Bug#1016762: not a hardware problem

[Cesar Enrique Garcia Dabo <cquike@arcor.de>]

FWIW: I don´t think it is a hardware problem, since I am able to change 
the brightness using the command line tool brightnessctl:

$ brightnessctl -d "intel_backlight" set 4500

Looking into the logs of journalctl I actually find some hint on what 
the problem might be:

$ journalctl --user

ago 06 21:43:53 hostname pkexec[122891]: user: Error executing command 
as another user: Not authorized [USER=root] [TTY=unknown] 
[CWD=/home/user] [COMMAND=/usr/sbin/xfpm-power-backlight-helper 
--set-brightness 4308]