LG 55UK6950PLB backlight but no picture

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  • notallbad
    Badcaps Legend
    • Oct 2012
    • 1190
    • UK

    #1

    LG 55UK6950PLB backlight but no picture

    On power up the backlight comes on but no picture
    Power on - 3.4v
    13.2v - 13.2v
    Drv_on - 3.25v
    V-Sync - 0.04v
    SIN - 0.02v
    SClk - 0.01v
    P-dim - 1.4v
    P-dim2 - 1.3v

    With the left tcon ribbon removed just backlight still on fulscreen, no change.
    With the right tcon ribbon removed that half of the screen is considerably darker.

    Any advise please.
    thanks
    Attached Files
  • notallbad
    Badcaps Legend
    • Oct 2012
    • 1190
    • UK

    #2
    Re: LG 55UK6950PLB backlight but no picture

    in stby the 13.2v line is jumping around between 8.2v and 8.6v

    Also dont seem to be able to get any sound.
    Last edited by notallbad; 11-12-2021, 08:10 AM.

    Comment

    • chopdre
      New Member
      • Jul 2012
      • 8
      • barbados

      #3
      Re: LG 55UK6950PLB backlight but no picture

      seems like a panel issue, you need to block the ckv lines on the faulty side of screen

      Comment

      • William1967
        Badcaps Veteran
        • Nov 2017
        • 203
        • Netherlands

        #4
        Re: LG 55UK6950PLB backlight but no picture

        The panel has a problem, it's a common fault with these models and several other models from LG. The AVDD must be around 17v and is only present on one side when you disconnect one of the LVDS cables.

        Comment

        • notallbad
          Badcaps Legend
          • Oct 2012
          • 1190
          • UK

          #5
          Re: LG 55UK6950PLB backlight but no picture

          thanks william
          shall check that out
          is it a fault within the actual panel or the boards attached to the panel? fixable or just scrap?
          thanks

          Comment

          • notallbad
            Badcaps Legend
            • Oct 2012
            • 1190
            • UK

            #6
            Re: LG 55UK6950PLB backlight but no picture

            Both ribbon cables connected theres no volts on AVDD, left or right.
            With the right ribbon cable disconnected the AVDD on the left is 17v.
            With the left ribbon cable disconnected theres 0v on AVDD on the right.

            There is 17v on both ribbon cables when disconnected.
            Last edited by notallbad; 11-15-2021, 05:48 AM.

            Comment

            • William1967
              Badcaps Veteran
              • Nov 2017
              • 203
              • Netherlands

              #7
              Re: LG 55UK6950PLB backlight but no picture

              I have 4 over here with the same problem, I only had a little time to investigate where it comes from and until now I have to say it's inside the panel...

              Comment

              • notallbad
                Badcaps Legend
                • Oct 2012
                • 1190
                • UK

                #8
                Re: LG 55UK6950PLB backlight but no picture

                ok may as well strip it down and trash the screen then.
                Anything you want me to check or do before its scrapped? Might help with your investigations later.

                Comment

                • William1967
                  Badcaps Veteran
                  • Nov 2017
                  • 203
                  • Netherlands

                  #9
                  Re: LG 55UK6950PLB backlight but no picture

                  I've gone a little further with one of the displays and by cutting some lines there was picture, unfortunately there were black flashing lines on the left side of the display.
                  On the second display I could not get any picture at all. I'm not going to open both other tv's, they will go back to the owners. In one word said these tv's are garbage!

                  Comment

                  • dskall
                    Badcaps Legend
                    • Oct 2016
                    • 2905
                    • usa

                    #10
                    Re: LG 55UK6950PLB backlight but no picture

                    You can run down the short if you are interested. Maybe able to bypass shorted area and go directly to COF with wire.
                    I assume no responsibility for any stupid suggestions I might post.

                    Comment

                    • Davi.p
                      Hobbist Tech
                      • Sep 2009
                      • 4314
                      • Italy - Milan

                      #11
                      Re: LG 55UK6950PLB backlight but no picture

                      The fault may be within the display distribution boards, maybe a shorted cap, needs slow current supplying on avdd line especially, to be safe 1,8/3,3v supply lines must be present.

