Re: gEDA-user: sparkfun 4 layer boards

[Greg Cunningham <greg@xxxxxxxxxxxxxxxxxxxx>]

On Sat, 2008-08-23 at 11:41 -0500, Mark Rages wrote:
> On Sat, Aug 23, 2008 at 12:52 AM, Dave N6NZ <n6nz@xxxxxxxx> wrote:
> > Eric Brombaugh wrote:
> >>
> >> What sort of shorts are you seeing? I'm assuming that on a 2-layer
> >> board they would ordinarily be pretty easy to correct by appropriate
> >> use of an knife. Or are they internal/inaccessible? Is that even
> >> possible on a 2-layers?
> >
> > You'd think they'd be easy to find.  On the board I blindly assembled,
> > there was a short to the ground plane somewhere.  I spent more time than
> > it was worth looking for it, and scraped away at a couple of suspicious
> > spots with an X-acto knife.  Never did isolate it.  On the second
> > shorted board, it was another short to the power plane somewhere.  After
> > I confirmed it, I just marked the board and threw it in the NFG pile.
> >
> 
> I've had moderate success clearing blind shorts with the 5V bus of a
> high-power computer power supply.  (This can be hazardous to other
> parts on an assembled board)  Otherwise, use a current-limited power
> supply to put a few amps into the stuck node.  Use a millivolt meter
> to measure different places on it.  Lower voltage means closer to the
> short.
> 
> Regards,
Mark
> markrages@gmail

Way back when I used to fix 16K pdp dram cards, Atari STs, Commodores, &
4MHz motherboards, :) I used the same technique to 'remove' a shorted
component from the 5V rail. Most times it would be a tantalum or a
ceramic bypass cap.  A dab with a good 5V supply would coax the errant
part to 'let its smoke out' & expose itself.   If it was a TTL or memory
chip, the case temp would climb after about 1 sec. Easily detected with
a quick hand wipe-over. 
-- 
Greg Cunningham <greg@xxxxxxxxxxxxxxxxxxxx>



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