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LG TV 32LD650N - Slow to turn on. No display

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    LG TV 32LD650N - Slow to turn on. No display

    I have an LG TV model 32LD650N. It's about 9 years old. The last year it has been slower and slower to turn on. When I power it on, the red LED flashes (normal during power on) but the screen stays off. After ~15 minutes turning if off and on again would make the screen go on. The TV would work fine from there.
    But now it just stays on the blinking power LED trying to turn on.

    What I have tried:
    I am very much a beginner when it comes to electronics repair. But I suspected a bad capacitor on the power-supply.
    After disassembly there was nothing to see during the visual inspection. All the caps look fine.

    The power-supply has 3 voltages (3.5v, 12v, 20v) and is connected to the 'signal board' with a 24 pin cable.
    The power-board has 2 fuses, both of which I measured and they are OK.
    The supply has 2 other connections going directly to the screen (marked with 1 on the annotated images).

    Measurements:
    When the supply is not connected to the signal board I can only measure 3.5v on the 24 pin jack.
    When the signal board is connected and the TV is trying to turn on, all 3 voltages are present on the 24 pin jack.

    Checking the caps:
    Next I de-soldered all of the electrolytic capacitors, one at a time. (Except 2 big ones on the primary side, they are glued down with some white adhesive).
    They all measured fine on my multimeter. 10% within the printed value. I can see nothing wrong with them.

    Since I was unable to de-solder the two big caps I have not been able to measure them. But they look fine...

    What's next?
    I have no idea what to try next so I'm posting here for some guidance.

    It's seems impossible to remove the big glued caps without damaging them. Any tips on removing the adhesive?

    Any ideas or advice on what to do next is very welcome.
    Attached Files

    #2
    Re: LG TV 32LD650N - Slow to turn on. No display

    1) Please provide the good clear straight shot pictures of the whole top and bottom side of the board.

    2) The connector on the power supply board that goes to the main board. Are there pin labels printed by the connector or on the board some where? We need those pin labels so we can see what Voltage each pin has when TV is working and when it stops working.

    3) Please also provide the pictures of the whole backside of the TV showing all the boards so we can see how the boards are connected together.

    4) To really test the cap, you need to test ESR of the cap too, not just the capacitance.

    5) "When I power it on, the red LED flashes (normal during power on) but the screen stays off" Do you still get sound? Also do you know if the backlights are still on or not? I am trying to understand the 'Stays off' meaning.
    Last edited by budm; 07-29-2020, 04:38 PM.
    Never stop learning
    Basic LCD TV and Monitor troubleshooting guides.
    http://www.badcaps.net/forum/showthr...956#post305956

    Voltage Regulator (LDO) testing:
    http://www.badcaps.net/forum/showthr...999#post300999

    Inverter testing using old CFL:
    http://www.badcaps.net/forum/showthr...er+testing+cfl

    Tear down pictures : Hit the ">" Show Albums and stories" on the left side
    http://s807.photobucket.com/user/budm/library/

    TV Factory reset codes listing:
    http://www.badcaps.net/forum/showthread.php?t=24809

    Comment


      #3
      Re: LG TV 32LD650N - Slow to turn on. No display

      Thanks for the reply.

      1) Here are some new pictures of the power board. I only posted the other one, because it was the only one I had, before de-soldering the caps. This picture has the caps de-soldered. I hope that's okay.

      2) Uploaded a picture of the pin-out of the 24 pin connector.

      3) Also uploaded, showing the power and main board on the back of the tv. The two multi-cables at the bottom of the main board goes to the speakers(the left one). And the side-panel buttons and the standby LED (the right one)

      4) I don't have an ESR meter. Is there any other tests I can preform with a multimeter or will I need to buy an ESR meter to really diagnose the caps?

      5) Let me try to clarify.
      When the TV worked properly the following would happen: Solid red LED was on when on standby. Pressing the power button the LED would flash 1-2 seconds. Then the screen would come on, displaying the time and an LG logo. Then it switched to live TV with sound.

      Gradually it got slower and slower and would stay in the blinked LED phase. Until it was "warm" (after 5-15 minutes, getting slower all the time) then if you pressed the power button to turn it off and on again the clock and the LG logo would appear (sometimes after a few tries). From there it would work fine.

