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LG 25UM58-P backlight works, but no picture and high pictched sound when assembled

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    LG 25UM58-P backlight works, but no picture and high pictched sound when assembled

    So I bought my monitor used (I know it wasn't a good idea), and the day I bought it after some movement the screen went black(only backlight) and I heard a high-pitched noise, but I found out if I grip the bottom-right corner tight it fixes itself (I know this isn't a good sign). I used it for around a half year it showed this problem maybe three or four times always fixed it with the said method. Around a month ago it showed vertical lines repeated and slightly washed-out colors. I tried to fix it with the grip method, but the picture went out and haven't shown anything since then. When I disassembled I tried to re-seat the cables also to have only one cable plugged into the T-CON at a time but no dice. Also interesting fact that the whining only occurs when the t-con's shielding is on which led me to check if there is any mechanical damage, and where I used to grip the monitor the screw-hole looked like the first attachment. Also, I found a (probably) blown-up transistor but I can't identify it based on the markings. Also, I think, I've measured all capacitors on the t-con and I haven't found any shorts.
    Attached Files

    #2
    Re: LG 25UM58-P backlight works, but no picture and high pictched sound when assemble

    Can anyone help?

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      #3
      Re: LG 25UM58-P backlight works, but no picture and high pictched sound when assemble

      That burnt Transistor looks to be for supplying VDD for running the COF.
      I would check the resistance between circuit ground and the VDD test point to see if it shows very low resistance reading or not first.
      Can you read the print on that Transistor (or MOSFET) at all?
      I can see N?HZA?
      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


        #4
        Re: LG 25UM58-P backlight works, but no picture and high pictched sound when assemble

        Check the other similar transistors for a similar number, maybe like Q6
        It might be a si2302cds-t1-e3 mosfet ?
        Last edited by R_J; 01-10-2020, 10:30 PM.

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          #5
          Re: LG 25UM58-P backlight works, but no picture and high pictched sound when assemble

          Vdd to ground resistance is 1.02K
          If I turn on the monitor on VDD I get 0.11V
          I am worried about the looks of that screw-hole, I suspect layers may be touching when the monitor is assembled.
          About the transistor, I suspect the markings are N[maybe 7 or Z]H[maybe 7 or Z]A
          Q6's markings are WYC4

          Comment


            #6
            Re: LG 25UM58-P backlight works, but no picture and high pictched sound when assemble

            I have several of these transistors: https://ebay.us/JnMfTt (IRLML2502). Maybe I shall try these to see if they are suitable replacements?Or shall I order the exact type that you 've suggested?

            Comment


              #7
              Re: LG 25UM58-P backlight works, but no picture and high pictched sound when assemble

              I believe the first 2 letters are the part code, and the others are date and lot codes. On another board, the part appears to be N7.
              Attached Files
              Last edited by will62; 01-11-2020, 03:56 PM.

              Comment


                #8
                Re: LG 25UM58-P backlight works, but no picture and high pictched sound when assemble

                Hi!
                Thanks for everyones help, I've replaced the broken part with an AO3401, panel worked fine until I put back the shielding then the magic smoke escaped again.
                I've done that twice, both times the same result.
                Now I've assembled the monitor without any shielding, and since the stand mount was part of the shielding no stand so the monitor is now mounted via the VESA mounts on the wall, and works fine. The panel is held in place with the integrated clips and via some hot glue for now its good

                Comment


                  #9
                  Re: LG 25UM58-P backlight works, but no picture and high pictched sound when assemble

                  I have the same monitor with the same fault; backlight on, no display and whining sound.

                  For the life of me I cannot open the case. The only part I've managed to remove is the gloss black bezel strip at the bottom of the front view of the unit.

                  I'm digging chunks out the case and have the feeling I'm missing something.

                  Does anyone have experience opening this unit please?

                  Thanks,

                  Comment


                    #10
                    Re: LG 25UM58-P backlight works, but no picture and high pictched sound when assemble

                    Hello, it's been a pain finding this exact thread but my 25UM58 is having the same problem, and if anyone can point me in the right direction to being able to disassemble it, I would be very thankful.

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                      #11
                      Re: LG 25UM58-P backlight works, but no picture and high pictched sound when assemble

                      see if it's similar to these 2 videos: https://www.youtube.com/watch?v=dlMphcRP_Zw

                      https://www.youtube.com/watch?v=ojQ4fzIG0Zk

                      Comment


                        #12
                        Hi

                        made an account just to comment, if you still have the monitor or if anyone else finds this thread from Google, you can follow this video, basically its a design flaw in the monitor and all you need to do is to cover the second shielding (closest to LCD that covers board) with tape or plastic wrap to make sure it can't come into any contact with the LCD board. https://youtu.be/XShvxtLexcg?si

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