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Weird Samsung LN55C750R2FXZA No Picture, Sound OK

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    Weird Samsung LN55C750R2FXZA No Picture, Sound OK

    Hi experts,

    My Samsung TV is having the same issue that most people is having with their TV sets, no video but there is sound. But my issue is also a bit different from other people because at first, it would show curly green lines along the contours of the pictures on the screen, then it will flicker on an off, then finally the picture goes away.

    I have checked the the backlight, it is ok, and there is a "glow" on the screen when the TV is on, but no picture, sound is ok. The funny story is, I had this problem a year ago at about the same time in July, back then, I though it was the T-con board, so I bought a used one from ebay and put it in, but the problem persisted, figuring it wasn't a T-con problem, I put the original T-con back in the TV and the problem magically went away, FOR A YEAR. This July, it happened again with the same problem (see the attached pictures), this time, I thought it was the PSB, so I bought used one and replaced it, same thing, problem still there. So now I am left with the main board. But there is no main board that I can find. A new one from Samsung will cost about 260 and shipping and will take 4-6 weeks for shipping, yikes!

    So I am hoping that some of you experts could help me diagnose my troubled TV, may be down to component level? I had a TV repair guy came to our house to fix it, but even he couldn't help. What is weird is he replaced the T-con board (I think it's a newer version) and it worked for about a day or so, then the same problem happened again. After that, he said he couldn't help with my problem, bummer.

    What I recently found out is that if I unplug the TV for a while or turn off the TV for a long time and turn it on, the pictures would show for a minute or two, the then problem develops again with the curly green lines and flickering image, then lose the picture. Is there a corrupt memory, out of sync crystal, overheating issue that would cause this weird phenomenon to happen? Or is there no fix and I have to get a new main board?

    P.S.: I have searched high and low for this problem with this TV set, but so far the only thing that came up was the power supply board, which is not the same issue I am having.
    Attached Files
    Last edited by badddsamsung; 08-12-2015, 10:42 PM.

    #2
    Re: Weird Samsung LN55C750R2FXZA No Picture, Sound OK

    Since you had success with that before, I'd take all connections and ribbon cables apart and clean them again. Then put it back together and see.

    Comment


      #3
      Re: Weird Samsung LN55C750R2FXZA No Picture, Sound OK

      I have re-seated and cleaned the parts before with electronic contact cleaner, with no luck. So I am pretty sure the problem is not in the T-con board, even changed the T-con board, but the problem quickly returned.
      Like I described originally, if I unplug the power for a while, then the picture will be good initially when I turn it on again, for about a minute or so, then the problem keeps coming back. I am leaning towards the main board but not 100% sure, hopefully it's not the panel itself. Does anybody actually diagnose the main board or am I looking at a new main board from Samsung?

      Comment


        #4
        Re: Weird Samsung LN55C750R2FXZA No Picture, Sound OK

        Also tighten up all the boards mounting screws, it may have poor grounding.
        Never stop learning
        Basic LCD TV and Monitor troubleshooting guides.
        http://www.badcaps.net/forum/showthr...956#post305956

        Voltage Regulator (LDO) testing:
        http://www.badcaps.net/forum/showthr...999#post300999

        Inverter testing using old CFL:
        http://www.badcaps.net/forum/showthr...er+testing+cfl

        Tear down pictures : Hit the ">" Show Albums and stories" on the left side
        http://s807.photobucket.com/user/budm/library/

        TV Factory reset codes listing:
        http://www.badcaps.net/forum/showthread.php?t=24809

        Comment


          #5
          Re: Weird Samsung LN55C750R2FXZA No Picture, Sound OK

          yup, tried that too, have taken it off, and re-tightened all of them, I even tried to cool the board by using fans behind them thinking may be that some components got too hot and may be over-heated. I even replaced some of the small ceramic cooling pads that they place on some of the chips with heat-sinks, but still no luck. They do run kind of hot, about 100 F to 120 F, depending on the chip.

          Comment


            #6
            Re: Weird Samsung LN55C750R2FXZA No Picture, Sound OK

            Am I going in the right direction as far as pin pointing the general area of the problem? Or am I going completely in the wrong direction? Could this be a power inverter problem causing the panel to not function correctly?

