LG 55LB6100 Backlights flashing 4 second interval

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  • jcamerox
    Member
    • May 2015
    • 34
    • Canada

    #1

    LG 55LB6100 Backlights flashing 4 second interval

    I tried disconnecting one LED strip and the backlights didn't come on at all. Disconnecting the other led strip and the backlights flashed at the 4 second rate. The capacitor voltage seems unsteady, with no backlights its about 210 v
    and with the flashing backlights reading about 250 v.
    Attached Files
  • Andrew F. Ali
    Badcaps Legend
    • Jan 2014
    • 2450
    • Trinidad & Tobago

    #2
    Re: LG 55LB6100 Backlights flashing 4 second interval

    From what I gather from the info you gave.....You seem to have a backlight issue....LEDs are open on the strips.....there could be shorting LEDs, too.

    Comment

    • jcamerox
      Member
      • May 2015
      • 34
      • Canada

      #3
      Re: LG 55LB6100 Backlights flashing 4 second interval

      Thanks for the reply Andrew. I thought that if i disconnected one strip and the other was good, I would get half the screen illuminated, but this is not the case. With one strip disconnected I get no backlights at all, with the other disconnected I get the flashing backlights. Any ideas on where to go from here?

      Comment

      • budm
        Badcaps Legend
        • Feb 2010
        • 40746
        • USA

        #4
        Re: LG 55LB6100 Backlights flashing 4 second interval

        So you have two LED driver circuits, and two LED strips.
        what DCV do you have for each set of the LED at the L+, L- of each set of the outputs with LED connector in place and without LED connector in place?
        https://www.badcaps.net/forum/attach...8&d=1493218780
        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

        • jcamerox
          Member
          • May 2015
          • 34
          • Canada

          #5
          Re: LG 55LB6100 Backlights flashing 4 second interval

          Thanks for the reply, BudM, I was hoping for you, I have seen some great posts from you.

          With the led strip connector plugged in and power on, between led- and led+ for strip 1, a varying voltage from 1.5 v to 22 v seems like open circuit, almost random. On strip 2 between + and - about 155v and 135v. It seems to charge up to 155v, the backlights flash very quickly and then it discharges to the 135 v or so and then charges up again.

          With led strips disconnected, Led strip 1 is varying from 50 to 60 v while strip 2 is varying from 90 to 110 v.

          Incidentally, with power connected and set not turned on there is about 90 v on the capacitors near the LED connector but the led + and - outputs are near 0

          thanks again, jim

          Comment

          • budm
            Badcaps Legend
            • Feb 2010
            • 40746
            • USA

            #6
            Re: LG 55LB6100 Backlights flashing 4 second interval

            I forget to tell you to use chassis GND as the GND ref for the meter and test all 4 pins of the connector with ref to Gnd. Please take the reading again.
            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

            • jcamerox
              Member
              • May 2015
              • 34
              • Canada

              #7
              Re: LG 55LB6100 Backlights flashing 4 second interval

              Voltages with respect to chassis ground,

              Power plugged in, power switch off, led strips connected
              Led strip 1, led - 1.4 v led + 90.0 v
              Led strip 2, led - 150 mv led + 90.2 v

              Power plugged in, power switch on, led strips connected
              Led strip 1, led - 1 to 12 v led + 111 to 115 v
              Led strip 2, led - 1 to 60 v led + 245 to 260 v

              Power plugged in, power switch on, led strips disconnected
              Led strip 1, led - 360 mv led +163 to 173 v
              Led strip 2, led - 380 mv led + 225 to 195 v slow drop as if it's discharging through

              voltmeter and then charging back to 225 v

              Comment

              • budm
                Badcaps Legend
                • Feb 2010
                • 40746
                • USA

                #8
                Re: LG 55LB6100 Backlights flashing 4 second interval

                So if you only have LED strip 2 connected, do you see the backlights flash on for seconds?
                All 3 sets of the readings do not have have logical relationship at all.
                Last edited by budm; 04-27-2017, 03:07 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

                • jcamerox
                  Member
                  • May 2015
                  • 34
                  • Canada

                  #9
                  Re: LG 55LB6100 Backlights flashing 4 second interval

                  With power on and led strip 1 connected and led strip 2 disconnected, the backlights flash in a sequence bright, dim, faint in about half a second then back to bright with bright to bright about 4 seconds.
                  the voltages at the connector are;

                  Led strip 1 led - 14 to 19 v led + 109 to 115 v
                  Led strip 2 led - 10 to 15 mv led + 200 to 260 v

                  But strip 2 is disconnected so where is the flash coming from??? Strip 1 doesn't have enough voltage to flash or it is too fast to see with my voltmeter ?

                  With power on and led strip 1 disconnected, and strip 2 connected there are no backlights or backlight flash

                  Led strip 1 led - 25 to 35 mv led + 165 to 175 v
                  Led strip 2 led - 45 to 55 v led + 200 to 220 v

                  Comment

                  • budm
                    Badcaps Legend
                    • Feb 2010
                    • 40746
                    • USA

                    #10
                    Re: LG 55LB6100 Backlights flashing 4 second interval

                    You have two individual LED driver circuits. The LED connector has Black (Cathode, L-) and Blue (Anode, L+) wires for one set of LED strip, Black (Cathode, L-) and White (Anode, L+) wires for another set of strip.
                    So which set of wires that are hook up and give the backlights for seconds?
                    Last edited by budm; 04-27-2017, 04:04 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

                    • jcamerox
                      Member
                      • May 2015
                      • 34
                      • Canada

                      #11
                      Re: LG 55LB6100 Backlights flashing 4 second interval

                      I'm calling the white and black pair strip 2. So when the black and blue pair are connected I get the backlights flashing. This strip would seem to be the top half of the led screen.

