On Mon, Mar 4, 2019 at 12:04 AM, fiftythreebuick wrote:
There's another way, that's to take a current limited supply and pulse
it on and off. For a supply of X amps, I'd limit it to x/10 amps.
Now, if you have an HP current probe, the one that's made for shorted
nodes, you can see where the bright lights go, and that shows you the
track where the short is.
Decoupling caps and tants and conducting PN junctions and regular power supply current would (partially) short out your pulse, thereby hiding the current info you're looking for, *unless* you use a low level, very low frequency, low slew rate signal.
A few months ago, I successfully used a low-level sinewave (about 0.4 Vpp) signal of about 10 Hz across the power supply pins with an HP 547A current tracer on a spectrum analyzer board, containing rows and rows of digital logic, 0.1" apart with dozens of interspersed decoupling caps. To my own amazement, it took about five minutes to find a shorted cap!
Raymond
Raymond Domp Frank