Mark Bass Little Mark Tube 800 malfunction

Discussion in 'Amps and Cabs [BG]' started by GiladCK, Nov 30, 2019.


  1. GiladCK

    GiladCK

    Nov 30, 2019
    Help! My MB amp stopped making any sound. Here’s what I’ve collected so far:
    - Clip light blinks when it should
    - The amp makes sound the second I turn it off until it is completely down
    - Cooling fan on the back works fine
    - The amp is not muted
    - Also no sound on phantom mode

    Any idea what the problem might be? I’m happy for any clue at all. Thanks!
     
  2. I had a similar fault on a LM3 which turned out to be a faulty pre amp board; the one that attaches to the front panel with all of the controls soldered to it.
     
  3. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    I would expect that this is something a qualified service tech can sort out easily.
     
    BassmanPaul likes this.
  4. 74hc

    74hc

    Nov 19, 2015
    Sunny California
    Some of the outputs can be used to test and narrow down which section of the amp is faulty. These are the effects send, the D.I., and the tuner out ports on the back.

    If you are comfortable, you can open the top and check the tube, whether it glows or not. Additionally, you read the tube's spec sheet and measure the voltages on it. That's easier if the tube leads are exposed.

    If your Markbass is like mine, there's too much goop to really replace anything but minor stuff at the component level. It's basically board swapping. Getting boards is tough for this brand, which means an authorized service center. Which in turn means a good chunk of one's paycheck in these parts.

    Too bad, it helps creates a throw-away, pollution-oriented society. Manufacturing semiconductors, whether active or passive, is a high pollution endeavor.

    So in the end, all you are doing is narrowing down what needs to be replace so that you can evaluate the tech's price better. Around here, some are willing to rip off the unaware.
     
  5. BassmanPaul

    BassmanPaul Inactive

    While I agree with Andy, if the amp has an effects loop you could try linking the send and return with a signal cable to see if it helps.
     
    AlexanderB likes this.
  6. AlexanderB

    AlexanderB

    Feb 25, 2007
    Sweden
    As the others say, check for signal from XLR out, tuner out and effect send.

    The below part is only if you have some basic understanding about electronics:

    I have not worked on that exact model, but the LMII and LMIII have a fair amount of internal cables.

    After leaving the amp unplugged (from the mains) a couple of hours, it is OK to remove the top plate and one by one detach and re-attach the cables from the connectiont points on the boards. A small (!) amount of deoxit in the connector sleeves can be applied as well. Reinstall the lid and try the amp again.
     
  7. 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.

     
    May 16, 2022

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