All 286 BIOSes are pretty much chipset-specific not board-specific, and C&T chipset (NEAT) is pretty much the most basic of them all (beside the original 5170 chipset)...
Any BIOS from NEAT motherboard will work fine. Have you already checked the VOGONs 286 BIOS repository?
Also - would you post a picture of the motherboard? I have several NEAT motherboards so I may just rip the correct .bins for you.

Thank you for the help. Pics of the motherboard attached. There's a 211C, 212B, 215, and a 206.

I also recommend getting a diagnostics card (POST card).. The ISA/PCI combo types are not that expensive.
Even though in case you haven't the list of POST codes at hand right now, it will show you something, so you see if it is working at all.
Also, they often have LEDs with the most important voltages (the 3.3v LEDs are useless on ISA, though. If they light up, they may refer to 5v instead.)

Edit: You can also have a look for an AMIBIOS for you C&T board. They may work better in your system.
- A few years ago, I was fixing my Schneider Tower AT and used the AMIBIOS instead of the custom one derived from Phoenix BIOS (?).
Well, it worked fine. If there hadn't been some proprietary on-board stuff, I had kept it that way.

Jo22 wrote on 2020-06-12, 05:58:

I also recommend getting a diagnostics card (POST card).. The ISA/PCI combo types are not that expensive.

I have been considering buying one of these, but in this case it won't help me as this is a laptop/portable without any ISA expansion slots. In particular, it is an NEC ProSpeed 286. It has a 100 pin expansion port labelled 'LTX' that I can imagine might be adaptable to ISA with the right documentation and connector availability, but it is currently beyond my skill or ambition.

A POST card does seem like a great idea if I will be doing many repairs in the future.

Edit: The LTX port is visible in the second photo.

I should also note that I haven't been able to prove that the CPU is good either (don't have another 286 board with that socket and can't get one from eBay because sellers are in places where they cannot ship due to pandemic). The CPU apparently has a max power consumption of 1.3 Watts and the machine drops in power consumption between 2 and 3 watts if I pull the CPU and test again. But other things might be inactive in absence of the CPU so I don't know if that is meaningful.

babtras wrote on 2020-06-12, 06:30:

I have been considering buying one of these, but in this case it won't help me as this is a laptop/portable without any ISA expansion slots.

Ah, I see, makes sense. 😅 Maybe you can try using an POST dongle for LPT-Port then ?
I haven't used such a device before, but I heard that some laptops/PCs had the ability to send POST codes via parallel port, as well.
Anyway, it's just an idea. I hope the other vogons users have other sugestions, too! 😀

Program a Supersoft-ROM. The beep-codes will tell you if the board is OK or not. If its OK, a BIOS from a similar board will work, too.

babtras wrote on 2020-06-12, 02:24:

Pics of the motherboard attached.

A bit OT but man, one look at that mobo and I knew it's a JP system. All these weird connectors and track layout... I hope you get it running.