this is an excellent project that's great fun to watch the progress of. keep up the great work.

i have no experience with altos but i have been wondering -- on day one of the restore, it was noted the alto in question had some modifications from stock issue[1], could the booting issues be related to the microcode or wiring changes necessary to support those modifications? is it trying to boot off of the now missing trident drive?

[1] from http://www.righto.com/2016/06/restoring-y-combinators-xerox-... "I suspect that the Y Combinator Alto originally had both a Trident drive and a Diablo drive (as well as four Orbit boards to drive a laser printer)"