LG 42LG50 no backlight or display

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  • Daveleone
    Badcaps Veteran
    • Apr 2016
    • 267
    • USA

    #21
    Re: LG 42LG50 no backlight or display

    Originally posted by budm
    If you can disconnect that cable to the T-CON board then the backlights come on and stay on then your inverters/lamps are OK. As I indicated, you should now see the pictures on the screen. You TV has what is called dynamic contrast, the T-CON controls the backlight level based on video scenes.
    Ok, there is still no picture, just backlight. What can I do as a next step to determine if the problem is the main board, the t-con, or the panel?

    Comment

    • budm
      Badcaps Legend
      • Feb 2010
      • 40746
      • USA

      #22
      Re: LG 42LG50 no backlight or display

      Find out if you do have 12VDC on both end so of the SMD fuse on the T-CON board with ref. to chassis GND.
      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

      • Daveleone
        Badcaps Veteran
        • Apr 2016
        • 267
        • USA

        #23
        Re: LG 42LG50 no backlight or display

        Originally posted by budm
        Find out if you do have 12VDC on both end so of the SMD fuse on the T-CON board with ref. to chassis GND.
        Yes. Measured 12.44v on both sides of FP1 (which I'm assuming is the fuse we're talking about).

        Comment

        • budm
          Badcaps Legend
          • Feb 2010
          • 40746
          • USA

          #24
          Re: LG 42LG50 no backlight or display

          OK, try having one ribbon cable between the LCD panel and the T-con board connected one at a time to see what you will get on the screen.
          Right now without that cable between the T-CON and the Master inverter board connected, do you still have full control of the TV, I.E. able to turn TV on and off?
          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

          • Daveleone
            Badcaps Veteran
            • Apr 2016
            • 267
            • USA

            #25
            Re: LG 42LG50 no backlight or display

            Originally posted by budm
            OK, try having one ribbon cable between the LCD panel and the T-con board connected one at a time to see what you will get on the screen.
            Right now without that cable between the T-CON and the Master inverter board connected, do you still have full control of the TV, I.E. able to turn TV on and off?
            Disconnected each T-Con->Panel ribbon cable one at a time. Made no difference.

            Yes, I can now turn the power on and off via the power button on the front bezel.

            Comment

            • lookimback
              Badcaps Legend
              • Aug 2013
              • 1489
              • USA

              #26
              Re: LG 42LG50 no backlight or display

              Originally posted by budm
              OK, try having one ribbon cable between the LCD panel and the T-con board connected one at a time to see what you will get on the screen.
              Right now without that cable between the T-CON and the Master inverter board connected, do you still have full control of the TV, I.E. able to turn TV on and off?
              Be sure to cycle power off whenever disconnecting or reconnecting the ribbon cables. I fried a 60" Sharp panel like that once. Additionally, if you removed each ribbon cable, but didn't cycle the power when doing so, then repeat that process, cycling power as I just described, and you may get different results.
              ------------signature starts here------------


              Comment

              • Daveleone
                Badcaps Veteran
                • Apr 2016
                • 267
                • USA

                #27
                Re: LG 42LG50 no backlight or display

                Originally posted by lookimback
                Be sure to cycle power off whenever disconnecting or reconnecting the ribbon cables. I fried a 60" Sharp panel like that once. Additionally, if you removed each ribbon cable, but didn't cycle the power when doing so, then repeat that process, cycling power as I just described, and you may get different results.
                I did. I unplugged the TV, removed one cable, plugged the TV back in. Then repeated for the other cable.

                Comment

                • budm
                  Badcaps Legend
                  • Feb 2010
                  • 40746
                  • USA

                  #28
                  Re: LG 42LG50 no backlight or display

                  Well, we need to check the Voltages on the test points on the T-CON board next.
                  You can see bare copper pads with label for each one, so far I can see:
                  VD33V
                  V25V
                  VDD,
                  VGH
                  VGL
                  VAA

                  so look for pad with V????.............
                  Last edited by budm; 07-17-2018, 10:05 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

                  • Daveleone
                    Badcaps Veteran
                    • Apr 2016
                    • 267
                    • USA

                    #29
                    Re: LG 42LG50 no backlight or display

                    Originally posted by budm
                    Well, we need to check the Voltages on the test points on the T-CON board next.... look for pad with V????.............
                    Here are all the pads I found and tested (I bolded the Vxx ones). These values are the same whether the ribbon cable from the master inverter is plugged in or not, except where noted in italics:

                    GND 0
                    SDA 3.3
                    VIN 12.44
                    SCL 3.3
                    TSTPGW 0

                    DRL1 0
                    OE1 3.3
                    STV 0
                    CKV 0
                    VSCN 0

                    VDD 3.3
                    VDA 0
                    VCOM 0
                    VGH 11.06
                    VGL -5.57


                    VST -0.18
                    SIN1 0
                    SIN2 0
                    GRL2 3.3
                    B_STH 3.3
                    B_TP1 0 (NOTE: when the ribbon cable from the master inverter is plugged in, this is 2.22v)

                    B_STHR 0 (rising slowly)

                    DIM_O 0
                    DIM_I 0.1 (rising slowly) (NOTE: when the ribbon cable from the master inverter is plugged in, this is 3.33v, even when the ribbon cable is disconnected if I test the pin on the inverter side it is 3.4v)

                    VD33V 3.3
                    VGHP 11.1
                    VAA 0
                    V12V 12.44
                    V25V_A 2.49
                    VREF 0

                    Comment

                    • Daveleone
                      Badcaps Veteran
                      • Apr 2016
                      • 267
                      • USA

                      #30
                      Re: LG 42LG50 no backlight or display

                      Originally posted by budm
                      .
                      What next?

