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LG 42LE7500 TV Backlighting but no Picture

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    LG 42LE7500 TV Backlighting but no Picture

    Good Evening All. I have a 42" LG TV that was given to me and my background is more automotive electronics so was hoping for some direction on this. I can get around the TV okay, just need pointing in the right direction. This TV starts up okay and backlighting comes on with no problem but there is absolutely no picture. I have ran an infrared monitor over the power supply and most areas that I think should get hot, are, but that is obviously no measure of anything so where should I start with this one?
    It has two boards in it. Mainboard and Power Supply I am assuming. I don't have any pictures yet but if you need them, I can upload some later on.
    Thank you in advance.

    #2
    Re: LG 42LE7500 TV Backlighting but no Picture

    Yep, throw up some good straight on pictures of all the boards and one of the whole back and how they are connected, try test number 3 below.

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      #3
      Re: LG 42LE7500 TV Backlighting but no Picture

      Okay here are the voltages I got with Power Off and then Power On
      ON 0.00 VDC 3.25 VDC 20V 0.00 VDC 21.4 VDC
      20V 0.00 VDC 21.40 VDC 20V 0.00 VDC 21.4 VDC
      GND 0.00 VDC 0.00 VDC GND 0 0
      GND 0.00 VDC 0.00 VDC GND 0 0
      3.5V 3.48 VDC 3.40 VDC 3.5V 3.3 3.3
      3.5V 3.48 VDC 3.40 VDC 3.5V 3.3 3.3
      GND 0.00 VDC 0.00 VDC GND 0 0
      GND 0.00 VDC 0.00 VDC V-SYNC 0 0
      12V 0.00 VDC 12.28 VDC DRV-ON 0 2.9
      12V 0.00 VDC 12.28 VDC SCLK 0 0
      12V 0.00 VDC 12.28 VDC PWR DIM 0 3.2
      SIN 0.00 VDC 0.02 VDC Error Out 0 0

      Pictures to follow momentarily
      Last edited by bwilliams60; 01-31-2020, 09:00 PM.

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        #4
        Re: LG 42LE7500 TV Backlighting but no Picture

        Here are my pics. I suspect that 20V circuit may be a problem?
        Attached Files

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          #5
          Re: LG 42LE7500 TV Backlighting but no Picture

          The cpu chip is in need of a re-balling, or a quick reflow with a heat gun on low for about 45 seconds. Remove the big black heatsink, then heat it evenly.

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            #6
            Re: LG 42LE7500 TV Backlighting but no Picture

            Thank you @tvtimmy for your response. I have seen where people have heated their mainboards in an oven at 380 for ten minutes. What you are saying is to just heat the cpu? Is that the only part that is losing connection? I can do that with my hot air station. Any recommended temperature? I generally run my station at 225 for most things. Thoughts?

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              #7
              Re: LG 42LE7500 TV Backlighting but no Picture

              Just heat up the chip under the black heatsink. A hot air station will work very well, only heat the chip . I put a towel under the board to prevent the surface mounted parts from falling off. Set the temp just over what it takes to melt leaded solder. Let it cool and try it out.

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                #8
                Re: LG 42LE7500 TV Backlighting but no Picture

                Did this fix your issue?

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