Lg 42pj550

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  • Blueaardvark46
    New Member
    • Jan 2011
    • 6
    • Wales

    #1

    Lg 42pj550

    Turns on fine with good sound but no picture. All voltages are present and
    correct and it seems that the Y and Z boards are doing their job because
    the heatsinks are getting warm. The curious thing is that there's a LED flashing
    on the LVDS board with a sequence of two short flashes, then a longer one, then another short one, then a very long one. This keeps on repeating and it
    looks like a fault code. Any ideas?

    Thanks
    John
  • sordids999
    Badcaps Legend
    • May 2013
    • 2149
    • uk

    #2
    Re: Lg 42pj550

    Test patterns from control board to eliminate main board ok ?
    Last edited by sordids999; 07-31-2018, 03:27 AM.

    Comment

    • vinceroger69
      Badcaps Legend
      • Mar 2012
      • 6714
      • uk

      #3
      Re: Lg 42pj550

      not sure what chassis your tv uses it may say on a sticker? but this maybe the service manual link
      https://servlib.com/lg/tv/42pj550-zd-chassis-pd01a.html

      Comment

      • Blueaardvark46
        New Member
        • Jan 2011
        • 6
        • Wales

        #4
        Re: Lg 42pj550

        The manual says to look for a waveform on P1004 but I can't see this test point.

        Comment

        • vinceroger69
          Badcaps Legend
          • Mar 2012
          • 6714
          • uk

          #5
          Re: Lg 42pj550

          does that manual match the tv chassis number if not maybe why you cant find the test point try running the test patterns if it dosnt say how too in the manual search this forum theirs a few threads on how too run them on lgs

          Comment

          • dick_barton
            Badcaps Legend
            • Aug 2015
            • 6642
            • Wales

            #6
            Re: Lg 42pj550

            Hi John, Can you post photo's of your circuit boards and how they interconnect?
            Willing to help but I'm no expert.

            Comment

            • dick_barton
              Badcaps Legend
              • Aug 2015
              • 6642
              • Wales

              #7
              Re: Lg 42pj550

              Disconnect the ribbon cable between the mainboard and logic board and short the two pads marked Auto Gen on the logic board. Power up and you should see test patterns displayed on the screen.
              Attached Files
              Willing to help but I'm no expert.

              Comment

              • Blueaardvark46
                New Member
                • Jan 2011
                • 6
                • Wales

                #8
                Re: Lg 42pj550

                No still no raster or test pattern. Here's some pics of the boards.

                Comment

                • Blueaardvark46
                  New Member
                  • Jan 2011
                  • 6
                  • Wales

                  #9
                  Re: Lg 42pj550

                  Here's the pics this time!
                  Attached Files

                  Comment

                  • dick_barton
                    Badcaps Legend
                    • Aug 2015
                    • 6642
                    • Wales

                    #10
                    Re: Lg 42pj550

                    OK so you need to measure and give the readings taken of Va, Vs, M5V, 17V, STB5V, 5V, Vz, +15VF, +5VF, VSC etc voltages along with all the others highlighted on the circuit boards. Possible logic board fault.
                    Last edited by dick_barton; 07-31-2018, 08:23 AM.
                    Willing to help but I'm no expert.

                    Comment

                    • Blueaardvark46
                      New Member
                      • Jan 2011
                      • 6
                      • Wales

                      #11
                      Re: Lg 42pj550

                      Ok here's the measured voltages:-
                      Va = 58.9v
                      Vs = 202v
                      M5v = 5.0
                      17v = 16.7
                      STDBY5 = 5.0
                      +5VF varies between 8 and 12v
                      +15F varies between 17 and 25v
                      SUSON varies between 3.6 and 6.5v
                      These variations occur when the picture brightness alters. ( I had scarted the
                      picture out to another set just to check the video processing)
                      I also noticed that where there are high voltage warnings on the 5 screw connections between the Y board and the buffer board there was only 45v on
                      the bottom screw and barely 8v on the other 4. Surely this should be higher?

                      Comment

                      • dick_barton
                        Badcaps Legend
                        • Aug 2015
                        • 6642
                        • Wales

                        #12
                        Re: Lg 42pj550

                        Va, Vs M5V and 17V supplies all look good. However it looks as thought the voltages on the Ysus board are fluctuating.
                        On the Ysus board measure Vsc which you measure between the two points marked and also measure the +15V point

                        Unfortunately your photo's are very blurred so I'm not sure what you mean about the screws. All screws should be firmly screwed down but not overtightened so as to crack the pcb.
                        Last edited by dick_barton; 07-31-2018, 09:47 AM.
                        Willing to help but I'm no expert.

                        Comment

                        • dick_barton
                          Badcaps Legend
                          • Aug 2015
                          • 6642
                          • Wales

                          #13
                          Re: Lg 42pj550

                          The +15VF and +5VF I believe should be measured with respect to Floating Ground (ie black meter lead connected to Floating Ground) which should be marked on the board.
                          Willing to help but I'm no expert.

                          Comment

                          • Andrew F. Ali
                            Badcaps Legend
                            • Jan 2014
                            • 2450
                            • Trinidad & Tobago

                            #14
                            Re: Lg 42pj550

                            Y-SUS Bd. not generating a proper 5V for the Logic Bd. to function. Yes I will say the issue is on the Y-SUS Bd.

                            Comment

                            • Josecarioca
                              New Member
                              • Nov 2017
                              • 1
                              • España

                              #15
                              Re: Lg 42pj550

                              Debes medir las 2 Resistencias de 22 Ohm 5W situadas en la parte superior de la fuente de alimentacion, cuando alguna de ellas está abierta o su valor no es correcto presenta fallo de Stby o parpadeo de LED.

                              Comment

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