Firstly I'm running Yosemite 10.10.2 on my Mini. I have my monitor connected through HDMI and just use the internal speaker in the Mini. Everything works absolutely fine until I use another audio device, for example I airplay a movie to my Apple TV or plug external speakers in. After doing one of the above if I turn the monitor off say while the film is being airplayed to the Apple TV, when I try and turn it back on the monitor will not find a signal. I can however use Screens for iOS to connect to the mini and restart it which then gives the HDMI signal again. So as it stands I cannot use external speakers and cannot Airplay from the Mini as this will cause loss of signal from the HDMI the next time I turn the monitor back on. I have also tried the Display Port and get the same result. The workarounds I am currently using: Using internal Mac Mini Speaker (not fun) Airplaying video files using the Beamer Mac App, which works great but does not help if I want to airplay a streaming video from the web. I thought this issue was meant to be fixed in a previous Yosemite update?