Reverse engineering vintage PCBs

[tony duell]

> I appreciate all the input from folks. With 3600 though holes and at
> least 4 layers, I'm afraid I will make mistakes using any manual method
> like ohm tracing without a check or balance. With so many permutations
> and little personal knowledge about the WE chipset, I'm sure I will miss
> an occasional trace that shoots to the other side of the board. I'm also
> worried that I might generate a false positive keeping most of the
> components wired. Something akin to body diodes (yes I know this isn't
> CMOS). Here is a wiki photo of the board for reference:

It would actually worry me more if a computer was tracing the connections
(as you suggest) rather than a person. A clueful person will spot obvious
errors, like outputs linked together, lines with nothing driving them, circuits
that could never be enabled, etc. I suspect a computer could be got to 
flag the more obvious ones, but not all. And you are much more likely
to spot errors as you go than by looking over the diagrams afterwards.

I mentioned using a good continuity tracer that is not fooled by diodes. This
will handle any parasitic junctions in ICs, etc. If you get to know the instrument
you will not have problems from false positives. 

-tony