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Markbass SD800 Problem

Discussion in 'Amps and Cabs [BG]' started by The Reff, Mar 9, 2010.

  1. The Reff

    The Reff

    Feb 11, 2004
    I've had this amp for over a year and I'm pretty much happy with it.

    But I have experienced now 2 times that while playing, the amp just stops working. The lights are on and the fan is running but there's no sound comming out. The input was not clipping and the master volume was never higher than 10 o'clock.

    I've had the amp checked by the shop after the first time, but they couldn't find anything wrong with it.

    1st time I was playing quiet jazz with a passive 6-string bass on a 1x12 cab (8ohm). The amp had been running for aprox. 1 hour. Suddenly the sound stops comming out and it doesn't return. The next day the amp is back to normal.

    The 2nd time I was playing an active 5-string on a 4x10 cab (4ohm). The amp had been running for maybe 6 hours and the sound starts to go on and off.

    The two incidents are roughly 7 months apart.

    Does anybody know what is causing this ?
  2. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    on and off, eh? try cleaning the effects loop jacks. sometimes they can get dirty if you don't use them and it can cause a short. a little deoxit and pushing a plug in and out of it a few times should work. if that doesn't work, you may have a short elsewhere. but a lot of times that works.
  3. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
    take Jimmy's advice. it most likely your problem. the loop's jacks have switches in them that break the signal from the preamp to the power when a 1/4" cable is inserted. if the switches in them become oxidized (very common), they will not pass signal and be 'open' causing the amp to cut out intermittently, have a weak signal, or cut out altogether. a simple test is to just use a short patch cable and jump the jacks to bypass the switches in them.
  4. The Reff

    The Reff

    Feb 11, 2004
    Thanks for the answers - is there any difference to the troubleshooting if my effects loop is parallel or serial ? (I'm pretty sure it's parallel)

    Edit - when you say "jump the jack", does that mean plug a patch cable into the effects loop and see if anything happens ? I've tried that and the amp seems to be working just fine....
  5. I have the same problem but I never use the effects loop.
  6. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

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