LG UltraFine 4K Display doesn't turn back on after sleep or screen saver after upgrading iMac to Ventura

We purchased an LG UltraFine 4K Display in March 2022 from Apple along with a 24-inch M1 iMac. It is connected to our iMac with a Thunderbolt 3 (USB-C) cable. Lately, after upgrading to Ventura, after the iMac has been on screen saver or asleep, the LG UltraFine 4K Display sometimes does NOT turn back on. Nor does it even appear under Display in System Settings. Since there is no power button on the display, the only thing that seems to work is to briefly put the iMac to sleep again and then wake it back up.

iMac 24″, macOS 13.0

Posted on Nov 5, 2022 4:43 PM

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Posted on Nov 7, 2022 9:23 AM

My issue is somewhat different from what I originally thought. I have had my LG UltraFine 4K Display plugged into a "Controlled by Master" outlet in my UPS unit; I did so because that's what I did with our older, conventional monitors, so they would power off when the iMac powered off.


Apparently, with Ventura, the UPS unit is not always detecting that the "master" (the iMac) is on, and so is not turning on the "Controlled by Master" outlets. Perhaps there has been some change in electrical usage on the iMac with the Ventura release.


At any rate, I plugged the LG secondary monitor into a regular backup outlet on the UPS and it now comes on whenever the iMac does, including after sleep and screen saver.


Since the LG UltraFine 4K Display has no power switch and it is turned on and off by the iMac it is connected to, use of the "Controlled by Master" outlet is no longer necessary anyhow.

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Question marked as Top-ranking reply

Nov 7, 2022 9:23 AM in response to JustForComment

My issue is somewhat different from what I originally thought. I have had my LG UltraFine 4K Display plugged into a "Controlled by Master" outlet in my UPS unit; I did so because that's what I did with our older, conventional monitors, so they would power off when the iMac powered off.


Apparently, with Ventura, the UPS unit is not always detecting that the "master" (the iMac) is on, and so is not turning on the "Controlled by Master" outlets. Perhaps there has been some change in electrical usage on the iMac with the Ventura release.


At any rate, I plugged the LG secondary monitor into a regular backup outlet on the UPS and it now comes on whenever the iMac does, including after sleep and screen saver.


Since the LG UltraFine 4K Display has no power switch and it is turned on and off by the iMac it is connected to, use of the "Controlled by Master" outlet is no longer necessary anyhow.

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LG UltraFine 4K Display doesn't turn back on after sleep or screen saver after upgrading iMac to Ventura

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