LG 42SL80 Not working

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  • powerflow
    Member
    • Dec 2009
    • 43
    • United States

    #1

    LG 42SL80 Not working

    Found an lg42sl80 that was thrown out. I'm trying to learn how to repair modern sets and figured this would be a good way to do it. The set will not power up, it goes through a self check or something, relay clicks on cycles through the LEDs then clicks off again and repeats. At first look I found two shorted power mosfets and a fuse as well as a four bad caps, all parts have been replaced and I've managed to get standby 5v. I've downloaded the service manual and tried the procedure to power up the power supply, but no luck the 12v and 24v should come on but they do not.Readings on conector p201 are

    Pin1 n/c Pin2 0 to 4.9v
    Pin3 - 6 Gnd Pin7 - 10 5.0 to 5.1v
    Pin11 - 12 Gnd Pin13 - 14 0v
    Pin15 - 16 Gnd Pin17 - 18 0v
    Pin19 n/c Pin20 0v
    Pin21 .2v Pin22 0.7 to 3.0v
    Pin23 n/c Pin24 0v

    Been trying to figure it out for some time now, could really use some help.
    Attached Files
  • budm
    Badcaps Legend
    • Feb 2010
    • 40746
    • USA

    #2
    Re: LG 42SL80 Not working

    Pictures of the whole back side of the TV so we can see how all the boards are connected together.
    No pin names for those pins?
    Also need good clear well focused straight shot pictures of the WHOLE boards and around the connectors.
    if you look at your pictures you took and cannot read the label, connector names, etc. then we cannot read them either.
    Last edited by budm; 06-11-2016, 07:08 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

    • powerflow
      Member
      • Dec 2009
      • 43
      • United States

      #3
      Re: LG 42SL80 Not working

      ok I've taken additional pics hope they are better.
      Attached Files

      Comment

      • dick_barton
        Badcaps Legend
        • Aug 2015
        • 6642
        • Wales

        #4
        Re: LG 42SL80 Not working

        Have you carried out the tests as shown on page 33 to check the 12V & 24V lines are working?
        Willing to help but I'm no expert.

        Comment

        • powerflow
          Member
          • Dec 2009
          • 43
          • United States

          #5
          Re: LG 42SL80 Not working

          yes, but i get no 12v or 24v. I do not know where to go from here.

          Comment

          • dick_barton
            Badcaps Legend
            • Aug 2015
            • 6642
            • Wales

            #6
            Re: LG 42SL80 Not working

            The pdf says that you must use a load (12V bulb in this case) as well as the resistors to power up the supply.
            Without the 12V bulb as a load the supplies will not power up.
            Please can you confirm once again that you have carried out the tests exactly as shown on pages 32/33. This is important.
            Willing to help but I'm no expert.

            Comment

            • powerflow
              Member
              • Dec 2009
              • 43
              • United States

              #7
              Re: LG 42SL80 Not working

              Yes I have done this procedure. I can confirm that the relay does click on when I run this test and stays on. However no other voltage is present (i.e. 12v or 24v) as the service manuals procedure indicates should be. So I'm pretty sure the problem is the power supply.

              Comment

              • ReeceyBurger123
                Never Give Up !
                • May 2014
                • 7325
                • Britain

                #8
                Re: LG 42SL80 Not working

                Your on the right track. Is the a CCFL Lcd set btw not Led backlight ? Also on the psu have you checked the voltage across the bulk Pfc caps ?
                Please Do Not PM My Page Asking For Help Badcaps Is The Place For Advise, Page Linked For Business Reasons Only. Anyone Doing So Will Be Banned Instantly !

                https://www.facebook.com/Telford-Tel...7894576335359/

                Comment

                • powerflow
                  Member
                  • Dec 2009
                  • 43
                  • United States

                  #9
                  Re: LG 42SL80 Not working

                  not sure what PFc caps are, but if your referring to the six long brown electrolytics, yes I have check the voltage across them and it is 387v steady.

                  Comment

                  • budm
                    Badcaps Legend
                    • Feb 2010
                    • 40746
                    • USA

                    #10
                    Re: LG 42SL80 Not working

                    PFC Voltage booster is working.
                    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

                    • dick_barton
                      Badcaps Legend
                      • Aug 2015
                      • 6642
                      • Wales

                      #11
                      Re: LG 42SL80 Not working

                      There are several fusable reisitors on that board prefix FR which I would check out with my meter.
                      Willing to help but I'm no expert.

                      Comment

                      • powerflow
                        Member
                        • Dec 2009
                        • 43
                        • United States

                        #12
                        Re: LG 42SL80 Not working

                        After a short vacation I was able to clear my head and managed to repair this TV. Upon rechecking the board I realized that the voltages were not correct at the high voltage resonant controller ST-L6599, I ordered a replacement from Digikey which arrived earlier today, I replaced it and the set is now working perfectly. Another TV saved from the trash bin.

                        Comment

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