Well I got some EGA...
First off I tried the 2nd CGA card, which settings were correct and booted with no funny noises or complaints, and gave good clear CGA output, seemed brighter than onboard, again that seems weird, it's logic not analog. Anyway, that behaved perfect, so it seemed there was nothing with the XT stopping separate gfx working in principle. Good. Now go over the EGA wonder for the eleventieth time.... okay there's another alternate switch setting for IBM XT I missed, try that, same roll again, but it's a straight roll not scrambled... maybe pin 9 vsync is not connecting, jiggle plug, THERE we go... straight/stable picture... I am still getting the beieieieip bip beieieip bip at power on with shimmering keyboard lights, I do not know what the hell that is, the ATI BIOS message comes up immediately after, is it the card's error? Now, runs some crap... low intensity, dark colors very dark, high intensity alright, fiddle with contrast, not much effect, doesn't change relationship between dark and light much just seems like another bright control. Hmmm... low intensity really dark in CGA stuff too. Try outrun ega, crash and the same bleeps and keyboard flicker I get at power up, but it's locked up with it. Huh. Entrap in low res EGA has weird yellow lines across...
Yeah so the card really hates this motherboard or has problems... The monitor is .... aged I guess ... might need to do a recap sooner rather than later. Weird how different cards have different brightness on it though. So theres something in the EGAW manual about it doesn't work with PS/2 keyboards, because of IRQ2 contention, I am using a PS/2 keyboard in XT mode, scancode set 1, XT keyboard controller, no IRQ 2, but I am wondering if ATI card has some code for "preemptive strike" against PS/2 keyboard to try to kill it before it kills card or some stupid shit and is "going off" on the keyboard somehow. But it's got that weirdness like it's dropping a line on a RAM chip in some modes too... gah.
Gonna recheck if it's i/o address is fighting with the disk controller, I don't think it should be unless ST11 is way off default...
Edit: the after supper update....
That first alternate CGA card didn't work.... because it was an Mono/herc card only.... heh, swear I've had some look like that which were autoswitching, not that one, all mono, all the time. Running some stuff on the EGA Wonder... I don't like it... well, if I got the utils I might be able to force it into civilised behaviour, but enhanced switch is off dammit, why you still ruining CGA stuff with flickery interlace and making them too tall. Load Elite and it's like "Why am I flying into a giant kinder egg capsule..... oh it's the sun, jeeze that is stretched." ... so apparently the "behave exactly like IBM" part of the disable enhancement mode is "enable snow" rather than disable hinky non mode 1 screenmodes, coz I'm seeing that on some stuff. I think you are meant to ignore how crappy it is on actual EGA because of it's dancing bear tricks on other monitors.... A: "Look it's a dancing bear." B: "It's not dancing very well, is that supposed to be a waltz?? A:"But it's a BEAR and it's DANCING."... hmmyeah. So can't wait to find my PEGA if I'm gonna actually enjoy EGA on an XT... I had thunk this one was going into the PC Portable though for it's all the modes on mono dancing bear trick. XT wasn't really the target for the monitor though, that was the Packard Bell 286... so need a good card for that... might cheat and use VGA Wonder 16... but that might be more dancing bears.
Unicorn herding operations are proceeding, but all the totes of hens teeth and barrels of rocking horse poop give them plenty of hiding spots.