I remember NT4 refusing to install on NexGen cpus. It detected them as 386. Worked fine if you installed on a different machine and moved the hard drive over to the NexGen system and ran wonderfully.
From the Model II Tech Ref, page 13, the keyboard screws are 6-19 x 3/4", page 12 says 'four thread forming and two machine screws'
page 139 (Parts list) shows 6-19 x 3/4" (6) and SFT 3-28 x 3/8" (2). Could swear they were all thread forming screws in the keyboard.
Page 177 "Case Assembly Parts...
I'm not famillar with those 5-pin connectors either.
Amazon's got something that claims to be a 5-pin to 4-pin adapter, but the 5 pin part looks similar to a CD-rom audio connector.
https://www.amazon.com/ITROLLE-6-89inch-Connector-Converter-Extension/dp/B099ZFQ2W6/
Tossed the whole thing (DOS, Windows for Pen, pcmcia drivers) onto Internet Archive--
https://archive.org/details/t200_20240329
Looks to be pretty much a clean original install.
Mine still lives outside, but I've wondered if you could fit one in the modem slot. If I remember correctly, the modem slot has power on the internal card edge, then connects to the external system bus connector with a short cable.
Sorry, pics have occasionally been showing up as 's-I1600.jpg' for me lately.
2 for $9
https://www.amazon.com/PNGKNYOCN-10-Pin-Serial-Motherboard-Cable(0-3m)/dp/B0BGQCYZMM
You've got 2x 1meg simms in bank 0, 286 motherboards typically either ignore the 384k in the Upper Memory Blocks or possibly uses it to 'shadow' the roms. You should be able to use 4x 44256 and 2x 41256 in the bank 1 dip sockets to give a total 2.176 meg (2048+512-384).
It's either/or per bank...
Sounds like sticktion. With the drive unplugged on a flat smooth surface, give the whole drive a quick spin. The idea is to use the inertia of the disk platters to 'unstick' the heads from the platters. Just don't get carried away and have it fall off the table.
Eproms don't need battery backup. My guess is there's an sram somewhere to hold configuration settings that the battery backs up. A dead battery _shouldn't_ keep it from working, but I've seen it happen. I'd clip the battery off and temporarily feed the board 3.6v and see if it works like that.
Looking closer at the pic, that's a _weird_ pin spacing. Closer vertically than horizontally? 3.5" drives used 2.54mm spacing, 2.5" drives used 2mm spacing. I've never seen an IDC connector with mixed pitch.