Additional Screen stays dark after standby

[Christian Benz]

Hi all,

I'm using Ubuntu 13.04 on HP Elitebook 8560p Notebook with an additional 
Samsung SyncMaster S24A650S connected via DP.

After returning from standby the Samsung Screen doesn't wake up from his 
standby. Notebook Display wakes up as it should.

Only option is to turn off and on the screen to use it again.
It's not critical but it annoys me every day.

Does somebody know how to fix this, if there's a way to fix it?

$ fglrxinfo
display: :0.0  screen: 0
OpenGL vendor string: Advanced Micro Devices, Inc.
OpenGL renderer string: AMD Radeon HD 6400M Series
OpenGL version string: 4.2.12002 Compatibility Profile Context 9.01
-- 
Grüße
Christian