lg 50pa650t no picture

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  • thuss
    Badcaps Veteran
    • Jul 2012
    • 317
    • uk

    #1

    lg 50pa650t no picture

    Hi

    My mates tv went on the blink its a lg 50pa650t.

    The tv comes on but no picture. The voltages seem fine

    I have removed the upper buffer board but still no picture.

    I have read in various threads that it could be damaged screen ribbons.I cant find any evidence of this.

    Any ideas could it be both buffers and y sus gone?

    thanks in advance for any help.
  • rccrasher65
    Badcaps Veteran
    • Mar 2014
    • 591
    • United States

    #2
    Re: lg 50pa650t no picture

    Check your voltages with a Digital volt meter. check VS and VA. Then check VSC. on y sus to see if they are to the panel label specs.

    Comment

    • thuss
      Badcaps Veteran
      • Jul 2012
      • 317
      • uk

      #3
      Re: lg 50pa650t no picture

      I got the following voltages va 53, nc 206, vs 206, and on the vsc with the buffer boards removed I get 2.5v, vy 2.2.

      I assume the ysus is blown?
      Last edited by thuss; 09-07-2014, 07:02 PM.

      Comment

      • thuss
        Badcaps Veteran
        • Jul 2012
        • 317
        • uk

        #4
        Re: lg 50pa650t no picture

        Sorry I rechecked the ysus voltages on the resistors and I get the following vsc+282, vsc-132 on the vy+321.9, vy-132.1 I think the ysus is ok? (Thats with the buffer boards disconnected)
        Last edited by thuss; 09-07-2014, 07:02 PM.

        Comment

        • RCA2000
          Senior Member
          • Sep 2014
          • 111
          • USA

          #5
          Re: lg 50pa650t no picture

          Originally posted by thuss
          I got the following voltages va 53, nc 206, vs 206, and on the vsc with the buffer boards removed I get 2.5v, vy 2.2.

          I assume the ysus is blown?
          Remember--you must measure VY and VSC to FLOATING ground, IIRC--VY--190v. or so-- is usually measured across a resistor. If it is low- with the buffers connected--it is VERY likely one of the buffers is bad.. If still low with then unhooked--Sustain board problem.

          Comment

          • thuss
            Badcaps Veteran
            • Jul 2012
            • 317
            • uk

            #6
            Re: lg 50pa650t no picture

            Sorry I dont really know what you mean by a floating ground? But I did get the following reading across a resistor i.e vsc+282, vsc-132 the following readings across a second vy+321.9, vy-132

            Comment

            • RCA2000
              Senior Member
              • Sep 2014
              • 111
              • USA

              #7
              Re: lg 50pa650t no picture

              PLasma tv sets use a "floating ground" supply--for some voltages that drive the panel. They are generated from the Y-sustain board--right on it. These drive the buffers.

              I need to see a picture of the Y sustain board up close--and I can guide you on the floating ground test.

              Comment

              • thuss
                Badcaps Veteran
                • Jul 2012
                • 317
                • uk

                #8
                Re: lg 50pa650t no picture

                one more question if anybody can help the VZB = 149.8 V (Measured at R412) on the z sustain board on the one side of the (-)resistor I'm getting a reading of 0 whilst the on the vzb+ i'm getting a reading of 149.8 is that to be expected?

                Comment

                • tom66
                  EVs Rule
                  • Apr 2011
                  • 32560
                  • UK

                  #9
                  Re: lg 50pa650t no picture

                  Yes. (On LG all panel voltages are measured across a marked component, red lead one end, black the other)

                  The Vscan (Vsc) is relative to the -Vy base, but measuring across resistor takes this into a account (on an LG at least)

                  Vsc is scan supply for buffer boards. If this is low with both buffers removed the y-sus may be bad.
                  Last edited by tom66; 09-08-2014, 01:31 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

                  • thuss
                    Badcaps Veteran
                    • Jul 2012
                    • 317
                    • uk

                    #10
                    Re: lg 50pa650t no picture

                    I have read the resistors incorrectly. I used the chassis of the tv for my black probe and then with the red probe I touched the resistors and read the voltages.

                    I thought it was never a good idea to have the black probe and red probe on either side of the same component I will try again Thanks

                    Comment

                    • tom66
                      EVs Rule
                      • Apr 2011
                      • 32560
                      • UK

                      #11
                      Re: lg 50pa650t no picture

                      Originally posted by thuss
                      I thought it was never a good idea to have the black probe and red probe on either side of the same component I will try again Thanks
                      No, just a different way of testing useful for some types of components.
                      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

                      • thuss
                        Badcaps Veteran
                        • Jul 2012
                        • 317
                        • uk

                        #12
                        Re: lg 50pa650t no picture

                        sorry about late reply I have done what Tom66 has suggested and I get the following with everything connected i get vzb(z sus) 137v, vsc 140 and -vy 190.

