Like Darrin suggested try matching Modelines and Modes :

On xorg.conf

Enable only this  (comment the rest of the modellines) :
Modeline "1680x1050_60.00"  147.14  1680 1784 1968 2256  1050 1051
1054 1087  -HSync +Vsync

Modify the screen section :

Section "Screen"
        Identifier "Screen0"
        Device     "Card0"
        Monitor    "Monitor0"
        DefaultDepth 24
        SubSection "Display"
                Depth   24
                Modes   "1680x1050_60.00"
        EndSubSection
EndSection

Marius

On 9/21/07, Genadijus Paleckis <lsd@nnt.lt> wrote:
quoted text
> I have similar problem and it is still unresolved. My video card Intel
> i810 and monitor is Samsung SyncMaster 226CW, I'm trying to use
> 1680x1050 with no success. What I found is that I cannot force to use
> 60Hz vertrefresh and card uses 75Hz instead.
>
> gtf's suggestion
> boo$ gtf 1680 1050 60
>
>    # 1680x1050 @ 60.00 Hz (GTF) hsync: 65.22 kHz; pclk: 147.14 MHz
>    Modeline "1680x1050_60.00"  147.14  1680 1784 1968 2256  1050 1051
> 1054 1087  -HSync +Vsync
>
> xorg.conf's monitor and screen sections:
>
> Section "Monitor"
>          Identifier   "Monitor0"
>          Option       "DPMS"
>
>         # from Xorg.0.log
>          HorizSync    30-81
>          VertRefresh  56-75
>
>         # GTF suggestion
>         Modeline "1680x1050_1"  147.14  1680 1784 1968 2256  1050 1051 1054
> 1087  -HSync +Vsync
>
>         # numbers from Xorg.0.log
>         ModeLine "1680x1050_2"  119.0   1680 1728 1760 1840  1050 1053 1059 1080
> EndSection
>
> Section "Screen"
>          Identifier "Screen0"
>          Device     "Card0"
>          Monitor    "Monitor0"
>          DefaultDepth 24
>          SubSection "Display"
>                  Depth   24
>                  Modes   "1680x1050_1" "1680x1050_2"
>          EndSubSection
> EndSection