lightdm on Intel NUC instantly dims screen

[Larry Hastings]

I installed Trusty Tahir (dated 2014/03/24) on a new Intel NUC (D54250WYKH). Ubuntu boots normally, but at the point it should display the login manager, instead it displays a black screen. If I use Ctrl-Alt-F1, I can switch to a working virtual terminal window. If I then switch back to the GUI desktop using Ctrl-Alt-F7, I see a momentary flash! of the login manager, and then the screen goes immediately black.

If I type in my password blind into this black screen, I log in successfully, and Unity comes up. When Unity is running, the screen is *not* dimmed--it works fine. If I log out, the screen goes black again.

I used the virtual terminal to switch from lightdm to gdm. gdm behaved the same way--black screen, if I typed in my password I could log in, if I logged out the screen went black again.

[Larry Hastings (larry-hastings)]

I edited my .dmrc to switch to Gnome 3, and Gnome displays the same "instantly go into power-saving mode" behavior. And if I switch to a different virtual terminal and back, I see a flash of the Gnome 3 desktop before the monitor shuts itself off.

So that's three things that instantly power off the screen: lightdm, gdm, and gnome. The only thing so far that doesn't is Unity.

In case it's relevant, the NUC is hooked up to a Dell U3014 monitor, via a Monoprice mini-HDMI-to-DMI cable.