LG 50PJ550 clicking/not staying on

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  • Tycoon
    New Member
    • Jun 2020
    • 5
    • Canada
    #1

    LG 50PJ550 clicking/not staying on

    I recently received a LG Plasma TV (50PJ550-UD) which clicks upon pressing the power button however after another clicks turns off. There is no image displayed during this time. I attempted to troubleshoot and unplugged both the YSUS and ZSUS board (the ZSUS board plugs in to the YSUS on this model). With the ZSUS board unplugged the power stays on. With the YSUS connected the 2 clicks and then power down occurs. I replaced the YSUS board and buffers thinking this was the issue however the issue remained. I also thought it might be the power board which I replaced and still the same issue. I was able to get the TV to stay on and have sound but no image if I removed the M_ON wire coming off of the Main Control board in to the power supply board however as soon at it is reconnected there is a hum from the YSUS and then the same 2 clicks and power down.

    I searched the forum and found some advice however slightly different issues as I fully replaced the board (YSUS, buffers and Power Supply) Does anyone have any suggestions as to how to troubleshoot this issue or am I at the point I should scrap the TV? Thanks in advance for any advice as I'm kind of at a loss right now.
    Tags: None
    • dick_barton
      Badcaps Legend
      • Aug 2015
      • 6642
      • Wales
      #2
      Re: LG 50PJ550 clicking/not staying on

      Have you downloaded the service manual here.
      Willing to help but I'm no expert.

        Comment

        • Tycoon
          New Member
          • Jun 2020
          • 5
          • Canada
          #3
          Re: LG 50PJ550 clicking/not staying on

          Thank you for the reply and for the link to the service manual. I started on the Power Up Boot troubleshooting measuring with a multimeter and below are the results. For plug 301 and 812 I have placed my measurements in brackets after the legend on the circuit board. I have to unplug the M_ON wire for the set to power up long enough to take these measurements. Thanks again for any advice and I am wondering on the measurements for IC301 (power board) as they seem off however the power supply output looks correct.

          P301 (plug 301)
          17V, 17V = (17.12V),(17.05V)
          GND, GND = (0V),(0V)
          5.1V, 5.1V = (5.17V),(5.16V)
          ERR_DET, 5.1V = (4.92V),(5.16V)
          GND, GND = (0V),(0V)
          GND, GND = (0V),(0V)
          STBY, STBY = (5.13V),(5.13V)
          AC_DET, RL_ON = (0V),(2.44V)
          AUTO_GND, M_ON = (0V),(3.3V)

          IC301
          Pin1= My meter goes to 1000V and is showing a 1 which indicates higher voltage
          Pin2=(60V)
          Pin3=(59V)
          Pin4=(44.7V)
          Pin5=(61V) (which I believe should be ground)
          Pin6=(58.8V)

          P812 (Out of Power Supply to YSUS)
          M5V = (5V)
          M5V = (5.19V)
          GND = (0V)
          VA = (60.3V)
          VA = (60.2V)
          GND = (0V)
          GND = (0V)
          NC = (0V)
          VS = (207V)
          VS = (207V)

            Comment

            • dick_barton
              Badcaps Legend
              • Aug 2015
              • 6642
              • Wales
              #4
              Re: LG 50PJ550 clicking/not staying on

              Have a read of this which may help
              http://www.coppelltvrepair.com/p/639...ing-on-and-off
              Willing to help but I'm no expert.

                Comment

                • tvtimmy
                  Badcaps Legend
                  • Mar 2015
                  • 1160
                  • usa
                  #5
                  Re: LG 50PJ550 clicking/not staying on

                  Post a picture of your power supply. These tvs are prone to the 10 ohm 5 watt resistors going open. Some have 3 and others have 2.

                    Comment

                    • Tycoon
                      New Member
                      • Jun 2020
                      • 5
                      • Canada
                      #6
                      Re: LG 50PJ550 clicking/not staying on

                      Thanks for the suggestions. I will post a picture of the power supply board shortly. It is the one with the 2 resistors in the upper right (5W22ROJ, Resistors R927 and R929). I tested them and they appear to be fine (22Ohms). I was doing some testing last night and may have a short on the ZSUS board if that makes sense for the symptoms I am having.

                        Comment

                        • satinser
                          Badcaps Veteran
                          • Oct 2012
                          • 214
                          • uk
                          #7
                          Re: LG 50PJ550 clicking/not staying on

                          It is a common problem with this power supply. There are many components which may fail or go faulty that can cause this issue. However its easy to test this power supply because with all connectors removed accept the power connector it should start up with all voltages being present so a good power board with just the power connector connected should when powered up click once with all voltages present. Obviously if tested this way and power supply clicks on closely followed by a futher click which is the power supply switching back off a fault on your power board will be the issue. If tested this way and your power board starts with just the one click it will be a short on either Ysus or the Xsus thats the cause of your power supply to shut down when connected.
                          I would say however that in my experience the Xsus rarely fails far more often the Ysus being at fault.
                          Last edited by satinser; 06-26-2020, 08:22 PM.

                            Comment

                            • Tycoon
                              New Member
                              • Jun 2020
                              • 5
                              • Canada
                              #8
                              Re: LG 50PJ550 clicking/not staying on

                              Sorry it ended up being a busy weekend and I didn't get a chance to work on it. I tested the power supply as mentioned (disconnecting cables) and it stays powered on without the YSUS/ZSUS boards connected and the voltages match the service manual. I am testing the YSUS/ZSUS boards now. Thank you for the suggestion on the YSUS board failing more often. It does look like I have a short on the ZSUS with Q20 going to ground. I have attached images of the Power Supply and will update on the ZSUS as soon as I get replacement parts. Thanks!
                              Attached Files

                                Comment

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