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Macbook Pro A1989 - No image, working fine with external monitor

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    #1

    Macbook Pro A1989 - No image, working fine with external monitor

    Hi everyone,


    I have a MacBook Pro A1989 that was likely exposed to liquid. It doesn't display an image on the built-in screen, but the screen is backlit (you can't see the Apple logo or any other elements when held up to light). The laptop provides 20V and 1.5-2A, and it works fine when I use it with an external monitor. Currently, the connector for the display (J8500) is disconnected. I'm writing to ask for help in diagnosing the issue. I've heard that when the J8500 is exposed to liquid, the processor pin responsible for the display might short-circuit, and I'd like to know how I can diagnose this problem and confirm this fault with 100% certainty. I have a multimeter and a boardview, so I can take measurements. Thank you very much for your advice.

    Device: Macbook Pro A1989 board number: 820-00850
    Tags: None
    #2
    When you get liquid into the connector, 50V from the backlight spills into the data line adjacent to it that goes to the CPU. Pin1 (EDP_INT_AUX_N) usually reads near short to ground in this instance. Only solution is to replace the CPU or just use external monitor.

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      #3
      I have 09.33k ohms on pin 1 (edp_int_aux_n) relative to ground.

      I also noticed a burned trace along with the ferrite bead L8504 and connected the traces with a wire, but I'm not sure if I correctly understood how the connection should be made (I'm attaching a photo).

      After this fix, the screen worked and displayed an image, but after turning the laptop on again, the screen is blank once more.

      Click image for larger version Name: IMG_4282-crop.jpg Views: 155 Size: 731.2 KB ID: 3331283

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        #4
        That is for the Ambient Light Sensor for the camera. If that is burnt, there is often damage in the flex connectors on the display assembly itself. There are two that are unpluggable, one for backlight, the other for the camera. Check both for liquid damage.

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          #5
          There are no visible signs of liquid damage, but I suspect that someone was there before me. I only found bends on the flex, but I doubt they are significant enough to cause the laptop to not display any image.

          Click image for larger version Name: IMG_4316.jpg Views: 141 Size: 528.0 KB ID: 3331360
          Click image for larger version Name: IMG_4315.jpg Views: 131 Size: 321.6 KB ID: 3331361

          Is there anything else I could check? Unfortunately, I don't have a replacement screen.

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            #6
            That's pretty typical of flex cable damage from dirt/dust/sand ingress and I see that all the time. Display failure is quite common as a result. Sometimes you get vertical bars instead.

            As far as I know, Apple is the only one that has this shitty design with flat ribbon cables and having them exposed to foreign material via a gap at the base. They've also known about it since 2016, and here we are in 2024 with the same shit design. No one seems to call them out for it. Apple has set expectations with their customer base that their laptops are only good for around 4 years or so. Most just accept it and buy another machine.

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              #7
              The question is whether such a flex could be the reason for the complete lack of an image. I would like to eliminate the risk of a motherboard malfunction before attempting to repair the display flex. What could I check to eliminate the possibility of a motherboard issue before I cut the display flex?

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