RPI falls back to 1280x720 from x1024.

I have an HDMI->VGA converter module connected to my 'pi, as I have a bunch of TFT VGA monitors lying around, but no HDMI ones.

When I boot the 'pi with the cable attached, it comes up nicely in 1280x1024 as I told it to:

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hdmi_drive=1
hdmi_group=2
hdmi_mode=35
hdmi_force_hotplug=1
config_hdmi_boost=4
disable_overscan=1


(hdmi_mode=35 is 1280x1024@60Hz in group 2)
However, somehow, the mode drops to a 60Hz 1280x720 mode when the monitor is not connected during boot. I was hoping to prevent these problems by specifying hdmi_force_hotplug=1, and directly specifying a mode that I want.
Why does it drop to a lower resolution if the monitor is not connected?
Just to be sure: the /proc/cmdline file shows "fbheight=720", so it is not my VGA converter that isn't booted correctly and somehow converting the 1280x1024 mode into 1280x720 (as if such a cheap piece of electronics would be capable of such a feat).

[dom]

A hack would be:

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sudo /opt/vc/bin/tvservice -d /boot/edid.dat

and add hdmi_edid_file=1 to config.txt. You would then always see your monitor's edid even when it is not plugged in.

OK. That will "hack" it into submission, but that leaves me with the question why it doesn't work in the first place. Wasn't there something with a maximum dot clock that was assumed if no edid data is available? Can I overrule that? This would come closer to my sense of "cleanlyness"....

I had a similar problem and have the display correctly working now. I'll explain what I did so others can benefit.

I have a Hp1825 hooked up with a hdmi cable to a hdmi-dvi converter in the dvi input.
The monitor works with hdmi and my laptop but the with raspberry pi the monitor is not displaying anything. The screen is 'on', the backlight is on.

tvservice -s only showed me the default (I think 1280x720)
tvservice -m CEA of -m DMT gives "Group CEA has 0 modes:" and "Group DMThas 0 modes:"
tvservice -d edid.dat followed by a "edidparser edid.dat' gives me a lot of correctly looking output !

The solution now was to save the edid.dat to /boot/edid.dat and to put 'hdmi_edid_file=1" in /boot/config.txt.

Combined with "hdmi_group=2" & "hdmi_mode=36" (1280x1024@75), hdmi_force_hotplug=1, config_hdmi_boost=4, in /boot/config.txt.

I tried "hdmi_ignore_edid=0xa5000080" before, that only gives me broken, partially output only after I killed startx.....
I tried a lot of "hdmi_group" and "hdmi_mode" combo's