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Lg 60PV250 / 60PV450 display issue. Can anyone identify?

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    Lg 60PV250 / 60PV450 display issue. Can anyone identify?

    Hi,

    Can anyone identify the cause of the following symptoms?
    Someone suggested I replace the lower Y-buffer but I am interested if there are any other qualified assessments? Have scratched round on the web for a few days and cannot find any other instances of this exact behaviour.

    Initially picture is fine, then some slight blackness appears in the lower 2/5ths of screen after about 4 minutes. As the set 'warms up' this gets worse until it is almost completely black but occasionally flashes through the picture if the frame is bright. The image is still there, just hard to see or overlain with a ghost image.

    Photo's below.. progress from no problem to almost complete blackout after 15 minutes.

    Often then it clears up for a few minutes than then the ghosting/rolling effect starts on the bottom of the screen only











    Example with screen set to full white raster..



    First off I checked and fine tuned all voltages ( VS, VA, -Vy, VSC, VZB) which had minor deviations of a volt or two.
    I dont have an oscilloscope so cannot check waveform.
    I completely removed the lower board Y-drive board (physically) including all ribbon and TCP cables and ran the set for a minute. This was the result:



    Checked the heat of the Ysus board as the issue seems to be heat related.

    One of these heatsinks gets astonishingly hot (see photo). But maybe that is normal?

    Checked the back of the board, no evidence of bad solder joints due to heat, touched up the transistor legs to be sure. Inspected all other components with magnifying glass, no obvious damage.



    At the bottom of the rightmost heatsink is a mosfet? which I suspect is the source of most of the heat on that heatsink as the board is much browner around it's legs than the other transistors along the line which are of a different type.

    The chip is stamped as K8A60DA 1:8



    I only have a 30w soldering iron, so I know it would be nigh impossible to get that line of chips on the heatsink out for testing.
    There is a chance I could get it off the heatsink in-situ and then de solder it, but will only attempt this if this sort of chip has a high probability of causing the effect I described.
    Apart from that the only observation I can make is a buzzing from the ysus board that corresponds to the lower half flickering but I guess that is only to be expected as signal frequency cuts in and out?

    Put is all back together and it is back to it's old behaviour - after a couple of minutes the bottom 2/5ths start flickering and it gets darker/worse with occasional brief flickers of clarity.

    I tried running a fan blowing cool air over the various components/boards to see if there was any effect of cooling on the symptom.

    To my surprise cooling components with air did not appear to have any effect so now I am starting to doubt whether it is heat related even though the problem only starts after 5 minutes or so.

    Starts off with an increasing darker section on the bottom of the screen, eventually it goes almost completely black, then after a few minutes is lightens up again but then there is this ghosting/duplication problem as demonstrated in this video - this is the second phase and more permanent problem once the set has been running for 20 minutes or so.

    ---- >>> View My Video <<< ---

    i still have no idea which board is the culprit.

    #2
    Re: Lg 60PV250 / 60PV450 display issue. Can anyone identify?

    I would be looking at the lower Y-buffer as well. What you can try is to heat up the lower Y-buffer with a hairdryer to see if you can make the problem occur quicker, as it will be heat that is causing the issue. If this works, then the lower Y-buffer is likely the fault. The Y-buffers usually aren't repairable parts; just replace them. In your case you only need to replace the lower board.
    Last edited by tom66; 06-25-2013, 12:29 AM.
    Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
    For service manual, schematic, boardview (board view), datasheet, cad - use our search.

    Comment


      #3
      Re: Lg 60PV250 / 60PV450 display issue. Can anyone identify?

      tom66, That was a very clever idea!

      I had tried cooling them down after the set was on but I had not thought of warming them up when the set was cold prior to turning it on.

      I tried that alternately with both the upper and lower boards and when the lower board was pre-heated the problem was pretty much from the get-go.

      Thanks for that great idea. It has put my mind at ease and now I am pretty confident that the lower Y buffer board is the board that needs replacement.

      One last question: All of these boards: Ysus and upper/lower buffer boards have a revision letter in addition to the part number. Is it important when replacing only a single board that that revision letter (in this case "J" ) is the same?

      If it is not important, can the board be replaced with both earlier and later revision letters for that part number?

      >>

      Another question: I was thinking of adding a 5v DC input filtered fan near the ysus board and driving it of the 5v ysus supply. so when the set powers up that board gets cooling. Is that a stupid idea? If not, should I place a capacitor of some value in-line to smooth any feedback to the circuit?
      Last edited by pnb; 06-25-2013, 06:17 AM. Reason: addendum

      Comment


        #4
        Re: Lg 60PV250 / 60PV450 display issue. Can anyone identify?

        It's best to replace them from the same revision, but there shouldn't be any issues if the particular board is used with the same Y-sustain board and all connectors are the same.

        A fan is not a bad idea, 12V or 5V can work. For best effect, place it at the top of the set, above the Y-sustain. It can pull air through the heatsinks that is already naturally rising.
        Last edited by tom66; 06-25-2013, 06:36 AM.
        Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
        For service manual, schematic, boardview (board view), datasheet, cad - use our search.

        Comment


          #5
          Re: Lg 60PV250 / 60PV450 display issue. Can anyone identify?

          Hi Tom66,

          Still waiting for the replacement board for this. I could not find a revision J so I had to get a board with a different revision (same part number) so they will be mismatched but hopefully it wont do further damage.

          I was wondering about buying a basic oscilloscope to check the ysus waveform, but I see it is a highly technical area and it seems it is easy to purchase the wrong equipment if one knows nothing about them, as I do..
          I dont want to fork out a couple of hundred for a peice of test equipment which will see little use elsewhere, so I was wondering: are any of the following viable for use in troubleshooting plasmas?

          http://www.ebay.com.au/itm/2-Channel...item3f1ed2bd62

          http://www.ebay.com.au/itm/New-Mini-...item51a939ce8c

          http://www.ebay.com.au/itm/Au-Stock-...item20d000c93e

          http://www.ebay.com.au/itm/Hantek-60...item2ec8bd91b1

          Comment


            #6
            Re: Lg 60PV250 / 60PV450 display issue. Can anyone identify?

            None are suitable. They are toys. A good, used, analog scope with 20MHz bandwidth or greater is suitable, and can be picked up for less than $50.
            Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
            For service manual, schematic, boardview (board view), datasheet, cad - use our search.

            Comment


              #7
              Re: Lg 60PV250 / 60PV450 display issue. Can anyone identify?

              The replacement lower buffer card arrived this morning and this has fixed the above problem. Thanks for your help with this Tom66. Specifically that idea to pre-heat the card to identify the faulty card was a good one and gave me peace of mind that the component I ordered was the correct card to be replacing. LG wanted $350 for that card brand new but I told them where they could put that and picked one up from salvage!

              Thanks for looking at those toy scopes, I will keep an eye out on the 2nd hand market for something better but I am a little remote so it might take a while.
              Can see this could be an enjoyable hobby, so I am keeping an eye out for another TV to try to save from the tip.

              Comment


                #8
                Re: Lg 60PV250 / 60PV450 display issue. Can anyone identify?

                Glad to hear it's working. Enjoy your TV.
                Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                Comment

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