            Comment


              #7
              Re: Weird Samsung LN55C750R2FXZA No Picture, Sound OK

              Backlights inverter is for producing lights so you can see the images on the screen, it will not cause distorted images or lines on the screen.
              The pictures you shown looks like it has bad GAMMA Voltages.
              Never stop learning
              Basic LCD TV and Monitor troubleshooting guides.
              http://www.badcaps.net/forum/showthr...956#post305956

              Voltage Regulator (LDO) testing:
              http://www.badcaps.net/forum/showthr...999#post300999

              Inverter testing using old CFL:
              http://www.badcaps.net/forum/showthr...er+testing+cfl

              Tear down pictures : Hit the ">" Show Albums and stories" on the left side
              http://s807.photobucket.com/user/budm/library/

              TV Factory reset codes listing:
              http://www.badcaps.net/forum/showthread.php?t=24809

              Comment


                #8
                Re: Weird Samsung LN55C750R2FXZA No Picture, Sound OK

                If I am guessing correctly, it is the VGMA voltages that is shown on the bottom right of the picture? I measured the voltages from VGMA1 to VGMA18 and they were in descending order. I searched around the forum and found your other posts that described the GAMMA voltage problem so I went ahead and checked those a couple days ago. But I don't have the same chip as the other units that had that problem, and the voltages seem good.

                Here are the voltages:
                VGMA1: 16.77
                VGMA2: 14.17
                VGMA3: 13.40
                VGMA4: 12.87
                VGMA5: 12.44
                VGMA6: 11.99
                VGMA7: 11.58
                VGMA8: 11.24
                VGMA9: 9.12
                VGMA10: 8.11
                VGMA11: 5.95
                VGMA12: 5.63
                VGMA13: 5.21
                VGMA14: 4.77
                VGMA15: 4.35
                VGMA16: 3.81
                VGMA17: 3.04
                VGMA18: 0.48
                Attached Files

                Comment


                  #9
                  Re: Weird Samsung LN55C750R2FXZA No Picture, Sound OK

                  They do not look like they are out of places.
                  Never stop learning
                  Basic LCD TV and Monitor troubleshooting guides.
                  http://www.badcaps.net/forum/showthr...956#post305956

                  Voltage Regulator (LDO) testing:
                  http://www.badcaps.net/forum/showthr...999#post300999

                  Inverter testing using old CFL:
                  http://www.badcaps.net/forum/showthr...er+testing+cfl

                  Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                  http://s807.photobucket.com/user/budm/library/

                  TV Factory reset codes listing:
                  http://www.badcaps.net/forum/showthread.php?t=24809

                  Comment


                    #10
                    Re: Weird Samsung LN55C750R2FXZA No Picture, Sound OK

                    So about half an hour ago I unplugged the the power from the TV and turned it on right now, same thing as described before, it would work for a minute, then the lines/distorted picture, and the the picture comes and goes, but there is a glow on the black screen when it flickers, then the picture completely goes away. I forgot to mention that whenever there is a commercial playing and switches to the next commercial, the black glowing screen flickers too, but it has no picture still, just changes in the brightness of the glow.

                    Comment


                      #11
                      Re: Weird Samsung LN55C750R2FXZA No Picture, Sound OK

                      Originally posted by budm View Post
                      They do not look like they are out of places.
                      I am running out of ideas on what to check next, it's been couple weeks since I looked high and low for a solution.

                      What was really weird was that the problem happened a year ago, then magically "fixed" itself for a year, then the problem comes back to haunt me.

                      Comment


                        #12
                        Re: Weird Samsung LN55C750R2FXZA No Picture, Sound OK

                        If you unplug half the tcon is the image affected?
                        (Obviously you'll lose half the picture but is it affected on half the screen)
                        Reverse the process and the other 50%.

                        Comment


                          #13
                          Re: Weird Samsung LN55C750R2FXZA No Picture, Sound OK

                          I tried that when it was not working (no picture, sound ok) and half the screen was glowing dark and the other half is white, same thing when I switched sides.

                          Comment


                            #14
                            Re: Weird Samsung LN55C750R2FXZA No Picture, Sound OK

                            Did you try replacing the flat connector from Main Bd to T-CON Bd?

                            Comment


                              #15
                              Re: Weird Samsung LN55C750R2FXZA No Picture, Sound OK

                              No, I have not replaced the connectors on either side of the main board to T-con, I tried flexing the boards and there doesn't seem to have any cold solder joints that would make it cause the problem I have now.

                              I inspected the cable connecting the two boards, it seem to be in good condition as well.

                              Comment

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