SyncMaster 740N strange lines

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  • gypsy
    Member
    • Nov 2009
    • 13

    #1

    SyncMaster 740N strange lines

    The backlight had no problems staying on, but I opened it up to look just in case. The PSU looks like this (image reused from another 740N thread):



    Same caps were blown, the infamous CapXons. 25V 820uF, replaced with Nichicon equivalents. The problem, both before and after the replacement, is THIS.

    Every time I power it up, the lines are different/begin in different positions, and are initially bright, then start fading to grey. Also, as you can see (compare the image with the reference on my netbook towards the end), vertical lines are fine and drawn to proportion, the issue seems to be only on horizontal lines (which exhibit the problem and are also out of proportion, the image is beyond stretched). I looked on the controller board and everything *looks* fine (a few chips, a lot of small resistors, and 3-4 small-value caps that look fine). Anyone know where the problem could lie?
    Last edited by gypsy; 11-25-2010, 02:08 PM.
  • retiredcaps
    Badcaps Legend
    • Apr 2010
    • 9271

    #2
    Re: SyncMaster 740N strange lines

    Originally posted by gypsy
    The PSU looks like this (image reused from another 740N thread):
    In the future, please use the manage attachments to insert pictures to threads (but NOT inline).

    Also, we prefer pictures of your particular board. Reusing other peoples pictures is only a last resort (i.e. you have no camera). Reusing someone else's picture, in the context of troubleshooting, is liking asking a surgeon to operate on you using their xrays.

    I looked on the controller board and everything *looks* fine (a few chips, a lot of small resistors, and 3-4 small-value caps that look fine). Anyone know where the problem could lie?
    Get a magnifying glass and check the solder joints on the input port (VGA and/or DVI). If there are no obvious poor joints, reflow them anyways.

    Also check your ribbon cable connections. Clean them and reseat them.
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    If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

    We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

    Please do not post inline and offsite as they slow down the loading of pages.

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    Comment

    • gypsy
      Member
      • Nov 2009
      • 13

      #3
      Re: SyncMaster 740N strange lines

      I reflowed both the VGA and panel connector (pictures taken before this was done) - no improvement. Note that this problem occurs even without a VGA signal, the OSD/no-signal screen exhibits the same issue.

      Apologies for the inline posting. I've taken pictures of all boards, front and back, and attached them properly this time.

      3,4,5 are the actual LCD driver board (attached to the top of the LCD).
      6,9,10 are the power board.
      7,8 are the LCD logic board.
      Attached Files

      Comment

      • Toasty
        Badcaps Legend
        • Jul 2007
        • 4171

        #4
        Re: SyncMaster 740N strange lines

        Looks like a bad panel or TCON. Hope PlainBill or Wizard catch this.

        Toast
        veritas odium parit

        Comment

        • jetadm123
          Badcaps Legend
          • Feb 2010
          • 2169

          #5
          Re: SyncMaster 740N strange lines

          You can also try checking the voltage regulators on the logic card. Bad regulator(s) can cause video problems. There are two on the left side of the board marked APL1117. One has a 3.3V output and I'm not sure what the other is. Measure and report voltages. Also, there seems to be a missing chip in the upper left corner. Did you remove it?

          Comment

          • gypsy
            Member
            • Nov 2009
            • 13

            #6
            Re: SyncMaster 740N strange lines

            The bigger one has 5V in and 1.8V out. The smaller one (right on the edge) has 5V in and 3.3V out. I did not remove anything from the board.

            Comment

            • jetadm123
              Badcaps Legend
              • Feb 2010
              • 2169

              #7
              Re: SyncMaster 740N strange lines

              Originally posted by gypsy
              The bigger one has 5V in and 1.8V out. The smaller one (right on the edge) has 5V in and 3.3V out. I did not remove anything from the board.
              These voltages look to be correct. Just wondering if there's some method to perform a factory reset? Usually, it's holding down a sequence of buttons while powering up the monitor.

              Comment

              • cynz
                New Member
                • Jun 2011
                • 5

                #8
                Re: SyncMaster 740N strange lines

                Originally posted by gypsy
                I reflowed both the VGA and panel connector (pictures taken before this was done) - no improvement. Note that this problem occurs even without a VGA signal, the OSD/no-signal screen exhibits the same issue.

                Apologies for the inline posting. I've taken pictures of all boards, front and back, and attached them properly this time.
                Check out the panel serial no. if it looks like AUxxxxxxx, or LG Samsung made. Mostly, the signal controller chip on the panel has burnt inside. I had the same experience before, by replacing another compatible panel, then it back to normal.

                Comment

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