                      Comment

                      • budm
                        Badcaps Legend
                        • Feb 2010
                        • 40746
                        • USA

                        #31
                        Re: LG 42LG50 no backlight or display

                        https://www.badcaps.net/forum/showpo...6&postcount=18

                        Some of the Voltages are low and some are missing, I.E. Vref. should not be 0V.
                        A this point you can try new T-CON board.

                        From Andrew in the link above:
                        1. Vin: 12V (we confirmed as present)
                        2. Vdd (Vlogic, Vddd): 3.3V
                        3. Vda (Vs, Vsource, Vdda Avdd): 14V to 20V
                        4. Vgh (Vgon, Von, Vddg): 20V to 30V
                        5. Vgl (Vgoff, Voff, Veeg): -5V to -7V
                        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

                        • Andrew F. Ali
                          Badcaps Legend
                          • Jan 2014
                          • 2450
                          • Trinidad & Tobago

                          #32
                          Re: LG 42LG50 no backlight or display

                          ,

                          Comment

                          • Daveleone
                            Badcaps Veteran
                            • Apr 2016
                            • 267
                            • USA

                            #33
                            Re: LG 42LG50 no backlight or display

                            Originally posted by budm
                            A this point you can try new T-CON board.
                            Ordered. I'll post results as soon as it arrives (scheduled to arrive 7/24).

                            Comment

                            • Daveleone
                              Badcaps Veteran
                              • Apr 2016
                              • 267
                              • USA

                              #34
                              Re: LG 42LG50 no backlight or display

                              Originally posted by budm
                              A this point you can try new T-CON board.
                              Received the new T-Con today.

                              No joy. Same exact results (same behavior, same voltages) with the new T-Con. So...main board? Is VDA on the T-Con supplied by the main board (over the LVDS cable)? If so, a bad main board would explain lack of VDA on the T-Con and the error signal sent to the inverters. And maybe the error signal sent to the inverter would also explain why DIM_I on T-Con, which is coming from DIM_O on the master inverter, is also high. Example: Main board is bad. It doesn't send the proper voltages to T-Con. It does send ERROR to master inverter. Inverter sends DIM_O high to T-con to indicate the error. Maybe? I don't know...thoughts?
                              Last edited by Daveleone; 07-21-2018, 04:45 PM.

                              Comment

                              • Daveleone
                                Badcaps Veteran
                                • Apr 2016
                                • 267
                                • USA

                                #35
                                Re: LG 42LG50 no backlight or display

                                Or do you think I got a 2nd bad T-Con?

                                Comment

                                • budm
                                  Badcaps Legend
                                  • Feb 2010
                                  • 40746
                                  • USA

                                  #36
                                  Re: LG 42LG50 no backlight or display

                                  So do you get the same readings as in post 30?
                                  What is the LCD panel model number?
                                  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

                                  • Daveleone
                                    Badcaps Veteran
                                    • Apr 2016
                                    • 267
                                    • USA

                                    #37
                                    Re: LG 42LG50 no backlight or display

                                    Originally posted by budm
                                    So do you get the same readings as in post 30?
                                    What is the LCD panel model number?
                                    Yes, same readings as post 30 with one minor exception - B_TP1 is 2.22v on the original T-con and it is 3.3v on the new T-Con, when the ribbon cable is unplugged. When the ribbon cable is plugged in B_TP1 is 0v on both T-Cons.
                                    The panel has the following labels on it: "M$44-D024408 - L$T13A423068433524" and "V420H1-L12 Rev. C1 - C4C140185120364 - E207943"

                                    Comment

                                    • syaoran123
                                      Senior Member
                                      • Jun 2014
                                      • 178
                                      • Australia

                                      #38
                                      Re: LG 42LG50 no backlight or display

                                      Can you inspect the blue polymer caps on the psu next to the transformers on the bottom left hand side? Look for any signs of damage.

                                      Comment

                                      • Daveleone
                                        Badcaps Veteran
                                        • Apr 2016
                                        • 267
                                        • USA

                                        #39
                                        Re: LG 42LG50 no backlight or display

                                        Originally posted by syaoran123
                                        Can you inspect the blue polymer caps on the psu next to the transformers on the bottom left hand side? Look for any signs of damage.
                                        I gave them a look over. No visible damage.
                                        Attached Files

                                        Comment

                                        • Andrew F. Ali
                                          Badcaps Legend
                                          • Jan 2014
                                          • 2450
                                          • Trinidad & Tobago

                                          #40
                                          Re: LG 42LG50 no backlight or display

                                          I am beginning to wonder if your Panel is bad now that I've read all the posts again.

                                          Comment

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