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ALWSR -ve 24V magic smoke

Discussion in 'd.i.y.' started by chrisn, Jan 23, 2021.

  1. chrisn

    chrisn pfm Member

    Completed a pair of -ve 24V ALWSRs acouple of months ago and they tested fine
    Wired them up today with a pos 24V pair to make a PS for an Exposure pre
    Confidently switched on. Smoke and burning from one of the neg boards

    I had connected the power input -ve 35V and ground the wrong way around
    I had just copied the input ground in the same way as the positive board which is wrong for neg boards

    Anyway tested one correctly connected, it only produces -ve 11.5V, the other produced more smoke and has a burnt LM337 and 100kR next to it

    Any ideas? My level of expertise means they go in the bin
    I'd welcome any help to see if they can be sorted out
  2. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    I had a problem with a positive board a while ago that someone else had built
    I ended up changing all the transistors and caps and the IC in the middle of the board
    It was just easier to change everything than mess about
    The (large) build manual that you can download has some very useful fault finding tips and you can test some bits in isolation....but the bootstrapping design does make it hard to test...hence my approach of " just change it"

    You probably have spare components anyway?
  3. Arkless Electronics

    Arkless Electronics Trade: Amp design and repairs.

    Assuming the boards were correctly assembled and properly tested before fitting.... it is likely to have been wiring error's. If the load had large electrolytics to be charged that could possibly have done it.

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