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Westinghouse LCM-22W2 backlight issue

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    #1

    Westinghouse LCM-22W2 backlight issue

    SUMMARY
    ======
    Backlight kicks in for about 2 seconds and there is a buzzing sound coming from the inverter board

    THINGS TESTED
    ==========

    1) Measured steady 161V across the main filter cap with power applied to the monitor, when the power button on the monitor is pressed the voltage drops to around 157 then creeps back up to about 160 and stays there.
    2) The board has not been recapped but I did test all caps in circuit with an ESR meter and they all come back well within the proper limits.
    3) 1 of the mosfets came back with ohm readings indicating it may be shorted but have not taken it out of the circuit to test

    PROBLEM
    ======

    1) Press the power button and the power LED comes and and the backlights kick in for about 2 seconds
    2) A buzzing sound it heard from the inverter board for the 2 seconds that the backlights do stay on.
    QUESTION
    =======
    Does anyone have an idea what might be causing this. Attached are pictures of the inverter board. Also here is the video of the buzzing on the inverter board.

    buzzing
    Attached Files
    Tags: None
    #2
    Re: Westinghouse LCM-22W2 backlight issue

    Originally posted by Phyrstorm View Post
    2) The board has not been recapped but I did test all caps in circuit with an ESR meter and they all come back well within the proper limits.
    There are entire discussions (or heated debates) wrt to in circuit ESR testing and the caveats of caps in parallel. Nice ESR meter by the way.

    3) 1 of the mosfets came back with ohm readings indicating it may be shorted but have not taken it out of the circuit to test
    That could be part of the problem.

    2 seconds to black can be

    a) bad caps
    b) bad ccfls
    c) bad ccfl wiring (the top return wire is the usual culprit and could be arcing to the chassis causing the noise)
    d) bad inverter transfomer (secondary windings)
    e) bad transistor/fet

    All explained in great detail starting with post #19 at

    https://www.badcaps.net/forum/showthread.php?t=10419

    I would focus on mosfet and bad ccfl wiring as the first two things to check.

    PS. Great format if I do say so myself! Refer to post #21 on the next page of the troubleshooting guide.

    PPS. jetadm123 knows these Delta boards pretty well.
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    Comment

      #3
      Re: Westinghouse LCM-22W2 backlight issue

      Which mosfet is the one you think may be shorted?

      Comment

        #4
        Re: Westinghouse LCM-22W2 backlight issue

        Sorry for the late response. I pulled the mosfets and they tested fine. I recapped the board and everything is up and working.

        Comment

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