Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

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  • GfilipeZ
    Member
    • May 2021
    • 43
    • Portugal

    #1

    Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

    Hi,

    This machine has no traces of liquid damage or corrosion and displays image normally on external monitors.
    So far the measurements I've made, lead me to conclude that the source of the anomaly must be the dpmux U9800.
    But I would like, if possible, to have your help and opinion.

    J8500:
    (4) BUF_EDP_PANEL_PWR_EN = 3,42V
    (45) PP5V_S0SW_LCD = 5,13V
    (44) PP3V3_S0SW_LCD = 3,29V
    (43) PPVOUT_S0_LCDBKLT = 0V

    DP_INT_HPD_R = 3,27V
    R8505 have normal value.

    U8900:
    (77) EDP_BKLT_EN = 0V

    U8510:
    (2) EDP_PANEL_PWR_EN = 3,28V
    (3) PANEL_FET_EN_DLY = 3,42V
    (6) DFR_DISP_PWR_EN = 3,42V
    (10) DFR_DISP_SMC_RST_L = 3,42V
    (12) SMC_RESET_L = 3,42V


    If I have to replace the IC U9800, it has to be from a Logic Board with the same number. Because this IC is programmed, right?


    Best regards!
  • mon2
    Badcaps Legend
    • Dec 2019
    • 13855
    • Canada

    #2
    Re: Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

    Check SMC_LID voltage on J4501.

    Also:

    SMC_LID_RIGHT

    SMC_LID_LEFT_R

    SMC_LID_LEFT

    Comment

    • GfilipeZ
      Member
      • May 2021
      • 43
      • Portugal

      #3
      Re: Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

      Originally posted by mon2
      check smc_lid voltage on j4501.

      Also:

      smc_lid_right

      smc_lid_left_r

      smc_lid_left

      smc_lid = 3,42v
      smc_lid_right = 3,41v
      smc_lid_left_r = 3,41v
      smc_lid_left = 3,41v

      Comment

      • GfilipeZ
        Member
        • May 2021
        • 43
        • Portugal

        #4
        Re: Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

        More anomaly analysis ideas?

        Comment

        • mon2
          Badcaps Legend
          • Dec 2019
          • 13855
          • Canada

          #5
          Re: Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

          Remove all power. Meter in resistance mode.

          What is the resistance to ground of EDP_BKLT_EN ?

          Resistance to ground of PPVOUT_S0_LCDBKLT ?

          With the adapter & LCD connected, what are the voltage readings of the following?

          F8400, pin # 1
          F8400, pin # 2

          ISNS_LCDBKLT_P
          ISNS_LCDBKLT_N

          I2C_BKLT_SCL
          I2C_BKLT_SDA

          Comment

          • GfilipeZ
            Member
            • May 2021
            • 43
            • Portugal

            #6
            Re: Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

            Originally posted by mon2
            Remove all power. Meter in resistance mode.

            What is the resistance to ground of EDP_BKLT_EN ?

            Resistance to ground of PPVOUT_S0_LCDBKLT ?

            With the adapter & LCD connected, what are the voltage readings of the following?

            F8400, pin # 1
            F8400, pin # 2

            ISNS_LCDBKLT_P
            ISNS_LCDBKLT_N

            I2C_BKLT_SCL
            I2C_BKLT_SDA
            Thanks mon2,

            EDP_BKLT_EN = 9,8Kohm
            PPVOUT_S0_LCDBKLT = 1,8Kohm

            F8400, pin # 1 = 12,62V
            F8400, pin # 2 = 12,62V

            ISNS_LCDBKLT_P = 12,62V
            ISNS_LCDBKLT_N = 12,62V

            I2C_BKLT_SCL = 4,89V
            I2C_BKLT_SDA = 4,82V

            Comment

            • mon2
              Badcaps Legend
              • Dec 2019
              • 13855
              • Canada

              #7
              Re: Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

              PPVOUT_S0_LCDBKLT = 1,8Kohm
              This resistance, in my opinion, sounds low.

              Can you remove the LCD display and check the resistance to ground again of this rail (PPVOUT_S0_LCDBKLT) ?

              If the resistance is still low WITHOUT the LCD display, then proceed to desolder one leg of the diode @ D8410. Then check the resistance again to ground of PPVOUT_S0_LCDBKLT.

              This method should allow us to isolate the possible bad cap between D8410 and the LCD display.

              Post your readings. Do not power up - just use resistance checks.
              Attached Files

              Comment

              • GfilipeZ
                Member
                • May 2021
                • 43
                • Portugal

                #8
                Re: Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

                Originally posted by mon2
                This resistance, in my opinion, sounds low.

                Can you remove the LCD display and check the resistance to ground again of this rail (PPVOUT_S0_LCDBKLT) ?

                If the resistance is still low WITHOUT the LCD display, then proceed to desolder one leg of the diode @ D8410. Then check the resistance again to ground of PPVOUT_S0_LCDBKLT.

                This method should allow us to isolate the possible bad cap between D8410 and the LCD display.

                Post your readings. Do not power up - just use resistance checks.
                Hi,

                PPVOUT_S0_LCDBKLT (no LCD) = 3,1Kohm

                PPVOUT_S0_LCDBKLT (no LCD neither D8410) = 2,5Kohm

                I injected voltage on the "cluster" (without LCD and D8410), to see if any capacitor warms up, but nothing happens.

                After that, I checked again the resistance on PPVOUT_S0_LCDBKLT, and the value was 178Kohm.

                So I found, every time I plug the display without power to the adapter, the resistance drops immediately to 1,8Kohm. And if I apply some voltage again, it goes up to 178Kohm.

                My only conclusion is that the display may be damaged.

                Comment

                • GfilipeZ
                  Member
                  • May 2021
                  • 43
                  • Portugal

                  #9
                  Re: Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

                  Originally posted by GfilipeZ
                  Hi,

                  PPVOUT_S0_LCDBKLT (no LCD) = 3,1Kohm

                  PPVOUT_S0_LCDBKLT (no LCD neither D8410) = 2,5Kohm

                  I injected voltage on the "cluster" (without LCD and D8410), to see if any capacitor warms up, but nothing happens.

                  After that, I checked again the resistance on PPVOUT_S0_LCDBKLT, and the value was 178Kohm.

                  So I found, every time I plug the display without power to the adapter, the resistance drops immediately to 1,8Kohm. And if I apply some voltage again, it goes up to 178Kohm.

                  My only conclusion is that the display may be damaged.
                  Hi,

                  Any idea?

                  Comment

                  • reformatt
                    Badcaps Legend
                    • Feb 2020
                    • 1398
                    • Australia

                    #10
                    Re: Macbook A1707 / 820-00281-A / Boot, but no image nor backlight

                    Any A1706/A1707/A1708 that come in with backlight issues are predominantly damaged flexes in the LCD. Try another known working LCD first.

                    MUX damage only usually occurs with liquid damage on the LCD connector since the backlight voltage is right next to a data pin that goes to the MUX. Of course on models without the MUX, it destroys the CPU in this case.

                    Comment

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