G550 + 193P + 1280x1024 = black screen

[Klass]

Hi

I'm running a Samsung SyncMaster 193P on a G550 at the DVI-output. The X.org version is 6.8.2 and the kernel is 2.6.13

Below is my xorg.conf file (comments stripped)

Section "Files"
    RgbPath     "/usr/lib/X11/rgb"
    FontPath    "/usr/share/fonts/local/"
    FontPath    "/usr/share/fonts/misc/"
    FontPath    "/usr/share/fonts/75dpi/:unscaled"
    FontPath    "/usr/share/fonts/100dpi/:unscaled"
    FontPath    "/usr/share/fonts/Type1/"
    FontPath    "/usr/share/fonts/TTF/"
    FontPath    "/usr/share/fonts/CID/"
    FontPath    "/usr/share/fonts/Speedo/"
    FontPath    "/usr/share/fonts/75dpi/"
    FontPath    "/usr/share/fonts/100dpi/"
    
    FontPath   "/usr/share/fonts/artwiz/"
    FontPath   "/usr/share/fonts/corefonts/"    
    FontPath   "/usr/share/fonts/kochi-substitue/"
    ModulePath  "/usr/lib/modules"
EndSection

Section "Module"
    Load "dbe"
    Load "extmod"
    Load "glx"
    Load "v4l"
    SubSection  "extmod"
        Option  "omit xfree86-dga"
    EndSubSection
    Load        "type1"
    Load        "freetype"    
    Load       "glx"
EndSection

Section "ServerFlags"
    Option      "blank time"    "10"    # 10 minutes
    Option      "standby time"  "20"
    Option      "suspend time"  "30"
    Option      "off time"      "60"
EndSection

Section "InputDevice"
    Identifier  "Keyboard1"
    Driver      "kbd"
    Option      "AutoRepeat"    "500 5"
    Option      "XkbModel"   "pc101"
    Option      "XkbLayout"  "de_CH"
EndSection

Section "InputDevice"
    Identifier  "USBMouse"
    Driver      "mouse"
    Option      "Protocol"    "IMPS/2"
    Option      "Device"      "/dev/input/mice"
EndSection

Section "Monitor"
    Identifier       "193P"
    VendorName "Samsung"
    ModelName   "SyncMaser 193P" 
    HorizSync     30-81
    VertRefresh  56-75
    Option          "dpms"
EndSection

Section "Device"
    Identifier          "MATROX DVI"
    Driver              "mga"
    VendorName    "Matrox"
    BoardName      "MGA G550 AGP"
    Option             "HWcursor"         "off"
    Option             "DigitalScreen"    "on"
    Screen  0
EndSection

Section "Device"
    Identifier         "Matrox VGA"
    Driver             "mga"
    VendorName   "Matrox"
    BoardName     "MGA G550 AGP"
    Option             "HWcursor"         "off"
    Screen 1
EndSection

Section "Screen"
    Identifier  "Matrox DVI/193P"
    Device  "Matrox DVI"
    Monitor  "193P"
    DefaultDepth  24
    SubSection "Display"
        Depth  24
        Modes  "1280x1024" "1024x768" "800x600" "640x480"
    EndSubSection    
EndSection

Section "ServerLayout"
    Identifier  "Simple Layout"
    Screen "Matrox DVI/193P"
    InputDevice "USBMouse" "CorePointer"
    InputDevice "Keyboard1" "CoreKeyboard"
EndSection

Section "DRI"
  Mode  0666
EndSection

The spec of the monitor says

Frequency:
    Horizontal:  30 - 81 kHz
    Vertical:      56 - 76 Hz
    Bandwidth: 140 MHz

If I run at 1280x1024 the screen is black and appears to have no signal (switching from `analog' to `digital') but if I look at the log, the X11 seems to start (I can shut it down with CTRL+ATL+BACKSPACE) and there is no `mode not supported'.
I tried to microtune the values 80, 80.5, 81, 76, 75 but that didn't make any difference.

If I run at 1024x768 with the code below, everything works.

    Modes  "1024x768" "800x600" "640x480"

If I run knoppix the samething happens, but I can CTRL+- several times and then change the resolution. When doing this several `mode not supported' appear.

I googled a bit and found two people with the same or similar problem:
http://lists.debian.org/debian-amd64.../msg00431.html, no real solution
http://forum.matrox.com/mga/viewtopi...highlight=g550, has a suggested solution but no feedback if it works. I would not like to switch to Matrox binary drivers unless there's another way. I can live with the X.org drivers and their limitations.

Update:
I tried the vesa driver and it works in 1280x1024 on DVI. So it really seems to be a problem with the driver.