External screen goes black

[Jonathan Adamczewski]

Hardware is a Dell XPS laptop, xorg log reports "Integrated Graphics
Chipset: Intel(R) Sandybridge Mobile (GT2)"

Running a custom configured 3.7.2 based kernel, xf86-video-intel-2.20.17.

I'm running the internal LVDS screen at 1080p and a Dell 2713HM monitor at
2560x1440 connected via display port.

Both screens run fine when X starts, but at some point the external monitor
will go black. The system doesn't recognize it as being disconnected - no
KDE popup asking if I want to change the monitor config as happens when
pulling the DP or power on the monitor.

Sometimes it will return to life after a short amount of time, most of the
time it stays black indefinitely. A full power cycle of the monitor
(pulling the plug) will usually bring it back to life, but typically not
for long.

The screen usually goes black while there's some degree of display activity
- a video playing, moving large windows around the screen, looking around
in google streetview, etc. It doesn't seem to matter which screen the
activity is on.

It *seems* to be less likely if I run the external display at a lower
resolution.

There's nothing that coincides with the screen going black in dmesg or the
xorg log.

I've had no problems with this monitor under Windows 7 (gaming, videos,
etc).

What I'm looking for: ideally a simple fix :) Otherwise, any suggestions
about where to look to gather more information on what could be happening
here - or other places to ask for help.

Many thanks

jonathan.
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