JW wrote:
On Thu, 14 May 2009 00:41:18 +1000 Bob Larter
wrote in Message id: :

JW wrote:
Let's say you know that a certain point on a data bus has a defective
device that is always trying to drive the bus low; Was wondering if anyone
has any good tricks in finding the defective device, other than
cutting/lifting pins?
Hang a CRO off each line in turn, & look for one that's stuck low.

Hi Bob,

I don't think you understand quite what I'm asking. For sake of argument,
let's say I have five ALS245 transceivers all located on a 8 bit bus. One
of them should be driving the bus at any given moment, but another one has
a defective output that is corrupting data bit 1. I'm looking for any
tricks that would help to narrow the fault to one device. So far, Phil
Hobbs has had the best idea.

Okay, that's something to work with. Here's how I'd tackle the problem:
Hook your CRO channel 1 to one of the 74x245 enable lines, & use that as
the trigger, while using the 2nd channel to look at the faulty data
line. Probe each of the 74x245 enable lines with channel 1 until you see
a stuck line on channel 2.

Once
you've found it, pulling chips out of their sockets is probably the
easiest way to find the culprit.

Sockets? Heh. If they were in sockets it would be a piece of cake. Have
you taken a look at a modern circuit board with SMD parts lately?

I guess I'm showing my age here. ;^)

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
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