12.04 - External monitor does not correctly display on GMA500

Asus "T91mt" (resolution 1024x600).
External monitor 17" VGA 1280x1024.
Ubuntu 12.04.1.
GMA500.

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I have solved a common gma500 issue of resolution own display, but i can't connect external monitor correctly.
The picture of external monitor is shown on 75% field. I mean i can see whole picture of desktop on 75% filed of view only, but other 25% is black color or plume(tail) of console.

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Addition info:

• xrandr does not see second screen (only default).


• I have modified grub file for optimization memory and
  resolution(1024x600) both at wiki-Poulsbo and it did not help.



• My new xorg.conf is:

Section "ServerLayout"
    Identifier     "X.org Configured"
    Screen      0  "Screen0" 0 0
    Screen      1  "Screen1" RightOf "Screen0"
    InputDevice    "Mouse0" "CorePointer"
    InputDevice    "Keyboard0" "CoreKeyboard"

EndSection

Section "Module"
    Load  "extmod"
    Load  "dbe"
    Load  "dri"
    Load  "glx"
    Load  "record"
    Load  "dri2"
EndSection


Section "Monitor"
    Identifier   "Monitor0"
    VendorName   "Monitor Vendor"
    ModelName    "Monitor Model"
EndSection

Section "Monitor"
    Identifier   "Monitor1"
    VendorName   "Monitor Vendor"

    ModelName    "Monitor Model"
EndSection
Section "Device"
        ### Available Driver options are:-
        ### Values: : integer, : float, : "True"/"False",
        ### : "String", : " Hz/kHz/MHz",
        ### : "%"
        ### [arg]: arg optional
        #Option     "ShadowFB"              # []
        #Option     "Rotate"                # 

        #Option     "fbdev"                 # 
        #Option     "debug"                 # []
    Identifier  "Card0"
    Driver      "fbdev"
    BusID       "PCI:0:2:0"
EndSection

Section "Device"
        ### Available Driver options are:-
        ### Values: : integer, : float, : "True"/"False",

        ### : "String", : " Hz/kHz/MHz",
        ### : "%"
        ### [arg]: arg optional
        #Option     "ShadowFB"              # []
        #Option     "DefaultRefresh"        # []
        #Option     "ModeSetClearScreen"    # []
    Identifier  "Card1"
    Driver      "vesa"
    BusID       "PCI:0:2:0"
EndSection


Section "Screen"
    Identifier "Screen0"
    Device     "Card0"
    Monitor    "Monitor0"
    SubSection "Display"
        Viewport   0 0
        Depth     1
    EndSubSection
    SubSection "Display"

        Viewport   0 0
        Depth     4
    EndSubSection
    SubSection "Display"
        Viewport   0 0
        Depth     8
    EndSubSection
    SubSection "Display"
        Viewport   0 0
        Depth     15

    EndSubSection
    SubSection "Display"
        Viewport   0 0
        Depth     16
    EndSubSection
    SubSection "Display"
        Viewport   0 0
        Depth     24
    EndSubSection
EndSection