ati driver + xrandr can't activate external monitor

[charlie]

Hello,

I am using Debian Sid on an ATI Radeon IGP 350M based laptop, with a 19' LCD
monitor.
When the external LCD connected, X can be started and shown on the LVDS(or
the Laptop panel),
'xrandr -q' shows LVDS and VGA-0 are connected and modes properly probed.
However, after the attempt to bring on the external monitor by 'xrandr
--ouput VGA-0 --auto',
the external monitor remains black and has no signal input. Meanwhile the
output of
'xrandr -q' does change with the VGA-0 monitor indicated as been activated
and in preferred mode '1280x1024+0+0'

I googled a lot and tried different approach to hack my way through, however
in vail.
So I can only ask for help here.
the detail of my problem is raised as a bug in bugzilla:
https://bugs.freedesktop.org/show_bug.cgi?id=15708

TIA for any advice

Chalie
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