      Now when it's connected to power the red standby LED is on (as normal). When I try to power it on the red LED starts flashing, but nothing else is happening. No sound and I'm 95% sure there is no backlight. But I can re-solder the caps and check to make sure. Trying the "trick" of powering it off and on no longer works.

      I appreciate you taking the time to reply. I'm really taking this as an opportunity to learn. If I forgot any information please let me know. And sorry about the picture quality, my phone is getting old. The image rotation changes when I upload, but I hope you can see it alright.
      Attached Files

      Comment


        #4
        Re: LG TV 32LD650N - Slow to turn on. No display

        Possible schematic for your power supply.
        Attached Files
        Willing to help but I'm no expert.

        Comment


          #5
          Re: LG TV 32LD650N - Slow to turn on. No display

          Can you post all the voltages on connector P201 Pins 1 - 24 giving Pin No, Pin Name and voltage when you first power up waiting for it to start.
          Willing to help but I'm no expert.

          Comment


            #6
            Re: LG TV 32LD650N - Slow to turn on. No display

            Originally posted by dick_barton View Post
            Can you post all the voltages on connector P201 Pins 1 - 24 giving Pin No, Pin Name and voltage when you first power up waiting for it to start.
            Thanks for the schematic. That’s great. Where did you find that?

            I will try to get the re-soldering of the caps done today so I can get you a read out of the voltages on the pins.

            Comment


              #7
              Re: LG TV 32LD650N - Slow to turn on. No display

              Okay, I got all the caps soldered back in.

              After I pressed the power button, the red LED is blinking and there is no backlight. Here are the voltages i measured when the TV is in that state.

              Code:
              +----------+------------+------+
              | Pin #  | Pin Name | Volt |
              +----------+------------+------+
              | 1    | Power-on  | 3.2 |
              | 2-4   | 20v    | 22.8 |
              | 5-8   | GND    |  0 |
              | 9-12   | 3.5v    | 3.4 |
              | 13-16  | GND    |  0 |
              | 17,19,21 | 12v    | 12.3 |
              | 18    | Inv on/off |  0 |
              | 20    | A-dim   | 0,06 |
              | 22    | P-dim   | 2,6 |
              | 23    | N.C    |  0 |
              | 24    | Error   | 0,7 |
              +----------+------------+------+

              Comment


                #8
                Re: LG TV 32LD650N - Slow to turn on. No display

                The inverter ON/Off signal is missing. You could check this voltage again once the set finally come on.
                I suspect this signal comes from the mainboard. This may well be indicative of failure of the BGA of the main IC on the mainboard.
                Last edited by dick_barton; 07-31-2020, 03:27 PM.
                Willing to help but I'm no expert.

                Comment


                  #9
                  Re: LG TV 32LD650N - Slow to turn on. No display

                  I have been able to get the TV to turn on by using the trick of waiting until it gets 'warm'. And then powering it off an on again. It didn't take as long as before, only about 5 minutes, but I don't know why.
                  Here are the measurements when the TV is ON:

                  Code:
                  +-------+------------+------+
                  | Pin # | Pin Name | Volt |
                  +-------+------------+------+
                  |   1 | Power-on  | 3.2 |
                  |  18 | Inv on/off |  3 |
                  |  20 | A-dim   | 1.6 |
                  |  22 | P-dim   | 1.2 |
                  |  24 | Error   |  0 |
                  |   9 | 3.5v    | 3.4 |
                  |  17 | 12v    | 12.1 |
                  |   2 | 20v    | 20.9 |
                  +-------+------------+------+
                  When the TV is on, turning it off and on again within ~10 sec works fine. But ~30 sec or longer I have to wait in the blinking LED state (but not so long), and the power off and on again to get it working. Strange.

                  Since it might be the main-board at fault I have uploaded a closer picture. I also looked around for a schematic but was unable to find one. I did find the service manual for the 55ld650n which is the 32 inch version I have. I have attached it. Maybe the block diagram can be useful. I also found a full pdf with the power-board(EAX61124201) schematic.

                  Thanks for the help so far.
                  Attached Files

                  Comment


                    #10
                    Re: LG TV 32LD650N - Slow to turn on. No display

                    INV_ON/OFF is controlled by IC8101 which switches transistor Q8005. Check the voltages on the 3 pins of Q8005.

