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macbook pro a1989 power on but black screen

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    macbook pro a1989 power on but black screen

    hi everyone, i have this macbook pro with 820-00850a motherboard,
    at the beginning it had burn marks on the flat connector on the display side, replaced the flat and connector on the display side but the problem remains,

    when I turn on I hear the boing, the keyboard lights up but there is no display activity, even in backlight there is no image,
    checked fuse, there are no short circuits,
    suggestions?
    I don't own spare display
    from the measurements are missing
    PPVIN_S0SW_LCDBKLT 0 V
    CPUGT_SW1 0V
    PVCCEDRAM 0V

    thanks
    Attached Files

    #2
    Re: macbook pro a1989 power on but black screen

    1) Try a PRAM reset

    2) Post the voltage readings for:

    PP5V_S0SW_LCD

    PPVOUT_S0_LCDBKLT

    PPVIN_S0SW_LCDBKLT

    LCDBKLT_EN_L

    PPVIN_S0SW_LCDBKLT_F

    BKLT_EN_R

    EDP_BKLT_EN

    I2C_TCON_SDA

    I2C_TCON_SCL

    Comment


      #3
      Re: macbook pro a1989 power on but black screen

      Originally posted by mon2 View Post
      1) Try a PRAM reset
      2) Post the voltage readings for:


      PP5V_S0SW_LCD

      PPVOUT_S0_LCDBKLT

      PPVIN_S0SW_LCDBKLT

      LCDBKLT_EN_L

      PPVIN_S0SW_LCDBKLT_F

      BKLT_EN_R

      EDP_BKLT_EN

      I2C_TCON_SDA

      I2C_TCON_SCL

      ok,mesure

      PP5V_S0SW_LCD 5 V

      PPVOUT_S0_LCDBKLT 0 V

      PPVIN_S0SW_LCDBKLT 0V

      LCDBKLT_EN_L 12.5 V

      PPVIN_S0SW_LCDBKLT_F 12.5 V

      BKLT_EN_R 0V

      EDP_BKLT_EN 0V

      I2C_TCON_SDA 3.3V

      I2C_TCON_SCL 3.3 V


      all measurements were made with the display disconnected with the power cable only

      replaced q8400, always no display signal
      thanks
      Last edited by reset1986; 10-12-2021, 06:51 AM.

      Comment


        #4
        Re: macbook pro a1989 power on but black screen

        PPVIN_S0SW_LCDBKLT must it always be 12.5v even with the panel disconnected?

        Comment


          #5
          Re: macbook pro a1989 power on but black screen

          Diode mode to ground EDP_INT_AUX_N EDP_INT_AUX_P
          OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

          Comment


            #6
            Re: macbook pro a1989 power on but black screen

            Originally posted by piernov View Post
            Diode mode to ground EDP_INT_AUX_N EDP_INT_AUX_P
            sorry for the delay, I had put this mac aside, today I try the values of the 2 signals and let you know, thanks:pensiero:

            Comment


              #7
              Re: macbook pro a1989 power on but black screen

              Originally posted by piernov View Post
              Diode mode to ground EDP_INT_AUX_N EDP_INT_AUX_P
              EDP_INT_AUX_N in short,

              EDP_INT_AUX_P correct value,

              measured in diode mode,


              EDP_INT_AUX_N is generated by the cpu,

              cpu broken?

              Comment


                #8
                Re: macbook pro a1989 power on but black screen

                Louis has covered this design issue a few times. Pin 43 (PPVOUT_S0_LCDBKLT) and Pin 1 (EDP_INT_AUX_N) are side by side on J8500. Any liquid damage to this connector can potentially allow that high voltage into that data line and damaging the CPU. Crazy design.

                Comment


                  #9
                  Re: macbook pro a1989 power on but black screen

                  Louis addressed this design issue a couple of times. Pin 43 (PPVOUT_S0_LCDBKLT) and pin 1 (EDP_INT_AUX_N) are next to each other on J8500. Any liquid damage to this connector could potentially allow this high voltage to enter this data line and damage the CPU. Doesn't the A1989 have a chip like the U9850 that can be swapped out, like the A1707? Is the CPU definitely affected in this case? On my board, pin 43 and pin 1 also had a short circuit!

                  Comment

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