One of my most regular board repairs (5-10 annually) will not come good any
more, and I seek wisdom from this list. I have a number of duds at this stage.
My Polar Analogue Signature analysis fails to discover anything. This has a
95% accuracy on hardware faults on this sort of stuff.
The databus has a HD6303 cpu, with HD46508PA-1 analogue input chip, HD6340
timer chip, and 82C55 interface adapter. I can replace all the chips, except
for the (Cmos) HD6340, for which I can only have Nmos EF6840s or MC6840s .
Signals are square enough except for some databus lines which have a very
slow rise in places. Very good, said I, and applied pullups, but no joy.
Pullups even stopped good boards from working. Bah!
Question: My suspicion is currently directed at the NMOS/CMOS thresholds on
the same bus. Any known way to compensate for this one?
I have the digital signature analyser going on it. I can trigger on a
watchdog pulse, and it produces a signature from the buses which I can
check, and all the boards repeat it. It is a short sample, however, and not
exhaustive enough. If I try for a longer data sample, the dsa goes unstable,
and becomes useless. That would indicate, however, that the bus traffic is
similar (HP say 6 cycles is enough for a check to be 99.98% accurate). But it
proves to be no guide.
--
Regards,
Declan Moriarty
Applied Researches - Ireland's Foremost Electronic Hardware Genius
A Slightly Serious(TM) Company
Experience is like a comb,
that Life gives you - AFTER all your hair has fallen out!
--
Author: Declan Moriarty
INET: [EMAIL PROTECTED]
Fat City Network Services -- (858) 538-5051 FAX: (858) 538-5051
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