6 Oct
2007
6 Oct
'07
12:40 a.m.
On Friday 05 October 2007 18:14, Tony Duell wrote:
The derogatory term I've seen used for that is calling it the "shotgun
approach" to troubleshooting. :-)
(Snip)
gates and so
on. I have a bit of theory, no practice. I could not
diagnose a faulty chip or anything; my troubleshooting consists of
swap bits until it works. And at this, I know more than most people I
You mean oyu've not been on the receiving end of my flames about this
:-). Suffice it to say I've just written a presentation where I describe
that as a 'ridiculous method'. 2) E very careful if the old and new boards are not
the same revision.
This caught me once, I swapped in what I thought was the same board (same
part number, etc), only to find (after _much_ testing) it was a later
version that needed a backplane modification to work.
I ran into a rather interesting situation one time in an industrial production
situation. The device in question consisted of several boards full of
4000-series CMOS and it was controlling some machinery. The "fixer" there
had been trying unsuccessfully to swap boards, and then to swap chips,
though they didn't have a complete set of spare chips on hand and were
getting them. I was called in as was a tech from another outfit, a rather
different situation than the usual one but we managed to work together. I
found a bad sensor (and no doubt the chip connecting to it was bad as well)
where they'd routed the wire for it through the same conduit as a 480VAC
line...
Anyhow, after a bit the factory rep arrived and that's when we found out that
the two sets of boards on hand were different revisions, and that they both
needed to be swapped at the same time, or they wouldn't work with each
other.
Oh yeah, and in a spare minute I described, and quickly sketched out, a
crowbar circuit for the fixer -- the light dawning on his face was quite
edifying. The apparent original cause of the problems was a power supply
having gone up to 22-24VDC, somewhere around there...
3) A fault elsewhere in the machine could have damaged
the origianl
board, and might damage the replacemetn too. An obvious example of this
is a defective power supply that's damaging chips on the logic boards
See above. :-)
(Snip)
In many of my machines (and those of others on the
list), theres isn't a
processor chip. The processor is several boards of fairly simple chips --
simple gates, flip-flops maybe some small RAMs or PROMs.
Which reminds me of trying to troubleshoot some hardware that was controlling
a milling machine once. There was a "logic diagram" that consisted of a
whole *mess* of OR gates, but there weren't any particulars in there at all
about which gate corresponded to anything at all physical. And in looking at
the boards themselves what I saw was a whole lot of discrete transistors and
no ICs at all. :-)
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin