🚀 go-pugleaf

I've had repeated problems apparently blowing out lines on one
of my 8520's.  How this happens I'm not sure...I may have gotten
careless plugging or unplugging things into the joystick port
while powered up (and I swear I'll NEVER do it again, heh).

Usually, the problem goes away when I replace the offending chip
(U300, I believe, which is used for the parallel port and some
of the joystick port lines).  However, this time it *didn't* change
the behavior of the problem - the FIRE0 line is always asserted
(the mouse fire button always thinks its down) and my printouts
come out with bad characters (mostly "e's" in place of the desired
character, but other transpositions as well).

Now, the possibility exists that I may have been sold a bum chip,
but otherwise, I'm stumped.  It doesn't appear in the schematics t
at any circuitry is in between the 8520 and the joystick fire button
or the parallel port.  I also can't see any relation between these
two functions (FIRE0 and printer lines) so this seems to be a very
strange coincidence.

Anyone have any ideas?  Chuck?


		Phil Stone	 (phil@eos.arc.nasa.gov | ames!eos!phil)