The title says it all. I upgraded to 12.3 and now my monitor will not wake from sleep. I have to reboot the Mac mini to get the monitor working. I'm not alone -- a thread on Reddit is discussing the same issue.
Apple, why do monitors continue to be a problem? MacOS 12 has had a steady stream of monitor-related issues since it's launch.
Answer: Change your cable from "standard" to "high speed" - see below for explanation.
There are loads of articles on the net saying that their external monitor stopped being recognised after a software upgrade ("No Signal" error showing on the monitor).
There are so many upgrades to the operating system these days, it seems like anything which goes wrong can be blamed on the latest OS upgrade. Probably a fair chunk of new problems are indeed due to upgrades. Some might be other causes.
In my case I think it was a combination of two causes.
1) The software upgrade, AND
2) The cable that I was using to connect the Mac (an iMac Pro) to the external monitor (a Samsung S27D590).
The monitor has a maximum resolution of 1080p.
I tried a lot of things, especially fiddling around with the settings in Apple logo>>System Settings, Displays, and in Desktop & Screensaver. Restarting the Mac sometimes worked.
After a lot of fiddling around, I came to the theory that the problem might have something to do with the cable connecting the the two devices (USB-C to HDMI).
Initially I found the one way to resolve the problem was to disconnect the USB-C to HDMI cable and then re-connect it. - Very irritating fix! Finally I changed the USB-C to HDMI cable for a new one. The problem has not occurred since I did that.
In conclusion, I think the problem was that the cable connecting the monitor to the Mac wasn't working with the latest software upgrade on startup.
Why did changing the cable work?
Answer 1: Cable Quality: There are loads of "inferior quality" cables, particularly ones bought cheaply from China. Such cheaper cables are more likely to suffer from a poor connection issue (e.g. a loose or broken strand of wire inside the cable, or the connecting ends). Also the wires may not be pure copper. To save money, the manufacturer may have used an amalgam of copper and aluminium, resulting in signal loss - especially for longer cables.
Answer 2: If you bought a cheaper cable, or if you bought it a long time ago, it is unlikely to be up to the latest standards.
Cables are grouped into one of four categories, standard, high-speed, premium high-speed, and ultra-high-speed. Standard is the slowest of all the cable types at around 4.9 Gbps. Normally this should suffice to handle 1080p but not much else. Given that newish Macs can output signals at much higher resolution than 1080p, it is possible that the latest software attempts to start out in the the higher resolution mode. A "standard" cable can't handle that, and therefore can't report back that the monitor is only 1080p.
Nowadays, most shops only sell "High-Speed" cables or higher. These HDMI cables will support at least double the bandwidth of a standard cable and can handle 4K video with ease. If you buy a new cable from a reputable shop, and check the specification is "high-speed", or "ultra-high-speed", you should be fine. In other words, do not buy the cheapest cable.
It’s extremely interesting that previously, the external monitor that couldn’t be waked was my Samsung Space Monitor 32” with HDMI connection. I doubted about the Anker HDMI-TypeC adapter so I got myself the Blackmagic eGPU Pro for direct HDMI. Now the issue reappeared after updating to 12.3, not with the HDMI but the Thunderbolt. I’m using the thunderbolt on Blackmagic eGPU Pro to connect to the USB-C on my M27Q, which, shows “no signal” for every wake up. I had to restart my MacBook Pro, open it from the clamshell mode, type in the password from the keyboard, put it back to the clamshell mode, and wait for the fan to stop jet-engine.
I can also confirm the issue on my Mac mini i7 2018. The problem would appear to be some sort of driver issue introduced with 12.3. On my Mac:
Same issue here except the monitor is an LG 27BK85U. It's not the Mac that's sleeping -- it's the DISPLAY(+).
* ALL Sleep and power management settings are disabled.
* I also tried this with enabled + disabled "Power Nap" (since help text wasn't clear whether this eliminated more power mgmt)
* Monitor has all PM disabled -- I literally turn off the monitor at night so the backlight doesn't bother me.
* Almost every morning, the system will not wake the display and I must power cycle.
(+)It's the display because: I can REMOTE IN via SSH just fine. I can trigger the backlight, but without a signal from the Mac there is nothing for the display to do. If I mash buttons on the mouse and keyboard I can force that "audio feedback" you would expect.
I've had this monitor connected to this mini since 2019 and it worked perfect up until 12.3.x
It's frustrating to see all the news that "12.3.1. fixes this" and that the only impacted systems were M1's... the problem feels unacknowledged.
I can't let go of this system as it's my final Intel version; I'm starting to consider selling the monitor at a loss.
for my dell vintage monitor usung the other plug wit an 8 usd adapter worked and it works since 3 days without any problem.
12.3.1 and 12.3.2 did not solve it, the adapter using the other plug did it ✅
Exact same issue - never had this problem before. My Mac is set to not sleep and the display is set to turn off after 15 minutes, when the display wakes up it goes black and turns off again almost immediately because it's not receiving any input from the Mac.
Only way to recover is to power off the Mac.
Same issue for me. LG 27UL850-W. usb-c connection to monitor seems to have this behavior every time after sleep. Tried HDMI, which doesn't happen every time it wakes, but still does fail. Also, once while trying to unplug/plug in the HDMI and usb-c cables to correct it without turning the mini off, the mini restarted itself with a kernel panic.
Only started happening with 12.3 update. No issues at all prior to the update. And it started immediately after the update (I was using a different input on the monitor while the update was running and had to hard restart it when I went to get back into the computer after the update completed).
I have a new ASUS monitor coming tomorrow (had on order prior to the 12.3 update), so I'll see how that one does.
I had swapped out my LG’s with pair of Samsung tonight from another Mac still on 12.1, same issue. I had this issue and reported it when it was in 12.3 was in Beta to deaf ears at Apple. I had to downgrade and revert back to public release at that time of 12.2. A seven hour process to restore system and files. I read from some other devs at the time that they thought it was related to the new feature for Universal behind the scenes and more affected larger format displays. Having only ultra-wides here, I couldn’t test on standard sized monitors.
I sent the behavior information to LG. Maybe you should send it into Dell as well. It could be some sort of non-standard implementation and the monitor firmware could be an issue. Hard to tell at this point.
Maybe not, but sleep is unnecessary on later Macs, disable and forget.
You can minimize the occurrence of this problem by disabling sleep (see earlier post on how to do it).
It’s monitor dependent, LGs appear to be the most vulnerable. Do you have a discussion link to your issue posted here? If not, feel free to start one. There could be other fixes you haven’t tried yet.
Yes, usage of non-Apple displays seems to be broken - again. I have the same issue with my 2018 Mac Mini
From the number of 12.3 update issues on the board, something is not right and we need to let Apple know.
I was afraid of that…file a bug report and hope for the best🤞keeping expectations low, appears to be the general consensus. Good luck!
You’re welcome. Try clearing Safari history?
Monitor not waking from sleep after 12.3 upgrade
