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LG 42LB5DF No Pic No Sound

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    #21
    Re: LG 42LB5DF No Pic No Sound

    UPDATE:

    Fifteen to twenty seconds after a power-on the backlight flashes (quickly). I only noticed this because I decided to try in a dark room.

    Not sure if that helps.

    Comment


      #22
      Re: LG 42LB5DF No Pic No Sound

      Ok. so you test the two fuses on each inverter boards with Ohm and Voltage. But there are FOUR fuses on each of the Inverter board.
      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


        #23
        Re: LG 42LB5DF No Pic No Sound

        Four ? I found THREE on the Master and only TWO on the Slave. Damn. Will look again. Are they all on the topside of the board ?

        Can you run the backlight with only one inverter plugged in (if it's good of course) as a way of verifying a failed inverter ?

        Comment


          #24
          Re: LG 42LB5DF No Pic No Sound

          Sorry, you are correct, Master has 3, slave has 2, I down load the wrong pictures from SJ. The slave does not have the PWM IC, the main PWM IC is on the Master board. You can disconnect the power cable to the Slave and see if the backlights will flash.
          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


            #25
            Re: LG 42LB5DF No Pic No Sound

            With the Slave power cable disconnected there is NO backlight flash at all.

            Does that mean anything to you ?

            Comment


              #26
              Re: LG 42LB5DF No Pic No Sound

              Bad Master inverter perhaps ??

              Comment


                #27
                Re: LG 42LB5DF No Pic No Sound

                That is what it sounds like since the master/slave setup work like push-pull type to get enough high voltage to drive long lamps in large TV.
                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


                  #28
                  Re: LG 42LB5DF No Pic No Sound

                  Originally posted by budm View Post
                  That is what it sounds like since the master/slave setup work like push-pull type to get enough high voltage to drive long lamps in large TV.
                  Haha that was going to be my next pursuit to find out why the master/slave technique for inverter design.

                  So should these be replaced as a pair or does that even matter ? I mean can one fry the other or anything of that sort.

                  Btw its my understanding that this set failed over time and not instantly. Would that be consistent with some inverter failure ?

                  Comment


                    #29
                    Re: LG 42LB5DF No Pic No Sound

                    So I decided to remove all connectors from the inverters except for one and I got a backlight which fired and stayed on.

                    So I kept plugging in until the backlight failed again to come on.

                    In the end I plugged in (from the top) lamps 1,2,3,4,5,7 and 8 on both Master and Slave. Plugging in 6,9 or 10 in either Master/Slave or both caused the backlight to fail.

                    Though the backlight stays lit there is nothing on the screen, menu, volume osd's, nothing. The set does power on and off normally with the power button. Perhaps a separate issue.

                    Any suggestions ?

                    Comment


                      #30
                      Re: LG 42LB5DF No Pic No Sound

                      If you have everything else hook up except some of the lamp, then you should see some image on the screen. So if you cannot even see the menu, then that is not right.
                      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


                        #31
                        Re: LG 42LB5DF No Pic No Sound

                        Well I figured it wasn't right cause I can't see anything lol.

                        I read somewhere here that if the inverter sees open it will shut down so I'm not sure how I even have any backlight. I would have like to verify the other lamps are working but of course the plugs are too damn short. And those connectors are damn tiny.

                        Might be safe to say at this point at least one, maybe both inverters have failed ? Is it possible to move forward from here without yet replacing the inverters ?

                        Comment


                          #32
                          Re: LG 42LB5DF No Pic No Sound

                          You should replace them in pair, but for no pictures on the screen is more problem to fix, the backlights are needed for the light source only, even if the backlights do not work you still should be able to see the pictures using the flashlight method.
                          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


                            #33
                            Re: LG 42LB5DF No Pic No Sound

                            So a mainboard or tcon problem or even the panel itself ?

                            Comment


                              #34
                              Re: LG 42LB5DF No Pic No Sound

                              May be the T-CON has blown fuse or not getting the voltage from the main board.
                              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


                                #35
                                Re: LG 42LB5DF No Pic No Sound

                                Great idea! Will check it out on the morrow.

                                Comment


                                  #36
                                  Re: LG 42LB5DF No Pic No Sound

                                  Though that reminds me... earlier I took the four screws off the TCon cover and the edge of it where it meets the top of the tv seems to disappear down to the panel and I could not get it off. Without seeing how it was attatched I was afraid I might do damage to the cables/wires/board underneath.

                                  This was AFTER having no picture btw

                                  Comment


                                    #37
                                    Re: LG 42LB5DF No Pic No Sound

                                    Pried up the T-Con cover to gain access (strange design!) and measured 11.84v on both sides of FP1. Nothing on the screen.

                                    There is a flat data cable going from the tcon to the Master Inverter. There are Dim In and Dim Out pins on it. The Dim Out (to the Inverter) reads 0v while the Dim In reads about 2v.

                                    There is a landing on the T-Con labelled TSTPGM. Is that used to generate patterns independently of the Mainboard and if so how do I activate it ?

                                    Comment


                                      #38
                                      Re: LG 42LB5DF No Pic No Sound

                                      Disconnect the cable between the TCON and the Inverter and see if you have backlight. I had a similar model and the TCON was the problem.

                                      Comment


                                        #39
                                        Re: LG 42LB5DF No Pic No Sound

                                        Wow that's interesting. I disconnected that cable and ALL backlights came on.

                                        Think I will replace the T-Con and see what happens next. Thanks.

                                        Comment


                                          #40
                                          Re: LG 42LB5DF No Pic No Sound

                                          Ha, I did not see the cable connected ot he T-CON, it looks like the cable bundle going to the right Inverter was close to the T-CON but not connecting to the T-CON, so it does have scene dimming control, glad you saw that flat ribbon cable. Noted that in my book of knowledge.
                                          http://assets.shopjimmy.com/media/ca...010061-top.jpg If you can live without scene dimming function, I would leaveit, it is one of the trick the manufacturers use to claim high contrast ratio.
                                          Last edited by budm; 10-09-2013, 04:58 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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