                      Comment

                      • notallbad
                        Badcaps Legend
                        • Oct 2012
                        • 1190
                        • UK

                        #12
                        Re: LG 55UK6950PLB backlight but no picture

                        Found the fault! Burnt out on one of the tab bonds.

                        Not a very good photo, sorry but you get the idea.

                        So this ones toast! Shall strip down for parts.
                        Thanks for the help! Appreciate it!!!
                        Attached Files

                        Comment

                        • dskall
                          Badcaps Legend
                          • Oct 2016
                          • 2905
                          • usa

                          #13
                          Re: LG 55UK6950PLB backlight but no picture

                          Thanks for follow up.
                          I assume no responsibility for any stupid suggestions I might post.

                          Comment

                          • Monty74
                            New Member
                            • Feb 2022
                            • 1
                            • uk

                            #14
                            Re: LG 55UK6950PLB backlight but no picture

                            Originally posted by notallbad
                            Found the fault! Burnt out on one of the tab bonds.

                            Not a very good photo, sorry but you get the idea.

                            So this ones toast! Shall strip down for parts.
                            Thanks for the help! Appreciate it!!!
                            Hi notallbad, did you have to trash the screen to get to the burnt out tab bond? I have one of these screens and wanted to attempt a repair as I too have backlight but no picture. Is this a ribbon cable of some kind that has burnt out? I cant really see as the picture is not so clear as mentioned. I just want to know if its repairable on a micro soldering scale? Regards Craig

                            Comment

                            • nomoresonys
                              Badcaps Legend
                              • Jan 2013
                              • 12137
                              • U.S.

                              #15
                              Re: LG 55UK6950PLB backlight but no picture

                              simple things first, try unplugging wifi and speakers, turn tv on see if there's any change.
                              Last edited by nomoresonys; 02-11-2022, 01:21 PM.

                              Comment

                              • viewerau
                                Badcaps Veteran
                                • May 2020
                                • 305
                                • Australia

                                #16
                                Re: LG 55UK6950PLB backlight but no picture

                                Originally posted by chopdre
                                seems like a panel issue, you need to block the ckv lines on the faulty side of screen
                                How is this process done please?
                                Signature:Seemingly hopeless tv fixer

                                Comment

                                • nomoresonys
                                  Badcaps Legend
                                  • Jan 2013
                                  • 12137
                                  • U.S.

                                  #17
                                  Re: LG 55UK6950PLB backlight but no picture

                                  tape cutoff method, video there and many more, youtube: https://www.youtube.com/watch?v=pfrRhw7-ZII
                                  Last edited by nomoresonys; 02-12-2022, 02:48 AM.

                                  Comment

                                  • viewerau
                                    Badcaps Veteran
                                    • May 2020
                                    • 305
                                    • Australia

                                    #18
                                    Re: LG 55UK6950PLB backlight but no picture

                                    Originally posted by nomoresonys
                                    tape cutoff method, video there and many more, youtube: https://www.youtube.com/watch?v=pfrRhw7-ZII
                                    Thank you...

                                    This is my t-con

                                    I see CLK 1-8 on the top right of my t-con, but unlike his board, which shows the lines going to the ribbon area, in mine, I see no lines like his were.

                                    So how do I know which one's to tape?

                                    Thank you.
                                    Attached Files
                                    Signature:Seemingly hopeless tv fixer

                                    Comment

                                    • lotas
                                      Badcaps Legend
                                      • Jan 2016
                                      • 4573
                                      • Russia

                                      #19
                                      Re: LG 55UK6950PLB backlight but no picture

                                      Originally posted by viewerau
                                      thank you...

                                      This is my t-con

                                      i see clk 1-8 on the top right of my t-con, but unlike his board, which shows the lines going to the ribbon area, in mine, i see no lines like his were.

                                      So how do i know which one's to tape?

                                      Thank you.
                                      ckv
                                      Attached Files

                                      Comment

                                      • viewerau
                                        Badcaps Veteran
                                        • May 2020
                                        • 305
                                        • Australia

                                        #20
                                        Re: LG 55UK6950PLB backlight but no picture

                                        Hi lotas.

                                        I am sorry, I do not understand your reply...my apology.
                                        Signature:Seemingly hopeless tv fixer

                                        Comment

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