30 Aug
2011
30 Aug
'11
1:12 p.m.
At this stage you need a good dvm (many digits) with good low
resistance measurement facilities.
pick some 0v place make a good connection to the dvm and them go
around the 5v line looking for the smallest resistance to 0v, You are
actually measuring the track resistance and minimizing the amount of
track to the short eventually one finds an area, now do the inverse
use that as the connection point and measure the 0v resistance to that
point you should arrive at the other side of the faulty part or very
near.
This is very difficult to do on a board with power and ground planes
since the reisstance is very low and you can't 'slide along' tje track.
With some many effective parallel paths in the power/ground planes, you
can't really 'home in' on the problem anyway/
You _might_ be able to do it uins a 4-wire technique. Apply a current
source (voltage limited to 5V!) between the power inptu conenctions and
measure the voltage across each dfecoupling capacitor in turn. The faulty
one will be the lowest (or even 0 if it's a dead short). But you need a
good millivoltmeter.
-tony