David Duffy (AVD) wrote:
> The first was to add a 100n capacitor (also tried 10n & 1u) to the
> MCLR line.

Whoa, that's way big!  Some programmers and debuggers may have a problem
with that.

> Faulty unit still does not function correctly when
> powered-up. If I shorted that cap (pulled MCLR low) momentarily, it
> did start working correctly.

OK, so it's not MCLR coming up too early.

> The second test was to remove the 47u capacitor on the 5V rail. Same
> as above;

As expected.  Duh.

> I guess the only other thing I can try before replacing the PIC is to
> add some debugging pin code, maybe to the UART ISR for starters.

The *only* thing!?  What about the obvious things like enabling brownout
detect and the powerup timer?  Also make sure the UART handler is properly
written to handle framing errors and not hang on overruns.


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