I'm running Ubuntu MATE on a samsung N210 netbook, which is rather old. I had it running Ubuntu 14.04, till yesterday, and the screen brightness control worked fine since day one.
After installing Ubuntu-MATE (from the the ubuntu-mate iso) the screen brightness is permanently at 100%, the fn combo works, and the overlay shows the brightness level being altered, but no actual change occurs. The same thing happens when altering from Power Management.
Any ideas?