                      Just went back and checked the voltages with strip 2 disconnected, the voltages are

                      Led strip 1 led - 15 to 25 v led + 110 to 115 v
                      Led strip 2 led - 10 to 15 mv led + 245 to 265 v

                      Comment

                      • budm
                        Badcaps Legend
                        • Feb 2010
                        • 40746
                        • USA

                        #12
                        Re: LG 55LB6100 Backlights flashing 4 second interval

                        OK, so "So when the black and blue pair are connected I get the backlights flashing." It means that strip does not have open circuit, but it does not mean it does not have shorted out LED/S.
                        So how about the WHITE/BLACK pair only, do you get the lights for seconds 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

                        • jcamerox
                          Member
                          • May 2015
                          • 34
                          • Canada

                          #13
                          Re: LG 55LB6100 Backlights flashing 4 second interval

                          When white/black pair connected only, nothing at all. No flashing.

                          Comment

                          • budm
                            Badcaps Legend
                            • Feb 2010
                            • 40746
                            • USA

                            #14
                            Re: LG 55LB6100 Backlights flashing 4 second interval

                            Originally posted by jcamerox
                            When white/black pair connected only, nothing at all. No flashing.
                            Well, there you go. You can also further verify by swapping the two set of the LED connection, just like swapping lamp socket to see if the problem will follow or stays the same.
                            Last edited by budm; 04-27-2017, 07:16 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

                            • jcamerox
                              Member
                              • May 2015
                              • 34
                              • Canada

                              #15
                              Re: LG 55LB6100 Backlights flashing 4 second interval

                              Good idea. I swapped the leads in the connector and the symptoms are exactly the same.
                              Therefore, not the power supply, one of the strips could be open circuit and the other could have a shorted led.

                              That's all for tonight, 11:30 pm here, thanks for the suggestions BudM

                              jim

                              Comment

                              • jcamerox
                                Member
                                • May 2015
                                • 34
                                • Canada

                                #16
                                Re: LG 55LB6100 Backlights flashing 4 second interval

                                One thing did change, the flash rate went from 4 seconds to about 2 seconds.

                                Comment

                                • RinusB
                                  Member
                                  • Sep 2017
                                  • 17
                                  • Canada

                                  #17
                                  Re: LG 55LB6100 Backlights flashing 4 second interval

                                  My issue is not the LEDs, it is the power going there.
                                  With power plugged in and TV on, the Blue/Black back light voltage goes from over 200 to zero exactly the way the LEDs flash. When I disconnect the back light LEDs the same power fluctuation occurs at those pins at the connector
                                  Might this indicate a main board issue?
                                  No trace of issues to be seen on both side of the boards.
                                  This issue started when I set my energy saver setting to any settings but off!
                                  Now it is like that full time even when the back lights are set to the lowest setting.
                                  Yes there is a normal picture as well as menu.
                                  Hope you can shed light on this.

                                  Comment

                                  • budm
                                    Badcaps Legend
                                    • Feb 2010
                                    • 40746
                                    • USA

                                    #18
                                    Re: LG 55LB6100 Backlights flashing 4 second interval

                                    It goes over 200V because you have open circuit is one of the two LED strings.
                                    See post 9, 10, 11 and read the whole thread.
                                    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

                                    • RinusB
                                      Member
                                      • Sep 2017
                                      • 17
                                      • Canada

                                      #19
                                      Re: LG 55LB6100 Backlights flashing 4 second interval

                                      Hi budm
                                      Yes read the whole thing and it might indeed be the LED string.
                                      The voltage on the black led- lead that should read 0v actually reads between 10 and 50 volts. That same lead on the white/black pair reads zero.
                                      Does it indicate an open circuit or a short or does it matter?

                                      Thanks.

                                      Comment

                                      • budm
                                        Badcaps Legend
                                        • Feb 2010
                                        • 40746
                                        • USA

                                        #20
                                        Re: LG 55LB6100 Backlights flashing 4 second interval

                                        You have two power supplies to drive each LED string, when the LED power supply does not see the load (I.E. open circuit in the LED string) the Voltage will go up high (that is why you see the Voltage goes up over 200V) and then the Over Voltage protection will kick in. The reason you see the backlights come on for seconds because one of the LED drive circuit ans the LED string are working, and one is not (the one that the output went up over 200V).
                                        Bad LED is common failure in TV with LED backlights, the worst one are the LG, it drive the LED at or beyond the limit of the LED.
                                        This one could have burn down the house.
                                        https://www.badcaps.net/forum/showth...ht=LG+47LN5790
                                        https://www.badcaps.net/forum/showth...hlight=latw%2A
                                        Last edited by budm; 09-16-2017, 03:55 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

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