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LG 49LB5500 LED Backlight Problem..

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    #1

    LG 49LB5500 LED Backlight Problem..

    Hi All,

    So... It's been a while since I was here and it seems all the knowledge I thought I had has gone and I'm totally at a loss (I've been searching all night too). So.. I thought I'd ask here and see if anyone can kick me off and point me in the right direction

    I've got an LG LED TV and the backlight keeps flicking on-and-off. It comes on for a second and then off for 5 and on for a split second and off...

    I've looked around the board and can't see any bulging caps, tried to fiddle with settings etc and got nowhere..

    I'm assuming it's going to be an LED strip but I thought before I rip it to pieces and get down to that I'd try and exhaust any simple tests I could with just the back open..

    So, I've taken some photos (which I hope aren't too terrible) and now I'm at your mercy Where shall I start do you think?

    Excited to be playing around with this stuff again and luckily I don't really watch much TV so this is as much for fun as anything else before I toss the TV out.

    Thanks in advance all!!!!!!!!
    Tags: None
    #2
    Re: LG 49LB5500 LED Backlight Problem..

    Where are the pictures?
    Never stop learning
    Basic LCD TV and Monitor troubleshooting guides.
    http://www.badcaps.net/forum/showthr...956#post305956

    Voltage Regulator (LDO) testing:
    http://www.badcaps.net/forum/showthr...999#post300999

    Inverter testing using old CFL:
    http://www.badcaps.net/forum/showthr...er+testing+cfl

    Tear down pictures : Hit the ">" Show Albums and stories" on the left side
    http://s807.photobucket.com/user/budm/library/

    TV Factory reset codes listing:
    http://www.badcaps.net/forum/showthread.php?t=24809

    Comment

      #3
      Re: LG 49LB5500 LED Backlight Problem..

      Sorry! Computer froze whilst downloading from my camera.. Take 2! (and hello again )
      Attached Files

      Comment

        #4
        Re: LG 49LB5500 LED Backlight Problem..

        measure the voltages on each LED string at the power supply. You have 2 strings.

        Comment

          #5
          Re: LG 49LB5500 LED Backlight Problem..

          Intermittent Led on these 5V ran Led sets.
          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 !

          https://www.facebook.com/Telford-Tel...7894576335359/

          Comment

            #6
            Re: LG 49LB5500 LED Backlight Problem..

            Capleaker - That's great, somewhere for me to start!

            Reecey - I'm not sure what that means, are you saying intermittend LEDs are a common fault with this TV?

            Thanks all

            Comment

              #7
              Re: LG 49LB5500 LED Backlight Problem..

              As there are two strings of LEDs, are both strings flashing on and off at the same time?

              Rich
              Follow me on YouTube
              ------------------
              Learn Electronics Repair
              https://www.youtube.com/channel/UCFX...R8UZ2vg/videos

              Comment

                #8
                Re: LG 49LB5500 LED Backlight Problem..

                Originally posted by stedmund08 View Post
                Capleaker - That's great, somewhere for me to start!

                Reecey - I'm not sure what that means, are you saying intermittend LEDs are a common fault with this TV?

                Thanks all
                There a few threads around where these leds are/can be intermitant and causing this type of issue

                Comment

                  #9
                  Re: LG 49LB5500 LED Backlight Problem..

                  Yeah... LED's can fail like that. Once a faulty LED gets hot, it fails, it cools off, then it turns on again. The cycle repeats. Measuring the voltage on the strings, will tell you on which string the problem is, then you have to disassemble the panel and find the bad LED.

                  Comment

                    #10
                    Re: LG 49LB5500 LED Backlight Problem..

                    Cool - what's/where's the best place to test the strings? At the power supply?

                    Comment

                      #11
                      Re: LG 49LB5500 LED Backlight Problem..

                      have you got a led tester?

                      Comment

                        #12
                        Re: LG 49LB5500 LED Backlight Problem..

                        sure.

                        Comment

                          #13
                          Re: LG 49LB5500 LED Backlight Problem..

                          Vince - no LED tester just a multi-meter... Do I need an LED tester...?

                          Comment

                            #14
                            Re: LG 49LB5500 LED Backlight Problem..

                            Also, can't find the bloody power lead at the moment, hence I've not been able to report any results yet. Doh!

                            Comment

                              #15
                              Re: LG 49LB5500 LED Backlight Problem..

                              Hurrah - found the cable... Now I just need to figure out where/what I'm testing? I assume I take the power supply board off and test the contacts on the rear? Or should I test on the T Con board?
                              Last edited by stedmund08; 06-10-2017, 06:24 AM.

                              Comment

                                #16
                                Re: LG 49LB5500 LED Backlight Problem..

                                can you post a good clear picture of the power supply and also picturs of the connectors on it so we can see the printing by them as you should be able too test the led volatges there too prove you do have a issue.Sometimes though you have to strip the lcd panel down so that you can see the leds then power the set on and hopefully you will see the led at fault.

                                Comment

                                  #17
                                  Re: LG 49LB5500 LED Backlight Problem..

                                  As requested
                                  Attached Files

                                  Comment

                                    #18
                                    Re: LG 49LB5500 LED Backlight Problem..

                                    Hmm, they still look somewhat blurry on the screen.. Let me know if they're no good.

                                    Comment

                                      #19
                                      Re: LG 49LB5500 LED Backlight Problem..

                                      Would have to take some LED backlight supply voltage measurements at start-up and at shutdown. I would just go ahead and replace all the LED strings, if it is cost effective.

                                      Comment

                                        #20
                                        Re: LG 49LB5500 LED Backlight Problem..

                                        Where do I measure from? The two coils at the bottom?

                                        Comment

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