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Marshall 6101 valve amp

Discussion in 'Electronic Repair' started by N_Cook, Oct 4, 2010.

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  1. N_Cook

    N_Cook Guest

    In for a problem in heater wiring, corrected and working fine on the bench.
    Reassemble in cab and no output now. I'm loathe to have to now take the main
    board apart unnecessarily if I'm doing somrthing silly as there are a number
    of awkward quirks about this model.
    Feed signal in the "Return" and it outputs to the speaker. Normal signal to
    the front input and output at "Send". There is 0R across all 4 un-inserted
    "return" socket contacts as per schematic. ch select switches and status
    LEDs work but pressing the muting switch does not mean the 3 LEDs come on
    together now as a reminder indicator (this function not mentioned in the
    user handbook). I've removed the digital board and nothing seems amiss with
    that (secret lock within the XLR). Relay click at initialisation at power
  2. N_Cook

    N_Cook Guest

    Something awry with the series/parallel sw. I noted the 3 LED on, if mute
    on, function with another 6101 but it is not the case here, makes perfect
    sense in the absence of a mute lamp on the front, anyone any knowledge? This
    one wrong or the other one wrong or just variants? or does it require jacks
    in place or something as well
  3. shrtrnd


    Jan 15, 2010
    Not familiar with your equipment, but sounds like a grounding problem.
    (ie: works fine on bench, but not when put back in 'cab').
    Carefully check all your electrical contacts where they might touch the cab, grounding out your electronics. I'll bet something electrical is touching the cab when you put the chassis (or printed circuit board), back in the 'cab'.
  4. dkxl5

    dkxl5 Guest

    dkxl5 had written this in response to

    N_Cook wrote:


    The mute button between the pwr amp send/return jacks does not have any
    indicator that I'm aware of.
    The channel leds can be finicky sometimes. Sometimes when I turn mine on
    all 3 leds come on and a quick
    on/off of the power switch snaps it back to the proper channel led. There
    are some awkward quirks with
    the amp. Make sure the mute switch is not engaged. If the series loop
    button is engaged you will not get
    any sound from the amp, though the effects knob will vary the loop send
    output and you can still send a
    signal into the return and hear it in the speaker. When switched to
    parallel you will have sound through
    the amp from the input.

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  5. N_Cook

    N_Cook Guest

    I'm wondering if the 3 LED lit thing is only at power up, I remember from
    the other one it also locks out ch selection and maybe use at all via the
    front input until de-muted. But maybe it was like your observation, poor
    initialisation.reset at power up
  6. N_Cook

    N_Cook Guest

    Amp not open at the moment, looking at schema if SW301 is the mute switch
    then no logic connection to the 8031A / LEDs. The ch sw lines go through the
    8031A to the HC574 to the LEDs so I suspect electro C301 of the p9 reset for
    random power-up problems
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