External monitor doesn't wake from sleep (MacBook Air M2, Mac mini M1)

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Tim St.Clair Author

Level 1

89 points

External monitor doesn't wake from sleep (MacBook Air M2, Mac mini M1)

I have a mba m2 with an external monitor (asus 4k via dispayport). I'm using comsol usbc to displayport adaptor cable.

I have a m1 mini as well, connected to another asus 4k via displayport, using comsol usbc to hdm1 cable.

both macs exhibit this problem. i've swapped cables several times, and found the comsol ones to be most reliable.

when the mac goes to sleep the external monitor goes to sleep.

when I wake the mac, the external monitor stays asleep. if I press the menu button, it comes up and says 'no signal' and goes to sleep again.

to resolve, i wake the mac, unplug the usbc, replug the usbc, and the monitor wakes.

To verify it's not the monitor, I used my msi windows 11 laptop with usbc displayport. i connect the monitor, let the laptop sleep, wake the laptop, and the external monitor also wakes. same monitor, same cable.

the problem is clearly with the mac. i've read through dozens of similar cases here on the community, but the unhelpful 'try updating macos' or 'apple do not monitor this forum' or 'try taking it to a genius bar' or 'let apple know by typing into the apple feedback black-hole page' type replies aren't solving it for me.

[Re-Titled by Moderator]

MacBook Air 15″

Posted on Jul 27, 2025 08:30 PM

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Answer 1

Jul 30, 2025 08:01 AM in response to Tim St.Clair

Your new cable looks like an better fit for a Mac. If the Mac detects any data errors, it drops the connection to the display.

The Apple standard for its built-in hardware-accelerated displays, makes them suitable for full-motion video for production/display of cinema-quality video with NO dropped frames, and NO dropouts or partial-blank scan lines due to memory under-runs or other issues. This requires a hardware rasterizer/display-generator for each fully-accelerated display, supported by Huge memory bandwidth to refresh each display 60 or more times a second.

The Windows standard is "if you like it, it's good enough." So "works under Windows adds NO helpful information except 'the wires are connected all the way through'.

Your 4K display is running at nearly the limit of switching speeds for the type of digital logic used for USB-C and for DisplayPort. The only way to assure 100 percent correct operation is to control BOTH the quality and the length of the cables.

For USB-C, that length is ONE meter, not longer. For DisplayPort, that length is One Meter, not longer. so when you have a 1.5 meter cable with the electronics at one end, that is SUSPECT.

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