Max,
Thanks and all you mention is good and correct. Bad news I have already checked all of these points.
As I mentioned in my response to Bob, I think the root cause is a hardware issue either a level issue or a timing issue. The good news is that I have the test equipment to look for the root cause in the form of a nice Agilent DSO and a LogicPort logic analyzer.
Of course all this takes time so it may be a while before I post definitive findings.
I have already tested every LS (or S in the case of the 74S03's) chip and they test good as does the 82C55-10. So I will be looking for not low enough lows or not high enough highs and a few nanoseconds of timing errors. It actually is kind of fun in a geek way! ;-)
Rich Leary