Hi Bob, got a link to this as a product?  Would be a great addition to=20
the toolbox.

Tx,
J


Bob Axtell wrote:
> 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
> from a current-limited 5V supply (in a test bed, or the actual product
> 5V supply.). The device could operate on as little as 50mA of
> short-circuit current (so as to locate partial shorts). If the primary
> supply is 3V, it would still work, but the sensitivity is adjusted for
> the lower voltage.
>
> Once the 5V was applied, we used a two-pin probe (made of small sharp
> pins spaced 1/2" apart). We then simply walked down the power trace,
> probing THRU the solder mask ; as long as there was voltage across the
> probe pins, that trace carried the short-circuit current. In a few
> minutes, the offending cap, solder bridge, or PCB defect is located
> where no more V-drop is detected. When we were finished, we coated the
> 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
> front-end op-amp had to be protected from overvoltage and spikes.
> Detection was in the form of a lighted LED whenever a V-drop was
> detected, located on the probe handle.
>
> ---------------
>
> About tantalums: sometimes it is the ONLY solution. EVERY design of mine
> uses a tantalum.  Just don't install 'em backwards.
>
>
> --Bob Axtell
--=20
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