Problems with additional LG ultra fine displays

Question

Problems with additional LG ultra fine displays

I have one Studio display and two LG ultrafine 21" (4K) displays attached via the the rear USBC ports of my Mac Studio (Ultra CPU 64GB RAM 48c GPU).

When I restart the computer (and sometimes even when waking from sleep). The second LG ultra fine display - to the right of the Studio Display - does not come on.

I have tried swapping the positions of the ultra fine displays and can tell from that it happens always to the display on the right of the Studio display whichever ultra fine is connected doesn't matter.

Changing which USBC ports the monitors are connected to makes no difference either. Always the one on the right of the Studio display. To make it work each time I have to disconnect and reconnect the USBC cable.

Does anyone else have this problem and knows how to fix?

thank you kindly

Posted on Apr 1, 2023 6:12 AM

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Answer 1

Top-ranking reply

Grant Bennet-Alder

Level 10

141,925 points

Apr 1, 2023 6:25 AM in response to Darragh Sinnott

Historically, one Thunderbolt Controller has been used to run Two Thunderbolt ports, typically placed right next to each other.

Try staggering your Studio display and one LG display on every-other connector on the back Thunderbolt ports, and run the second LG display off one of the front USB-C ports. this distributes the load over the maximum number of controllers.

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Answer 2

den.thed

Level 10

92,602 points

Apr 1, 2023 7:47 AM in response to Darragh Sinnott

Test the following work-around, it works for me and prevents un-plugging/re-plugging.

Setup a Hot Corner to "Put Displays to Sleep" Then if and when one display fails to light-up, put all the displays back to sleep using the Hot Corner and re-wake all of the displays.

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Answer 3

Apr 1, 2023 7:45 AM in response to Grant Bennet-Alder

Thanks for taking the time to reply, much appreciated.

Yes indeed, I have tried all of that, every combination of ports, including connecting the second display to the front ( ultra Mac Studio, all six ports are TB4).

I suspect a communications issue, either Mac is not sending the power-on/wake or the monitor is not acknowledging it. Breaking the TB4 connection and re-connecting resolves the problem but is a tiresome manual step especially since this also happens upon sleeping the computer (but not always!).

BUG!!!??

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Answer 4

den.thed

Level 10

92,602 points

Apr 1, 2023 8:00 AM in response to Darragh Sinnott

Bingo! This is a macOS issue and has been for sometime now.

Feedback - macOS - Apple

Feedback - Mac Studio - Apple

It's not just the Mac Studio, it happens on our Mac mini's with multiple displays as well.

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Answer 5

Apr 1, 2023 7:48 AM in response to den.thed

Thanks, yes I have a variation of that work around already. Sleeping the computer and re-awakening via keyboard shortcut several times will eventually lead to the third monitor coming on again, eventually!

Again, a tiresome procedure. I think maybe this is a O/S issue.

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Answer 6

Apr 1, 2023 8:06 AM in response to den.thed

Thanks for the help everyone. We wait and hope....

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Answer 7

den.thed

Level 10

92,602 points

Apr 1, 2023 9:09 AM in response to Darragh Sinnott

You’re welcome.

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Problems with additional LG ultra fine displays

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