820-3115 no backlight / no lcd

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  • mtiago182
    New Member
    • Jul 2020
    • 7
    • Brasil
    #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
    • mtiago182
      New Member
      • Jul 2020
      • 7
      • Brasil
      #2
      Re: 820-3115 no backlight / no lcd

      Originally posted by mtiago182
      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

        • piernov
          Super Moderator
          • Jan 2016
          • 4435
          • France
          #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

            • mtiago182
              New Member
              • Jul 2020
              • 7
              • Brasil
              #4
              Re: 820-3115 no backlight / no lcd

              Originally posted by piernov
              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

                • piernov
                  Super Moderator
                  • Jan 2016
                  • 4435
                  • France
                  #5
                  Re: 820-3115 no backlight / no lcd

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

                    Comment

                    • mtiago182
                      New Member
                      • Jul 2020
                      • 7
                      • Brasil
                      #6
                      Re: 820-3115 no backlight / no lcd

                      Originally posted by piernov
                      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

                        • MtapeK
                          Member
                          • Sep 2020
                          • 35
                          • Zimbabwe
                          #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

                            • judamex
                              Active Member
                              • Jan 2021
                              • 183
                              • Mexico
                              #8
                              Re: 820-3115 no backlight / no lcd

                              same problem

                                Comment

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