Short Finder

I use my digital ESR meter.

For a PC board with a short, I connect a power supply to the shorted circuit and run, say, an amp into it. Then you can do two things: measure voltages with a bench DVM that can resolve microvolts, or - the fast but expensive way - thermal image it.

If it blows the 'fuse' then the amp will go through one of those FPGA's. :(

Somebody ate their breakfast.

Cheers

Phil Hobbs

I use the same trick for over 20 years. Ofcourse you'll need to set the supply to a harmless voltage.

Somewhere in my sketch-book (BC: Before CAD) I designed, at GenRad, a micro-voltmeter for such PCB tracking that used a quad of TL084's and a package of 4016 switches.

I'll look for it, but it'll take a while... I had 5 file cabinets of paper schematics before I got CAD and then saved stuff to CD's. ...Jim Thompson

Set the power supply voltage low, of course.

HP used to make a Hall-effect current probe intended for this application. To find a short the probe was placed on the trace and sensitivity set with a thumbwheel. The probe was then moved the probe along a trace and when the LED went out you found the short. I used it successfully for interplane shorts, too. But the smoke method was faster. ;-)

That worked for traces with AC putting current into the short. IF used in combination with the current pulser, it made a very useful short finder.

If you mean the HP current probe, it was a DC probe. It took some practice but it worked fairly well.

I use a DCR bridge.

Jamie

The magazine 'Electronics Australia' published a project in Feb 89 which consisted of a 741 amplifier with a resistive bridge on the input (the shorted pcb track forms one limb of the bridge). The varying output of the 741 drives the control pin of a 555 configured as an astable driving a speaker. As the pcb resistance changes so does the pitch from the speaker. I built one at the time, it does seem to work although I've not had much need of it.

-- Regards Malcolm Remove sharp objects to get a valid e-mail address

You could have enough current flow through the radio to kill you.

That could be a good thing ;-) ...Jim Thompson

On a modern board, high density and lots of layers, the hall thing would be challenged. HP also did digital signature analysis, also now gone.

At 1 amp, with a good DVM, you can tell which via the current is flowing through. A typical via has hundreds of micro-ohms of resistance, tons of signal.

How is that going to help, when it has to be powered by the AC line to use that method to find shorted power lines? As far as on the bench, it's a stupid idea when you have a lot of noise from test equipment & the HVAC.

Thanks, I saw it on abse and printed it out. I was going to ask if the IC was a 741. You answered that. Mikek