LG 50LB6100 Backlight on/off flicker

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  • jason123
    Badcaps Legend
    • Oct 2015
    • 1068
    • USA
    #1

    LG 50LB6100 Backlight on/off flicker

    Hi folks.. got this TV that has the backlight unstable. On / off (just the backlight) - when on, you can see some intelligence on the screen. Frequency of on/off every few seconds

    Disconnected the TCOn, and no luck ... still on/off backlight

    Naturally I would start tear down to replace LED strips, but when I forced the power supply board to on (Shorting PR--ON and DRV-ON to 3.5V) I measured the left LED set (LED+ and LED-) and I get roughly between 54 and 64 V seems to fluctuate - not very stable. The other set of LED+ and LED- is reading 25 - 35V and occasionally spikes to 102 V or so.

    I'm thinking this is possibly a power supply issue? I can order a new one or attempt repair, but curious to know what you guys think? I don't have any load on the LED Driver- Just a note
    Thanks
    Attached Files
    Last edited by jason123; 07-31-2018, 09:17 PM.
    Tags: None
    • budm
      Badcaps Legend
      • Feb 2010
      • 40746
      • USA
      #2
      Re: LG 50LB6100 Backlight on/off flicker

      You need to provide the LED Voltage readings of all 4 pins with ref. to chassis GND by keeping the black probe on the chassis, red probe one of the four pins then turn on the TV to see how high the Voltage jumps up to and then wait 5 ~10 seconds to see how low it goes down to and then turn off the TV, do the same on the other 3 pins. LED connector must be in place while you are doing this test.
      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

        • jason123
          Badcaps Legend
          • Oct 2015
          • 1068
          • USA
          #3
          Re: LG 50LB6100 Backlight on/off flicker

          Ok, so the connector is labeled from right to left Pin1 = LED-, Pin 3 = LED+, Pin 5 = LED -, Pin 7 = LED+

          Pin 1 as low as 8.xx V and as high as 14 V
          Pin 3 as low as 88 and as high as 92 V
          Pin 5 Stable at 0.175 V
          Pin 7 as low as 194 V as high as 212 V

            Comment

            • budm
              Badcaps Legend
              • Feb 2010
              • 40746
              • USA
              #4
              Re: LG 50LB6100 Backlight on/off flicker

              Originally posted by jason123
              Ok, so the connector is labeled from right to left Pin1 = LED-, Pin 3 = LED+, Pin 5 = LED -, Pin 7 = LED+

              Pin 1 as low as 8.xx V and as high as 14 V
              Pin 3 as low as 88 and as high as 92 V
              Pin 5 Stable at 0.175 V
              Pin 7 as low as 194 V as high as 212 V
              The LED string connected to pin 5 and 7 has open circuit.
              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

                • jason123
                  Badcaps Legend
                  • Oct 2015
                  • 1068
                  • USA
                  #5
                  Re: LG 50LB6100 Backlight on/off flicker

                  So teardown...i was hoping to avoid it. Can you elaborate how you determined this?
                  Thanks

                    Comment

                    • jason123
                      Badcaps Legend
                      • Oct 2015
                      • 1068
                      • USA
                      #6
                      Re: LG 50LB6100 Backlight on/off flicker

                      One LED was open as diagnosed - Thanks budm!! Set is up and running

                        Comment

                        • budm
                          Badcaps Legend
                          • Feb 2010
                          • 40746
                          • USA
                          #7
                          Re: LG 50LB6100 Backlight on/off flicker

                          Glad to hear, just make sure to turn down the backlights level as low as possible on all input modes.
                          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

                            • jason123
                              Badcaps Legend
                              • Oct 2015
                              • 1068
                              • USA
                              #8
                              Re: LG 50LB6100 Backlight on/off flicker

                              Done.. Thank you again for the help.

                                Comment

                                • jangammitesh@gmail.com
                                  New Member
                                  • Sep 2016
                                  • 5
                                  • india
                                  #9
                                  Re: LG 50LB6100 Backlight on/off flicker

                                  nice Co opreation

                                    Comment

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