LG 43UF640V backlight good but black screen and no sound

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  • totof
    Senior Member
    • Feb 2017
    • 157
    • france

    #1

    LG 43UF640V backlight good but black screen and no sound

    Good morning.
    I have a problem with my LG Smart 43UF640V TV. It starts, the backlight comes on but nothing is displayed on the screen and there is no sound.
    I thought it was a TCon problem and ran various tests. If I disconnect one or the other of the cables from the tcon to the panel then the screen is white on the side where the cable is disconnected and black on the other side. If the two cables are disconnected the screen is completely black.
    In the 4 configurations I measure exactly the same voltages on the tcon card (model V15 43UHD TM120 Ver0.4) :

    HVDD : 7,28 V
    VGL1 : -4,99 V
    VGL2 : -9,96V
    VCOM1 : 5,71V
    VCOM2 : 5,69V
    VGH_ODD and VGH_EVEN : switch between 27,96V and -9,94V
    VDD : 14,45V
    VCORE : 1,21V
    VCC18 : 1,8V

    These voltages seem correct to me and so I don't know if the problem could be the panel, the tcon or the motherboard. Do you have any advice to help me with my research ?

    Thanks
    Attached Files
    Last edited by totof; 04-14-2024, 12:26 AM.
  • Bholu
    Member
    • Feb 2024
    • 48
    • Saudi Arabia

    #2
    hello friend this fault comes with y line shorting u need to locate ckv ckv1 ckvb ckvb2 stvp points they are always go through right and left source pcb to the glass.first cut right side if picture ok then good or picture is not good you need to jumper them and cut other side lines.try this
    Attached Files

    Comment

    • totof
      Senior Member
      • Feb 2017
      • 157
      • france

      #3
      Originally posted by Bholu
      hello friend this fault comes with y line shorting u need to locate ckv ckv1 ckvb ckvb2 stvp points they are always go through right and left source pcb to the glass.first cut right side if picture ok then good or picture is not good you need to jumper them and cut other side lines.try this
      Thank you Bholu for your help.
      I don't found ckv ckv1 ckvb ckvb2 stvp points but I found service manual for my TV and signal name are different (see the attached document).
      Attached Files

      Comment

      • Bholu
        Member
        • Feb 2024
        • 48
        • Saudi Arabia

        #4
        These are the ckv lins first of all block right side then try left side check it one by one with the help of cello tape.
        Attached Files

        Comment

        • totof
          Senior Member
          • Feb 2017
          • 157
          • france

          #5
          I blocked all CLK signals, one by one, on each left and right side, and screen remains always with no video.
          Just to notice that for CLK4 signal half of the screen is black deep.

          Comment

          • totof
            Senior Member
            • Feb 2017
            • 157
            • france

            #6
            Is somebody has another idea to help me to determine the origine of the problem ?

            Comment

            • Diah
              Badcaps Legend
              • Feb 2013
              • 6343
              • Germany

              #7
              try replace t-con incase only you have sound

              if no sound then the issue at maunboards
              Last edited by Diah; 04-15-2024, 02:25 PM.

              Comment

              • totof
                Senior Member
                • Feb 2017
                • 157
                • france

                #8
                Thank you Diah.
                There is no sound and when I disconnect only one nappe between tcon board and lcd panel I have no video, even on the side still connected to the lcd panel.
                I don't know how to check the mainboard. Maybe it can existe a debug port.

                Comment

                • Diah
                  Badcaps Legend
                  • Feb 2013
                  • 6343
                  • Germany

                  #9
                  Originally posted by totof
                  Thank you Diah.
                  There is no sound and when I disconnect only one nappe between tcon board and lcd panel I have no video, even on the side still connected to the lcd panel.
                  I don't know how to check the mainboard. Maybe it can existe a debug port.
                  in general what you did to disconnect half screen and it show for you half white mean communication and panel with t-con are fine..... NO sound mean the fucking mainboards didn't work at all. so no signal to damn T-CON.

                  so why you go to involve with VG and CK... hope you are just testing didn't damage parts.

                  Comment

                  • Diah
                    Badcaps Legend
                    • Feb 2013
                    • 6343
                    • Germany

                    #10
                    Originally posted by Bholu
                    hello friend this fault comes with y line shorting u need to locate ckv ckv1 ckvb ckvb2 stvp points they are always go through right and left source pcb to the glass.first cut right side if picture ok then good or picture is not good you need to jumper them and cut other side lines.try this
                    welcome in this forum... but please DON'T JUDGE WITH OUT EXPLANATION;: SERVICE MANUAL AND SCHISMATIC COVERED THE NET OVER ALL::: HERE NEEDED ADVICE WITH EXPLANATION SO OTHER WILL LEARN AND FOLLOW:

                    Comment

                    • totof
                      Senior Member
                      • Feb 2017
                      • 157
                      • france

                      #11
                      Finally I was wrong and there is sound on the TV.
                      I checked all the resistances and capacitances on the panel PCB and nothing abnormal (no short circuit, 3 resistance values noted: 0 ohm, 30 ohms and 100 ohms).​

                      Comment

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