TCL 65S421 No Backlight

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  • m4a2t0t
    Badcaps Veteran
    • Mar 2013
    • 276
    • USA
    #1

    TCL 65S421 No Backlight

    I can see an image on the screen with a flashlight. Is P_ON at 2.6v acceptable or does it need to be 3.3?

    Main Connector
    1- 3.3 - BL_ON
    2- 3.3 - P-DIM
    3- 2.6 - P_ON
    4- 0 - GND
    5- 2.6 - A_DIM
    6- 0 - NC
    7- 0 - GND
    8- 0 - GND
    9- 12 - 12v
    10- 12 - 12v
    11- 12 - 12v
    12- 12 - 12v
    13- 0 - 3D_EN
    14- 12 - 12v

    I see no voltage on either side of TS2 or TS3. Is something else causing U601 to not drive TS3?

    U601(OZ9976GN)
    1- -.038 DRV1
    2- -.036 GNDA
    3- 12.1 VCC
    4- 3.28 ENA
    5- 6.01 VREF
    6- 3.285 PWM
    7- 2.159 ADM
    8- -.036 STATUS
    9- 2.36 RT
    10- .036 ISEN
    11- 1.02 OVP1
    12- 1.02 OVP2
    13- -.035 SFON
    14- -.035 SSTCMP
    15- -.036 GNDP
    16- -.036 DRV2
    Attached Files
    Tags: None
    • EazyBone
      Badcaps Legend
      • Jun 2023
      • 1306
      • United states
      #2
      Re: TCL 65S421 No Backlight

      Just use a LED tester. Ive had a few of these and it was always the backlight so far, not the psu

        Comment

        • Storyteller12
          Badcaps Veteran
          • Jun 2020
          • 624
          • USA
          #3
          Re: TCL 65S421 No Backlight

          Originally posted by eazybone
          just use a led tester. Ive had a few of these and it was always the backlight so far, not the psu
          +1

            Comment

            • vinceroger69
              Badcaps Legend
              • Mar 2012
              • 6714
              • uk
              #4
              Re: TCL 65S421 No Backlight

              8 out of 10 tvs i get for free/repair are backlight issues, i always do a quick visual check on the boards then test the backlights saves so much time trouble shooting

                Comment

                • EazyBone
                  Badcaps Legend
                  • Jun 2023
                  • 1306
                  • United states
                  #5
                  Re: TCL 65S421 No Backlight

                  Originally posted by vinceroger69
                  8 out of 10 tvs i get for free/repair are backlight issues, i always do a quick visual check on the boards then test the backlights saves so much time trouble shooting
                  Agreed. These psus on the Roku TVs do weird things also when then lights have a short. Plus it's pretty much always the BLs lol

                    Comment

                    • vinceroger69
                      Badcaps Legend
                      • Mar 2012
                      • 6714
                      • uk
                      #6
                      Re: TCL 65S421 No Backlight

                      Originally posted by EazyBone
                      Agreed. These psus on the Roku TVs do weird things also when then lights have a short. Plus it's pretty much always the BLs lol
                      I have actually just fixed a 43 inch roku tv i got for free and yes was backlights at fault, first tapped in screen repair i have done it went ok i just took my time when removing the screen and cleaning it up used 3m foam tape for re assembly.

                        Comment

                        • m4a2t0t
                          Badcaps Veteran
                          • Mar 2013
                          • 276
                          • USA
                          #7
                          Re: TCL 65S421 No Backlight

                          It looks like LED2 is bad. The tester stays at 330v when I probe the pins. Thanks

                            Comment

                            • EazyBone
                              Badcaps Legend
                              • Jun 2023
                              • 1306
                              • United states
                              #8
                              Re: TCL 65S421 No Backlight

                              Yup that's your answer. Next time on these Roku TVs with same problem, just skip right to testing LEDs, then if they are good then look at PSU

                                Comment

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