LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

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  • KennyC
    New Member
    • Sep 2012
    • 9
    • USA

    #1

    LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

    This weekend my LG 42" LCD TV decided to go blank as I was watching it. It then began constant rebooting, accompanied by a "pop" from the speakers (not an electronic/circuitry pop, thank goodness!), and that now repeats for as long as you want while it's plugged in. There is no display. The only response you get from the TV is the power indicator will pulse like a normal startup, then the "pop," and then the repeat. I couldn't find anything quite like that using search, so here I am.

    I took a quick video of what it does:
    http://www.youtube.com/watch?v=KUCq00gsD8Y
    (again, the "pop" is from the speakers, NOT directly from the TV circuitry!)

    I haven't opened to TV up to investigate yet - about to do that now. But here are the specs:

    LG 42" LCD TV
    42LG50-UA
    42LG50-UA.BUSHLJM
    Manufactured June 2008


    I know it's not a whole lot to go on at the moment, but if anyone has any pointers or has seen something like this before, please let me know! Thanks!
  • KennyC
    New Member
    • Sep 2012
    • 9
    • USA

    #2
    Re: LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

    Didn't find anything obvious inside - no bulging caps, no fried components. Forgot to check for blown fuses (oops) but I will. Any hints on where they're all located on this thing?

    The only thing I noticed was that there is a small green LED on the main board that does come on when the TV is plugged in. It flickers off and then back on as it reboots. I will say that it seems to reboot right when I believe the screen should be powering up.

    Attached are some pics of the internals.
    Attached Files

    Comment

    • tibimakai
      Badcaps Legend
      • Jan 2012
      • 3680
      • USA

      #3
      Re: LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

      I'm struggling with a 42LG70, mine it's shorted something in the power supply.
      There are two fuses, one it's in the center of the board and the other at the red connector.

      Comment

      • t.j.
        Badcaps Veteran
        • Apr 2010
        • 383
        • canada

        #4
        Re: LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

        here link to service manuals! the might have something on it in the trouble shooting section~!

        just enter lg 42lg50 an it will pop up list of manuals for you!

        http://elektrotanya.com/?q=showresult

        Comment

        • KennyC
          New Member
          • Sep 2012
          • 9
          • USA

          #5
          Re: LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

          On a whim I decided to unhook the T-Con board from the main board. And...it powered up and stayed powered up! Not that I could see anything, but both the power indicator on the front and the LED on the main board indicate that it's booted "normally" (minus the screen, of course).

          Pic of the T-Con board is attached.

          So, probably a bad T-Con board? Anything I can do to confirm that, or do I just go ahead and replace it since it's a relatively cheap part?
          Attached Files

          Comment

          • Mr Bill
            Badcaps Veteran
            • Nov 2011
            • 648
            • USA

            #6
            Re: LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

            Check the fuse on the tcon is about all i can recommend. I'm going to go look in my box of goodies and see if i have a tcon. It looks very familiar.

            Comment

            • Mr Bill
              Badcaps Veteran
              • Nov 2011
              • 648
              • USA

              #7
              Re: LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

              The ones i have aren't the same. You'll need to match the numbers on the white sticker on the left side. 35-D023305

              Comment

              • KennyC
                New Member
                • Sep 2012
                • 9
                • USA

                #8
                Re: LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

                Thanks for checking!

                Fuse is good. For anyone else reading, I found this thread which has a great reference on this exact T-Con board and how to find and check the fuse.

                One thing I did notice after I unhooked the T-Con board and started it up was that the backlight does blink once but doesn't stay on. Not sure if that's significant or not. I just hope it's that the TV is smart enough to realize that the panel isn't working and turns off the backlight and isn't an indication of a bigger problem!

                Anyway, I think I'll go ahead and order another T-Con board. It seems like a pretty good gamble at this point.

                Comment

                • Mr Bill
                  Badcaps Veteran
                  • Nov 2011
                  • 648
                  • USA

                  #9
                  Re: LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

                  I think the tcon has to tell the inverter to turn on via that small flat cable on the side of the tcon.

