Snayperskaya wrote:

What's even weider is the fact that it outputs while on POST

Actually that's to be expected when hardware itself is working correctly, because at that point in the booting process, the video card is yet to be subdued by the OS' display drivers, which appear to be the problem here.

I've seen this happen from time to time with different video cards and there usually isn't a magic fix (I personally had problems with composite>s-video converter cables on my GF6200 that refused to output in color)

I'd try uninstalling the display driver, wiping out any leftover registry entries/dependencies/etc and reinstalling it without having any monitor plugged in just to see what happens.

Just for sake of completion, I've tried to use the same setup without the AMD drivers (relying on Microsoft ones) and it worked! Pretty weird problem.

I have an AGP HD3850 in a system connected to a big CRT TV w/S-Video. Nothing plugged into VGA or DVI. It works 100% perfectly, displays textmode/BIOS/GRUB/etc. and any graphics/OpenGL mode up to a max res of 1024x768 on the TV. That machine is running XP and whatever the final version of ATI/AMD's driver for AGP HD cards was.

There are a bunch of options in the ATI control panel relating to TV output but I don't remember if there's a "force, always" thing you could set.

Sorry I don't have any advice to offer but just thought I'd post that it *should* work.

I've never had this problem personally but I've been asked about it more than once in the past, the solution/workaround I used to give was to build a dummy VGA plug in order to trick the video card into seeing that a (non-existent) monitor is plugged in, to do this you just need to put the right impedance on the RGB lines which is 75Ω, just stick three 75Ω resistors like this and away you go:

xjas wrote:

I have an AGP HD3850 in a system connected to a big CRT TV w/S-Video. Nothing plugged into VGA or DVI. It works 100% perfectly, displays textmode/BIOS/GRUB/etc. and any graphics/OpenGL mode up to a max res of 1024x768 on the TV. That machine is running XP and whatever the final version of ATI/AMD's driver for AGP HD cards was.

There are a bunch of options in the ATI control panel relating to TV output but I don't remember if there's a "force, always" thing you could set.

Sorry I don't have any advice to offer but just thought I'd post that it *should* work.

That machine won't benefit of having the drivers installed anyway. It's a very bizarre problem, no options or software to force it worked.