42PB4D-AA Power PCB VS 4A fuse blowing - suggestions?

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  • matthewr88
    Member
    • May 2014
    • 10
    • Australia

    #1

    42PB4D-AA Power PCB VS 4A fuse blowing - suggestions?

    Hi guys,

    Ive got a LG 42" plasma here thats got an issue on the Power PCB, firstly ive read the basic guides put on here(very informative btw) and did a forum search before starting a new thread, but im after a little more specific advise

    The first issue noticed is the power light would be on stndby at the front of the tv, pressing the power button or applying power you could hear a relay fire after a couple of seconds.

    So the first thing i did was checked the input fuse all good, the board was so dusty at the time i couldn't even see the second one between the heatsinks.

    I checked the boards output, 5v = 4.8v steady, but the VS and VA would both go up to around 58~v then the relay would fire and back to 0v

    after giving it a damn good clean out I found the blown 250v 4A fuse(pictured below) in the center of the board, replacement just blew again, removed all other connectors to the power PCB and tested again same result. Fuse blows as soon as power is applied.

    So im guessing the issue is with the VS power circuit, Im also at this point guessing its a short as the fuse really pops when powers applied

    Inspected the board and i cant see any bloated caps or dry joints, all that said i need to start chasing the circuit, can anyone with a bit more experience with plasmas point me to a possible source.

    Power PCB model number is: EAY32808901
    5v, VA=61 VS=190
    Attached Files
  • tw2005
    Badcaps Legend
    • Oct 2011
    • 6458
    • Australia

    #2
    Re: 42PB4D-AA Power PCB VS 4A fuse blowing - suggestions?

    I'd start with checking the FETs on the heatsinks, possibly the 2 on the opposite side of the fuse. I'd also check the Vs inputs on both the ysus and zsus boards and see if they're shorted too or Possible blown IPMs .


    The PSU may not be the only failed board in this TV. Best to find out now before you start sinking more $$$ than it's worth.

    Not familiar with LGs , someone else may have worked on this generation.

    Comment

    • matthewr88
      Member
      • May 2014
      • 10
      • Australia

      #3
      Re: 42PB4D-AA Power PCB VS 4A fuse blowing - suggestions?

      cheers, will start there and post results

      Comment

      • matthewr88
        Member
        • May 2014
        • 10
        • Australia

        #4
        Re: 42PB4D-AA Power PCB VS 4A fuse blowing - suggestions?

        Quick update during my lunchbreak

        So ive checked the VS inputs on both the ysus and zsus. No shorts between the VS and Ground rails, The YSUS boards fuse is still in tact which im guessing is a good sign.

        So on checking the FETs i have found the two tw2005 mentioned were indeed faulty (shorted) I believe. Checked them with a Metre and had a ~0 Ohm reading so that im taking as a short?

        Would anything else be damaged by these two going to short?
        Hoping fuse will have prevented too much damage

        Havent done any more research on the FETs themselves or anything else around. busy day at work fixing everyone elses problems lol, will investigate further tonight.

        Comment

        • matthewr88
          Member
          • May 2014
          • 10
          • Australia

          #5
          Re: 42PB4D-AA Power PCB VS 4A fuse blowing - suggestions?

          Hi guys so after some futher testing, and a bit clearer head the FETs that i believe are dead are marked W20NK50Z all pins goto zero on the dmm from the data sheet its marked as a 500v 17A N-Channel FET

          does this sound right?
          can anyone confirm if i need to check any other circuitry surrounding this?

          cheers for any help in advance

          Comment

          • tom66
            EVs Rule
            • Apr 2011
            • 32560
            • UK

            #6
            Re: 42PB4D-AA Power PCB VS 4A fuse blowing - suggestions?

            I would always replace any driver IC connected to the FETs, because it could also be damaged. Failure to do so could kill your new FETs on power up.
            Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
            For service manual, schematic, boardview (board view), datasheet, cad - use our search.

            Comment

            • matthewr88
              Member
              • May 2014
              • 10
              • Australia

              #7
              Re: 42PB4D-AA Power PCB VS 4A fuse blowing - suggestions?

              Cheers tom66 exactly the information i was looking for

              Comment

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