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Craig mentioned that error comes from the extended I/O, if the
memory switch is in the 32K position when you remove the A25 card
the extended I/O would not be available, this would suggest that
the A25 card is participating with remapping the the ROMs. This
may indicate that the A25 is at least partially functional and the
problem might be the RAM array on the card.
On 2017-01-31 1:59 PM, Jack Rubin
Interesting - not much time to play around this morning before
leaving for a few days, but I did find that with A25 in place
and 64K selected, the system would note the presence/absence of
the tape drive (i.e. error 43) if the Monitor Bus cable was
_removed_. If the cable was in place, no error was reported
whether the tape drive was connected or not. Clearly
_something_ is happening on A25 and the Monitor Bus cable is
providing some signals.
More tantalizing than conclusive. When I return home later in
the week, I'll go ahead with a full physical tear-down and
inspection of the other end of the Monitor Bus cable.
More to come ...