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LG 37LC55 almost fixed.

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    #1

    LG 37LC55 almost fixed.

    Hello, my friend gave me his LG 37LC55 to have a look at.
    It took ages for the picture to come on.
    I replaced all of the caps on the power board with Panasonic and the TV turned on straight away....success....then the picture went off after 15 minutes but i still had sound.
    I'd read this post https://www.badcaps.net/forum/showth...ghlight=37lc55 so i put some freeze spray on C901 i could then restart the TV with a picture.
    I have replaced C901 and C533 with Panasonic FK.
    The problem still exists. With the back on the TV lasts about 12 minutes before the picture cuts out.
    I have tested the voltages on the two connecters to the mainboard and get

    19v - 19.3v
    6v - 6.29v
    3.4v - 3.48v
    12v - 12.25v
    5v - 4.85v
    6.5v - 6.3v
    3.4v - 3.43v

    Any ideas what i have missed or what i could test ?
    Thanks
    Attached Files
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    #2
    Re: LG 37LC55 almost fixed.

    can you see something if you put a flash light on the screen?

    there is a big difference when its off and turn on without backlight.
    Just cook it! It's already broken.

    Comment

      #3
      Re: LG 37LC55 almost fixed.

      Did you try spraying c901 again? Could be something like a bad solder
      joint around c901.

      Comment

        #4
        Re: LG 37LC55 almost fixed.

        Thanks guys, sorry when the picture goes, its just the picture, the backlights are still lit.
        If i spray freeze spray when the picture goes with the tv still on and the picture off the picture comes and flickers, but i can turn the tv off and straight back on and the picture is back for a few minutes. Without the freeze spray the picture stays off when i turn it back on.
        I initially replaced C901 with one out of a chinese selection i had, then one from ebay then finally a Panasonic from cpc.
        They aren't the easiest thing to solder but they seem on ok, i've given them a gentle tug.

        Comment

          #5
          Re: LG 37LC55 almost fixed.

          There is a switching diode that is before C901. KDS226 1.2V 85V 300MA.
          I've measured the voltages.
          Attached Files

          Comment

            #6
            Re: LG 37LC55 almost fixed.

            After swapping a couple more caps, one on the power board and the one on the main board that were both out of spec I was unsure where to go next.
            As it seems heat related i have tried to rig a laptop fan in the back. It is looking like it is working with the TV not turning off in over an hour (10 minutes without fan), however at present the fan is powered by my bench power supply.

            I have found 3.4v ON. Can i use a trim pot to lower it to 3v for the laptop fan ?
            Last edited by diif; 09-25-2014, 11:27 AM.

            Comment

              #7
              Re: LG 37LC55 almost fixed.

              Laptop fans run on 5v at full tilt. 3.4v will be no trouble. However, i would be more inclined to dig deeper and see what part is causing the shutdown. You're just delaying the inevitable now.
              Originally posted by PeteS in CA
              Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
              A working TV? How boring!

              Comment

                #8
                Re: LG 37LC55 almost fixed.

                Try heating the area around C901 with a hair dryer before it's been turned on and see if the heat will prevent it from showing a picture. I'm with the earlier poster that said cold solder joint in the area of C901

                Comment

                  #9
                  Re: LG 37LC55 almost fixed.

                  You're right ! I wasn't happy with the fan solution and my friends mrs kept asking if the house was going to burn down !
                  I have warmed C901 and the area around it with my hot air station. The TV turns on fine with a picture and sound. The customer also said that once the set was warm the picture would come on and stay so maybe i've read too much into the problem and c901 was not the issue.
                  I had made an error when i redid the caps, I used a nichion but whoever sold me them in the past had put the 470uf 35v in with some 4.7uf 350v caps and i fitted the wrong one. This has now been replaced with a Panasonic FM of the correct value.

                  Could the problem be caused by the 12v being a little high at 12.25v ?

                  Comment

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