LG 42" Plasma Display Model 42PT350R

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  • angelos
    Badcaps Veteran
    • Dec 2012
    • 567
    • South Africa
    #1

    LG 42" Plasma Display Model 42PT350R

    Hello Guys,

    I am not familiar at all with plasma tv's but i tried my luck anyway since business is so bad. We gotta try, right?
    Anyway, the original problem was a tv clicking and not starting due to a short circuit on the Z-Sustain board (on the right side from the rear).
    I found two transistors shorted (30F123) and changed the gate driver ic's as well. I think they were FAN73711. I soldered for dry joint on power supply, Y-Sustain and Z-sustain. Started up the TV and the short was gone so i had an image but.....
    Lots of colorful speckles on the image and also there seems to be "mal discharge". I keep seeing the previous image on the new image.
    I had color bars been generated via my color bar generator tester and when i went to a white image i could still see the bars bleeding through in the image.
    The white raster is also not right its more patchy and gray. Images to follow
    Tags: None
    • angelos
      Badcaps Veteran
      • Dec 2012
      • 567
      • South Africa
      #2
      This is the board layout.
      Attached Files

        Comment

        • angelos
          Badcaps Veteran
          • Dec 2012
          • 567
          • South Africa
          #3
          Click image for larger version Name: Panel Voltages.jpg Views: 130 Size: 2.09 MB ID: 3264935 Close ups of boards
          Attached Files

            Comment

            • angelos
              Badcaps Veteran
              • Dec 2012
              • 567
              • South Africa
              #4
              Some pictures of the problem
              The white raster is gray and it has the color bars of the previous image
              Attached Files

                Comment

                • angelos
                  Badcaps Veteran
                  • Dec 2012
                  • 567
                  • South Africa
                  #5
                  I just don't know where to measure Vscan and what to use as ground reference. Is chassis ground ok?
                  Vy is ok, Vs and Va is according to panel sticker, some other voltages on Y-SUS also ok according to panel sticker. I think it was a 200V and a 120V. I am at home now so i am recalling from memory. I do have an oscilloscope but don't know what to measure.
                  on Y-SUS +5VF and +15VF measure weird with chassis ground as reference. its not 5V and 15V.
                  I suspect something is wrong on this board, not sure.
                  I did take oscillogram images of the waveform on the buffer board and it looks right, not sure what the peak voltages must be.
                  Specific question might narrow this down.🤭

                    Comment

                    • angelos
                      Badcaps Veteran
                      • Dec 2012
                      • 567
                      • South Africa
                      #6
                      There was a +15V rail that measured 18.2V somewhere there.

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