LG tv shows no power or light or sound

Discussion in 'General Electronics Chat' started by huckle189, Sep 29, 2015.

  1. huckle189

    Thread Starter New Member

    Sep 29, 2015
    3
    0
    One day I was watching tv when it just turned off after a bub sound.
    TV is LG 47LH50.
    It has not turned back on since, no pic, no sound NOTHING, can any one please help. Below is my efforts I have put so far, but not gotten success yet.

    First my skills - I am ok with soldering, have done it. I have a multimeter, and try to use it when I can.
    I checked the fuses with multimeter, there were two fuses on power supply board. One farther from the AC plug had blown on the original power supply board. I thought it was easy fix. I changed that fuse, but no change.

    Next, I bought a power supply board, from a used parts shop for same model, connected it, that blew the fuse right close to AC plug. That time I had all connections to the board as they were supposed to be. I am not sure if that board was bad. Then my next step, I fixed the fuse taking the one from my original board and this time I didnot connect anything but that power supply board directly to AC power through a extension cord, and it blew the same fuse again. I am thinking the board is bad and the used supply store probably had a lemon. I am not sure. Could it have been good initially, but gone bad after connecting it to the TV which I think maybe I shouldn't have done? Any comments? Should I buy a power supply board again and try? Any suggestions?

    In both the power supply boards, I don't see any raised or blown capactitors by looking. I don't know how to check other components on the board. I did check the ports out of the power supply, both are not giving any DC voltage on the metal pins which connect to main circuit board of TV.

    Thanks,
    -huckle189
     
  2. ISB123

    Well-Known Member

    May 21, 2014
    1,239
    526
    You could have damaged the MOSFET(it's shorted) by connecting it to a TV which can have a short somewhere else than PSU.
     
  3. huckle189

    Thread Starter New Member

    Sep 29, 2015
    3
    0
    Thanks ISB123, Is there a way to debug it any further to find where else the short is, if not the PSU?
     
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,963
    743
    I would say its the tv chassis thats got a fault, not the psu, i would get another psu and check the outputs first, check the supply lines for shorts, then connect it to the tv,

    Best to get a service manual first...
     
  5. ISB123

    Well-Known Member

    May 21, 2014
    1,239
    526
    Check the MOSFET for a short in the new PSU first.
    And visually check other boards in the TV for burned parts or areas.
     
  6. huckle189

    Thread Starter New Member

    Sep 29, 2015
    3
    0
    ISB123, I don't see any burned areas on the other boards.

    Where can I get tv service manual, LG said they couldnot give it out, its only for their technicians.
     
  7. bwilliams60

    Active Member

    Nov 18, 2012
    721
    88
    Lets start from scratch. It sounds like your experience is limited so we do not want you to mess with mains voltage unless ypu feel really comfortable in doing so. There are voltages here that can kill you.
    Put the old power supply board back in and turn the set on if it will. There will be a connector with output voltages marked beside it. You need to find the one marked 5V. Test all the voltages on this connector but 5V is the one we want to concern ourselves with for now.
    Take some really good pictures of the back of the TV, and the boards that are on there and post back on here. Get clear closeups where possible, especially of the connector. You will reference chassis ground. Keep left hand away from the TV at all times and watch where you poke around.
     
  8. peter taylor

    Member

    Apr 1, 2013
    106
    5
    The last few monitors I repaired had shorted diodes at the secondary side of the transformer. You know the type that come in a plastic bolt on package that contain two diodes. The cathodes are connected in common with the center pin. If there is a fault in another part of the TV, the PSU shouldn't blow when disconnected from it. It sounds like you bought a dud, but I'm skeptical.
     
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