Michael Rigby-Jones wrote:
> Was the device being used outside of the specifications originally
> though?  Lots of history on the list to suggest the injecting any amount
> of current into PIC pins is a bad idea and not within the operational
> spec.
> 
> Mike

Regarding latent damage, I once saw a cmos part get damaged and appear 
to work but later go to a hard short on the power supply.  A data logger 
in a box with a gel cell battery was experiencing strange failures 
involving an Intersil 7660 charge pump.  When a new chip was put in and 
power cycled a few times, a puff of smoke would sometimes be emitted but 
the part would seem to keep working.  Then a little later, it would go 
to a hard short.

The circuit design was fine; the problem came from a non-electrical 
person who did the wiring plan and believed that wire had no resistance 
and no inductance.  In this case it certainly did. A ground line that 
should have gone direct from the battery to the electronics went instead 
out 3 feet and back to power a solenoid.  A turn on current surge caused 
one of the I/O lines to go below ground 5 to 10 volts and the 7660 was 
the victim.

A little o'scope work spotted the culprit and a slight re-wiring of the 
main wiring harness fixed it.
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