LG, Model 47LG50, not coming ON

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  • tictac
    Member
    • Nov 2014
    • 26
    • Canada

    #1

    LG, Model 47LG50, not coming ON

    SYMPTOMS: At standby the front LED is solid red. When turned ON, it flashes brighter red twice, then goes out. From the inside of the TV, I can see the light change to blue but it is barely visible on the front of the TV. There is no picture and no sound.

    TESTS DONE: Visually all the boards look normal, no burnt marks, no fat caps, no smoke. All cable connections were re-seated but made no difference.

    With power unplugged, using "diode test" on a meter, all diodes and bridge rectifier tested OK. Although the Dual-Diode packages showed continuity between the outer terminals (I assumed that was normal). None of the MOSFET gate-drain legs showed shorted. Two fuses tested OK also.

    With the TV turned ON, the measured voltages were as follows:
    AC on bridge rectifier=124 VAC
    DC on bridge rectifier=122 VDC (should this not be higher?)
    5V output at connectors=5 VDC
    12V output at connectors=0 VDC
    16.5V output at connectors=0 VDC
    24V output at connectors=3 VDC

    Attached is a photo of the PS Board. Could someone please advise me on how to proceed. If it's a power supply problem I'm fine with replacing parts, but I'm not sure how to find the bad part. Thank you in advance.
    Attached Files
  • budm
    Badcaps Legend
    • Feb 2010
    • 40746
    • USA

    #2
    Re: LG, Model 47LG50, not coming ON

    'DC on bridge rectifier=122 VDC (should this not be higher?)'
    Is that what you are getting measured between the two legs of the main filter cap?
    We need the dcv readings of each pin of the connector with the name of each pin so we can see what your are missing.
    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

    • tictac
      Member
      • Nov 2014
      • 26
      • Canada

      #3
      Re: LG, Model 47LG50, not coming ON

      Previously, I measured the 122 VDC directly on the PLUS & MINUS terminals of a bridge rectifier. Today, I measured the two large caps near the bridge rectifier and they were 384 VDC each. Following are the DC voltages on the 3 connectors on the PS board as you requested.

      P201 (to main board)
      LABEL DC Voltage
      16.5 0
      GND 0
      12V 0.01
      GND 0
      5V 5.11
      5V 5.11
      GND 0
      GND 0
      ACD 0
      ON/OFF 2.8
      PMW-DIM 1.16
      N.C. 0

      P205 (to inverter on right side)
      ON/OFF 3.02
      BRI 1.61
      GND 0
      GND 0
      GND 0
      GND 0
      GND 0
      24V 0.37
      24V 0.37
      24V 0.37
      24V 0.37
      24V 0.37

      P204 (to inverter on left)
      ERROR 0
      PWM-DIM 1.35
      ON/OFF 3.02
      BRI 1.61
      GND 0
      GND 0
      GND 0
      GND 0
      GND 0
      24v 0.37
      24v 0.37
      24v 0.37
      24v 0.37
      24v 0.37

      Thanks for your quick reply, Budm.

      Comment

      • tictac
        Member
        • Nov 2014
        • 26
        • Canada

        #4
        Re: LG, Model 47LG50, not coming ON

        Budm,
        The voltage readings in the previous post are poorly formatted. On each line the connector label is followed by a space and then the DC Voltage. When you get a chance, could you please give me an idea of what to check next.
        Thank you.

        Comment

        • tictac
          Member
          • Nov 2014
          • 26
          • Canada

          #5
          Re: LG, Model 47LG50, not coming ON

          Originally posted by budm
          'DC on bridge rectifier=122 VDC (should this not be higher?)'
          Is that what you are getting measured between the two legs of the main filter cap?
          We need the dcv readings of each pin of the connector with the name of each pin so we can see what your are missing.
          BudM,
          I have posted the voltage readings. When you get time, could you please let me know what I could check next. Thank you.

          Comment

          • budm
            Badcaps Legend
            • Feb 2010
            • 40746
            • USA

            #6
            Re: LG, Model 47LG50, not coming ON

            OK, the power supply is getting the correct command signals and the PFC Voltage booster is working because you are getting the 384VDC on the filter cap but the switched 12V/24V power supply section is not coming on, that will be the section to check next.
            One signal Voltage that I ma not sure is the 'ACD 0' AC detect, I do not know if 0V is normal or not.
            http://www.shopjimmy.com/lg-eay40505...upply-unit.htm
            Last edited by budm; 01-25-2016, 01:16 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

            • tictac
              Member
              • Nov 2014
              • 26
              • Canada

              #7
              Re: LG, Model 47LG50, not coming ON

              There are a number of dual diodes with their cathodes connected to large heat sinks. If I measure the anodes, with ground as a reference, should I be getting AC or pulsating DC?

