LG 55LN5400 LED flash then dark troubleshooting

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  • rmoody
    Learning Member
    • Jul 2011
    • 262
    #1

    LG 55LN5400 LED flash then dark troubleshooting

    Hey guys, been a while since I've been in here but had some spare time to troubleshoot a tv that has had an issue for a bit. I initially assumed I had bad LEDs and tore the set down to test. LEDs all lit up and seemed fine using my tester. Reassembled and went to troubleshooting boards. PS board has all correct voltages across the outputs. Not really sure what to test in the main board… I did check the fuse on the T-con and it has continuity but no voltage tested to chassis ground. Am I wrong in my assumption the main board has failed somewhere? Shouldn't the Tcon board have 12v dc?
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    • rmoody
      Learning Member
      • Jul 2011
      • 262
      #2
      Re: LG 55LN5400 LED flash then dark troubleshooting

      I forgot to mention. Power button changes nothing on my voltages. Tv is always in power on state when plugged in. This has mostly been main board in the past for me. I found one off eBay for $15 so I’m gonna go ahead and give it a shot.

        Comment

        • neilc6
          Badcaps Legend
          • Nov 2015
          • 1550
          • Canada
          #3
          Re: LG 55LN5400 LED flash then dark troubleshooting

          Flash of backlights is a symptom of bad backlights. They sometimes may test good with a LED tester. Just replace all the strips with new. I rarely test with LN, LB or LF series with symptoms of bad backlights. The 55 LN uses the thick lens style of LB series. You can remove the panel, record the flash and go frame by frame to see which LEDs aren't lighting up.
          Last edited by neilc6; 03-30-2022, 09:58 AM.

            Comment

            • rmoody
              Learning Member
              • Jul 2011
              • 262
              #4
              Re: LG 55LN5400 LED flash then dark troubleshooting

              Originally posted by neilc6
              Flash of backlights is a symptom of bad backlights. They sometimes may test good with a LED tester. Just replace all the strips with new. I rarely test with LN, LB or LF series with symptoms of bad backlights. The 55 LN uses the thick lens style of LB series. You can remove the panel, record the flash and go frame by frame to see which LEDs aren't lighting up.
              I have a set coming in today or tomorrow….. I may wait til main board comes in anyways as one of the hdmi ports are jacked up. I think my output voltage was around 110v dc for the backlights when testing to chassis ground. Hoping I don't have to replace the LEDs but I'll have them if I need to. They all looked pretty darn good when testing though.

                Comment

                • rmoody
                  Learning Member
                  • Jul 2011
                  • 262
                  #5
                  Re: LG 55LN5400 LED flash then dark troubleshooting

                  New LEDs still haven't arrived.... Stupid DHL! put the tv back together to get out of the way, plugged it in and it worked for a little bit but then went black again. Is it really possible to have faulty LED's even if they all light well? Maybe heat causes solder seperation. The set works fine and all are lit when testing.

                    Comment

                    • neilc6
                      Badcaps Legend
                      • Nov 2015
                      • 1550
                      • Canada
                      #6
                      Re: LG 55LN5400 LED flash then dark troubleshooting

                      LGs have shutdown protection for the backlight circuit. Failing LEDs can have fluctuating voltages or go open circuit triggering the shutdown. https://techhometravel.com/lg-ln-ser...ed-backlights/
                      Last edited by neilc6; 04-05-2022, 04:20 PM.

                        Comment

                        • R_J
                          Badcaps Legend
                          • Jun 2012
                          • 9514
                          • Canada
                          #7
                          Re: LG 55LN5400 LED flash then dark troubleshooting

                          You should also check the connections on the led strips, sometimes they develop poor solder connections as well.

                            Comment

                            • rmoody
                              Learning Member
                              • Jul 2011
                              • 262
                              #8
                              Re: LG 55LN5400 LED flash then dark troubleshooting

                              Originally posted by neilc6
                              LGs have shutdown protection for the backlight circuit. Failing LEDs can have fluctuating voltages or go open circuit triggering the shutdown. https://techhometravel.com/lg-ln-ser...ed-backlights/
                              Is there a point that i can check for fluctuation? I checked the PSU output and it was a steady 116vdc. Hopeful DHL can get off their rump and get me some LED's in the next day or two. I'm ready to be done with this set already.

                                Comment

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