Samsung LE40B550 flickering backlight

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  • satinser
    Badcaps Veteran
    • Oct 2012
    • 214
    • uk

    #1

    Samsung LE40B550 flickering backlight

    Occasional flicker on start up with backlight set to max of 10. If you turn backlight down it gets worse. Mostly more apparent on TV setting rather than external inputs. Anybody know of a fix or might it be failing CCFLs?
  • satinser
    Badcaps Veteran
    • Oct 2012
    • 214
    • uk

    #2
    Re: Samsung LE40B550 flickering backlight

    Forgot to mention in my last post. Its a PSU with built in inverter BN44-00264C rev1.3. There are no swollen caps and everything tests ok.

    Comment

    • dick_barton
      Badcaps Legend
      • Aug 2015
      • 6642
      • Wales

      #3
      Re: Samsung LE40B550 flickering backlight

      How about some photo's to start you off. Clear sharp pictures of your boards and back of the set would be useful.
      Willing to help but I'm no expert.

      Comment

      • Hamie
        Badcaps Legend
        • Apr 2014
        • 1383
        • UK

        #4
        Re: Samsung LE40B550 flickering backlight

        Do the backlights still flicker with the main board unplugged?

        Comment

        • budm
          Badcaps Legend
          • Feb 2010
          • 40746
          • USA

          #5
          Re: Samsung LE40B550 flickering backlight

          Is the DCV between the two legs of the main cap steady and close to 380~400VDC?
          It may be due to UVLO is detecting border line PFC Boosted Voltage, or the detection circuit itself (Resistor network, ICP802, PCI801S), similar problem with the other SAMSUNG that people cut the jumper off the UVLO Opto circuit instead of fixing the PFC Voltage problem due to drifted resistors value in the PFC feedback circuit.
          I suspect the resistors string in the RP802/06/09/13 string for PFC Voltage feedback, or the RP837/803/810/807/823 string for the UVLO detection circuit.
          Attached Files
          Last edited by budm; 05-27-2016, 03:36 PM.
          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

          • budm
            Badcaps Legend
            • Feb 2010
            • 40746
            • USA

            #6
            Re: Samsung LE40B550 flickering backlight

            Originally posted by hamie
            do the backlights still flicker with the main board unplugged?
            +1
            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

            • satinser
              Badcaps Veteran
              • Oct 2012
              • 214
              • uk

              #7
              Re: Samsung LE40B550 flickering backlight

              Thanks for your response. Shortly after posting this fault found out it was caused by the PFC micro (FAN 7530). Once this was replaced together with 4 smd resistors (RP802,RP806,RP809,RP813) the fault cleared. Appreciate all of your replies.
              Last edited by satinser; 05-27-2016, 07:36 PM.

              Comment

              • budm
                Badcaps Legend
                • Feb 2010
                • 40746
                • USA

                #8
                Re: Samsung LE40B550 flickering backlight

                Thanks for the follow-up.
                So was the PFC Voltage was <360VDC?
                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

                • satinser
                  Badcaps Veteran
                  • Oct 2012
                  • 214
                  • uk

                  #9
                  Re: Samsung LE40B550 flickering backlight

                  Yes it was between 350 - 358vdc.

                  Comment

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