Re: Finding an open on pcb

"Uriah" (uriahsky@xxxxxxxxxxx) writes:
Thanks but I think I didn't state my problem clearly enough.

What I need to do is follow node or pin on a chip around a large pcb.
and find out where it ends and if there is an open. The problem is
that
the traces are so small and they go from top to bottom it takes a long
time to track down one trace. I need to track down a hundred of these.
The short locator has a AC probe that pulses when you are on the
trace and when you go the wrong way it shows you that you are off
track. Is there anything like that for an open?

But you're asking for two things.

A short is easy, because you know something should not go to ground
unless it's a ground because you have one common point, ground, and
then you just have to put the other lead on the trace you are checking
for a short.

But if a trace is broken, there is now way anything can know that
it's a broken trace unless it knows the circuit and can note
the absence of a connection.

Either you look at the schematic to check that (and if you have
a schematic then you don't have to follow traces, just make
sure there is continuity between points A and B like in
the schematic.

Or you trace out the circuit and hope that what you think is no
connection is actually no connection and not an open circuit.

YOu can streamline all this.

If the issue is not tracing the circuit but troubleshooting, then
at least you can use other clues to figure out what area is not
working properly, which narrows down your search. Unless the board
has seen a lot of rough handling, chances are good it's not a bad
broken trace. (Note that shorts to ground can come from shorted
components.)

You can look at the board, and can impose certain guesses, and
then figure out if the guesses are correct. Like if you see
an IC that is common but which is not a common gate, the manufacturer's
data*** will likely give a sample circuit to use it in, and if
you start with that schematic and trace the board, it's often
easier than tracing blind. "This pin should go to that pin, and
there should be a capacitor on that other pin" is a lot easier to
verify than just tracing the circuit from start.

Michael

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