need some help ...

[Hans Schneidhofer]

hi list,
have installed a new Ubuntu 16.04 lts with kernel 4.10.
My Hardware :
Mainboard : M5A78L-M PLUS/USB3
CPU : AMD Phenom(tm) II X2 511 Processor
RAM : DDR3 8 GB
Graphic : RS780L [Radeon 3000]
Display : LG 32LH301C (32")

Now - my problem is, I had to change my old mainboard to the above new
one. And there was an nvidia graphic-chip on the mainboard.

I didn't reinstall the system but started the PC with the new
Mainboard. Ubuntu installs automatically the new ATI-driver.

Now, with the new ATI-3000 Graphicchip I have some trouble with the
size of displaying the correct size. The screen is first too big or so
called oversized. With the option "xrandr --output HDMI-0 --set
underscan on I get a screen near the right size, but still I get a size
1 cm lower in both x- and y-axis AND I have to change the resolution of
1920 x 1080 by hand.

Could anyone give me some light on how to reorganize the resolution and
the size of the screen ?

It seems, that xorg.conf has changed to a newer file-model and I can
not handle the new structure. 
So - where do I have to make which entries ?

Hope, anyone could give some hints ?
Thanks in advance
bye hans