Samsung 4K UN55KU6490 backlight issue

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  • Forks
    New Member
    • Aug 2019
    • 6
    • Canada
    #1

    Samsung 4K UN55KU6490 backlight issue

    Hey,
    I have a Samsung 55” 4K curves TV UN55KU6490F.
    The TV started flashing it's backlights on and off. On for not even a second and stay off for up to a minute.
    I pulled the back off and checked the voltages on the power board they seemed ok. I'll post a photo with them.
    I pulled the panel off and checked the LEDs when they flash on they all flash on so I don't think it's the LEDs.
    I started playing with the settings and found that when I have the backlights at 20 (scale is 0-20) the tv stays on and quickly flashes off once every couple of minutes.
    The back lights are only at 71V across both sets when they are on. When measured individually set 1 is 43V set 2 is 41V. Doesn't seem high enough to me.
    With the back lights at 10/20 (backlights off) there is still voltage on them set 1 34V and set 2 34V
    Anyone had a similar issue or have any tips?
    Sorry for the long winded message.
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    • R_J
      Badcaps Legend
      • Jun 2012
      • 9514
      • Canada
      #2
      Re: Samsung 4K UN55KU6490 backlight issue

      Place your meter positive on the test point CH1, and meter negative on chassis ground, then turn on the tv, what is the voltage? it should be around 270vdc

        Comment

        • Forks
          New Member
          • Aug 2019
          • 6
          • Canada
          #3
          Re: Samsung 4K UN55KU6490 backlight issue

          263V.
          A bit more playing around with it. When I get the Netflix sign in page up on it the tv acts normal. I can adjust the backlights to minimum. At max backlight I have 255v across my backlights.
          Checking the ana_dim pin from the main board with the backlights at 20 it’s 3.3 and drops by .3V each step down on the backlight. So at 19 it is 3.0V, 18 2.7V, 17 2.4V, 16 2.1V, 15 1.8V, 15 1.5V until down to 10 when it get to 0.
          So it seems it just has issues when there is no input so a blank screen.

            Comment

            • Forks
              New Member
              • Aug 2019
              • 6
              • Canada
              #4
              Re: Samsung 4K UN55KU6490 backlight issue

              At a blank input screen the Ana_dim acts the same although backlights turn off when the backlights get to 18

                Comment

                • R_J
                  Badcaps Legend
                  • Jun 2012
                  • 9514
                  • Canada
                  #5
                  Re: Samsung 4K UN55KU6490 backlight issue

                  The power supply is supplying the proper voltage to the led's so you likely have at least one bad led in the string.

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