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.
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.
That's frustrating :( I have an LG 27UK850 running off a Mac Mini (2018 — hence Intel not Apple silicon). The 12.3.1 update did resolve the issue for me (exactly as you describe — monitor not waking (or 'being woken')).
If you haven't done so already, it would be worth checking for any firmware updates for your specific monitor, just in case.
And then, I wonder if there's a difference between HDMI and USB-C(/thunderbolt/displayport) connectivity? IIRC most of us reporting issues were not using HDMI... if you are, that might be something to try.
Sorry I can't help more!
For me, in the end, after exhausting all ideas, I went and spent the $ on expensive thunderbolt 4 cabled figuring I'd return them if they didn't work. And it fixed it. I tried new HDMI, new USB-C... But it was Thunderbolt 4 cables that did the trick. Several users had reported that also, I just didn't realize for me, it was Thunderbolt that was the communication issue apparently, not USB-C and HDMI. Your experience may vary, but if you haven't tried really high end ones, try it and return cables if not. I used 2 OWC 1m $34 from Amazon.
I can confirm that 12.3.1 fixes this issue!
I can confirm that 12.3.1 fixes this issue for me to! Thanks Apple for the support.
Same here, 12.3.1 resolved the wake up from sleep issue on the primary monitor. As some of us were also experiencing dual monitor issues, it has not resolved that issue unfortunately.
I'm sorry, but did you infer I am making this up for some bizarre troll reason? I have attached the Samsung model plate of the monitor(s) in question. This is NOT specifically an LG issue regardless of your interpretation, as there is plenty evidence in general that it is happening to other brands also. I swapped out a non working pair of LG's to a non-working pair of Samsung's and you have the audacity to question the validity of my statement? I have better things to do as a 39+ year developer, 10-software patents holder and full time iOS developer since iOS 3.2 than to 'troll' tech boards with fake claims. You have one heck of a lot of nerve responding to a user with such a response.
Attached is the model info from the NOW Samsung pair of monitors attached to my Mac mini 2018 running 12.3 that the monitors work fine on my Mac mini 2018 running 12.1 in other office.
Spoke with Apple support last night, other than SMS, NVRAM & PRAM reset standard bits, they ultimately escalated to a senior and after about 15 minutes hold time came back and said they are aware of growing issues with users on this subject and to try recovery mode reinstallation of Mac OS 12.3. I will report back if reinstallation helped. Obviously this will be a multi-hour initiative.
-Kevin.
[Edited by Moderator]
And past 2 days I’ve discovered a little tweak that at least helps the wake up for me. Wake up does not display the primary single monitor (even though dual set up, never got second to work). Anyhow, I see the monitor backlight go on and the screen is lit, but solid black. So Mac can’t seem to wake it up even thought he monitor relieved some sort of signal to turn on the backlight of display. Here’s the tweak. If I press the monitor on button, this wakes from sleep, still black screen. But I press a menu button on monitor, then START my Mac Mini or wake and the pork Mary wakes up fine and shows display. Not at all an answer, but it. Does save me rebooting after sleeping by displaying the monitor menu. This was on a pair of Samsungs. Does this work for anyone else with sleep issues out of curiosity?
-Kevin.
update 12.3.2 did not solve . Using the other plug with an 8 usd adapter solved the problem definitely ✅
Disable Sleep, it’s unnecessary on later Macs, all pain, no gain. To disable, set your Energy Saver settings to as shown:
Separately, avoid manual sleep, use screen lock instead or let the display switch off/auto-lock on timer. For long or overnight absences, shut.
Same issue with me. LG 27UK850-W. After 12.3 monitor will turn black and no wake up. Have tried many of the updates/suggestions listed.
Ended up moving back to 12.2.1 to solve the issue.. but now having to run an older firmware/OS version to make this work...
SOLUTION
The back of your Mac has a USB-C connector. USB-C connectors work with USB-C cables, Thunderbolt 3 cables and Thunderbolt 4 cables. Following the OS upgrade you need to make sure that your cable is a Thunderbolt 4 cable, not one of the earlier types.
You can tell if the cable is Thunderbolt 4 by looking at the connector end. It will have a picture of a lightening flash and the number 4 on it.
[Edited by Moderator]
12.3.1 seems to have solved the issue for me!
12.3.1 certainly fixed the issue for my two LG monitors from 2018.
Apple support has not been able to fix this for me. I have exhausted their suggestions so far. Let's do a simple summary recap of what I have tried at Apple's suggestion or on my own from threads I've read:
NOTE: For Mac Book users with same issue, you would also have to include turning off SLEEP & graphics card settings as mentioned in this and other threads. I am on a desktop and don't have the same issue as I am always on power, but I did disable all the sleep settings just in case they were the problem. They don't appear to be the problem with desktops.
Some responding messages claim this is an LG only issue, it is clearly not from this and other threads AS WELL AS MY OWN EXPERIENCE of swapping late model 2021 LG monitors with late model 2021 Samsung Monitors to no avail. Both sets of monitors worked fine as individual monitors on 12.3, but NOT when connected as dual monitors. Both sets of monitors also work fine in Mac mini running 12.1 as DUAL MONITORS.
Meanwhile, My identical Mac-Mini 2018 running 12.1 happily shows both sets of monitors that are not working on 12.3 (Samsung and LG). No flicker, in 4k, sharp/clear text, no stagger/blur motion. Connect said monitors to Mac-Mini 2018 running 12.3, left (second monitor for me) monitor is blank and floating USB-C No connection text is floating around telling you monitor is powered, but no signal.
For those of us who are developers, we can't simply ignore this and downgrade as we need the latest Xcode and its' support for iOS 15.4 and the fixes and implementations it contains, not to mention configuration compatibility with others on teams. Therefore, it's quite a predicament to be in.
The B _ _ _ word for testing seems to get Moderator editing. so I will state that I not only had this issue with 12.3 while it was in 'B-testing' (as most developers download them as soon as they are available for Xcode fixes and compatibility which many times come hand in hand not to mention Xcode supporting apps (Symbols, Instruments, etc.)). I also reported it on both the B-Testing expected path and in the critical/system is down path of phone support. The first method has never been commented back on by Apple. The second, after 30-minutes+ of escalation, the highest escalation simply said "That's B-Testing software and we do not support it, that's why its called B-Testing".
Not what I wanted to hear, but OK, fair enough. So I spent about 5-hours the next day rolling my system back to a clean install of 12.1 public release. So this has been a known issue for Apple, from my own submissions as well as others, for many weeks now and obviously not fixed in the final version.
With nothing else to try, I ordered 2x$25 each top of the line Thunderbolt 4 and USBC 3/4 cables to see if they make any difference. Cables expected to be delivered tomorrow and I will post if they make any difference.
-Kevin.
Monitor not waking from sleep after 12.3 upgrade
