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[Launchpad Bug Tracker <786781@xxxxxxxxxxxxxxxxxx>]

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Display corruption may result when using multiple monitors when one of
the monitors is connected to the video card but does not have power.

Ubuntu version is 11.04, desktop 32-bit edition. I was running the live
version off a 4 GB USB drive. The problem occurs regardless of whether
using persistence or not.

I am using an ATI Radeon X600 which has dual DVI-I connectors. One
connector was attached to a Dell flat panel, E197FP, and the other to an
LG L1750S. Both connections were analog, using a DVI-VGA adapter.

The problem occurs under these circumstances: Both monitors are
connected to the video card. The Dell monitor is on and being used as
the main display. The LG monitor does not have a power connection. Note!
This does not mean it was simply not turned on; I mean it actually did
not have the power cable plugged in.

In this scenario, severe display corruption may result. I repeated this
test many times. I observed that after the splash screen, the desktop
would display fine for one or two seconds and the mouse would be
movable. However after those one or two seconds, the mouse would freeze,
and the display would go blank for one or two seconds. When the display
returned, the desktop wallpaper was gone and the display was behaving
very strangely. I will attach some screen shots.

This problem does NOT occur if:
* only one monitor is connected to the video card, and it is receiving power
* both monitors are plugged in and receiving power--regardless of whether they are actually turned on or not

Having the monitor on or off is irrelevant; it is when the monitor is
connected to the video card but does not have a power connection at all.
This causes the software to be unable to read the monitor's
configuration.

Another interesting note is that I could switch back and forth to the
text terminals (Ctrl+Alt+F#) and the graphic display. While the text
terminals were always displayed correctly, the graphic display would be
corrupted in different ways when I switched back to it each time.
Sometimes it would look and act normal. Other times it would act like it
does when it first boots (no wallpaper, things not erasing, background
not redrawing). Other times it is completely corrupted, displaying only
colored bars and patterns. Even in this state, though, I could sometimes
switch to a text terminal and back and the graphical display would be
semi-usable.

Screenshot 1: Background does not redraw when dragging window until the
mouse is released. IMPORTANT: The right half of the image appears in the
screen shot but not on screen. The vertical program bar is NOT actually
visible on the monitor.

Screenshot 2: Example of menus not erasing. In this screenshot, I first
pulled down some of the menus from the menu bar at the top of the
screen. When the menu closes, the background is not redrawn, but the
menu simply turns a light gray. Notice the remnants of the menu to the
upper left corner of the window. You can see the "Location" menu item
somewhat. IMPORTANT: Again, in this screen shot, only the left half is
visible in reality. The right half of the image, including the vertical
program bar, is not visible on screen.

Screenshot 3: Colored bars/pattern corruption. IMPORTANT: In reality the
pattern covered the ENTIRE screen and the right half of the screen was
not visible. On the actual display, the left half of the image was
completely covered in colored bars, and the right half of the image,
including the vertical program bar, were not visible.

At the end of the dmesg output there is a very good hint.

Screenshot attachments and dmesg output coming momentarily.

** Affects: xserver-xorg-video-ati (Ubuntu)
     Importance: Undecided
         Status: New

-- 
Display corruption, multi monitor, Radeon X600, Invalid EDID
https://bugs.launchpad.net/bugs/786781
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