Well, the situation had worsened on my M9301 to the point where every single
word was affected, and then it was easy to see that it was always in the
least-significant four bits. So I pulled and reseated that PROM, then went
ahead and did the other three as well for good measure (really should have just
tried this first!), and things got totally back to normal.
Even better news: I was subsequently able to dump the contents of my M9301-YB,
and found they do indeed exactly match the contents that Noel has posted in his
M9301-YB disassembly. So I think Noel’s dump can be considered
verified/authoritative.
cheers,
—FritzM.
