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Behringer BXL 1800A finally working

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  • Behringer BXL 1800A finally working

    Well after an unrealistic amount of time the Behringer bass amp is finally going.
    It initially had blown IRFP9140N and IRFP140N mosfets and a couple of burnt
    220 ohm resistors with the main supply copper track also fried.
    It turned out the reason for DC at the output after replacing the damaged components was lack of supply to one of the MJE 340/350 drivers.
    This was due to track damage I missed.
    It didn't look pretty but it worked!
    I think next time I may pass on repairing small boards with extensive track damage.
    I think the owner was "celebrating" at the time and pushed the amp way too hard.
    I noticed it was tricky setting the bias for 5mV over R1. The pot seemed very sensitive and initially on turn on it would go to a higher setting then settle back to a lower reading before starting the slow climb as the amp warmed up.
    I got it stable at about 4.6mv.
    Thanks Enzo for your help, your knowledge and ability to cut to the chase is invaluable.
    Also thanks to miguelplus from Peru ..

  • #2
    For a bias seting like that, don;t fight it, let it be a little low if it wants. A tiny bit of crossover distortion would never be heard.
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      Hy everybody,
      Thousand Thanks for all your informations. I am new in this forum, my english is poor but you all give me what I need to repair my friend's amp (Behringer PMP518). I change amp board (LPA1180). 6 months to receive my new part, but it's working good.
      Just want to know if the bias shoud be adjust with signal input and speaker plugged or not ?
      Thank you and I hope I can help for other troubleshootings.

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      • #4
        Solid state amp bias.
        No Signal.
        No Load.

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