macOS, sleep mode, and external monitors

TidBITS Talk
1

There seems to be a problem with MacOS regarding sleep mode and external displays. I’ve recently upgraded my MacBook Air from an 2017 Intel unit to a recent M3 unit and started experiencing problems I never had before.

So, initially, due to the lack of ports on the current gen Apple Silicon MBA, I bought a UGreen Revodock to connect peripherals, including an external display. Worked fine right away, no drivers needed. One cable for everything, that’s cool.

I was happy until one day when I came back to my MBA after stepping away, woke it up from sleep mode and the second display stayed dark. Mouse and external disk still functioned, but the external monitor could not be detected. The fix was always either: (1) a reboot or (2) disconnect/wait/reconnect the dock.

Since the UGreen device is an inexpensive device, I thought, OK they must have cut corners somewhere to make it cheaper, let’s get a more expensive dock that should be designed/built to meet all the software/hardware requirements for external stuff. So I bought a DisplayLink-compatible Targus dock, the exact same kind of unit we use at the office.

Besides discovering that DisplayLink lets you use two external displays in addition of the built-in monitor on a M3 MBA, I eventually ended up seeing the same issue, i.e.: on wake-up, the external display not being available (but no problem with other peripherals). The fixes are the same as with the cheaper dock.

The only difference I’ve seen with the Targus device, is that the purple “screen sharing/copy” status, er, “widget” in the menu bar is no longer visible when the second monitor is no longer detected. It’s as if part of the DisplayLink software stopped working. The main DisplayLink manager “widget” is still there, but doesn’t offer me a means to re-launch whatever stopped working.

(Note, FWIW: I’m running MacOS X v15.1 & the most recent DisplayLink software on a 16GB M3 MacBook Air. The dock is a Targus DOCK177USZ USB 3.0 Universal Docking Station.)

Anyway, I don’t think the issue is with the DisplayLink software, because the no-driver, no-software-required UGreen Revodock has the same issue. I think it’s more with MacOS X, but I don’t have the foggiest what the issue is exactly. I must also add that the problem doesn’t happen every time my Mac goes to sleep, but it’s not a very rare occurence either.

(Afterthought edit) I want to emphasize that the issue is display-centric. All external peripherals (storage, mouse, etc.) always work, it’s the external display that is problematic.

So, am I the only one that has that issue? Are there others who are going through this? Is there a better fix than a reboot or a disconnect-connect manoeuvre?

*** One more thing: I think that DisplayLink support should be baked in MacOS; it’s a way to get around limitations on the number of external displays that can be used with, say, an M3 MBA. I’ve tested it with two external monitors AND the built-in monitor: this works fine. Apple should look into this for a future release of MacOS.

2

I’ve had the very same problem for well over a year now. After waking the Mac from sleep, my primary monitor fails to detect a signal from the Mac. To fix it, I have to unplug the cable from the Mac and plug it back in. This happens roughly 1/3 of the time I wake the Mac.

My current mitigation solution is to power down the Mac each night and then power it back on the next time I want to use it. This cuts the problem down to maybe 1 in 10 times.

My setup is:

  • M1 Mac mini w/ 16 GB running macOS 15.1
  • Dell 27" 4k (primary) using HDMI port going to HDMI/USB-C adapter and then into a Thunderbolt port on the Mac
  • Dell 27" 4k (secondary) using HDMI port going directly to HDMI port of the Mac

I’ve tried switching which monitor uses the HMDI vs. the Thunderbolt, but it doesn’t seem to really matter.

3

I have 2 Dell 27" monitors connected to my 2019 16" MBP and frequently encounter the same issue. One monitor won’t turn on after waking the computer from sleep but all the other attached peripherals still work.

Maybe you’ve tried it and just didn’t mention it, but what always works for me is to simply turn off the screen for a second or two by pushing the small white glowing button under the monitor frame, and then pushing it again to turn the screen back on. Never had to disconnect cables or reboot, etc…

4

I’ve had the same problem with a MacBook Air M1 in clamshell mode (and only one monitor, obviously), but much less frequently (maybe four times per year).

That has worked for me, but usually not. In my experience, there seem to be too many variables and too infrequent occurrences (that’s a good thing!) to track anything down.

5

I experience about the same frequency with my M1P 14" MBP in clamshell with a 27" Dell connected through a TB4 hub.

Although I will say that it feels to me like it happens way less these days than it used to. On macOS 12/13, I felt like it could happen as often as 1 out of 3 wakes from sleep.

For me it happens irrespective of hub or not. When it does happen, I usually can regain display to the external monitor by opening the MBP lid and then closing it again while hitting a key or moving the mouse. I suspect what that does it just wake, sleep, and wake again which somehow gets display signals going to the monitor again.

I can also regain external display if I unplug the hub and then plug it in again, but since the hub also connects a whole bunch of disks, I usually don’t like just pulling that plug. Unplugging the display from the hub alone does not get the display to wake up.

6

What happens if you enable Settings > Battery > Options > Prevent automatic sleeping on power adapter when the display is off?

You can still turn the display off after an interval (or with a hot corner) but without the Mac sleeping.

I have a MacBook Pro, M3 Pro with a 4k display on HDMI and not sleeping the Mac ever was a solution to completely reliable display wake and rid myself of a slew of other sleep-related issues that had been a pestilence for years.

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7

I’m with @Diletante in not enabling sleep on my Macs. I shut the displays off after a short time but computers stay running. Energy use is negligible.

8

From the replies I see here (and elsewhere), it appears that the issue can occur no matter how an external display is hooked up to a Mac, either directly or via a docking station. Furthermore, it seems that even ThunderBolt docks are affected by this.

Considering that, from what I see at work and from my own personal experience, Windows machines don’t appear to suffer from such an issue, I find incomprehensible that Apple has not looked into such a basic bug.

We’re not talking about some freak set of circumstances, here.

We’re talking about a situation so common (computers falling to sleep after you’ve stepped away for some reason) that it should be one of the first bugs that should be tested for and fixed if it needs to be. If Microsoft can correct this, so can Apple.

I am not happy that the only apparent fix for now is to disable sleep mode whilst letting screens to go blank. But I guess I have no choice.

The only remaining unknown seems to be if it is new to Apple Silicon or not, because I don’t remember ever seeing anything like that with previous generation Macs (Intel, PowerPC and Motorola).

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9

It’s not a matter of the external screen just going blank but still using full power because the Mac is not sleeping - your monitor will still go into idle mode in the same way when the Mac signals displays should idle while the Mac itself continues to run.

Give it a try.

10

That was my go-to solution, until it didn’t work. Well, it still is my go-to solution (since I don’t have external disks plugged into the hub), but it has failed me at least once (and I think only once).