We are having a minor problem that is turning into a huge headache since upgrading our teachers to new Mac Mini's on 10.10. Whenever their Mac's go to sleep, they don't recognize the secondary display (projector) on wake and we have to unplug the mini-display dongle in the back and plug it back in for it to detect the projector (or go to preferences and detect displays).
I know it seems kind of petty, but our teachers are LOSING THEIR MINDS over this. When the display becomes recognized again, all settings are reset (Mirrored, Resolution, etc...) Does anyone know of a fix for this?
Just a little more info:
-Most of the Mac Mini's go HDMI to DVI to the monitor, and Mini Display to VGA to the projector. Some are MD to VGA to both and the problem persists.
-"Detect Displays" in preferences doesn't always work, unplugging and replugging the dongle does.
I've experienced much of the same with several Mac minis and 2013 Mac Pros, however not with projectors but with displays. I'm not using VGA (that's probably the one thing I haven't tried). I've tried connecting from the Mini DisplayPort to DVI, Mini DisplayPort to Dual-Link DVI, and thrown in variations of HDMI.
It seems to be limited to certain models of displays. Apple displays work, and Eizo displays work. But some models of NEC displays exhibit this behavior.
One of my own minis does this with an Eizo, but I have a KVM in the mix.
I've pulled my hair out over this for over a year but I've been fortunate enough to be able to replace the temperamental displays with Eizos or shuffle displays around among departments. I've also replaced a few minis with iMacs because of this.
We are leaning towards this being more related to the brand of projectors we are using. We are going to test going straight HDMI from the MM to the Projector and see what happens. If it doesn't help we are going to start replacing projectors and see what what that does.
I will update as we figure things out.
Unless there is a compelling reason to allow them to sleep, why not just keep them up all of the time? They are plugged in, so battery life isn't an issue. The extra electricity will almost certainly be cheaper than replacement projectors.
Review the settings on the projector or monitor for their sleep settings. Do they have sleep or idle off timers?
Some projectors/monitors auto scan/detect the port to use between DVI, VGA, HDMI. If the Mac is always connected via VGA for example, you might want to set the projector to default to VGA instead of auto-scan.
It might be a case where the projector is switching to another video port when the Mac goes to sleep. You wake the Mac and it checks for external monitors. Since project has jumped to a different port, the Mac thinks there is nothing at the other end.