              Comment

              • budm
                Badcaps Legend
                • Feb 2010
                • 40746
                • USA

                #8
                Re: LG, Model 47LG50, not coming ON

                At this point we need the good clear pictures of the whole bottom side of the power supply board.
                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

                • tictac
                  Member
                  • Nov 2014
                  • 26
                  • Canada

                  #9
                  Re: LG, Model 47LG50, not coming ON

                  Originally posted by budm
                  At this point we need the good clear pictures of the whole bottom side of the power supply board.
                  Here they are. I may be able to get better closeups tomorrow in the daylight if you need.
                  Attached Files

                  Comment

                  • budm
                    Badcaps Legend
                    • Feb 2010
                    • 40746
                    • USA

                    #10
                    Re: LG, Model 47LG50, not coming ON

                    Thanks, they are a little too much glares from the flash, I may also need you to take the closed up pictures in section so I can stitch them together to able to see the traces in details.
                    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

                    • budm
                      Badcaps Legend
                      • Feb 2010
                      • 40746
                      • USA

                      #11
                      Re: LG, Model 47LG50, not coming ON

                      https://www.badcaps.net/forum/attach...9&d=1453766077

                      What are the P/N as printed on those two ICs with 16 pins (or may be 20 pins)?
                      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

                      • tictac
                        Member
                        • Nov 2014
                        • 26
                        • Canada

                        #12
                        Re: LG, Model 47LG50, not coming ON

                        Originally posted by budm
                        https://www.badcaps.net/forum/attach...9&d=1453766077

                        What are the P/N as printed on those two ICs with 16 pins (or may be 20 pins)?
                        I will get good closeup pictures in the daylight tomorrow morning.
                        The IC part numbers are on the attached picture.
                        Attached Files

                        Comment

                        • budm
                          Badcaps Legend
                          • Feb 2010
                          • 40746
                          • USA

                          #13
                          Re: LG, Model 47LG50, not coming ON

                          NPC1396 is the SMPS IC for the 12V/24V power supply, we need to find out if it is getting the Voltage between VCC pin and GND pin to run.
                          Attached Files
                          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

                          • tictac
                            Member
                            • Nov 2014
                            • 26
                            • Canada

                            #14
                            Re: LG, Model 47LG50, not coming ON

                            Originally posted by budm
                            NPC1396 is the SMPS IC for the 12V/24V power supply, we need to find out if it is getting the Voltage between VCC pin and GND pin to run.
                            With the TV plugged in and turned OFF, VCC-pin12 is at 2.69V. With the TV turned ON, VCC-pin12 is at 14.32V. These are measured with pin 10 as the reference.

                            A new observation: Just after measuring these voltages, the back lights came on for about 15-20 seconds and then went off again. I had no time to measure any other voltages while the lights were ON. I tapped the power supply everywhere, thinking there may be a bad connection some place, but I couldn't get the back lights to come on again.

                            Attached are 6 new pictures of the board.
                            Attached Files

                            Comment

                            • budm
                              Badcaps Legend
                              • Feb 2010
                              • 40746
                              • USA

                              #15
                              Re: LG, Model 47LG50, not coming ON

                              Originally posted by tictac
                              With the TV plugged in and turned OFF, VCC-pin12 is at 2.69V. With the TV turned ON, VCC-pin12 is at 14.32V. These are measured with pin 10 as the reference.

                              A new observation: Just after measuring these voltages, the back lights came on for about 15-20 seconds and then went off again. I had no time to measure any other voltages while the lights were ON. I tapped the power supply everywhere, thinking there may be a bad connection some place, but I couldn't get the back lights to come on again.

                              Attached are 6 new pictures of the board.
                              So the IC gets enough DCV to run (VCC ON Threshold level min is 12.3V, Typ is 13.4V, Max 14.3V).
                              I would resolder the legs of the power transformers T101, T102, MOSFET Q110, Q111, Caps C114, C125.
                              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

                              • tictac
                                Member
                                • Nov 2014
                                • 26
                                • Canada

                                #16
                                Re: LG, Model 47LG50, not coming ON

                                I re-soldered the components you suggested and the TV turned on as normal. Both, picture and sound, are good. I will leave it on to test run for 4-5 hours just to be sure that was the problem. Thank you for your advice and time.

                                Comment

                                • budm
                                  Badcaps Legend
                                  • Feb 2010
                                  • 40746
                                  • USA

                                  #17
                                  Re: LG, Model 47LG50, not coming ON

                                  Please also make sure all the boards mounting screws are tight since the GNDs to the chassis are done through the board mounting screws and the GND pads on the circuit boards..
                                  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

                                  • tictac
                                    Member
                                    • Nov 2014
                                    • 26
                                    • Canada

                                    #18
                                    Re: LG, Model 47LG50, not coming ON

                                    Originally posted by budm
                                    Please also make sure all the boards mounting screws are tight since the GNDs to the chassis are done through the board mounting screws and the GND pads on the circuit boards..
                                    OK. It's been working fine for a number of hours now, so I believe we fixed it.
                                    Thanks again. I'll leave a donation.

                                    Comment

                                    • theyankeemoto
                                      New Member
                                      • Dec 2016
                                      • 3
                                      • usa

                                      #19
                                      Re: LG, Model 47LG50, not coming ON

                                      Hi guys, I have the exact same problem with my 47lg50 tv.

                                      I replace the power supply board with one off eBay that I thought would most likely be the problem, but didn't fix it. Could it be the backlights inverters ?

                                      Comment

                                      • budm
                                        Badcaps Legend
                                        • Feb 2010
                                        • 40746
                                        • USA

                                        #20
                                        Re: LG, Model 47LG50, not coming ON

                                        Read post 3 and later and then tell us what Voltages you have like what the OP had provided..
                                        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

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