track points. New tantalum 22J 6kV inserted into C46.
    Next up will be replacing the two dodgy caps and remounting the board.
     
  16. Yamariv

    Yamariv Active Member

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    Very cool to see how you did that fix! So what's the secret to scraping off the trace properly, is there still a bit left on the board?
     
  17. Parsonic

    Parsonic New Member

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    COMO DRILL.JPG

    Hi Yamariv, I used a Dremel like tool and medium coarse conicle grinding wheel and gentle pressure along the track. Just kept going until the black carbon track was gone. Although the depth of charring is dependent on the arc as the track burnt away, luckily it didn't go right through.
     
  18. Yamariv

    Yamariv Active Member

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    Very cool brother, thanks! I'm subscribed, please keep us posted on the repair if you have the chance. Cheers!
     
  19. anitoli

    anitoli Well-Known Member

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    Nice work.
     
  20. thunderstruck507

    thunderstruck507 Well-Known Member

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    What does C46 do in this amp? IIRC mine was burned up in my TSL when I had it apart to install a Dr Tube Bias Mod kit.

    I am fairly certain I found something about it being unnecessary and removed it entirely.
     
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