LG 42PC1DA Plasma Sound but blank screen

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  • LesWoollam
    Senior Member
    • Nov 2012
    • 69
    • United Kingdom

    #1

    LG 42PC1DA Plasma Sound but blank screen

    I have an LG 42PC1DA plasma TV with good sound but a completely blank screen (nothing at all even in a blacked-out room).
    The Y-sus heatsink is warmish but the Z-sus heatsink is cold.
    Voltage measurements are:
    Y-sus VS 180.5v VA 60.1v VSC 120.1v -VY 199.9v 5vdc 4.9v
    Z-sus VS 180.5v VA 60.1v Vzbias 100.2v
    Any ideas??
  • randtek
    Badcaps Veteran
    • Oct 2011
    • 280
    • US

    #2
    Re: LG 42PC1DA Plasma Sound but blank screen

    Here's a trick that may help you. It will immediately tell you if you have a main board problem, or a panel drive board failure.

    1) Unplug the TV from AC.
    2) Disconnect the power supply cable going to the main board at the main board end.
    3)Disconnect the LVDS cable going from the main to the Digital board.
    5) On the digital board find 2 test point holes, probably labeled "Ext. Gen.". Short these 2 points together.
    6) Plug the unit in to AC.

    This process will generate test patterns from the digital board. If you see the test patterns begin to cycle on the screen, you know everything is working properly except your main board. If you do not see the test patterns, you have an issue in the panel drive circuitry.

    Comment

    • LesWoollam
      Senior Member
      • Nov 2012
      • 69
      • United Kingdom

      #3
      Re: LG 42PC1DA Plasma Sound but blank screen

      Thanks for the tip.
      Checked but no pattern on screen - still completely blank.
      Any suggestions?

      Comment

      • tom66
        EVs Rule
        • Apr 2011
        • 32560
        • UK

        #4
        Re: LG 42PC1DA Plasma Sound but blank screen

        Check the fuses on the Y-sustain and Z-sustain boards.
        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

        • LesWoollam
          Senior Member
          • Nov 2012
          • 69
          • United Kingdom

          #5
          Re: LG 42PC1DA Plasma Sound but blank screen

          All fuses (including the 5v fuses) on both boards are good.

          Comment

          • tom66
            EVs Rule
            • Apr 2011
            • 32560
            • UK

            #6
            Re: LG 42PC1DA Plasma Sound but blank screen

            We have sometimes seen the hybrids fail on these TVs without shorting out. Do you have 193V both ends of the fuses?

            Try without Z-sustain disconnected. You should get a dim, blurry picture if Y-sustain is still working.
            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

            • LesWoollam
              Senior Member
              • Nov 2012
              • 69
              • United Kingdom

              #7
              Re: LG 42PC1DA Plasma Sound but blank screen

              There's 186v5 at both ends of the fuses, I believe this is the VS supply from the smps. I've completely unplugged the Z-sus board but the screen remains completely blank.

              Comment

              • tom66
                EVs Rule
                • Apr 2011
                • 32560
                • UK

                #8
                Re: LG 42PC1DA Plasma Sound but blank screen

                It is possible the Z-sus is failed in such a way that means the plasma panel is not lighting. Try with the ribbons disconnected from the plasma panel on the Z-sus side. Otherwise, the Y-sus may also have a problem.
                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

                • LesWoollam
                  Senior Member
                  • Nov 2012
                  • 69
                  • United Kingdom

                  #9
                  Re: LG 42PC1DA Plasma Sound but blank screen

                  I've removed the ribbon cables from the Z-sus board - no difference, screen still blank. Are there any more tests I can do on the boards?

                  Comment

                  • tom66
                    EVs Rule
                    • Apr 2011
                    • 32560
                    • UK

                    #10
                    Re: LG 42PC1DA Plasma Sound but blank screen

                    Unless you have access to an oscilloscope, unfortunately, no...
                    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

                    • LesWoollam
                      Senior Member
                      • Nov 2012
                      • 69
                      • United Kingdom

                      #11
                      Re: LG 42PC1DA Plasma Sound but blank screen

                      I have a dual trace 60mhz scope.

                      Comment

                      • tom66
                        EVs Rule
                        • Apr 2011
                        • 32560
                        • UK

                        #12
                        Re: LG 42PC1DA Plasma Sound but blank screen

                        Brilliant... do you have a 10X probe which is capable of 400V measurements? (Peak voltage on Y-sustain can be 350V+)
                        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

                        • LesWoollam
                          Senior Member
                          • Nov 2012
                          • 69
                          • United Kingdom

                          #13
                          Re: LG 42PC1DA Plasma Sound but blank screen

                          Yes. What is the test?

                          Comment

                          • tom66
                            EVs Rule
                            • Apr 2011
                            • 32560
                            • UK

                            #14
                            Re: LG 42PC1DA Plasma Sound but blank screen

                            Connect the probe to the Vscw test point, set your scope to 2ms/div, 10V/div, and see if you get any waveform (set trigger to auto for now.)
                            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

                            • LesWoollam
                              Senior Member
                              • Nov 2012
                              • 69
                              • United Kingdom

                              #15
                              Re: LG 42PC1DA Plasma Sound but blank screen

                              Is that the "Waveform" test point on the Y-Drive board on the far left of the TV?

                              Comment

                              • tom66
                                EVs Rule
                                • Apr 2011
                                • 32560
                                • UK

                                #16
                                Re: LG 42PC1DA Plasma Sound but blank screen

                                That might be it. I might be getting confused with the older generation LG plasmas.
                                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

                                • LesWoollam
                                  Senior Member
                                  • Nov 2012
                                  • 69
                                  • United Kingdom

                                  #17
                                  Re: LG 42PC1DA Plasma Sound but blank screen

                                  I'll scope it and post the results.

                                  Comment

                                  • LesWoollam
                                    Senior Member
                                    • Nov 2012
                                    • 69
                                    • United Kingdom

                                    #18
                                    Re: LG 42PC1DA Plasma Sound but blank screen

                                    Scope set to 10V/Div (probe x10) 0.2ms/Div.
                                    Scope trace attached.
                                    Attached Files
                                    Last edited by LesWoollam; 11-13-2012, 07:42 AM.

                                    Comment

                                    • tom66
                                      EVs Rule
                                      • Apr 2011
                                      • 32560
                                      • UK

                                      #19
                                      Re: LG 42PC1DA Plasma Sound but blank screen

                                      Y sus is working, that looks normal. Check Z sus too.
                                      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

                                      • LesWoollam
                                        Senior Member
                                        • Nov 2012
                                        • 69
                                        • United Kingdom

                                        #20
                                        Re: LG 42PC1DA Plasma Sound but blank screen

                                        Scope set to 5V/Div (probe x10) 0.2ms/Div.
                                        Z-sus scope trace attached.
                                        Attached Files

                                        Comment

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