Apple MacBook A2337 - No backlight

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  • tommy97
    Senior Member
    • Mar 2023
    • 151
    • United Kingdom
    #1

    Apple MacBook A2337 - No backlight

    Hi guys, I've got MacBook Air a2337 with no backlight. Once while testing it displayed with the backlight, however after restart problem come back.

    The laptop was tested with fully working screen.

    PP5v_BKLT_A/B 5V
    PP5v_BKLT_D 5V
    PP5V_S2 5V
    PP5V_SW_LCD 0.4V
    P5VS2_PWR_EN 1.8V
    P5VS2_BST_R 8V
    P5VS2_SW 5V
    PPBUS_5VS2_VIN 5V
    PPVOUT_LCDBKLT - Doesn't short 0V
    FP800 - Both sides 12v
    BKLT_EN_R & BL_PWR_EN - around 1.8v

    LP800 0.014V On both sides (should be 12? / no short)
    UC300 & UP800 Replaced with tested one - no difference.
    Just to clarify, no backlight - I can see display very dim.
    Tags: None
    • tommy97
      Senior Member
      • Mar 2023
      • 151
      • United Kingdom
      #2
      Any ideas?

        Comment

        • mon2
          Badcaps Legend
          • Dec 2019
          • 13969
          • Canada
          #3
          What are the voltage to ground measurements for:

          I2C_BKLT_SCL
          I2C_BKLT_SDA

          Share the voltage to ground of the mosfet @ QP800:

          source
          gate ; LCDBKLT_EN_L
          drain

            Comment

            • tommy97
              Senior Member
              • Mar 2023
              • 151
              • United Kingdom
              #4
              I2C_BKLT_SCL 5.1V
              I2C_BKLT_SDA 5.1V

              QP800 - LCDBKLT_EN_L​ (3) 12V, (leg 1,2,6,5 - 0.4v PPVIN_LCDBKLT_Q), PPVIN_LCDBKLT_R (4) 12v.
              During test again I've got display, however after restart same thing with no backlight, while backlight were on Each side had 12v on the QP800

                Comment

                • mon2
                  Badcaps Legend
                  • Dec 2019
                  • 13969
                  • Canada
                  #5
                  Take a piece of wire and short pin # 3 on QP800 to ground. This action will force enable the P-channel mosfet @ QP800. Be careful to touch only pin # 3 on QP800.

                    Comment

                    • tommy97
                      Senior Member
                      • Mar 2023
                      • 151
                      • United Kingdom
                      #6
                      After shorting pin 3 same problem, rest of the pins 12v

                        Comment

                        • mon2
                          Badcaps Legend
                          • Dec 2019
                          • 13969
                          • Canada
                          #7
                          The thread below this one is with a similar fault.

                          Check the FB pin on the backlight IC. Confirm the FB resistors are present. Confirm the diode @ DB800 is not defective.

                          What is the voltage to ground of IPD_LID_OPEN_1V8?

                            Comment

                            • tommy97
                              Senior Member
                              • Mar 2023
                              • 151
                              • United Kingdom
                              #8
                              IPD_LID_OPEN_1V8 - 1.8v
                              DP800 - 0.350 One way, checked same reading on the spare board
                              PPVOUT_LCDBKLT_SW 0.3V
                              PPVOUT_LCDBKLT - 0.15V

                                Comment

                                • mon2
                                  Badcaps Legend
                                  • Dec 2019
                                  • 13969
                                  • Canada
                                  #9
                                  Is PP5V_SW_LCD voltage to ground stable?

                                  Measure the LCDBKLT_HS_ISENSE signal on the board. This signal is a gauge of the current sense of the display assembly.

                                  Confirm the details of the mosfet @ QP801. Test with the meter in resistance mode.

                                  source / drain
                                  source / gate
                                  gate / drain

                                  A low resistance means the mosfet is defective.

                                  Suggest to flux and reflow the replaced known good backlight IC. Test again.

                                    Comment

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