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medium-cool Author

Level 1

19 points

After Monterey 12.3 upgrade, can't run 2 usb-c monitors

I upgraded my 2018 Macmini to Monterey 12.3 tonight and after the upgrade lost the ability to run 2 usb-c monitors simultaneously. I've got 2 LG monitors and they've worked great with this mini for almost 4 years until this upgrade. I've tried a bunch of things, resetting the SMC, NVRAM/PRAM, disconnecting and reconnecting them multiple times and ways. Nothing is working. Both monitors are picked up by the macimini fine, it's just that it will only use them one at a time (whichever is plugged in last gets used after boot.)

Mac mini 2018 or later

Posted on Mar 14, 2022 9:38 PM

Top-ranking reply

ahvlima

Level 1

28 points

Posted on Mar 15, 2022 10:20 AM

Indeed I've seen it with LGs monitors on 3 different Mac mini 2018, all using USB-C connections and one of the displays "vanished" after upgrading to 12.3.

My take: Macos cannot distinguish the monitors, because LG monitors (at least those that I have 32UL750) Don't present a serial number and thus 12.3 is only "recognizing"one of them (the one that "answers" first).

Macos up to 12.2 had a terrible time properly identifying the monitors and they would often swap on boot or sleep (I have my own keyboard shortcut to force them to swap). Again because there is no way to do it otherwise.

If they have "fixed" this swap issue, there could be an explanation for the whole problem, if monitors are indeed "equal".

We have 3 minis back in the game by switching one of the monitors to HDMI and used the following procedure to have it recognize the monitors properly:

Shutdown
Leave the HDMI connected and remove the USB-C cable from the mini (not the monitor as the cable may be active)
Start, check the monitor, screen size and refresh rate. Shutdown
Now power the second monitor and connect the USB-C cable
Start the machine.

On all 3 minis both monitors came back.

I will try the procedure with 2 USB-C later, but for now I have to get back to work.

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84 replies

den.thed

Level 10

83,554 points

Mar 15, 2022 8:29 AM in response to hcsitas

Perhaps.... No I've had updates bork my setup in the past and so I tend to be more cautious.

hcsitas

Level 6

13,376 points

Mar 15, 2022 6:38 AM in response to padams35

You have it, I’m using your link for “Up to two displays.” They don’t mention mandatory HDMI but that’s how I read it for hooking two displays.

hcsitas

Level 6

13,376 points

Mar 15, 2022 7:57 AM in response to den.thed

FWIW, it's looking like only LGs taking the hit...I assume you're on 12.3, right?

hcsitas

Level 6

13,376 points

Mar 15, 2022 8:31 AM in response to den.thed

Understood, thanks.

Mar 15, 2022 8:34 AM in response to den.thed

Thanks for posting the links.

I've responded under Mac mini but had to pick 12.2.1 as the operating system - Apple hasn't even updated the OS dropbox to include 12.3 as an option yet!

Mar 15, 2022 11:38 AM in response to hcsitas

It worked fine with 12.2.1, so something was changed by Apple in 12.3 to break it again.

The workaround made my LG monitor usable via HDMI, but USB-C still doesn't seem to work.

Mar 15, 2022 1:33 PM in response to hcsitas

It worked fine before yesterday and 12.3! How can that be "LG's booboo"?

ahvlima

Level 1

28 points

Mar 15, 2022 1:53 PM in response to hcsitas

Hummm... why not having a unique ID can be a security hole on a consumer grade monitor?

hcsitas

Level 6

13,376 points

Mar 15, 2022 2:12 PM in response to ahvlima

Same as mac-IDs, it depends on how strict one is about security. Remember, not one consumer monitor claims full workability with Apple, backs it up progressive fixes//updates/drivers etc.

hcsitas

Level 6

13,376 points

Mar 15, 2022 2:23 PM in response to ahvlima

It’s an issue for HDCP content which Apple has a huge stake in. To me, plugging the hole is very, very Apple.

hcsitas

Level 6

13,376 points

Mar 15, 2022 2:25 PM in response to ahvlima

Apple sells lots of 3p; they don’t do it to endorse, just pick up some easy commission revenue. There’s no support from them for any 3p stuff whether sold by them or not.

hcsitas

Level 6

13,376 points

Mar 15, 2022 4:22 PM in response to ahvlima

👍, good work! Sleep is unnecessary, serves no purpose (unless you like mystery problems to pop up unexpectedly).

hcsitas

Level 6

13,376 points

Mar 15, 2022 5:19 PM in response to ahvlima

Let’s try again: Sleep is unnecessary, serves no purpose (unless you like mystery problems to pop up unexpectedly).

But wait, you like mystery problems 😁, ignore.

Voluntar

Level 1

8 points

Mar 17, 2022 1:19 AM in response to Malcolm J. Rayfield

That solution worked for me.

Setup:

1) LG OLED48C1PUB (4k, 48") HDMI->HDMI

2) Phillips Momentum PHL436M6VBP (4k, 42") Thunderbolt3 -> miniDP

warpdag

Level 1

17 points

Mar 18, 2022 5:58 AM in response to ahvlima

Yes, it's a bug. Will they fix it anytime soon? Given how long it took them to get the graphics/displays layer stable on the mini, I'm not sold. I did file a bug report.

After Monterey 12.3 upgrade, can't run 2 usb-c monitors