820-3437 no backlight

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  • kingskie
    Badcaps Veteran
    • Oct 2014
    • 249
    • indonesia
    #1

    820-3437 no backlight

    i recieved macbook air A1466 820-3437..
    checked..no backlight..disassemble and have water damage on the dc in board connector (flexible conenctor).
    now i focus on backlight first..
    on start up i have chime and backlight on for 1 second but suddenly off

    PPHV_S0SW_LCDBKL 24V WHEN CHIME
    BKL_PLT_RST_l 3.3V
    EDP_BKLT_EN 3.3V
    LCDBKLT_DISABLE 0V
    LCD_BKLT_EN_L 0V sometimes 8.5v
    LCDBKLT_BOOST 8.6V
    PPVOUT_SW_LCDBKLT_FB 24V and drop to 8.5V
    measure all the resistor near U7701 all ok
    change U7701 2 times but still the same

    any help will be appreciated...thanks before
    Tags: None
    • mon2
      Badcaps Legend
      • Dec 2019
      • 14002
      • Canada
      #2
      Re: 820-3437 no backlight

      Hi. From memory, the A1466 820-00165 has current sense circuit on this backlight rail. Guessing that your logic board will as well. Check to see that current sense circuit is ok. What is voltage going into the current sense circuit? What is the voltage leaving? If this circuit is not complete, the logic board may sense incorrectly that there is a fault and shut off the rail after sampling the false current draw for the backlight.

        Comment

        • kingskie
          Badcaps Veteran
          • Oct 2014
          • 249
          • indonesia
          #3
          Re: 820-3437 no backlight

          already tried with another lcd but still the same

            Comment

            • kingskie
              Badcaps Veteran
              • Oct 2014
              • 249
              • indonesia
              #4
              Re: 820-3437 no backlight

              Originally posted by mon2
              Hi. From memory, the A1466 820-00165 has current sense circuit on this backlight rail. Guessing that your logic board will as well. Check to see that current sense circuit is ok. What is voltage going into the current sense circuit? What is the voltage leaving? If this circuit is not complete, the logic board may sense incorrectly that there is a fault and shut off the rail after sampling the false current draw for the backlight.
              i believe the current sense resistor is R7788 and R7789 right?
              the value is ok and the voltage runs through it is 8.5V

                Comment

                • kingskie
                  Badcaps Veteran
                  • Oct 2014
                  • 249
                  • indonesia
                  #5
                  Re: 820-3437 no backlight

                  my bad...the current sense resistor is R7717, R7718, R7719, R7720, R7721 and R7722 and all 4.5V when chime and drop to 0.9V slowly

                    Comment

                    • piernov
                      Super Moderator
                      • Jan 2016
                      • 4435
                      • France
                      #6
                      Re: 820-3437 no backlight

                      DC-in board contains lid sensor. Must be working to get backlight.
                      OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

                        Comment

                        • kingskie
                          Badcaps Veteran
                          • Oct 2014
                          • 249
                          • indonesia
                          #7
                          Re: 820-3437 no backlight

                          Originally posted by piernov
                          DC-in board contains lid sensor. Must be working to get backlight.
                          100% correct @piernov thanks for the help...but which line connect to lid sensor?

                            Comment

                            • piernov
                              Super Moderator
                              • Jan 2016
                              • 4435
                              • France
                              #8
                              Re: 820-3437 no backlight

                              Schematics/boardview → Ctrl+F "lid"
                              OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

                                Comment

                                • kingskie
                                  Badcaps Veteran
                                  • Oct 2014
                                  • 249
                                  • indonesia
                                  #9
                                  Re: 820-3437 no backlight

                                  Originally posted by piernov
                                  Schematics/boardview → Ctrl+F "lid"
                                  thanks @piernov

                                    Comment

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