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Panasonic TX-48CX400B 50" (Vestel) - Damaged COF's? Repair Possible?

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    #1

    Panasonic TX-48CX400B 50" (Vestel) - Damaged COF's? Repair Possible?

    Hi All,

    I was gifted a 50" Panasonic (Vestel Version) LCD, which the previous owner had disassembled and gave to me completely in parts, which had some failed backlight LED's.
    I replaced the LED's and got it working, but found some issues with the picture which I have never experienced before.

    Having looked on YouTube and various forums, it seems that one of the COF gate drivers has failed.
    None appear overheated or physically damaged, but if the gate drivers on the left side of the panel are touched with a bare hand while the set is on, the picture disappears. The gate drivers on the right don't give an issue if touched.

    The attached pictures show the issue I have; basically the picture is dark on the left side, and the data on the left side is in "slow motion", i.e. the picture remains longer on the screen than it should, giving a slow motion effect.
    There are also vertical blank lines at various points and the top of the picture appears "in reverse", which is more noticeable when text is displayed.

    I have read that fully removing the gate drivers from the side of the glass LCD can revive the picture, sometimes only temporarily, but that was with a Sharp TV, where the COF gate drivers were connected to the driver boards on the bottom edge of the screen.
    These gate drivers are connected only to the glass screen.

    Can I gauge opinion if I should remove ALL the gate drivers from the left side (viewed from the front) of the LCD to fix the issue, even if only a temporary fix?

    Thanks in advance

    Russ
    Attached Files
    Last edited by SMDFlea; 10-23-2021, 03:19 PM. Reason: TX-48CX400B
    Tags: None
    #2
    Re: Panasonic 50" (Vestel) - Damaged COF's? Repair Possible?

    Edit:
    There are Horizontal lines, not vertical lines as I previously stated.

    I have tried disconnecting the two ribbons (one at a time) which drive the two separate edge connection PCB's which attach to the bottom on the LCD panel, but this results in no picture at all if either are disconnected. I expected an image on half the screen.

    Comment

      #3
      Re: Panasonic 50" (Vestel) - Damaged COF's? Repair Possible?

      Model number is TX-48CX400B

      Here is a picture of one of the gate driver COF's

      Forgot to add that have already replaced the T-Con board with no improvement in symptoms.
      Attached Files
      Last edited by Russ17; 10-22-2021, 12:34 PM.

      Comment

        #4
        Re: Panasonic 50" (Vestel) - Damaged COF's? Repair Possible?

        Hi, my cousin's Samsung TV 55" that he gave to me for free has got the same behaviour, after many minutes of study i have noticed that by slightly bent the screen the Image improves much or worsen respectively, i was noticing if i remember that a little presssure on the side cof zone changes the Image, i think that there is a possibility that the cof is slightly desoldered by the tab, so a cure can be possibly to pass the soldering iron tip on to the soldering side of the cof. Please give me an useful info, is there a Samsung sticker on the panel chassis?
        Last edited by Davi.p; 10-22-2021, 05:47 PM.

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          #5
          Re: Panasonic TX-48CX400B 50" (Vestel) - Damaged COF's? Repair Possible?

          I have tried flexing the COF's on both sides of the LCD (8 on each side). touching some cause the picture to disappear. The only way to recover the picture is the to power off and then on again.
          I tried gently flexing the screen, but this made no different to the picture.

          One of the COF's ribbons has been bent and has a crease in the ribbon, maybe causing a break in one of the fine tracks - touching this one regularly causes the picture to go off.
          None of the COF's get hot, even after 30 minutes running - they are all about the same temperature - just a little warm.

          The screen is likely a Samsung as the T-Con has a Samsung Chip on it.

          The screen type label on the inside of the TV is shown in the attachment.

          Is it possible to isolate the signals that feed these COF's to see if removing the signal to the suspect COF will remove the issue?

          I have seen this done using tape on the ribbon from the T-Con to the LCD edge driver PCB's, to isolate the clock lines from the T-Con, and this sometimes improves the picture, but after studying the T-Con, I cannot work out which lines to isolate.

          Any suggestions gratefully received
          Attached Files

          Comment

            #6
            Re: Panasonic TX-48CX400B 50" (Vestel) - Damaged COF's? Repair Possible?

            No i think the clock signals must not be touched because here i think there's possibly an interruption of signals, not a damage of the cof chip, so i don't know what it means crease, if it means a scuff mark or scratch so the traces must be restored. Strangely LCD is marked Vestel but i know Vestel does not produce screens.. those traces can maybe fixed with needle tip and silver paint. For side cofs you mean those on vertical side right?

            Comment

              #7
              Re: Panasonic TX-48CX400B 50" (Vestel) - Damaged COF's? Repair Possible?

              I have attached some pictures of the "damaged" COF.

              The film has been bent (this is a crease), which "may" have broken a track or two.

              Would removing this one COF make the COF on the other side of the screen do the work? I have read that the COF's "share" the job of addressing and that the panel would still work with just one COF for each particular horizontal row of pixels.

              These are the side COF's - there are 8 on each side. I have seen where people have removed them, when one is shorted, which causes bad picture like I am getting. I assume the COF receives it signals through the LCD itself, as they are not connected to a PCB externally.
              Attached Files

              Comment

                #8
                Re: Panasonic TX-48CX400B 50" (Vestel) - Damaged COF's? Repair Possible?

                Yes it really has not a good wax like we say in Italy, that means is not in good shape; removing the cof is not the best way for me, or better it is a risk, then maybe you can try to disable the cof by covering some pins in the thruth, but not clock ones, so search in the tcon for a testpoint called STVP or STV or VCST and cover it on the faulty cof side direction..
                if it will not work try cover together VGL, VGH , plus the pevious, if isn't enough trace the 3,3v or 1,8v to the panel distribution board and to the far side cut it where it enters trough the external traces of the last tab..
                Last edited by Davi.p; 10-24-2021, 03:27 PM.

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                  #9
                  Re: Panasonic TX-48CX400B 50" (Vestel) - Damaged COF's? Repair Possible?

                  So on the T-Con, we have STV1 and STV2. They both go to the PCB that is on the right side of the screen (when viewed from the front). The damaged COF is on the left of the screen.
                  I will try to isolate them both and report back.

                  I don't see a VGL or VGH - I see a VCS1 & VCS2 could they be worth isolating? These two lines go to the PCB for the left side of the LCD.
                  Attached Files

                  Comment

                    #10
                    Re: Panasonic TX-48CX400B 50" (Vestel) - Damaged COF's? Repair Possible?

                    If you use continuity mode of multimeter you'll see that both VCST and STV are present on both connectors so block both , all 4 (1&2) in the bad side and see the result..

                    Comment

                      #11
                      Re: Panasonic TX-48CX400B 50" (Vestel) - Damaged COF's? Repair Possible?

                      I did find that the signals STV1, STV2, VC1 & VC2 go through both ribbons, as you stated.

                      I isolated the the tracks for the left side of the screen, but the result was not conclusive.

                      See attachment.
                      Attached Files

                      Comment

                        #12
                        Re: Panasonic TX-48CX400B 50" (Vestel) - Damaged COF's? Repair Possible?

                        Follow the other options i have told previously..

                        Comment

                          #13
                          Panel issue

                          Hi everyone

                          I have 50" LED TV hisense that burn 101 smd resistor on the picture panel, anyone to assist?

                          Comment

                            #14
                            Re: Panasonic TX-48CX400B 50" (Vestel) - Damaged COF's? Repair Possible?

                            what the hell means to resume this thread? open your own one..

                            Comment

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