At 07:17 AM 11/10/2011, Forrest Christian wrote: >So I on occasion have a board that for whatever reason is effectively >'shorted' to ground. That is, something is drawing so much current that >the onboard switcher shuts down.... I've used a variety of methods over the years. My earliest technique (and one that I still use occasionally) was an=20 old HP logic pulser and its companion current trace probe. The=20 pulser was rated to dump something like an Amp of current with a very=20 short pulse width into a line or node, the current trace probe was=20 sensitive to pulses down to less than 10mA. I'd use a multi-meter to=20 find the shorted traces, then apply the pulser to one end of those=20 traces (or trace and ground). The current probe has a LED that=20 lights when it sees the pulse. The downside with that method is that the current probe's pickup=20 sensor is directional, which means that you have to continuously=20 rotate the probe about its' axis while moving it along a meandering=20 trace. Small price to pay for the ability to actually find the short. Another technique used a current-limited DC power supply and my old=20 HP 6.5 digit DVM - inject the current into the shorted line (usually=20 a power rail) and use needle-point test probes to follow the voltage=20 drop. Works very well. A few years ago, I purchased something called the 'Leak Seeker'=20 which is essentially a single-box=20 version of the 2nd technique that I mentioned (immediately=20 above). It works by injecting a relatively small current into the=20 shorted node, then using a test probe to follow the voltage=20 drop. Voltage variations are indicated on both a LED bar-graph and=20 as tones through a speaker. Very, very quick and easy to use. You would think that something like the Leak Seeker would have=20 limited dynamic range - which it does. They compensate for that by=20 having both manual and auto-zeroing in the box - as you get closer to=20 the short, the detection range auto-adjusts. The builders of the Leak Seeker have been around for decades - their=20 primary market was Radio and TV repair shops. They also built the=20 very first capacitor ESR analyzer that I ever saw, again, 20 plus=20 years ago. I'm not sure just how busy they are these days - the Radio / TV=20 repair shop industry has pretty much died off. None of the old shops=20 and guys that I used to visit are around anymore. But the website=20 for the Leak Seeker is still up and running, so I guess that they=20 still sell their stuff. dwayne --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .