I just bought a Sony 520GS 21" CRT monitor, which is quite large compared to my old 14" unmarked monitor, so I need to change the resolution and refresh rate:
- I was using 800x600 @ 75Hz, (I think the refresh rate was that)
- I want to use 1280x1024 @ 100Hz
I know my new monitor supports this as I've done it in windows, here is some more info...
/etc/X11/xorg.conf's monitor and screen sections:

Section "Monitor"
Identifier "Monitor"
HorizSync 30-70
VertRefresh 60-160
Modeline "1280x1024@100" 244.64 1280 1312 2240 2272 1024 1041 1058 1076
Option "DPMS"
EndSection

Section "Screen"
Identifier "Monitor"
Device "Card0"
Monitor "Monitor"
DefaultDepth 24
SubSection "Display"
Depth 24
Modes "1280x1024"
EndSubSection
EndSection

First - is this config right? does it have any errors I haven't seen?
If not.... here's what happens: X starts up in the screen resolution defined by "Modes" in the Screen section, and refreshes at the rate of 60Hz, which is the minimum value I use at VertRefresh, and, in my experience, takes no notice of the Modeline.
I have tried adding new modelines, and switching between them (obviously adding the resolutions in Modes too), but I can't seem to make any difference, and X.org gives me no errors... I don't know where to look, which is why I came here.

Thanks for any help

Your horizontal sync rate is out of range.
With a dot-clock of 244.64 million pixels per second, at 2272 pixels per line (including the sync pulses), you are drawing at a rate of 107.676 kHz, with an allowable horizontal resolution of only 30-70 kHz.

So that mode isn't valid for the given monitor settings.

I'd also change your available modes to:
Modes "1280x1024@100" "1280x1024"


You might also want to look at using the logverbose server option; it can give you more information about why modes get rejected in the log files.

hehe, thanks, I suppose I would have got that eventually...
I've gone for 1024x700, but it seems out of shape, any more vertical pixels and it goes over the monitor's horizontal range with 100Hz... and any less horizontal pixels and my monitor can't zoom in fully to take the full screen up :S
I'll get round it, thanks a lot

You may be able to get a better resolution by trading off some of the refresh rate, e.g. try 1024x768 at 95Hz
If you do a google search for “XFree86 Modeline HOWTO” then you'll find quite a good guide to how to work out the best modeline for your monitor.

Yea, I've gone for 1024x768 @ 90Hz
But now I'm thinking, 1280x1024 @ 80Hz or less? But I spent too long in front of this screen to sacrifice that much refresh rate...