                    You could try heating up IC8101 and see if the backlights come on quicker.

                    I'm suspecting that IC8101 has problems with its solder joints (BGA)
                    Willing to help but I'm no expert.

                    Comment


                      #11
                      Re: LG TV 32LD650N - Slow to turn on. No display

                      Here are my observations so far.
                      The IC8101 (not a BGA, but a 48 pin LFQFP package, see image) pulls the base of transistor q8005 high to turn OFF the INV On/Off.

                      So when I turn on the tv and the LED is blinking, but there is no backlight. I measure 0.7 on the base of Q8005 (0v on the collector and emitter) this pulls INV on/off to 0v/GND. Otherwise the 3.3V_NORMAL line would make it high. And that is exactly what happens when I get the backlight to turn on using the on/off trick.
                      Then the voltage on the base is 0, and the collector is 3.0 going to the Inv on/off line.

                      I also checked the 3.3V_NORMAL regulator. It's gets it's enable signal also from IC8101 (POWER_ON/OFF2_2) and that is present as soon as I press the power button. So that seems to work as expected converting 12v to 3.3v.

                      I have no experience, but maybe IC8101 is waiting for a signal from elsewhere before allowing the Inv on/off the be enabled. But there is a ton of signals going to and from that chip, so I have no idea how to narrow it down.

                      I have not tried heating IC8101 up to see what that does, because it's operations seems to working. But I can try with an old hairdryer just to see what happens.
                      Attached Files

                      Comment


                        #12
                        Re: LG TV 32LD650N - Slow to turn on. No display

                        You could check if there's a delay with PIN 29 receiving the Power On/Off and also check PIN 6 receiving the 3.3V Not anticipating an issue but may be worth checking.
                        Willing to help but I'm no expert.

                        Comment


                          #13
                          Re: LG TV 32LD650N - Slow to turn on. No display

                          Originally posted by deltini View Post
                          Okay, I got all the caps soldered back in.

                          After I pressed the power button, the red LED is blinking and there is no backlight. Here are the voltages i measured when the TV is in that state.

                          Code:
                          +----------+------------+------+
                          | Pin #  | Pin Name | Volt |
                          +----------+------------+------+
                          | 1    | Power-on  | 3.2 |
                          | 2-4   | 20v    | 22.8 |
                          | 5-8   | GND    |  0 |
                          | 9-12   | 3.5v    | 3.4 |
                          | 13-16  | GND    |  0 |
                          | 17,19,21 | 12v    | 12.3 |
                          | 18    | Inv on/off |  0 |
                          | 20    | A-dim   | 0,06 |
                          | 22    | P-dim   | 2,6 |
                          | 23    | N.C    |  0 |
                          | 24    | Error   | 0,7 |
                          +----------+------------+------+
                          I Just re-read your earlier post where the results at switch on from cold is given above.

                          The only signal missing when cold is the Inverter On/Off.

                          Generally if you connect a DVD player to the SCART input the mainboard normally switches over to that input so although you would have no backlight you should have sound and a picture if you shine a light at the screen.

                          I'm wondering if something else is being delayed like the Relay being switched on by IC8101, Pin 36
                          Willing to help but I'm no expert.

                          Comment


                            #14
                            Re: LG TV 32LD650N - Slow to turn on. No display

                            Just wondering if there was ever any resolution to this, deltini? I have a 32" LG that is exhibiting very similar, if not exactly the same, symptoms and behaviors.


                            ~ kca

                            Comment


                              #15
                              Re: LG TV 32LD650N - Slow to turn on. No display

                              Originally posted by kca View Post
                              Just wondering if there was ever any resolution to this, deltini? I have a 32" LG that is exhibiting very similar, if not exactly the same, symptoms and behaviors.


                              ~ kca
                              Hey, real life got in the way of spending more time on this repair. But I hope to get back to it later in the year. I still have the TV disassembled on my workbench.

                              I will post again when I hopefully get some more time.
                              - Deltini

                              Comment


                                #16
                                Re: LG TV 32LD650N - Slow to turn on. No display

                                Guessing about capacitors is a pain, maybe try to get an esr meter to take the guesswork out, ebay has them for about 10 to 15 dollars.

                                Comment

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