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Broken Marshall JCM2000 DSL 100 ??????

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D28boyD28boy Frets: 6
in Amps

At rehearsal yesterday my amp suddenly went super loud and then totally silent...No smoke or fire...Still all the lights are on..all the tubes are lit and you can hear the Transformer (?) humming a little as usual. Tested the cab and it's fine ...So any suggestions as to what the problem maybe?

Fyi I was running it on the 16 ohm output into a 1960A cab ...16 ohm input ...as usual.

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Comments

  • martinwmartinw Frets: 2149
    tFB Trader

    Take your pick, there's a few to chose from. :(

    My money would be on the known bias drift problem though.

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  • D28boyD28boy Frets: 6
    edited November 2015
    Not fantastically helpfull Martin.The amp was serviced at Marshall last year and has been used daily since without a fault. Could a bias drift cause the symptoms...sudden sound boost then nothing but no other obvious damage? No smoke ,flames smell of burning or red hot tubes?
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  • martinwmartinw Frets: 2149
    tFB Trader
    D28boy said:
    Not fantastically helpfull Martin.The amp was serviced at Marshall last year and has been used daily since without a fault. Could a bias drift cause the symptoms...sudden sound boost then nothing ut no other obvious damage?H

    Hard to be too helpful by remote control ;) The problem is that there are a few known issues with these amps, so diagnosing it requires having a look.

    Sounds like the HT fuse has blown if there's no obvious damage to the valves, which is good as it protects the rest of the amp. There are various potential causes for this; could be as simple as one duff output valve, or as bad as the bias drift problem, which can require a replacement PCB. If Marshall serviced it, I would take it back there, they might do a repair pro bono.

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  • siraxemansiraxeman Frets: 1935
    oh that bias drift thingy...heard that was a TSL problem, didn't realise the DSL suffered it as well.
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  • D28boyD28boy Frets: 6

    Well that was helpful Martin ! Being ignorant I didn't realise you could have a blown HT fuse but still have an amp that lights up.....Changed fuse now have  working amp...It's funny actually coz as i was wandering around and the sound suddendly went really loud I saw that my lead had caught the output control on my ME-80 and initially I hought hat was the reason for the volume hike....then when I had no output at all I thought I must have been mistake an d the fault had caused the spike...I'm guessing now that it actually was the reason and that sudden surge blew the fuse?

     

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  • martinwmartinw Frets: 2149
    tFB Trader
    Sounds like it. Result then :)
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  • siraxemansiraxeman Frets: 1935
    what caused the HT fuse to blow ?  Is there an underlying issue that needs  looking at............?
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  • ICBMICBM Frets: 72675
    It's probably biased way too hot if it hasn't been adjusted since it was new, and maybe even if it has if it was set to the original spec.

    Or they can sometimes randomly arc when they're turned up really loud.

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Only two things are infinite - the universe, and human stupidity. And I'm not sure about the universe." - Albert Einstein

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