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LG 55LA620S Black Screen Issue

lerreg Posted messages 2 Registration date   Status Member Last intervention   -  
 Lerreg -
Hello everyone,

For the past 2 days, I've been having a problem with my LG TV model 55LA620S from 2013.
When I turn it on, after about 15-20 minutes, it turns off by itself.
After checking with a phone flashlight, I can make out the image but the screen is black.

Could this problem be due to a backlight defect in my TV? But why after more than 15 minutes?

What points should I check?
Given the symptoms, do you think it can be repaired?

Thank you for your help.
Best regards

3 answers

  1.
    lolomusic667 Posted messages 2527 Status Member 11
     
    Good evening,

    Three things to check: -When you turn on your TV, do you see the LG logo?
    -Is there any sound?
    -If you shine a sufficiently powerful lamp on the screen, do you see an image?

    If yes, it might be a backlight issue.
    At startup, the display enters safety mode, since the current coming back from the LED bars is not the same as the one arriving.
    2
  2. lerreg Posted messages 2 Registration date   Status Member Last intervention   2
     
    Good evening, thank you for your quick response.

    Yes, I can make out the logo. (For your information, the TV has been on for 10 minutes without any problem)
    Yes, there is still sound even when the black screen appears
    Yes, with a bright light I can see the picture.

    I can't understand why if it were a backlight issue, the problem would appear 20 minutes later and not right from when the TV is turned on....

    Best regards.
    2
    1. lolomusic667 Posted messages 2527 Status Member 11
       
      All right. First of all, I want to warn you if you plan to attempt the repair yourself.
      It's better to be somewhat handy and have some space (especially when the panel is removed, as the television is bulky).

      If you don’t feel up to it, go to a professional.

      In fact, no special tools are needed. A single Philips screwdriver is enough.
      I can detail the disassembly steps for you if you wish. For now, I will just explain how to detect the defective bar(s)...


      This model contains 7 LED bars. They are powered by two connectors.
      The first connector powers 3 bars and the second (darker, if I’m not mistaken) powers 4.

      To test, simply plug in the device. As the LEDs light up for a brief moment, you can tell if the LEDs are good or not.
      Since it shines brightly and briefly, it’s easiest to proceed logically.

      First of all, it’s important to understand that the bars are connected in series (if you follow one of the two cables coming from the motherboard, it connects to the end of the first bar. The other side of the bar is connected with a small cable to the second bar, and so on, until reaching a termination cable.
      If, in this entire circuit, one LED is out of service, everything will remain off when powered on.
      What saves us here is that we have two power supplies (one for 3 bars and another for 4 bars) and that the connecting cables between the bars can be easily moved.

      - At this stage, I would take a photo of the entire setup, as afterwards we will disconnect all or part of the circuit for testing.

      - We disconnect one of the two power supplies. We plug in the TV (and don’t forget to unplug it before putting your hands back in the television). If the bars still powered light up for a brief moment, they are okay. If not, the problem lies with one of the bars in this circuit.
      By testing the 4 bar circuit first, then the 3 bar circuit, we can already see that 3 or 4 bars are okay.

      Note, at this stage, it is important to note that the circuit powering 4 bars is meant to be tested with 4 bars and vice versa for the 3 bar circuit...

      - Now, we leave the 4 connector unplugged and use only the 3 connector.

      - We disconnect all links and terminations. We redo a circuit of 3 bars, starting with the 3 connector and ending with a termination, using 2 working bars and one third to test. We connect and then disconnect electrically.

      By proceeding this way several times, we find the faulty bar(s).

      I don’t know if my explanations are clear, but actually, it’s relatively simple.

      Have you tried this, and does it work?
      1
  3. Lerreg
     
    Hello,

    I finally had the time to take apart my TV thanks to some tutorials.

    Unfortunately or fortunately, all the LEDs are working. The problem doesn't come from there...
    The TV has been on for 30 minutes and they are still on.
    Where could the problem be coming from in this case??? Thank you for your help.

    Best regards.
    0