Gareth Magennis wrote:
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.
That's how i confirmed the problem with the reset pin driver chip on the
other unit. All was the same except one pin, the reset pin.
The one that goes into la la land i can make some assumptions.
I swapped CPU, UART, RAM, ROM from a working unit and the
symptoms were the same. And the swapped chips worked in the
working unit. SO, i would assume its NOT a problem with any of
the socketed chips. The unit will go into self test and gets up
to the DUART test before it goes south. SO i would assume the
basic data and address lines are intact. Power seems to be OK,
but further tests are always in order.
I think it some sort of chip addressing issue. Since i have no print
and its NLA from Lexicon, i will have to wait until i can trace
the chips down and draw one out. The one unit that did this i
modified with the V4 roms, but all seems to be OK with that.
Bob
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.
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