Hi Adrian,

not that I have any specific knowledge about eMacs.
But somewhere along the line you mess up horizontal
and vertikal sync; and I am not shure to which one
the eMac monitor restriction applies.
Please reassure yourself which one matters.

Because
horizontal frequency: Pixelclock / number of pixels per line
vertical frequency    Pixelclick / total number of pixels
both including the invisible pixel that make the time for the
backtravel of the e-ray in CRTs.

Adrian Christiansen wrote:
..
> ModeLine        "800x600" 112 800 816 824 840 600 616 624 640 -hsync -vsync

This gives:
horizontal: 112 MHz / 840 = 133 kHz
vertical:   112 MHz / (840 x 640) = 208 Hz

More than 200Hz vertical frequency or refresh-rate, I don't think
many monitors out there can follow that quickly.

> ModeLine        "1024x768" 100 1024 1108 1280 1408 768 768 780 796
> +hsync +vsync

horizontal: 100 MHz / 1408 = 71 kHz
vertical:   100 Mhz / ( 1408 x 796) = 89 Hz

> 

> #Modeline "1280x960" 122.25 1280 1328 1424 1696 960 961 964 1002
> +hsync +vsync -csync
> That modeline is from a working XFree86.config... at least if you are
> using Gentoo. And maybe only 1.25GHz modell?
> 
> Is there something about the diffrent eMac modelles? The 700MHz one
> have an nVidia card, the 1GHz ATI Radeon 7500 and the 1.25GHz has an
> ATI Radeon 9200.
> So maybe the modelines are different for the different modells?
> 
> According to the eMac manual, the monitor will only work in 72kHz
> h.sync and these resolutions:
> 640x480@138Hz
> 800x600@112Hz
> 1024x768@89.0Hz
> 1152x864@80.0Hz
> 1280x960@72.0Hz
> 
> Which is strange, because I remember there being 60 and 72Hz in
> 1280x960... I could be wrong though.

If you add about 5% for backtravel and assume progressive mode (i.e.
non-interlaced as in TVs)  that backs up what is initially
stated, you will always end up around 72kHz horizontal.

Okay, so the requirement clearly applies to horizontal frequency.

Having two different vertical frequencies (refresh-rates) for one
resolution would work with adjusting the time you allow for vertical
backtravel because the time you spend per line is fixed by the 72kHz
horizontal requirement of your monitor.

> 
> Maybe it would be a good thing to have a list of working modelines
> collected on NetBSD.org somewhere?
> 
> Take care!
> 
> 
There is some good and short documentation for xfree what the modeline
means and how it translates to the "physics" of the device,
and how to construct modelines for specific requirements with that
knowledge.
I don't have a link available right now, though.

HTH

Rudi