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LG 42LG3000 LCD TV Fault Finding.

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    #1

    LG 42LG3000 LCD TV Fault Finding.

    Hi Badcaps, great forum, incredibly helpful members and hopefully kind enough to lend a hand with this TV I'm having problems with.
    Searched the forum and found similar issues with no definitive answer, so had to create a new thread.
    I am new and only repaired a couple of sets in the past, so please go easy and have some patience with me. Thanks.

    Took my 42LG3000 apart in the lounge and trying to suss out the faulty board.

    Here is a video of the symptoms...
    http://www.youtube.com/watch?v=LCWH8EON5j8

    It can't really be seen in the video, but after the backlight flashes, the LED light on the right is a steady faint blue, so power still remains. I'm not sure of what the LED colours are meant to be when operational as I've only just acquired the set 'as is'.

    At first I suspected the Invertor boards. Disconnected them and tried the TV. LED remains faint blue.
    Next, disconnected TCon board. Same thing. LED remains faint blue.

    Only boards left are the PSU and the mainboard. The mainboard controls the LED so from here I'm a little stumped. All Capacitors appear in good shape, although I do not know for certain.

    Anyone willing to lend some experience on how to test the boards or advise what I'm doing wrong or even to just take the mickey because I've done it all completely wrong?

    As recommended, here are the images of the inside of the set and the boards. Not shot the TConn Board yet, still covered over with the plate.

    Photo's on Dropbox -
    https://www.dropbox.com/sh/1wope3wgily61mh/JIPb_JyU8b
    Tried embedding them, but didn't work.
    More available on request.

    Opinions on another forum point towards the PSU, but I'm not sure as it powers on and stays on. So thought I'd 'Ask the Experts'.

    Will post all findings and results in here to help any other members in the future needing assistance with this Telebox.
    Last edited by DejaVu; 09-16-2013, 12:00 PM. Reason: Typos. I do it a lot! :D
    Tags: None
    #2
    Re: LG 42LG3000 LCD TV Fault Finding.

    First thing I would check is the resistance on each coil of the backlight transformers. See if they are the same. Use a mutimeter on Ohms, Next check would be the output voltages on the power supply- most of the time the values are written on the board next to the connectors.
    Liberating magic smoke one part at a time

    Comment

      #3
      Re: LG 42LG3000 LCD TV Fault Finding.

      Just used a multimeter on the PSU outputs of 5v and 12v.

      5v reports 5.13v.
      12v reports nothing at all.

      Seems the PSU is at fault then? Is it worth fault finding and replacing components or better to just replace the board?

      Comment

        #4
        Re: LG 42LG3000 LCD TV Fault Finding.

        Check the PS ON signal from main board is turning on first, if it does not send that signal 12V will not come up.
        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

          #5
          Re: LG 42LG3000 LCD TV Fault Finding.

          Forgive my n00bness tom66, but how might I go about doing that with this board? I'm guessing you mean this one?

          https://www.dropbox.com/sh/1wope3wgi...2017.13.15.jpg

          From what I understand, what you're saying is, the mainboard is checked using 5v - perhaps for Standby, if everything checks out and the power button is pressed, the mainboard tells the PSU to fire up the 12v to power the backlight. If the mainboard is failing to tell the PSU (or the PSU is failing to provide 12v) to fire up, it wouldn't be there... hence why the screen is going off - although the backlight does fire up, but goes out within a blink of an eye.
          Last edited by DejaVu; 09-16-2013, 05:23 PM.

          Comment

            #6
            Re: LG 42LG3000 LCD TV Fault Finding.

            You are looking for a pin tagged ps on or bl on to test for the signal turning on the power supply. Try having your test probes on the 12v and get it when the back lights flash on. Usually if they come on then extinguish the inverters are at fault, but could be power supply, main or bulbs too. BTW the link is to an empty folder
            Liberating magic smoke one part at a time

            Comment

              #7
              Re: LG 42LG3000 LCD TV Fault Finding.

              Hunted all round both boards and found this on the PSU. It's about as close as I can find.

              https://www.dropbox.com/s/6vw3ehayll...2019.34.41.jpg

              I'm guessing its the third pin from the left at the top marked ON/OFF. Is this the one that would be activate 12v?

              I'm thinking I'll have to wrap a small wire around it, replace the connector and test it with the multimeter. This is the same connector that powers the Mainboard and looks to be the only one that does.

              Comment

                #8
                Re: LG 42LG3000 LCD TV Fault Finding.

                Been checking pins today following this thread https://www.badcaps.net/forum/showthread.php?t=20824 - which has excellent descriptions of what to do and how! Checked the Invertor fuses, both have continuity.

                Then I got to the part of '24v to the Invertor boards' and while everything is connected (and in what would be standby mode) I get nothing, nuda, zip. I've checked the 24v on the actual PSU and doesn't seem to be there either.
                https://www.badcaps.net/forum/showth...937#post241937

                What does this mean?
                Is the TV waiting to be taken out of Standby before it feeds 24v to the Inverter Boards or should that be there already?
                Or is the PSU screwed?

                Originally posted by Caleb View Post
                You are looking for a pin tagged ps on or bl on to test for the signal turning on the power supply. Try having your test probes on the 12v and get it when the back lights flash on. Usually if they come on then extinguish the inverters are at fault, but could be power supply, main or bulbs too. BTW the link is to an empty folder
                Still looking for this, but I'm going to try and see if I can get 24v from the Fuse on the Invertor board to the Chassis when the LCD Panel switches on. Is it OK to do this?
                Last edited by DejaVu; 09-23-2013, 08:02 AM.

