Ubuntu 16.04 seemingly random freezing on AMD system

I had the same thing with Ubuntu 14.05 and 16.05, but with an i5 intel processor. So, I don't think this will work for you, but perhaps there is an analogous solution for the A6.

In my case the screen would blank, keyboard power would be cut, but the PC power light would continue and the DVD Drive would still respond to hardware open/close. The only way out was a hardware shutdown with the power button. The bug did not depend on any particular action or installation of software or anything else I could discover.

You might blame memory or other hardware, but Windows 10 would run fine for days and I could run Ubuntu 14 or 16 off of a USB (uninstalled) without incident for many hours also. Then one time it happened even before I logged in. That gave be the idea that the fix would have to be a kernel boot parameter or patch.

Here is a fix that worked for me. It appears elsewhere as a solution to other similar issues:

 sudo nano /etc/default/grub

then in that file change

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"

to

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash intel_idle.max_cstate=1"

 sudo update-grub
 sudo reboot

This is apparently not good for a battery powered PC (laptop), as the full power CPU state drains the battery.