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820-3115 no backlight / no lcd

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    #1

    820-3115 no backlight / no lcd

    Hello everyone!

    I have a 820-3115 motherboard that don`t show image (no lcd and no bkl), external display works fine and J9000 looks fine.

    LCD_IG_PWR_EN = 0V (missing)
    PP3V3_LCDVDD_SW = 0V (missing)
    PP3V3_S0_LCD_F = 3.317V
    PPVOUT_SW_LCDBKLT = 0.011V

    Already replaces U9000 and R1984, although the diode and resistance measurements are ok. Every diode and resistance measurements from pin 7 to 17 at J9000 seens ok. LCD_IG_PWR_EN, PP3V3_LCDVDD_SW diode and resistance measurements are also ok.

    I'm starting to think my problem is with U1800

    Does anyone have any idea what it might be? Thank you very much in advance.
    Tags: None
    #2
    Re: 820-3115 no backlight / no lcd

    Originally posted by mtiago182 View Post
    Hello everyone!

    I have a 820-3115 motherboard that don`t show image (no lcd and no bkl), external display works fine and J9000 looks fine.

    LCD_IG_PWR_EN = 0V (missing)
    PP3V3_LCDVDD_SW = 0V (missing)
    PP3V3_S0_LCD_F = 3.317V
    PPVOUT_SW_LCDBKLT = 0.011V

    Already replaces U9000 and R1984, although the diode and resistance measurements are ok. Every diode and resistance measurements from pin 7 to 17 at J9000 seens ok. LCD_IG_PWR_EN, PP3V3_LCDVDD_SW diode and resistance measurements are also ok.

    I'm starting to think my problem is with U1800

    Does anyone have any idea what it might be? Thank you very much in advance.
    Forgot to mention, SMC_LID and SMC_LID_R = 3.44V

    Comment

      #3
      Re: 820-3115 no backlight / no lcd

      PRAM reset done?
      Tried another LCD?
      Communication happening over DDC?
      OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

      Comment

        #4
        Re: 820-3115 no backlight / no lcd

        Originally posted by piernov View Post
        PRAM reset done?
        Tried another LCD?
        Communication happening over DDC?
        Thanks for answering.

        PRAM reset yes.
        I've tried with 2 LCD, both work on another Mac.

        Sorry I didn't understand the meaning of "DDC".

        Comment

          #5
          Re: 820-3115 no backlight / no lcd

          Display Data Channel
          LVDS_DDC_CLK
          LVDS_DDC_DATA
          OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

          Comment

            #6
            Re: 820-3115 no backlight / no lcd

            Originally posted by piernov View Post
            Display Data Channel
            LVDS_DDC_CLK
            LVDS_DDC_DATA
            Ah ok.

            LVDS_DDC_CLK = 3.3V and 0.643 in diode mode
            LVDS_DDC_DATA = 3.3V and 0.649 in diode mode

            unfortunately I don't have an ocilloscope to measure the clock
            Last edited by mtiago182; 07-14-2021, 09:36 AM. Reason: add important info

            Comment

              #7
              Re: 820-3115 no backlight / no lcd

              i have the same board behaving in a same manner, isnt this the u1800`s problem

              Comment

                #8
                Re: 820-3115 no backlight / no lcd

                same problem

                Comment

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