Announcement

Collapse
No announcement yet.

LG TV 42LW4500 does not starts up LED red white red

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    LG TV 42LW4500 does not starts up LED red white red

    Hi, my LG TV LG 42LW4500 stopped powering on one day, when I insert power cord cable to power socket the LED light turns on red color.
    When try to power on with remote it changes slowly from red to white (can hear clicking relay) and again slowly from white to red and TV stays off.
    Could you give me some suggestions where should I look for problem?
    I inspected the power board visual, looked for bad caps but found nothing.
    Thx for any help.

    #2
    Re: LG TV 42LW4500 does not starts up LED red white red

    adding some pictures of the power board:
    Attached Files

    Comment


      #3
      Re: LG TV 42LW4500 does not starts up LED red white red

      correct me please if I am wrong, is this the correct service manual for my tv?
      Attached Files

      Comment


        #4
        Re: LG TV 42LW4500 does not starts up LED red white red

        #3 below is a good place to start, try to do it just as instructed.

        Comment


          #5
          Re: LG TV 42LW4500 does not starts up LED red white red

          Very good instructional video there: https://www.youtube.com/watch?v=ocqnqmBxiqY

          Comment


            #6
            Re: LG TV 42LW4500 does not starts up LED red white red

            The LW series LG TVs have a common problem with the BGA Chip. Try heating the BGA chip at 350F with a Hot Air Station for 10Mins.

            Comment


              #7
              Re: LG TV 42LW4500 does not starts up LED red white red

              from the lg service repair process I should go to A19 and A22, but
              can someone explain me the attachment
              Contents of LCD TV Standard Repair Process Detail Technical Manual A22.png
              how to do so?
              which is the IN-START button of the remote?
              Attached Files
              Last edited by mrobo; 11-17-2019, 09:36 AM.

              Comment


                #8
                Re: LG TV 42LW4500 does not starts up LED red white red

                today I made some measurements and here are results, look attachment
                as you can see when I press power on on remote the votages on column pins2 - PWM jumps from 0,28V to 0,38V then (relay cycles) 0,01V again to 0,28V, any advice where should look next?
                Attached Files
                Last edited by mrobo; 02-09-2020, 09:09 AM.

                Comment


                  #9
                  Re: LG TV 42LW4500 does not starts up LED red white red

                  It seams that all voltages are correct only pin18 DRV-ON (Inverter On/Off) I have 0V, which voltage should it have?

                  Comment


                    #10
                    Re: LG TV 42LW4500 does not starts up LED red white red

                    Suspect mainboard.

                    Comment


                      #11
                      Re: LG TV 42LW4500 does not starts up LED red white red

                      Originally posted by mrobo View Post
                      It seams that all voltages are correct only pin18 DRV-ON (Inverter On/Off) I have 0V, which voltage should it have?
                      That is the control voltage which comes from the main board, likely 3.3 volts. It appears the main board is not sending the control signal, and likely the pwm control signal is also missing. Like others have said, likely main board fault
                      Last edited by R_J; 02-10-2020, 11:10 AM.

                      Comment


                        #12
                        Re: LG TV 42LW4500 does not starts up LED red white red

                        Do you mean that voltage from pin2 PWM which jumps from 0,28V to 0,38V is low and should be 0 powered off and 3.5V when powered on?
                        Even the voltage pin18 DRV-ON (Inverter On/Off) on which I have 0V, should have 3.5V when turned on TV?

                        Comment


                          #13
                          Re: LG TV 42LW4500 does not starts up LED red white red

                          Yep, 0 volts DRV-ON means no backlights.

                          Comment


                            #14
                            Re: LG TV 42LW4500 does not starts up LED red white red

                            Originally posted by mrobo View Post
                            Do you mean that voltage from pin2 PWM which jumps from 0,28V to 0,38V is low and should be 0 powered off and 3.5V when powered on?
                            Even the voltage pin18 DRV-ON (Inverter On/Off) on which I have 0V, should have 3.5V when turned on TV?
                            The PWM pin is "Pulse-Width Modulation", you would need a scope to look at the waveform.
                            DRV-ON needs to be high(3.3v) to turn on the backlight, but you can't force it on with the main board connected as you could damage the main board.
                            Look at the main board and see if you can find Q405. This is the inverter control transistor, It might be shorted. The INV_CTL signal comes from IC1002 (microprocessor) and drives Q405 base
                            Last edited by R_J; 02-10-2020, 05:35 PM.

                            Comment


                              #15
                              Re: LG TV 42LW4500 does not starts up LED red white red

                              Originally posted by R_J View Post
                              The PWM pin is "Pulse-Width Modulation", you would need a scope to look at the waveform.
                              DRV-ON needs to be high(3.3v) to turn on the backlight, but you can't force it on with the main board connected as you could damage the main board.
                              Look at the main board and see if you can find Q405. This is the inverter control transistor, It might be shorted. The INV_CTL signal comes from IC1002 (microprocessor) and drives Q405 base
                              Today I found the NPN transistor Q405 2SC3052 and measured it on board like diodes with digital multimeter and here are results:
                              -pin1 Base to +pin2 Emitter = 1969 mV
                              -pin1 Base to +pin3 Collector = infinity
                              -pin2 Emitter to +pin3 Collector = 965 mV
                              reverse measurement:
                              +pin1 Base to -pin2 Emitter = 627mV
                              +pin1 Base to -pin3 Collector = 624 mV
                              +pin2 Emitter to -pin3 Collector = 724mV
                              for me it does not look like shorted, but not sure if it is good or bad, any next idea? advice?
                              Attached Files
                              Last edited by mrobo; 02-16-2020, 10:20 AM. Reason: adding picture

                              Comment


                                #16
                                Re: LG TV 42LW4500 does not starts up LED red white red

                                I have a 42LW5400 which doesn't turn on and has the led pulsing red. I tried heating the mainboard but nothing changed.

                                Comment


                                  #17
                                  Re: LG TV 42LW4500 does not starts up LED red white red

                                  Originally posted by mrobo View Post
                                  Today I found the NPN transistor Q405 2SC3052 and measured it on board like diodes with digital multimeter and here are results:
                                  -pin1 Base to +pin2 Emitter = 1969 mV
                                  -pin1 Base to +pin3 Collector = infinity
                                  -pin2 Emitter to +pin3 Collector = 965 mV
                                  reverse measurement:
                                  +pin1 Base to -pin2 Emitter = 627 mV
                                  +pin1 Base to -pin3 Collector = 624 mV
                                  +pin2 Emitter to -pin3 Collector = 724 mV
                                  for me it does not look like shorted, but not sure if it is good or bad, any next idea? advice?
                                  compared measurements on Q401 same transistor type
                                  -pin1 Base to +pin2 Emitter = infinity
                                  -pin1 Base to +pin3 Collector = 1963 mV
                                  -pin2 Emitter to +pin3 Collector = 1521 mV
                                  reverse measurement:
                                  +pin1 Base to -pin2 Emitter = 628mV
                                  +pin1 Base to -pin3 Collector = 631 mV
                                  +pin2 Emitter to -pin3 Collector = infinity
                                  Attached Files

                                  Comment


                                    #18
                                    Re: LG TV 42LW4500 does not starts up LED red white red

                                    Originally posted by WhiteWolfHellas View Post
                                    I have a 42LW5400 which doesn't turn on and has the led pulsing red. I tried heating the mainboard but nothing changed.
                                    does the relay clicks when powered on with remote, then you have probably same problem like me

                                    Comment

                                    Working...
                                    X