Electronics > PCB/EDA/CAD

How do you find shorts?

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yanir:
Hi does anyone have any recommendations for an inexpensive tool or technique for finding shorts on a pcb. I know about the the resistance method, I just don't have a fancy high resolution DMM like Dave (jealous). I found something online called the leak seaker which will do the job, but looks a bit home made.

alm:
Inject a fairly high current. Voltage drops are proportional to current, so if the current is a few amps, measuring sub-ohm resistances can be done with almost any DMM. This is essentially a four terminal measurement.

Bob Pease described a very sensitive voltmeter with audio feedback especially for this purpose in his 'Troubleshooting Analog Circuits' book, and possibly in an EDN article.

Another crude trick is to feed it even more current, and hope that the short burns up before the rest of the PCB does. Not recommended with mains voltages, especially if there are components on the board.

Bloch:
Not jused it myself and not inexpensive ! but look really nice 8) . Iprober 520 it a current probe for use on the PCB. www.farnell.com/datasheets/1387648.pdf and http://uk.farnell.com/aim-tti-instruments/iprober-520/probe-current-positional-on-pcb/dp/1908148

Bloch:

--- Quote from: alm on March 21, 2012, 08:37:15 pm ---Another crude trick is to feed it even more current, and hope that the short burns up before the rest of the PCB does.
--- End quote ---

Yep that can work and at the same time use a finger as a temperatur sensor will help find something  ;D

yanir:
The short I need to find is on the tx line of a uart connection between a micro and a blue tooth module. The board is populated. The high current method will destroy my components and my 5mil traces. The short is probably under one of those components (or inside) and I would like to avoid removing both to find out.

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