Probably a shorted decoupling capacitor (if it's a
'dead short' or close
to one). I have been known to carefully cut power traces to find out
which section is shorted, and then home in on the problem.
That's the way that I've traced shorts down. However since then I've bought
a HP Current probe, they're supposed to be able to trace a short down the correct
path. I've never had a need for it since I bought it so I dont know how well it works.
Has anyone had any experience using one?
Or you can
desolder components to test them.
Don't use the trick I once saw recomended of applying a high current
(10's of amps) PSU to attempt to burn out the short. Something will burn
out, it's true, but it will just be the weakest connection, not
necessarily the shorted component.
OUCH! I've never seen that recommended and I sure wouldn't try it. In my
experience, a hard short will completely remove the circuit runs from the board. And those
can be a real pain to replace, I've seen some runs disappear so completely that it was
nearly impossible to tell that they were ever there.