Comment 48 for bug 1218547

Same issue here with a Schenker S413, identical to clevo W740SU, Sager NP240 and System 76 Galago ultrapro.

Probem is worse than described, though.

If you attach an external monitor and

xrandr --ouptput HDMI2 --auto --output eDP1 --off

(i.e. switch on external monitor, off internal one)

then going back to

xrandr --output eDP1 --auto

leaves the laptop screen at brightness 0 (black). Since the brightness keys are not working, the only way to go back to a usable laptop is to reboot.

The system 76 package in the system76 ppa may have a fix for this, but cannot be setup on machines that do not include the system76 signature in the bios.