14 Apr
2010
14 Apr
'10
9:48 a.m.
On 14 Apr 2010 at 12:27, Dan Roganti wrote:
But you really want a Milli-Ohm Meter to find shorts
with more
precision when it comes to connections with several components on
there, about 0.1 milli-ohm resolution. That lets you pinpoint the
short directly to the sport on the pcb, even between the next pin on a
chip. I just found a place online the other week that has one for $150
from Ruby Electronics, other costs 3 times as much, but I still have
to wait to get one myself--other bills still have priority :)
http://tinyurl.com/y4d7op5
As long as you don't require calibration, isn't a milliohmmeter for
this application pretty much a matter of wiring up an inexpensive op-
amp with a small current source?
http://baec.tripod.com/DEC90/ohmmeter.htm
Here's a neat little circuit that uses an LM317 regulator. You could
build it out of components in your hellbox in a matter of minutes:
http://www.edn.com/article/CA408390.html
The basic idea is that you don't actually need an accurate
quantitative measurement, but rather a relative one as you probe down
the PCB.
Alternatively, one could use a wheatstone or kelvin bridge with a
microammeter.
While a lab milliohmmeter would be a cool thing to have, it's not
necessary.
Cheers,
Chuck