LG 50PJ550 Plasma tries to turn on then turns off

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  • canadaboy25
    What is normal?
    • May 2013
    • 509
    • Canada
    #1

    LG 50PJ550 Plasma tries to turn on then turns off

    Hey guys,
    I have a LG 50PJ550 plasma that will not power on.
    When plugged in, the relays click and the screen lights briefly before the relays click again and it shuts right down. It then tries starting up again before giving up and just sits there with the red LED on. Pressing the power button again repeats the process.

    During the moment where the screen is on, there is a slight fuzz that starts to go away as most plasma's do when they turn on. So i do not think it is a panel issue as I get a normal looking image for a split second.

    I have tested the Vs and Va voltages to be around 60V and 150V when it is trying to turn on. These are not accurate measurements just rough values to see if there was voltage present. If something seems fishy about these values I can retest them properly.

    I have read that it is common for the large 2.2 ohm resistors on the Y-sus board to go bad but I tested them and they are fine.

    I have also read on this thread https://www.badcaps.net/forum/showth...hlight=50pj550 post number 7, that the power supply board can be powered up with no connectors connected to it. I unplugged all of the connectors from the power supply except for the AC input and the power supply clicks once when it is turning on then immediately clicks off again. While it is on I have 5V on the connector going to the Y-sus board. I also have around 60V and 150V on Vs and Va for the same connector. Since the board immediately powers itself off again, this suggests a fault with the power supply? Not sure what to check as it is still generating voltages.

    The story on this TV is that it was working fine before they turned it off for the night and then would not turn on the next day.
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    canadaboy25

    -Sometimes the light at the end of a tunnel is an on-coming train
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    • canadaboy25
      What is normal?
      • May 2013
      • 509
      • Canada
      #2
      Re: LG 50PJ550 Plasma tries to turn on then turns off

      Well, I found that there are power supply kits made for this TV so I looked at what parts are included and sure enough, that is my problem.

      The top-right ceramic power resistor on the power supply board is open circuit.
      The repair kit also comes with a new diode located beside the power regulator and the power regulator itself.

      I tested the diode in-circuit and it tested shorted. I removed the diode and it read 0.21V in diode mode. The datasheet says it is a Schottky Barrier Rectifier with very low forward voltage. So it seems the diode is fine.

      The large orange-blue-silver-gold-black resistor measures 0.5 ohms. I would guess this means 0.36 ohms so I guess it is alright.

      I am not sure how to test the voltage regulator IC. It is a 3BR1565JF. However, in other threads I have seen that it is recommended to replace the regulator anyways.
      On one of my other scrap plasma power supplies I found a 3BR2565JF. The difference between the two is the FET on-resistance is 1.5 ohms for the original and 2.5 ohms for the extra one I have. Will this difference be enough to cause problems? I do not test any shorts between the pins so I might just try it for now to see if the blown resistor is the only problem until I can get a new one from China.

      I will try to find a power resistor locally tomorrow.
      Last edited by canadaboy25; 11-18-2020, 01:22 AM.
      canadaboy25

      -Sometimes the light at the end of a tunnel is an on-coming train

        Comment

        • tvtimmy
          Badcaps Legend
          • Mar 2015
          • 1160
          • usa
          #3
          Re: LG 50PJ550 Plasma tries to turn on then turns off

          More than likely the open resistor is the only problem, very common on that set.

            Comment

            • canadaboy25
              What is normal?
              • May 2013
              • 509
              • Canada
              #4
              Re: LG 50PJ550 Plasma tries to turn on then turns off

              Originally posted by tvtimmy
              More than likely the open resistor is the only problem, very common on that set.
              Yep, replaced the resistor and the TV is up and running. Was just worried there might be more wrong from reading all the other threads about this TV.
              canadaboy25

              -Sometimes the light at the end of a tunnel is an on-coming train

                Comment

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