55le5400

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  • Spector
    Member
    • Oct 2018
    • 17
    • USA

    #1

    55le5400

    I'm back again. Sorry for just how disjointed my thread was last time.

    The history of the TV is that I recieved it for free, and it wouldn't power on. When I would plug it in, there would be a click or two, and then nothing.

    Shortly after getting it apart, while checking voltages, I bridged across a mosfet. I believe it's the one I circled in red: Click image for larger version

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    (I'm an idiot apparently. There's no need to ask what I was thinking, or how it happened, or any of that. Just assume I've taken all the criticism needed.)

    That blew the 6.3a 250v fuse on the bottom of the board.

    After asking a bit here, and showing just how novice I am, I decided to get a different power board rather than try messing with things that are currently above my level. (I can solder in a new fuse, that's no problem, but since I didn't originally even know that it was a mosfet that I shorted, I figured the less actual SMD diagnosis I had to do the better.)

    The "new" power board is a take off from a unit with a broken screen. It is used.

    Once I installed it we were back to the original complaint, which was that the screen wouldn't power on, and the power board would click a time or two whenever plugged in, and once when unplugged.

    I tested the voltages at the connector that leads to the main board, and the 3.5v and 24v were where they are supposed to be. I honestly don't remember then 12v.

    Knowing that this model has a common issue with the BGA processor, I took a hairdryer to it for a few seconds to see if symptoms would change. Upon the next power up the clicks were still present, the LED board had a blue light that was blinking about every second, and the ethernet port on the main board had very dim lights on the green and yellow LEDS. I also observed that when reset, the capacitive touch points on the front would light up for a few seconds and then go off again. Also I could hear a high pitched ring from the area of the mainboard.

    I gave the processor another heat, and then, nothing. Now no light on the LED board, no ethernet light, no clicks when plugged in or unplugged. Completely unresponsive.

    I've checked all three fuses on the power board, and they're fine. The power source is still at 116v (tested where the cable connects to the board). The connector that runs from the PB to the MB reads as such (left to right):
    0, 0, 0, 0, 0, 0, 3.3, 3.4, 0, 0, 0, 0

    So now I no longer have 12v or 24v.

    Is it possible that this could still be caused by a problem on the main board, or am I right to assume that I am right back to power board issues? What components would you recommend I check next?

    So sorry for the long read.
  • Spector
    Member
    • Oct 2018
    • 17
    • USA

    #2
    Re: 55le5400

    My apologies for not putting the make in the title of the thread. It's an LG 55LE5400. I can't figure out how to edit the post, but I'll keep looking.

    Comment

    • R_J
      Badcaps Legend
      • Jun 2012
      • 9514
      • Canada

      #3
      Re: 55le5400

      You are missing the power on signal from the main, thats why there is no 12 & 24 volts, That plug has 24 pins.
      Try pushing the reset button on the main board
      Last edited by R_J; 11-17-2018, 08:21 PM.

      Comment

      • Spector
        Member
        • Oct 2018
        • 17
        • USA

        #4
        Re: 55le5400

        Originally posted by R_J
        You are missing the power on signal from the main, thats why there is no 12 & 24 volts, That plug has 24 pins.
        Try pushing the reset button on the main board
        I did. Unfortunately no change. So there's a chance that the main board continues to be the problem then?

        Comment

        • R_J
          Badcaps Legend
          • Jun 2012
          • 9514
          • Canada

          #5
          Re: 55le5400

          You could download the service manual, it has the main board schematic
          The main board gets standby voltage from the power supply, that powers up the microprocessor (IC8101) that reads the power button state. When the button is pushed the micro outputs a POWER_ON signal to the power supply, that POWER_ON signal also turns on voltage regulators on the main board.
          Shopjimmy does have a eeprom (ic9000) available so that could be the problem,
          If you have som cold spray or an inverted can of air, you can try freezing the ic
          You need to have the tv UNPLUGGED, freeze the eeprom, PLUG IN the tv and try turning it on.

          You could also check the power supply (12 volts) by disconnecting P201 from the main board and connecting the 3.5 volt standby pin (50r6) to the PW ON pin (1), that should turn on the power supply 12 volts
          You should be able to short pin 1 of P201 to J235 jumper, that will turn on the +12 volts
          Last edited by R_J; 11-18-2018, 12:15 PM.

          Comment

          • Spector
            Member
            • Oct 2018
            • 17
            • USA

            #6
            Re: 55le5400

            Thanks a lot.

            I'll give that all a try as I have time over the next couple days.

            Comment

            • Spector
              Member
              • Oct 2018
              • 17
              • USA

              #7
              Re: 55le5400

              Alright. Turns out my noobishness strikes again. The change in behavior after I heated it with a hair dryer was caused by it no longer being on upon being plugged in. I didn't think before to hit the power button since the lights on the front and the clicks from the power board were originally happening any time it was plugged in.

              Now it's just a no screen issue. When plugged in, and the power button pressed, there's a beep (I assume as their should be) and the capacitive touch buttons on the front light up, as well as the LG logo. The LED board has the blue light blinking about every second, and the main board has dim light in the ethernet port's LEDs.

              From what I read, this could still very well be a BGA issue with the processor or ram chips.

              I also tried the freeze on IC9000 but nothing changed.

              Thank you very much for your suggestions so far.

              Comment

              • Spector
                Member
                • Oct 2018
                • 17
                • USA

                #8
                Re: 55le5400

                I also just checked the voltage at the connectors on top of the power board. The connector to the main board reads as such (left to right):
                0, 12, 12, 12, 0, 0, 3.3, 3.4, 0, 0, 24, 3.3

                The only reading of those that isn't close to it's declared voltage is the furthest right pin, which is supposed to be at 24v.

                The connector for the LED board is as such (left to right):
                0, 2.8, 0, 0, 0, 0, 0, 0, 0, 24, 24, 24, 24, 24

                Also, you mentioned the service manual to this television. I'll see if I can find one as that would definitely be a big help.

                Comment

                • Spector
                  Member
                  • Oct 2018
                  • 17
                  • USA

                  #9
                  Re: 55le5400

                  I found the service manual: https://www.electronica-pt.com/esque...ileinfo/29968/

                  Mostly french to me, but I'm still pouring through it.

                  Comment

                  • Spector
                    Member
                    • Oct 2018
                    • 17
                    • USA

                    #10
                    Re: 55le5400

                    Update:

                    I did a "redneck reflow" and it seems to have worked. The only think I notice is that the capacitive touch buttons on the front are a pain to get to respond sometimes, but I feel that's probably more a matter of poor design than a continuing problem. I'll be testing all the functions out soon.

                    Thank you very much for the help offered here! I apologize for how green I am to this sort of thing.
                    Last edited by Spector; 11-20-2018, 05:40 PM.

                    Comment

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