This one will have to wait since i robbed the max 690 out of it.
But i am still looking for theories. Since it goes through self test
fine until it hits the DUART, its got to be some problem there.
The Duart is socketed, and i swapped it with a good one an
there is no change. So it cannot be the chip. But, i could be some
issue with the addressing of the chip. Maybe an address decoder?
If i had a Z80 Micro emulator to hook to it i could easily track it down.
But that's
not a tool i have laying around


In my experience, if you have a working one to compare it with you're
laughing. Well, maybe a slight chuckle. Scope all the pins of the working
UART and you may be able to see roughly what kind of signals should be there
and those that are missing or corrupted on the duff one.

Or you could try removing both UARTS and then compare signals - maybe a more
obvious boot up difference/failiure mode may become apparent. (You would
have to constantly reset each machine to see these boot up procedures
working)

Good luck,

Gareth.