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UN65NU6900F - Backlight No Picture

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    UN65NU6900F - Backlight No Picture

    Set turns on normally, backlight stays on, after about 20secs or so thin vertical colored lines appear on the left side of screen.

    First i tried disconnecting the lvds ribbon cables one side at a time to see if i would at least have half a picture, i got nothing.

    Hooked both back up and started probing voltages on both ribbon cables, got nothing, disconnected one and got all the main voltages/signals on both ( supply - 3.2v, 26.2v and 1.8v for signals).

    So started checking for shorts on this side - right driver board, mainly caps, nothing found, so decided to hook it back up and try the reverse with the left driver board and to my surprise the voltages all came up nice and steady, so hooked both back up, voltages all gone.

    So went checking further into both driver boards and found these packs (see pics below) all reading short across their pins on both boards, my question is are these the famous diode packs or resistor packs, if they are diode packs, how should these normally read/test.

    only d17 on right side board and d47 on left side board shorts on half of the pins, all the other packs on both sides read dead short/continuity across all pins, there are 4 driver boards, the two boards with the packs are the ones on the outer ends, i disconnected the other inner boards and still had the shorted readings, any ideas or help is appreciated as always.


    Also if i disconnect the outer driver boards one at a time i get a white segment, one side is all white,no lines (right side) and the left side is same white segment but with thin colored lines see last pic.
    Attached Files

    #2
    Re: UN65NU6900F - Backlight No Picture

    Remove all those diodes. As far as I remember those are for protection purposes. You can either replace them or leave the board without diodes.

    Comment


      #3
      Re: UN65NU6900F - Backlight No Picture

      Originally posted by ducky29 View Post
      Remove all those diodes. As far as I remember those are for protection purposes. You can either replace them or leave the board without diodes.
      So they are diode packs i take it, my screen must be really screwed for all those to be shorting like that, i will try your suggestion and get give an update later, Thanks so much for your HELP.

      Comment


        #4
        Re: UN65NU6900F - Backlight No Picture

        Removed all packs on both sides, still shorting across on all points as seen in my previous pics above, packs give no reading by themselves, so i'm guessing they are open?

        checked remaining diodes in the area where packs were removed, they don't give me any readings, it's difficult to get my needle meter leads on the contact points but as far as i can tell i am making good contact on the pins while checking, as i said i don't get any readings, so there's not much else left in the surrounding area's, do you guys think i may have a totally shorted out panel,maybe the COF's?, as far as i can tell i don't see any signs of burning as they are under some sort of glue.
        Attached Files
        Last edited by TVAddict; 03-11-2022, 11:08 AM.

        Comment


          #5
          Re: UN65NU6900F - Backlight No Picture

          Originally posted by TVAddict View Post
          Removed all packs on both sides, still shorting across on all points as seen in my previous pics above, packs give no reading by themselves, so i'm guessing they are open?

          checked remaining diodes in the area where packs were removed, they don't give me any readings, it's difficult to get my needle meter leads on the contact points but as far as i can tell i am making good contact on the pins while checking, as i said i don't get any readings, so there's not much else left in the surrounding area's, do you guys think i may have a totally shorted out panel,maybe the COF's?, as far as i can tell i don't see any signs of burning as they are under some sort of glue.
          Something will be causing a short, any Mlccs near by showing up shorted ?
          Please Do Not PM My Page Asking For Help Badcaps Is The Place For Advise, Page Linked For Business Reasons Only. Anyone Doing So Will Be Banned Instantly !

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          Comment


            #6
            Re: UN65NU6900F - Backlight No Picture

            Try a small voltage injection and see what gets hot. It might be a component or the screen itself.

            Comment


              #7
              Re: UN65NU6900F - Backlight No Picture

              Originally posted by ReeceyBurger123 View Post
              Something will be causing a short, any Mlccs near by showing up shorted ?
              Yeah, looking more and more like the screen itself.

              May i ask what's Mlccs??

              Thanks for your reply.

              Comment


                #8
                Re: UN65NU6900F - Backlight No Picture

                Originally posted by ducky29 View Post
                Try a small voltage injection and see what gets hot. It might be a component or the screen itself.
                Yep, nothing to lose at this point, i might try it but i think the screen is toast.

                Thanks for your reply.

                Comment


                  #9
                  Re: UN65NU6900F - Backlight No Picture

                  mlcc's are the little ceramic capacitors.

                  Comment


                    #10
                    Re: UN65NU6900F - Backlight No Picture

                    Originally posted by nomoresonys View Post
                    mlcc's are the little ceramic capacitors.
                    OK, Thanks, yeah i've been over those no shorts detected, a few read around a couple hundred ohms, they were next to resistors.
                    Maybe i'll start cutting a couple of those vgh vgl ckv tracks etc..that lead to the screen and see what happens, when i get some spare time though.

                    Thanks for your reply

                    Comment


                      #11
                      Re: UN65NU6900F - Backlight No Picture

                      maybe try the tape cut-off method, might work, sometimes you need to play with how many signals are blocked by the tape, one of many videos there: https://www.youtube.com/watch?v=XCJAx92JwPs

                      Comment


                        #12
                        Re: UN65NU6900F - Backlight No Picture

                        Originally posted by nomoresonys View Post
                        maybe try the tape cut-off method, might work, sometimes you need to play with how many signals are blocked by the tape, one of many videos there: https://www.youtube.com/watch?v=XCJAx92JwPs
                        Yeah, i did try it from the mainboard side, didn't think to try it on the driver boards side of things, but you see the short is still there even with both ends driver boards disconnected, i was expecting to have picture in the middle at least, oh well, Thank you guys for all your HELP and suggestions.

                        Comment


                          #13
                          Re: UN65NU6900F - Backlight No Picture

                          I have the same TV as you - UN65NU6900F.

                          Upon plug in, the TV will turn on by itself, displaying a black screen with backlights on. No sound. Doesn't really do anything.

                          I spent countless hours looking and testing for shorts and poking and prodding. Nothing would make this TV work. Turns out it was a bad panel. TV gets sound when the ribbon cables to the panel are disconnected from the mainboard (there is no TCON in the TV in any one is wondering).

                          After removing the metal covers that protect the scalar boards, I found one of the ribbon cables from the scalar board to the panel must have shorted out and caused the problem. Under a magnifying lens, there was evidence of heating and damage caused by the heating.

                          See my post in another thread here:

                          https://www.badcaps.net/forum/showpo...6&postcount=28

                          Interestingly, I wonder if this TV has been refurbished since of the 4 scalar boards along the bottom of the panel (call them 1, 2, 3, 4), the left one (1) is blue color PCB, and boards 2, 3, 4 are green like all the other boards in this TV. Perhaps this blue board and the associated COF (chip on flex) cables were replaced before I ever bought the TV.

                          Anyways, this TV is a piece of crap. 2nd UN65NU6900F I've seen fail locally in the same way. And yours. And probably countless other people out there. the NU series is not a very good TV.

                          I hate these new 4K TVs that seem built to fail.
                          Last edited by Unspun01; 03-18-2022, 09:20 PM.

                          Comment


                            #14
                            Re: UN65NU6900F - Backlight No Picture

                            Thanks for your reply and info Unspun01, totally agree with what you said, TV's in general have become so disposable.

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