Sierra broke display on headless Mini Server

Identical symptoms. Works fine when plugged into my HD TV, and continues to work if I unplug from the TV after logging in. But if I reboot when not plugged into the TV I only get a black screen, or a partially-refreshed screen, and the login textbox will not accept keystrokes.

I had this exact same situation on my Mac Mini 4,1 just as you describe it - black screen unless it detected an HDMI display.

I found a hardware fix: you can purchase an HDMI plug (there are a number on Amazon - search for "display emulator"; I selected the "NewerTech HDMI Headless Video Accelerator" option which is telling my Mac that it is a 2560 x 1080 @ 30Hz "NT HEADLESS" display - note that's not what the NewerTech spec says it will do). Now when the system boots it thinks there is a display attached. The only down side is I can't figure out how to change the resolution down to something that makes more sense for remote access. The 'hold down option while selecting "Scaled" in the "Displays" control panel' trick isn't working via VNC or with a physical keyboard attached.

Not what I was hoping for originally (I was hoping for a checkbox somewhere) but for me worth the ~$20 to make the problem go away. Allegedly this makes remote access faster as well since the Mac uses the built-in graphics acceleration once it detects a connected display.

There's a DIY dongle you can make with just one resistor and a normal DP to VGA connector. Full details on how to do this from four years ago at https://macminicolo.net/blog/files/build-a-dummy-dongle-for-a-headless-mac-mini. html.

I haven't updated to Sierra yet, but have you tested DisplayMenu to see if it can make a virtual display for you?

https://itunes.apple.com/us/app/display-menu/id549083868?mt=12

DisplayMenu did allow me to select a different display resolution! Thanks for the suggestion! 🙂

I was hoping 10.12.1 would fix my 😟.. after no joy i went for a hardware fix, worked great, all fixed now. thanks!

What did you end up using for a fix? One of the homemade versions, or something purchased online?

I used the home made VGA version, I didn't have an 85Ω resister so I used a 100Ω and it worked great.

OK, thanks, good to know!

Identical problem. My 2 Macmini servers are both in 2 different WebFarms (and of cours 100km appart) very difficult to access so a hardware solution is no option yet.

Is there no SSH command do lock the Display setting to a certain resolution?