LG 50PJ350 Mal Discharge

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  • Ltank
    Badcaps Veteran
    • Jun 2013
    • 776
    • USA

    #1

    LG 50PJ350 Mal Discharge

    Hi,
    This TV has Mal Discharge according to all I read. This is the first time I have seen this. I downoladed a service manual. I made sure all the cables were seated. I checked The SMPS Va:60/ VS:206, Y board -VY was 198.
    My question here is it was labeled -198 on pannel but the place on the Y board has marked - and + for polarity for meter and meter showed 198.
    Z board Zbias was 95. All the voltages were good but My 60Mhz scope could not capture the Y drive signals. I tried my 100Mhz scope but I think it has a broblem. I need a 200Mhz scope with a 2g samping rate?
    I read that Mal Discharge could be caused by the Y or Z or Control Board or all three. The Y has the highest failure Rate then the Z board. But how do I single out the correct board. if I get another scope what signals do I really need to look at? What scope settings are best? I tried using a white screen but it did not help. The Red, Green and Blue screens all had the same problems but I only posted the Red. it does have picture if you apply video to the HDMI input.
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  • Ltank
    Badcaps Veteran
    • Jun 2013
    • 776
    • USA

    #2
    Re: LG 50PJ350 Mal Discharge

    I know to you guys this seems stupid but I did ROV underwater robotics for 28 yrs that had industrial electronics, camers, telemetry systems, motors, relay logic etc..being retired, this year I started repairing TVs. I did tv 30 yrs ago and alot has changed but I am learning the new stuff. it is fun and challanging at the same time. Thanks for any help.

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    • Ltank
      Badcaps Veteran
      • Jun 2013
      • 776
      • USA

      #3
      Re: LG 50PJ350 Mal Discharge

      I removed the Y board and checked all the cap ESR with Cap Wizard, checked transistor and mosfets with Sencore Cricket and diodes wiith Fluke 97 meter. No problems.
      Removed Z board checked caps-good. Found Q312 bad FQPF9N25C a 250 volt N channel mosfet. I had a service manual but no full schematics only partials. I will replace the other one next to it while I am at it. Hopefully this will fix the problem. The customer wanted a new board. Found a refurbished for 28 bucks plus shipping from Encompass had same warrenty as new. I will fix this board as a spare for future use. Is this ethical?

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      • tom66
        EVs Rule
        • Apr 2011
        • 32560
        • UK

        #4
        Re: LG 50PJ350 Mal Discharge

        I can't see a problem with keeping customer's old board... ask them if they want it first.

        A 20MHz scope is sufficient for viewing sustain waveforms, I've used one before. There is a point marked VS_DA which provides a trigger signal synchronised to the sustain waveforms.
        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

        • Ltank
          Badcaps Veteran
          • Jun 2013
          • 776
          • USA

          #5
          Re: LG 50PJ350 Mal Discharge

          Z board come in today and the set works great now. Thanks Guys

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