M1 Mac Mini not recognizing external monitor upon boot-up/wake-up

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Level 1

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M1 Mac Mini not recognizing external monitor upon boot-up/wake-up

Hi, so I’ve recently bought an LG 32UL950-W monitor and I use it with my M1 Mac Mini which I bought a month ago.

Whenever I turn on the Mac Mini and the monitor, or sometimes when I wake them up from sleep, the monitor doesn’t recognize any input source. The only working option is to unplug and replug the thunderbolt cable.

It's worth to note that before getting the LG 32UL950-W I've used an older 1440p 25" Dell monitor through HDMI, and that worked flawlessly with the M1 Mac Mini.

I've tried connecting the LG 32UL950-W monitor to my work Macbook Pro 16" 2019, and the issue doesn't occur there.

I’ve been in contact with LG, they gave me some simple tips which I've tried out, and advised me to contact Apple. I've been in contact with Apple and we haven't come to any real solution. They advised me to clear the SMC, which I've tried, and also start in Safe Mode, however that's not possible because whenever I turn off my mac the monitor goes to sleep, and when I turn the mac on again I need to unplug the Thunderbolt cable and replug it again, and then I don't get an image until it's on the progressbar stage right before login screen.

I use the Thunderbolt cable that was provided with the monitor, in the correct input. I’ve tried using different inputs and different options in monitors menu.

I've searched for similar issues on the internet and these forums and I see that this is a quite common issue with the M1 Macs.

This is clearly a software issue from Apple's side since everything works fine with my 16" Macbook Pro, I'm not planning on getting another cable/dongle/adapter or use any other cables.

Really hope somebody can help me out, or that Apple can give an estimate for a software update on this, I have no plans of returning neither the Mac Mini nor the monitor.

Thanks

Mac mini, macOS 11.1

Posted on Jan 26, 2021 10:45 PM

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Answer 1

Feb 7, 2021 11:47 AM in response to nikitamanko

I have this exact problem as well, the LG 32UL950-W will not wake from sleep.

Some interesting behaviors I've observed:

• In macOS 11.2, if you had the LG 32UL950-W on Thunderbolt and another HDMI display attached, the computer would restart from system failure automatically after about 15 minutes, probably when it was trying to do some low power/power nap operation during sleep, or sometimes when you tired to move the mouse to wake it from sleep.

As of macOS 11.3 Beta (20E5172i), this configuration will no longer restart the machine and wake the HDMI monitor but the Thunderbolt LG 32UL950-W will not come back without reconnecting the cable after user login.

• If you have any external hard drives attached to the LG USB 3.0 Bus in the back of LG 32UL950-W, sleeping the computer will trigger a power blip and automatic reboot, presumably because it tried to sleep the Thunderbolt Display but didn't know what to do about the spinning drives that need to be in low power mode to stay connected to the system.

• Reconnecting the thunderbolt cable to the Mac mini can cause a power dip to the thunderbolt bus, which sometimes causes the device connected to the other thunderbolt bus to disconnect/restart. In my case, a powered CalDigit Thunderbolt hub with 4 external project drives will restart and loose all drive mounts when trying to get the machine to see the LG 32UL950-W display again.

Something in the power management EFI of the Mac mini M1 needs a serious update in order to get these machines from panic rebooting.

• Also very curious: the M1 treats the LG 32UL950-W 4K monitor as an 6K Apple Pro Display XDR, meaning it renders the display as 6K and DOWNSCALES to 4K... meaning your RAM is being consumed to render approximately 20 megapixels to display a maximum 8 megapixel display. If you need your RAM free to render stuff, your display is could be using up to 2.5x more GPU RAM than necessary just sitting idly awake. (see image attached).

Thoughts?

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Answer 2

nikitamanko Author

Level 1

9 points

Feb 8, 2021 8:10 AM in response to redacted_username

Oh wow, very interesting to hear about all the behaviour you have noticed. I've definitely noticed the machine restarting because of some sort of failure and seen the 6K resolution over Thunderbolt as well. But do you really think that it's rendering at that and downscaling?

I'm using HDMI currently and here is what it's showing, I guess it just has something with the 2x Retina interpretation to do since the Scaling seems to be 2 times less than the resolution it shows in several cases.

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Answer 3

Mp41

Level 1

9 points

Jan 27, 2021 3:54 PM in response to nikitamanko

I am having the same issue with the 32UL950 not waking up with M1 Mac Mini when connected via Thunderbolt. Issue seems to go away with HDMI. Rookie question: is there a difference (resolution, refresh, Hz, etc) when connected via HDMI vs Thunderbolt. I want to make sure I’m getting everything out of this pricy monitor. Thanks.

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Answer 4

nikitamanko Author

Level 1

9 points

Jan 27, 2021 11:22 PM in response to Mp41

This. Exactly my current situation. I started using HDMI yesterday and it seems like the input recognition issue is gone now. I've tried reading about HDMI 2.0 vs Thunderbolt 3 and it seems like everything important (resolution, colors, refresh rate) is the same, extra Thunderbolt features such as power and data etc isn't really needed since it's a Mac Mini, so I'm fine with HDMI.

However I did discover that the Scaling of UI to look like 3360x1890 (you do get full 4K resolution no matter the scaling ofc, this is just the size of things appearing on the screen), which I prefer to use with my work machine and this monitor, isn't available over HDMI.

So all I can hope for right now is that Apple pushes a fix for the Thunderbolt issue as soon as possible, and I can just live with HDMI meanwhile. Just glad this isn't a monitor issue, I love it so much.

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Answer 5

hcsitas

Level 6

11,348 points

Jan 26, 2021 10:53 PM in response to nikitamanko

Disable sleep and avoid shut down unless absent for long periods. Separately, connect over HDMI. Thunderbolt give you nuthin'.

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M1 Mac Mini not recognizing external monitor upon boot-up/wake-up

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