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Dell U2311Hb 2 sec. to black, advanced edition

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    #1

    Dell U2311Hb 2 sec. to black, advanced edition

    I posses multiples of this monitor so it was easy to rule out the CCFLs by swapping power boards. The issue followed the board.

    A full recap did not fix it.

    Been probing between the bad board and a good one off and on for 2 days, as much as I can stand it. xfmrs, HV output caps, all 2 and 3 legged silicon all check out the same with a multimeter.

    Couple hours under the microscope looking for bad joints, finally in frustration resorted to baking the board...no change.


    sometimes this hobby is not so much fun

    Power board in question is 4H.14W02.AF0 which is based on the more general E162030 VOL.3 design if I am guessing right. That latter google search returns many similar boards.

    I am a capable board mechanic, but certainly no theory genius. I am a bit reluctant to start probing a live board without a better idea what I am looking for. Switch mode supplies frequently confound me.

    Any suggestions are greatly appreciated.

    board pics attached per the sticky, thank you
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    #2
    Re: Dell U2311Hb 2 sec. to black, advanced edition

    hmmmm, I had rather feared that the replies would be slim on this one,

    probably best just order a new board from China 'eh?

    Comment

      #3
      Re: Dell U2311Hb 2 sec. to black, advanced edition

      My guide lists all the possible problems (well 95%) with 2 second to black.

      1) Did you check the 8 pin mosfets on the back side of the pcb to see if they are shorted?

      2) What resistance readings do you get on the inverter transformer (secondary windings)?
      Last edited by retiredcaps; 11-03-2015, 01:34 PM.
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        #4
        Re: Dell U2311Hb 2 sec. to black, advanced edition

        I suppose you still can see image on it with a flashlight when it goes to black?
        Looks like something in inverter triggers protection and it goes into shutdown.
        Inverter circuit is the big black (not yellow!) transformer and surrounding components.
        Check the transformer itself, and maybe you forgot to check those two SMD chip-like components (8-legged ones) on the back of the PCB? Those are MOSFETs that drive the inverter transformer. They can go short.
        stay classy

        Comment

          #5
          Re: Dell U2311Hb 2 sec. to black, advanced edition

          I also had this problem with this monitor type. In the beginning I thought the power supply was faulty, but after some while, I discovered it was caused by a broken backlight wire. When the monitor was cold and I turned it on, I could here a spark that was arcing between the wire and the ccfl tube. And I could smell ozone as well. I diassembled the lcd panel and I indeed found a broken wire. I reconnected the wire and the monitor is working perfect again.
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