Marshall JCM2000 LEDs on but no signal?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Hugo Da Rosa, Oct 14, 2008.

  1. Hugo Da Rosa

    Hugo Da Rosa Silver Supporting Member

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    My friend has a Marshall JCM2000 2x12 combo that worked fine not along ago but suddenly stopped working. All the LEDs turn on and the channels can still change, but absolutely no signal passes through. Here is what we've checked so far:

    1. The tubes seem to be ok - not sure if he checked to see if any of the tubes were dead but he made sure they were snug in the sockets.

    2. It's not the guitar or the guitar cable - played it through his boss tuner and picked up a signal.

    I've told him to look inside the chassis and see if there are any visible issues but I don't know how much that helps. Can anyone help us please? :(
     
  2. jamme61

    jamme61 Supporting Member

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    Did you check the fuses? on the back of the amp they're fuses. If one of the HT fuses went it may be because one of your power tubes went. If you replace a fuse, make sure you replace it with right kind (slow blow and same rating) Radio shack should have the fuses if you need them. Also if the fuses are all ok, check the peamp tubes.
     
  3. slider313

    slider313 Silver Supporting Member

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    How about the speaker(s)? Did you cross it over to another know good speaker(s)?
     
  4. WesKuhnley

    WesKuhnley Member

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    There are also internal fuses for each tube. If you don't have experience with amps, I would bring it to a tech for troubleshooting.

    The HT fuse is a fast-blo...only the mains fuse is a Slo-blo
     
  5. FortinAmps

    FortinAmps Member

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    If you need a schematic for your DSL, I'd be more than happy to email them to you. Just send me a PM.:AOK
    Cheers,
    Mike
     
  6. Hugo Da Rosa

    Hugo Da Rosa Silver Supporting Member

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    thank you all for all the help you have provided. The amp works now...turns out it was a HT fuse problem. My friend replaced it and it's in working condition. Thanks again! Love TGP :AOK
     
  7. TopBooster

    TopBooster Member

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    The problem was actually an output tube short, which blew the HT fuse. Your friend should think about replacing the output tubes ASAP, because that HT fuse is going to get blown again, sooner or later...Hopefully not at a gig!
     

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