Had same exact issue with the Radeon HD 6520G on an Asus A53Z laptop.
Install was Linux Mint 14 (Nadia) Cinnamon 64-bit.
Under Software Sources > Additonal Drivers there were 3 options...
1-Using X.Org X server -- AMD/ATI display driver wrapper from xserver-xorg-video-ati (open source, tested)
2-Using Video driver for the AMD graphics accelerators from fglrx (proprietary)
3-Using Video driver for the AMD graphics accelerators from fglrx-updates (proprietary)
The first option was initially selected so I decided to try option 2. This FIXED the issue and everything was running smoothly. Mind you, occasionally with the first option the screen might go black randomly and the only way to fix it was to restart the computer. This issue is gone too.
I haven't tried the 3rd option yet and I am kind of worried to do so because some people have said that these 'updated proprietary' drivers cause issues sometimes, is there a way to check for this or what's the deal? Should I give it a go and hope for the best? Suggestions please!
Asus A53Z running Linux Mint 14 (Nadia) - Cinnamon 64bit
Processor: AMD A6-3420M @1.5GHz --- Graphics: Radeon HD 6520G