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LG 60LB7100 Intermittent No Backlighting

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    #1

    LG 60LB7100 Intermittent No Backlighting

    Any help and input much appreciated, Its been a tough one for me to diagnose so any help there is also welcomed.

    So I have an LG 60LB7100-UT and it will occasionally loose backlighting, I can shine a flashlight at the screen and see the picture perfectly, so I have tried to catch it to diagnose and so far all my test readings are as follows, but also these readings so far are without failure:

    (I will update as soon as I get it to fail again as it is getting more frequent )

    The following readings are the TV staying on for 20min after I took the back off during a failure:

    VC6 - .925
    VC5 - .920
    VC4 - 2.08
    VC3 - .926
    VC2 - .930
    VC1 - .928

    LED 1-6 where all 68.9

    I did see LD701 blink 4 times (I dont know what that code means ? Does that mean the 4th set of LED's with the higher reading of 2.08 is bad ?) but I didn't have my MultiMeter ready to test any voltages and by the time I set up and plugged the TV back in and it has worked since so far.

    EDIT:

    After 4 hours I finally caught it acting up...... here are the readings from that :

    Initial ON - LED Out Failure (about 5 seconds after turning on)
    VC6 - 11.5 - 8.80
    VC5 - 11.5 - 9.09
    VC4 - 11.5 - 12.98
    VC3 - 11.5 - 9.08
    VC2 - 11.5 - 8.78
    VC1 - 11.5 - 9.13
    Last edited by Steveakus; 07-21-2017, 06:55 PM. Reason: TV Finally Failed
    Tags: None
    #2
    Re: LG 60LB7100 Intermittent No Backlighting

    Any sharp focused pictures of the boards?
    Willing to help but I'm no expert.

    Comment

      #3
      Re: LG 60LB7100 Intermittent No Backlighting

      If different pics are needed please let me know, thanks
      Attached Files

      Comment

        #4
        Re: LG 60LB7100 Intermittent No Backlighting

        These may be better pics?
        Attached Files

        Comment

          #5
          Re: LG 60LB7100 Intermittent No Backlighting

          The pictures are not focused well so I can't quite make it out but it looks like the circuit board legend says output (leds) 56.3V at 1.2Amp.
          Could you take readings as given below when the backlight is on and when they go out.


          These are readings from an earlier thread for An LG 60LB7100-UT
          Backlights off:-

          SCLK / .086
          Vsync / .011
          Sin / 3.19
          P-Dim1 / 2.44
          P-Dim2 / 1.735
          Dry on / 3.128
          Pwr on / 3.14
          24v , 12v , 3.5v working

          Voltages to backlights connector
          Led + \ 55.5v
          VC1 / 9.96v
          Led + \ 55.5
          VC2 / 9.05
          Led + \ 55.5
          VC3 / 11.9
          Led + \ 55.5
          VC4 / 8.82
          Led + \ 55.5
          VC5 / 9.3
          Led + \ 55.5
          VC6 / 9.3


          Backlights on
          Ok so running tv with no picture for almost an hour then turning it off then back on I get a picture back . Here are voltages that are different when it works .
          Sin / no picture 3.189v - with a pic .128v
          P-Dim2 / no picture 1.735v -with a pic 3.53v

          On the led output connector :
          Led+'s \ when not working 55.5v when has a pic 72v
          VC 1 thru 6 / when not working voltages range from 9v to 11.9 - when has a pic they range from 9v to 18v
          Last edited by dick_barton; 07-22-2017, 08:11 AM.
          Willing to help but I'm no expert.

          Comment

            #6
            Re: LG 60LB7100 Intermittent No Backlighting

            Here is close up of that legend

            And a pic from ShopJimmy of the same model board just for clarity. I cant seem to get a good enough pic.
            Attached Files
            Last edited by Steveakus; 07-22-2017, 08:22 AM. Reason: adding pic

            Comment

              #7
              Re: LG 60LB7100 Intermittent No Backlighting

              The leds should have 69.3V when running but it would be worth your while taking the measurement as above when backlights on and then when they go off.
              Willing to help but I'm no expert.

              Comment

                #8
                Re: LG 60LB7100 Intermittent No Backlighting

                Originally posted by dick_barton View Post
                The leds should have 69.3V when running but it would be worth your while taking the measurement as above when backlights on and then when they go off.
                Yes, I do have that as well

                LED 1-6 ON = 69.0

                LED 1-6 OFF = 55.6

                Comment

                  #9
                  Re: LG 60LB7100 Intermittent No Backlighting

                  What about the following pins when backlight on then off

                  SCLK
                  Vsync
                  Sin
                  P-Dim1
                  P-Dim2
                  Dry on
                  Pwr on
                  Willing to help but I'm no expert.

                  Comment

                    #10
                    Re: LG 60LB7100 Intermittent No Backlighting

                    Originally posted by dick_barton View Post
                    What about the following pins when backlight on then off

                    SCLK
                    Vsync
                    Sin
                    P-Dim1
                    P-Dim2
                    Dry on
                    Pwr on

                    _______ on ________ off
                    SCLK = 1.0 _____ 87.3
                    Vsync= .9 _____ 11.2
                    Sin = .9 _____ 3.27
                    P-Dim1= 2.66 _____3.28
                    P-Dim2= 1.76 _____1.75
                    Dry on = 3.13 _____3.13
                    Pwr on = 3.41 _____3.41
                    Last edited by Steveakus; 07-22-2017, 09:21 AM.

                    Comment

                      #11
                      Re: LG 60LB7100 Intermittent No Backlighting

                      Do you notice any dark spots on screen when it is working?
                      I assume no responsibility for any stupid suggestions I might post.

                      Comment

                        #12
                        Re: LG 60LB7100 Intermittent No Backlighting

                        Originally posted by dskall View Post
                        Do you notice any dark spots on screen when it is working?
                        No looks great when working

                        Comment

                          #13
                          Re: LG 60LB7100 Intermittent No Backlighting

                          Looks like vc4 string has problem.
                          I assume no responsibility for any stupid suggestions I might post.

                          Comment

                            #14
                            Re: LG 60LB7100 Intermittent No Backlighting

                            It looks like VC4 string may have leaky/shorted LEDs.
                            Try turning down the backlights to as low as possible to see if the backlights will stay on longer than 20 minutes.
                            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 60LB7100 Intermittent No Backlighting

                              Originally posted by budm View Post
                              It looks like VC4 string may have leaky/shorted LEDs.
                              Try turning down the backlights to as low as possible to see if the backlights will stay on longer than 20 minutes.
                              How hard are these to replace ? also not finding parts readily available anywhere ?

                              Comment

                                #16
                                Re: LG 60LB7100 Intermittent No Backlighting

                                Also yes that seemed to help by turning the backlight down to minimum ... so you still think the VC4 LED String is the main culprit ?

                                Comment

                                  #17
                                  Re: LG 60LB7100 Intermittent No Backlighting

                                  stayed on for almost 2 hours after turning the backlight down to minimum, but now shuts off every few minutes after turning back on.

                                  Comment

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