Comment 7 for bug 1174368

Hi! since 11.10 dual monitor works fine but since upgrade 12.10 to 13.04 is not able. Only the mirror was permited but try to unmirror some erratic behavior occur on login screen(total black) I do re-installed 13.04 and problem still.
 my config is the following

*-display
       description: VGA compatible controller
       product: Trinity [Radeon HD 7640G]
       vendor: Advanced Micro Devices [AMD] nee ATI
       physical id: 1
       bus info: pci@0000:00:01.0
       version: 00
       width: 32 bits
       clock: 33MHz
       capabilities: pm pciexpress msi vga_controller bus_master cap_list rom
       configuration: driver=radeon latency=0t
       resources: irq:54 memory:e0000000-efffffff ioport:3000(size=256) memory:f0300000-f033ffff
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 13.04
Release: 13.04
Codename: raring
Linux A8-G4-HP-NOTE 3.8.0-19-generic #30-Ubuntu SMP Wed May 1 16:36:13 UTC 2013 i686 athlon i686 GNU/Linux

External monitor is a Samsung Syncmaster 721s