Ideally I’d harvest one of these capacitors that are right next to the crystal on an old isa modem if that would work.

nope, those are in pico range for crystal, TOYOCOM is a generator. C29 from that modem looks like 100nF and should be fine.

rasz_pl wrote on 2024-12-23, 11:00:

nope, those are in pico range for crystal, TOYOCOM is a generator. C29 from that modem looks like 100nF and should be fine.

Ok, thanks. Did you assess the capacitance by the color or the location ?

Location. C67 68 go under crystal so those are tiny external load caps. C29 C65 are soldered to the big copper plane , most likely ground = decoupling for something.
I would guess that on your controller caps are called:
TC = tantalum, maybe ~10uf?
BC = bulk capacity, maybe 1uf? or anything above 100nF
C= everything else

You can just check where missing cap is wired to, if ground and +5V then its 100nF or maybe even 10nF and probably in parallel with BC27.
If between ground and output then its a load capacitor after all (rare) and you can use C67 C68 like you intended (they might be too big) or just leave it missing, its not that critical (mostly EMC I think? controls rise time speed).

Thanks for the details. I really appreciated it. I lost patience yesterday before you first response and used the C68 capacitor because it seemed low risk and the iron was still hot after doing the tantalum cap. The card is working ok so far. Just needs a BIOS upgrade.