One thing that hasn't been mentioned. His system
may be
unintentionally over clocking. I've seen systems where the
crystal will take of at an overtone. It is even possible that
the crystal is broken and running at some higher frequency.
Good idea - unfortunately one of the first things I checked
was the clocks and they all look good - decent waveforms,
correct frequency etc.
Dave
--
dave06a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools:
www.dunfield.com
com Collector of vintage computing equipment:
http://www.classiccmp.org/dunfield/index.html