                  Comment

                  • budm
                    Badcaps Legend
                    • Feb 2010
                    • 40746
                    • USA

                    #10
                    Re: LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

                    Do you have the LCD panel model number? I need to see the spec and find out if this T-CON has the ERROR signal out put pin or not. Did you check any DC voltage on both ends of the fuse on the T-CON yet?
                    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

                    • KennyC
                      New Member
                      • Sep 2012
                      • 9
                      • USA

                      #11
                      Re: LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

                      Is the picture I posted above have the LCD panel number? If not, I can look again.



                      10V on both sides of the fuse. Of course the voltage drops to zero as it reboots/resets.

                      Comment

                      • budm
                        Badcaps Legend
                        • Feb 2010
                        • 40746
                        • USA

                        #12
                        Re: LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

                        OK, it is Chi Mei model V420H1-L12 Revision C1. Let me see if I can find the spec sheet for it.
                        OK, I found the spec sheet, the T-CON board only receive signals from the main board, the T-CON does not any feedback pin that goes out to the main board to tell its condition if it is good or bad.
                        So the T-CON may have short circuits and load down the voltage on the main board, the main board may have current sensing circuits to see how much the T-CON board is pulling the current, if too much current being pulled, the main board tells the circuits to shutdown, that is my theory. You may have to download the TV service manual to verify.
                        See page 15 of the spec sheet for the pin out of the T-CON board.
                        On page 8, you have indicate that you are getting 10V at the T-CON fuse, the min VCC for T-CON is 10.8V, typical is 12V which I also expect, not 10V. That may be an indication of the problem, you need to leave the T-CON cable disconnect and check the VCC pin on the main board side to see if you still have 10V also, I expect to see 12V. pin 48~51 are the VCC +12V pins, just trace out those pins on the main board side connector.
                        Attached Files
                        Last edited by budm; 09-17-2012, 10:57 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

                        • KennyC
                          New Member
                          • Sep 2012
                          • 9
                          • USA

                          #13
                          Re: LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

                          Thanks! I'm getting 12.38V on those 4 pins.

                          Comment

                          • budm
                            Badcaps Legend
                            • Feb 2010
                            • 40746
                            • USA

                            #14
                            Re: LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

                            "I'm getting 12.38V on those 4 pins" with T-CON board disconnected?
                            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

                            • KennyC
                              New Member
                              • Sep 2012
                              • 9
                              • USA

                              #15
                              Re: LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

                              Yes, with T-Con disconnected.

                              Comment

                              • budm
                                Badcaps Legend
                                • Feb 2010
                                • 40746
                                • USA

                                #16
                                Re: LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

                                So when the T-CON is connected, the voltage drops down to 10 V and also causes the voltage to swing up and down. It looks like you have bad T-CON board, you can try fixing it or replace it.
                                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

                                • KennyC
                                  New Member
                                  • Sep 2012
                                  • 9
                                  • USA

                                  #17
                                  Re: LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

                                  I have a replacement on the way; should be here Thursday or Friday. I'll be sure to report back once I get it in. Thanks again, you've been helpful as always!

                                  Comment

                                  • budm
                                    Badcaps Legend
                                    • Feb 2010
                                    • 40746
                                    • USA

                                    #18
                                    Re: LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

                                    Keeping my fingers crossed.
                                    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

                                    • KennyC
                                      New Member
                                      • Sep 2012
                                      • 9
                                      • USA

                                      #19
                                      Re: LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

                                      It's alive!!!

                                      New [to me] T-Con board installed and all is good! Super big thanks to everyone here. I wouldn't have even tried this if it wasn't for this forum.

                                      Comment

                                      • tom66
                                        EVs Rule
                                        • Apr 2011
                                        • 32560
                                        • UK

                                        #20
                                        Re: LG 42" LCD TV 42LG50 - Will not boot, continuous rebooting, no display

                                        Nice to hear you fixed it.
                                        Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                                        For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                                        Comment

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