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Released in November 2020, the 13" MacBook Pro features Apple's Arm-based M1 SoC with both an 8-core CPU and 8-core GPU. (Model A2338 / EMC 3578 with two Thunderbolt 3 ports)

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Weird black screen behaviour when connecting MacBook Pro M1

Hey everyone, experiencing a very weird problem. My work upgraded me from a Macbook Pro M1 8GB to a 16GB (different one to my post about the Camera).

They the exact same models (2020 A2338 M1). I have a external monitor with a USB-C hub it is connected to. It works perfectly on the 8GB mac, but when I connect my new Mac to it, it detects that the monitor is connected and it even shows the second monitor in the Display settings but for some reason the monitor is just black and turns off after a few second (but the Mac stays convinced that there is another monitor connected).

I have tried the following:
- Updating
- Restarting/Hard rebooting
- Other USB-C port
- Another monitor
- Another USB C dock

However, I can get the monitor to work by plugging the USB-C port in, waiting for the Mac to register the monitor is connected, then I switch the power on the monitor off at the wall, then turn it on again with the Mac still plugged into the monitor, it then connects fine.

I don't have to do any of this with my other exact same M1, or any of my other old Macs/friends Macs. It seems to just be this one. Not sure if there is a hardware or software issue, or the HDMI handshake is being disrupted somehow.

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Check the displays settings, you should be able to alter the externals settings.

What can happen is the setting is too high a setting. With the external connected, close the lid (Clamshell Mode) in single display it can achieve 6016x3384 (6K) at 60 Hz. If that works then you know the internal is shutting down to put all of the needed resources to the external. Otherwise in Mirror or Extended desktop the max is 2560x1600 at 227 ppi.

In addition, the internal also supports scaled resolutions of 1680 by 1050, 1440 by 900, and 1024 by 640.

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It's the external screen that's black, built in stays on.

I did check the externals settings when its black and it's running 1920*1080 @ 60hz (but 120hz is also available).

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@jordan63460 - OK, that aims us to a bad USB-C cable to the monitor if connected to the systems USB-C ports. If connected via a hub then the additional cable and hub are suspect.

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Im connected to a hub, which is connected via HDMI to the Monitor. I tried 2x other Macs, which work perfectly fine. Also tried another hub while I was at work and had similar issues but less consistent.

I feel like the Mac may be struggling with the initial HDMI handshake? I dont know if there is a separate logic board for the USBc ports or if they are direct to the main Macs motherboard.

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@jordan63460 - It been awhile since i’ved worked on this series. Looking at the iFixit parts listing it does appear the USB-C port assembly is independent, that wasn’t the case in the Intel two port model MacBook Pro (A1989, A1990, A2141, A2159, A2251, A2289, A2338 Mid 2018-2022) USB-C Board even so, replacing it would only effect a bad contact issue not deeper within the systems firmware or OS files.

What is the macOS versions between the two systems working vs not working correctly? Also go into the system inspector (the button within ‘About This Mac’) comparing the firmware versions there.

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