42" LG no backlights

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  • cbriggz
    Member
    • Oct 2012
    • 18
    • USA

    #1

    42" LG no backlights

    hey guys i am new at this but was looking for some help. I have a 42" LG lcd (model #42LG50-UA) that when i turn it on the power light flashes twice then turns blue just like it did when it was working correctly. I havent ever had any other problems with this unit and this was def. out of the blue. I took apart the back of unit and dont see any visual damage. the screen turns on for about 3 seconds and then shuts off. there is sound so was wondering if anyone can help walk me through this?
    Thanks
    chris
  • budm
    Badcaps Legend
    • Feb 2010
    • 40746
    • USA

    #2
    Re: 42" LG no backlights

    Post good clear pictures using GO ADVANCED/FILE ATTACHEMENT function.
    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

    • cbriggz
      Member
      • Oct 2012
      • 18
      • USA

      #3
      Re: 42" LG no backlights

      what should i take pictures of? all the boards? the back of the unit is off already.

      Comment

      • budm
        Badcaps Legend
        • Feb 2010
        • 40746
        • USA

        #4
        Re: 42" LG no backlights

        The whole back of the TV so we can see how all the boards are connected together, then pictures of each 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

        • cbriggz
          Member
          • Oct 2012
          • 18
          • USA

          #5
          Re: 42" LG no backlights

          ok will do when i get home from work. thanks

          Comment

          • cbriggz
            Member
            • Oct 2012
            • 18
            • USA

            #6
            Re: 42" LG no backlights

            here are some pics
            Attached Files

            Comment

            • cbriggz
              Member
              • Oct 2012
              • 18
              • USA

              #7
              Re: 42" LG no backlights

              can anyone help?

              Comment

              • gilly1984
                Badcaps Veteran
                • Jun 2012
                • 751
                • UK

                #8
                Re: 42" LG no backlights

                Have you checked all the voltages? Be careful not to touch any heatsinks with your hands when it is plugged in.
                Do NOT touch heatsinks when testing for voltages as they may be LIVE!

                Comment

                • cbriggz
                  Member
                  • Oct 2012
                  • 18
                  • USA

                  #9
                  Re: 42" LG no backlights

                  i am new to this so not too sure where to begin checking the voltages. There is power at the main board and i see there is power to the board where you plug the components into(there is a little green light that is on). I have looked at the master and slave inverters and cannot see anything burnt or shorted out.

                  Comment

                  • gilly1984
                    Badcaps Veteran
                    • Jun 2012
                    • 751
                    • UK

                    #10
                    Re: 42" LG no backlights

                    Is the voltages marked on the board near these wires? (Circled)

                    If so, switch tv on and test all voltages.
                    Attached Files
                    Do NOT touch heatsinks when testing for voltages as they may be LIVE!

                    Comment

                    • cbriggz
                      Member
                      • Oct 2012
                      • 18
                      • USA

                      #11
                      Re: 42" LG no backlights

                      not sure will check when i get home and repost thanks again. If so how do i go about testing the voltage on these?

                      Comment

                      • gilly1984
                        Badcaps Veteran
                        • Jun 2012
                        • 751
                        • UK

                        #12
                        Re: 42" LG no backlights

                        Originally posted by cbriggz
                        not sure will check when i get home and repost thanks again. If so how do i go about testing the voltage on these?
                        Multimeter.

                        Black probe on chassis then check each pin with red probe. The connectors going to the inverters should be half gnd and half 24v, Should tell you on the board.
                        Do NOT touch heatsinks when testing for voltages as they may be LIVE!

                        Comment

                        • cbriggz
                          Member
                          • Oct 2012
                          • 18
                          • USA

                          #13
                          Re: 42" LG no backlights

                          ok thanks

                          Comment

                          • budm
                            Badcaps Legend
                            • Feb 2010
                            • 40746
                            • USA

                            #14
                            Re: 42" LG no backlights

                            Can you check the voltages and fuses as shown, and also good clear pictures of the area I redlined?
                            Attached Files
                            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

                            • cbriggz
                              Member
                              • Oct 2012
                              • 18
                              • USA

                              #15
                              Re: 42" LG no backlights

                              i will take some close ups of that area tonight. i was looking for a small black fuse but didnt see one. will post later thanks!!!!

                              Comment

                              • cbriggz
                                Member
                                • Oct 2012
                                • 18
                                • USA

                                #16
                                Re: 42" LG no backlights

                                Ok guys sorry it took me so long to repost had a very busy weekend. Had
                                24v coming off the board to the master and slave inverters. I then tested all the fuses and inspected the boards a little closer. Looks like i found the problem.... check this pic out tell me what you think. One of the little black fuses that was labeled Zero just fell off when i moved the board right were it looks burnt.
                                Attached Files

                                Comment

                                • budm
                                  Badcaps Legend
                                  • Feb 2010
                                  • 40746
                                  • USA

                                  #17
                                  Re: 42" LG no backlights

                                  Can I see the front side closed up of that section to see what that connections are for?
                                  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

                                  • cbriggz
                                    Member
                                    • Oct 2012
                                    • 18
                                    • USA

                                    #18
                                    Re: 42" LG no backlights

                                    here is the area that you are looking at on the front side.
                                    Attached Files
                                    Last edited by cbriggz; 10-23-2012, 09:42 AM.

                                    Comment

                                    • jetadm123
                                      Badcaps Legend
                                      • Feb 2010
                                      • 2169

                                      #19
                                      Re: 42" LG no backlights

                                      Fuses are usually identified with an "F". The component that fell off is identified with "JP", which usually indicates a jumper. The "0" stamped on the component indicates zero ohms, which is the same as having a jumper wire across the two points. What's the resistance reading of the component that fell off?

                                      Comment

                                      • budm
                                        Badcaps Legend
                                        • Feb 2010
                                        • 40746
                                        • USA

                                        #20
                                        Re: 42" LG no backlights

                                        The jumper that burnt up can be due to shorted load (MOSFET, Transformers, etc) or it has cold solder joints (lots of current flows through these jumpers).
                                        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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