On 11/10/2011 8:44 PM, peter green wrote:
>> In any case, I'd love to hear people's experiences with finding
>> shorts/defective components and suggestions about tools to isolate
>> (usually) a defective component.
> My technique is to set up a bench supply with a current limit of 1A and
> a voltage limit of a couple of volts and use it to apply a current
> through the short.
>
> I then set a multimeter on it's most sensitive voltage setting and use
> it to follow the current arround the board.

I'm disappointed in you guys.

I hold a patent on a short-locating device. The design we sold operated=20
from a current-limited 5V supply (in a test bed, or the actual product=20
5V supply.). The device could operate on as little as 50mA of=20
short-circuit current (so as to locate partial shorts). If the primary=20
supply is 3V, it would still work, but the sensitivity is adjusted for=20
the lower voltage.

Once the 5V was applied, we used a two-pin probe (made of small sharp=20
pins spaced 1/2" apart). We then simply walked down the power trace,=20
probing THRU the solder mask ; as long as there was voltage across the=20
probe pins, that trace carried the short-circuit current. In a few=20
minutes, the offending cap, solder bridge, or PCB defect is located=20
where no more V-drop is detected. When we were finished, we coated the=20
tiny punctures (in the soldermask) with drops of  clear fingernail polish.

The detection circuit was sensitive to a V drop as small as 2mV, so the=20
front-end op-amp had to be protected from overvoltage and spikes.=20
Detection was in the form of a lighted LED whenever a V-drop was=20
detected, located on the probe handle.

---------------

About tantalums: sometimes it is the ONLY solution. EVERY design of mine=20
uses a tantalum.  Just don't install 'em backwards.


--Bob Axtell
--=20
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