                        But when I disconnect the ysus I get vzb 150, vsc 150 and -vy 190.

                        I have changed the buffer boards but still get no picture do you think its the screen? The buffers are new.

                        I dont get any glow or anything on the screen . But when I disconnect the ysus the tv led light works as it suppose to and responds as it should.

                        But when I reconnect the ysus the tv tries to stay on but after a few second goes back onto standby.

                        Also when I disconnect the upper buffer I still do not get half a picture. could it be the tcon board? any help would be appreciated

                        Comment

                        • tom66
                          EVs Rule
                          • Apr 2011
                          • 32560
                          • UK

                          #13
                          Re: lg 50pa650t no picture

                          Did you check -Vy and Vsc on your new board and compare them to readings before, also test them with and without buffers installed.
                          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

                          • thuss
                            Badcaps Veteran
                            • Jul 2012
                            • 317
                            • uk

                            #14
                            Re: lg 50pa650t no picture

                            Yes sort of. The old y sus had the same readings more or less (+- 5 volts). But when I attached my old buffers the voltage would drastically reduce but when I remove the old buffers the voltage would come back, I suppose one possibility both ysus boards are faulty or screens faulty?

                            Comment

                            • tom66
                              EVs Rule
                              • Apr 2011
                              • 32560
                              • UK

                              #15
                              Re: lg 50pa650t no picture

                              Can you perform this test on your buffer boards?
                              https://www.youtube.com/watch?v=51SZ...Y&noredirect=1
                              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

                              • thuss
                                Badcaps Veteran
                                • Jul 2012
                                • 317
                                • uk

                                #16
                                Re: lg 50pa650t no picture

                                yes I did this before I installed them I was getting no beeps I will check again thanks maybe not so new boards

                                Comment

                                • thuss
                                  Badcaps Veteran
                                  • Jul 2012
                                  • 317
                                  • uk

                                  #17
                                  Re: lg 50pa650t no picture

                                  yes I did do the tests again as per the above link that you posted. Just to get any beeps on continuity I had to 60 M ohms.(there was no continuous beep on any connector block)

                                  strange I'm getting beeps all down the 4 connector blocks but I have read its usually the top chip that blows

                                  Comment

                                  • thuss
                                    Badcaps Veteran
                                    • Jul 2012
                                    • 317
                                    • uk

                                    #18
                                    Re: lg 50pa650t no picture

                                    I thought I let you know the ysus was playing up even though the voltages on the resistors were within range.

                                    I replaced the upper buffer tv works fine apart from one black horizontal 1/2mm thick line across screen in line with the top chip, top buffer board.

                                    Comment

                                    • tom66
                                      EVs Rule
                                      • Apr 2011
                                      • 32560
                                      • UK

                                      #19
                                      Re: lg 50pa650t no picture

                                      Originally posted by thuss
                                      I replaced the upper buffer tv works fine apart from one black horizontal 1/2mm thick line across screen in line with the top chip, top buffer board.
                                      So, bad panel.
                                      The TV will stop working soon as the buffer chip will be over stressed. You will find the buffer board blown again.
                                      Sorry, don't think it can be fixed.
                                      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

                                      • Alastair E
                                        Chief Womble
                                        • Mar 2013
                                        • 1963
                                        • U.K.

                                        #20
                                        Re: lg 50pa650t no picture

                                        Not always a bad panel where just 1 row of pixels out....

                                        I had a Samsung 50" just recently. It was the actual plug where the ribbon attaches. The connection in the plug was damaged and a very careful 're-alignment' (Bending) completely cured the problem...

                                        Check carefully with a magnifying-glass all the connections on that plug and even follow the dead pixel line from the pixel line along the glass through to the orange mylar and then into the plug/buffer-board...

                                        A Break in the panel or the mylar orange tab conductor will be easily seen as a black/burned or injured spot on the conductor affected.

                                        You'll have to de-case the panel to check properly, suggest you draw a line on the panel with chinagraph pencil while set de-cased and on, so as to see which line the affected one is while set is off, and safe to closer examine.....

                                        --It worked for me tracing out that 50" samsung....
                                        TELEFIX

                                        How PLASMA SCREENS WORK, X-SUS and Y-SUS what they do--
                                        http://www.irf.com/technical-info/appnotes/an-1088.pdf
                                        PLEASE DO NOT EMAIL ME PRIVATELY FOR REPAIR ADVICE. QUESTIONS BELONG ON THE FORUM!

                                        Comment

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