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    LG 55 LED No video

    Hi,

    I have a LG 55 inch LED tv which has no video. I tested the SMPS board and looks like voltage to backlight LED is missing. I could hear the sound and able to change volume and source so concluded that main board is ok. I'm getting around 0.06V when checked against LED + and - terminals. Also able to get 3.2V on DRV on from mainboard. Any idea whats going wrong?
    Attached Files

    #2
    Re: LG 55 LED No video

    Model number? Looks like you have no backlight instead of no video. If you have no backlight, bad LEDs are suspect. Typically you will get a flash on power up but an open LED string will cause the backlights not to flash.

    Comment


      #3
      Re: LG 55 LED No video

      Typical LG. Do the flashlight test.

      Comment


        #4
        Re: LG 55 LED No video

        Yes, I have video on screen when tested with flash light. It's backlight problem, but I suspect the power supply as there are no voltages on the board even after disconnecting backlight from the board.

        Comment


          #5
          Re: LG 55 LED No video

          With tv powered on VERY CAREFULLY check the voltage between the legs of looks to be C510 the big capacitor, note it says 450 volts, THIS IS DEADLY VOLTAGE so be careful not slip with the probes or touch anything with your hands etc, set meter to 200 or 600 vdc, what voltage do you have? don't do test if you are uncomfortable doing it.
          Last edited by nomoresonys; 11-17-2020, 04:41 PM.

          Comment


            #6
            Re: LG 55 LED No video

            I have 390V on main cap. All standby, 12V and 24V are present. Picture on screen but no backlight. I suspect issue with LED driver circuit but not sure.

            Comment


              #7
              Re: LG 55 LED No video

              What is the full model of the TV?
              You have two separate LED driver circuit, you can see that you have two boost converters there on the board.
              I assume that you verify you do have BL-ON and DIM control signals, correct?

              1) Turn TV off, out all connectorS back in place, meter set to 200VDC. Keep the black meter probe on the chassis, Red on one of the L+ of the LED connector.

              2) Turn the TV on while watching the meter to see how high it jumps up to and then wait 10 seconds to see how low it goes down to.

              3) Repeat step 1 and 2 with the other 3 pins of the LED connector..It is important that you follow the steps.
              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


                #8
                Re: LG 55 LED No video

                Looks like your model is 55LN or 55LA series with backlight failure very common. LGs have shutdown protection of the backlights. https://techhometravel.com/lg-ln-ser...ed-backlights/

                Comment


                  #9
                  Re: LG 55 LED No video

                  YEP, will not be surprised if it has blown LED, the test steps I give will tell you if the LED power supply is OK or not.
                  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


                    #10
                    Re: LG 55 LED No video

                    Originally posted by budm View Post
                    YEP, will not be surprised if it has blown LED, the test steps I give will tell you if the LED power supply is OK or not.
                    +10, Yep, do Buds test, see where you stand.

                    Comment


                      #11
                      Re: LG 55 LED No video

                      I did the test suggested by budm and below are the readings -

                      LED+ Jumps to 128V (high) and then goes to 84.5V (low)
                      LED- 0V
                      LED+ Jumps to 210V (high) and then goes to 85.5V (low)
                      LED- 0V

                      Looks like issue with the LED strips only, could you confirm if anything else is going wrong?

                      Model - 55LN5100
                      Last edited by anupkg1985; 11-18-2020, 02:37 PM.

                      Comment


                        #12
                        Re: LG 55 LED No video

                        Originally posted by anupkg1985 View Post
                        I did the test suggested by budm and below are the readings -

                        LED+ Jumps to 128V (high) and then goes to 84.5V (low)
                        LED- 0V
                        LED+ Jumps to 210V (high) and then goes to 85.5V (low)
                        LED- 0V

                        Looks like issue with the LED strips only, could you confirm if anything else is going wrong?

                        Model - 55LN5100
                        Time to open up panel and check out the LED strips. I would replace the whole set.
                        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


                          #13
                          Re: LG 55 LED No video

                          Finally opened the panel this weekend and fortunately nothing wrong with the strips, only one of the joint between two strips was loose. Everything light up as soon as fixed the joint. TV is back on, thanks to every one!

                          Comment


                            #14
                            Re: LG 55 LED No video

                            Thanks for the follow-up.
                            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


                              #15
                              Re: LG 55 LED No video

                              Surprised the LEDs are still good or the lenses havent fallen off. If you want your LEDs to last, turn down the backlight level for all inputs and all smart apps.

                              Comment

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