                Comment

                  #9
                  Re: LG 42LG3000 LCD TV Fault Finding.

                  The 12v/24v power supply section is turn on by the Main board, the signal is typically called PS_ON. That is the pin on the power supply board you need to find out if it is receiving the turn on signal from the main board or not, PS_ON is typically about 2~5vdc. Please read my Basic LCD TV troubleshooting guide.
                  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

                    #10
                    Re: LG 42LG3000 LCD TV Fault Finding.

                    Great guide and explained a ton!
                    But this is why I'm getting a little lost because PS_ON and BL_ON doesn't seem to exist on this board.

                    I *think* I've got it in this picture and I'm guessing it's the ON/OFF (24v?) pin I should be looking at?

                    Also got something called BRI there too (Somesort of Bridge?)
                    As well as INV_ON... which is quite obvious now I've thought about it! = BL_ON I guess?
                    AND Power_On also lives there too!

                    https://www.dropbox.com/s/6uksajpon0...2016.06.56.jpg

                    Confusion!
                    Last edited by DejaVu; 09-23-2013, 09:13 AM.

                    Comment

                      #11
                      Re: LG 42LG3000 LCD TV Fault Finding.

                      If you trace the inverter on around and down it goes to the on/off pin, then right next to it is the power on which = ps on. You will want to test both and see if they are receiving a signal from the main board to turn on, as Budm said somewhere between 2-5v. If you are not receiving the signal you can force on the power supply by putting a 1k resistor between the 5v pin and the power on, same thing for the inverter on signal.
                      Liberating magic smoke one part at a time

                      Comment

                        #12
                        Re: LG 42LG3000 LCD TV Fault Finding.

                        The on/off turns the Power supply (12 and 24V) on. the inv on is the same as BL on.

                        Comment

                          #13
                          Re: LG 42LG3000 LCD TV Fault Finding.

                          Aha, after turning on (and the backlight flickers and the LED goes a faint Blue)
                          All voltages are as they should be.

                          Invertor boards are receiving 24.2v.
                          12v is pushing out 12.3v
                          5v is pushing out 4.8v

                          Will check what INV_ON is using, but I'm expecting 24v right?

                          -edit
                          Nope. INV_ON is at 4.7v after the backlight flickers.
                          But on 0v before trying to turn it on (Switch at wall and before Remote Power pressed). So I'm guessing that's correct?

                          I'd just like to say, thank you all soooo much for your help with this. Hugely appreciated!

                          This looks to me like it could be the Invertor board's yeah? I've checked the surface mounted fuses and they appear fine.
                          Last edited by DejaVu; 09-23-2013, 10:06 AM.

                          Comment

                            #14
                            Re: LG 42LG3000 LCD TV Fault Finding.

                            OK, the inverter on can be 2~5VDC, so it looks like you have all the correct voltages but there is problem in the inverter board.
                            I cannot see the pictures in your DROPBOX in the earlier post.
                            Which one of these are the inverter boards in your TV?
                            http://www.shopjimmy.com/catalogsear...?q=LG+42LG3000
                            Last edited by budm; 09-23-2013, 10:44 AM.
                            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 42LG3000 LCD TV Fault Finding.

                              I'll take some fresh ones. Not sure what happened to the old ones...

                              Galaxy S3's have a pretty good camera!

                              Master Invertor Board
                              https://www.dropbox.com/s/rra4ivv8xx...2019.18.01.jpg
                              (I've tested F2 and appears OK)

                              Slave Invertor Board
                              https://www.dropbox.com/s/feb1j1emfo...2019.18.17.jpg
                              (I've tested F200 and appears OK)

                              VT71053.50 & VT71053.51
                              Last edited by DejaVu; 09-23-2013, 12:25 PM.

                              Comment

                                #16
                                Re: LG 42LG3000 LCD TV Fault Finding.

                                D'you reckon these need replacing or can they been repaired perhaps?

                                If not, can I replace them with VT71053.54 & VT71053.55 as they seem to be more widely available.
                                Last edited by DejaVu; 09-24-2013, 04:57 AM.

                                Comment

                                  #17
                                  Re: LG 42LG3000 LCD TV Fault Finding.

                                  Have you tested those transformers yet? You want to test primary and secondary sides with ohm meter and see if they are the same (pins marked 9 and 12 are secondary) Unless you happen to have a ring tester handy?
                                  Liberating magic smoke one part at a time

                                  Comment

                                    #18
                                    Re: LG 42LG3000 LCD TV Fault Finding.

                                    Looking back on the thread I referenced earlier, I got an idea what exactly you meant and have probed them.

                                    This is what I get back measured using the DMM on 20k Ohms.

                                    Master -
                                    https://www.dropbox.com/s/dex5ce1ba91gwwk/Master.jpg

                                    Slave -
                                    https://www.dropbox.com/s/9xkzl4i6x32qj0z/Slave.jpg

                                    Both are the same, so I'm hoping it's right?
                                    Looking at them points close up like that makes them look a right mess!
                                    Last edited by DejaVu; 09-24-2013, 01:54 PM.

                                    Comment

                                      #19
                                      Re: LG 42LG3000 LCD TV Fault Finding.

                                      Major update.

                                      Unplugged the Slave and left the Master in.
                                      Turned on the TV.

                                      Stays on and can see 'The Fly' for a around 3 seconds.
                                      Left hand side (Slave's side) is dark, then goes off.

                                      Think the faulty board has been located!! Can it be diagnosed!?

                                      Comment

                                        #20
                                        Re: LG 42LG3000 LCD TV Fault Finding.

                                        Check fuse on it, check for burnt components.
                                        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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