[comp.sys.nsc.32k] "Dead" PC532 developments

news@daver.bungi.com (02/16/91)

My first PC532 is being stubborn about coming alive.  This is basically a
status report.  I haven't heard about similar problems, but if you've got
any clues or guesses, please drop me a line!


I've just spent a day with a few friends and $xx,000 worth of logic analysers,
CROs, etc trying to solve the problem.

Obvious symptoms (as reported previously): no LEDs, no serial I/O, no nothing.

Examining the activity on the EPROM showed fetches up to the location of the
BRanch instruction that jumps to the high EPROM location, at which stage the
same four bytes are repeatedly fetched ad infinitum.
The initial accesses looked a bit strange, from the following locations:
0, 1, 2, 3, 4, 5, 6, 7, 8, 7, 4, ...
Strangely enough, fetches from addresses in the range ...4xxx (hex) also
showed up occasionally.

Examining a working board (with the same EPROM) showed quite different
behaviour (ie. the fetches looked reasonable and the board worked).

Surmising that the data coming out of the ROM was not the same as that going
into the CPU (a bit hard to check, as we don't have a chip rig that large)
we started exploring the back of the CPU with a CRO.  Some very weird-looking
waveforms emerged.

By the time we called it a night we'd tracked down an intermittent fault
between BD06 on the EPROM and BD06 on the buffer next door (on the way
to the CPU).
I'd like to think that this is the only problem, but I'm not that confident.
We'll find out tomorrow night I suppose.

Stategies we've tried along the way included swapping various parts with a
working board: EPROM, PALs, even using a spare CPU.
Hmmm... now I can say that I've seen a 175-pin PGA chip successfully extracted
from its socket......
___________________________________________________________________________
David Burren (Athos)				img Consultants
Systems Development (general dogs-body)		G.P.O. Box 3304GG
						Melbourne, VIC 3001
Email:	athos@img.uu.oz.au			Australia
Phone:	+61 3 819 4554


P.S. When this board finally works I'm going out and getting solidly pissed!
     Seeing as we've only got the test equipment for another day I'm hoping
     to get drunk soon :-)

Ironically enough, with all that test equipment, we still didn't have a simple
multimeter :-)  Probably something to do with setting everything up on
someone's lounge-room floor, and me not realising I should take along my VOM...