I need info on a Carvin MX842 Powered Mixer - "Protect" light keeps coming on

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Denny, Feb 3, 2012.

  1. Denny

    Denny Member

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    I've had this mixer for years, got it used and never had a problem with it - I take excellent care of my gear so I know this hasn't been abused, or used with the wrong impedance speakers. It's been flawless until about a year ago when it started cutting out during gigs - the protect light keeps coming on after about 5 minutes, knocking out our monitors. I build tube amps and feel comfortable working on this mixer so if anyone knows what's wrong and feels like spreading some knowledge, that would be great? We'd also be keeping one less piece of hazardous waste from entering our landfills (just to be green;)) Thanks ahead-of-time.

    Denny
     
  2. JJuran

    JJuran Member

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    From the manual online, "The master PROTECT LED indicates that the internal relays
    have disengaged the amplifiers from the speaker output jacks on the rear panel."

    http://www.carvinservice.com/crg/manuals/mx640_mx842.pdf

    Use the link above - the schematic is in that manual. Since it happens after a few minutes, it's likely heat related. You may have a transistor or op-amp burned out or possibly even loose and not firmly attached to heat sinks.

    Open it up and look for signs of overheating on the board, loose transistors, or melted op-amp leads and /or toasted components. Careful and thorough visual inspection first.
     
  3. Denny

    Denny Member

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    thanks - any more info from anyone??
     

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