@frog If I could give you reddit Gold, I would do so! I never thought of the power supply. I changed out my cheap usb brick with a real power supply and voila, all was good in the land of Magic Mirror except I can’t yet rotate my display.

THANK YOU SO MUCH!!! this was driving me crazy!

So I’ve got MM running on my RPi 3 and am pleased. Oddly however, when I disconnect the RPi from my ‘programming monitor’ by unplugging the HDMI and the micro-usb power and plug in my MM monitor (mounted in my frame), on power-up my MM monitor simply displays the ‘rainbow cube’ in a slow pulsing mode (every 10 seconds or so). All I disconnect is the power and the HDMI. I can connect a different RPi (a zero) successfully to the MM monitor so I know that the HDMI and monitor are working well. There must be some setting that is allowing it to work with one but not the other monitor. Any ideas? Going crazy. Thought it was the cable until I found that my zero works just fine with my MM monitor…

Thanks!