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I have an old laptop, a 2014 MacBook Pro, which I use with an external display connected by an HDMI-to-DVI cable. The trouble comes when I leave the machine connected for a long time and it goes to sleep. (Full sleep, not display sleep.)

Sometimes, waking the machine while it's connected to the external display causes the computer to hang; it shows a black screen on the external and laptop displays and I can't use it. I have to force-restart the machine to be able to use the computer again.

I don't really want to have to keep restarting my computer because of this, so I'd like to prevent all sleep (including display sleep) while the computer is connected to an external display. However, I also use the computer on power adapter without the external display, and on battery. I'd like it to go to sleep normally in those cases.

Is there an automated way to make this happen?

Note: The machine is running macOS Sierra (10.12), so any solution must run on that OS.

SoItBegins
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  • If your external monitor supports DisplayPort, use that instead. If it’s HDMI only, get an active HDMI adapter so the video signal is stable. – Allan Jan 07 '23 at 20:46
  • The monitor's DisplayPort is occupied by another computer that is also connected to it (a windows PC) and it has no HDMI port of its own. That's why I'm using its DVI port. – SoItBegins Jan 07 '23 at 21:19
  • The HDMI signal lacks a clock signal and what happens is that when the screen goes into power save, everything goes out of sync. The Mac is alive, but not in sync with the monitor. An active adapter fixes that. The Thunderbolt port is also your DisplayPort. If you have. a TB device, you can daisy chain the monitor off of it. Either way, it’s an HDMI issue not a Mac issue – Allan Jan 07 '23 at 22:23
  • I'm not connecting the monitor to the Thunderbolt port. It's connected to the mac's HDMI port via a straight HDMI cable, then through a 3-way HDMI switcher box (not powered), then through the HDMI-to-DVI cable to the monitor. – SoItBegins Jan 07 '23 at 23:13
  • It’s not a Mac problem, it a problem that’s inherent to HDMI. Then you convert from HDMI with no clock signal to DVI with a clock signal. Adding a switch box to the mix only adds to your issues. Try removing the switch box and see what happens. Ikm even more cinvinced you need an active HDMI to DVI adapter. – Allan Jan 07 '23 at 23:20
  • Is it at all relevant if I mention the monitors are set up to mirror one another? – SoItBegins Jan 08 '23 at 00:25
  • You mean the Mac’s built in display and external monitor? No, that doest matter. The problem is the HDMI link. Computers use a clock signal to manage when data gets processed/transmitted. HDMI being a consumer electronics technology doesn’t have a clock signal but your Mac does and your DVI monitor expects one. Can the monitor work without it? Sure, but when it gets out of sync, you need to reset which temporarily kills then restarts the HDMI port. Your Mac hasn’t failed. The HDMI signal dropped when the Mac went into power save and can’t get back in sync with the monitor when it wakes – Allan Jan 08 '23 at 01:10
  • Let us continue this discussion in chat. – SoItBegins Jan 08 '23 at 06:36
  • Removing the HDMI switch fixed it. – SoItBegins Jan 24 '23 at 18:37

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