James Nick Sears wrote :

> I replaced the max3221 and the supply is still noisy as all
> hell but the false !INVALID signals are not occurring.
> Probably if I add some extra capacitance now I'll be ok


Perhaps you should have put a "driver" between the PIC pin
and the power supply of the MAX chip. Everything looks like
the MAX has a varying current drain depending on what it's
currently "doing". If it's feeding current out on the RS232
line, the charge pump have to work a little harder for a
short while. Or put something like 100uf as a reservoar
that is charged through current limiting resistor of around
200 ohms from the PIC pin. Or put a simple FET in between
and switch the MAX chip directly to 5V. Or an ULN type of
driver chip.

>
> By the way, I think I first heard about it on this list but
> if anyone hasn't tried Chipquik removal solder yet it is
> great stuff.  I paid $18.50 for my kit and it has already
> paid for itself several times over and I probably haven't
> used 5% of it.

Any URL that shows what this is ?

Regards
Jan-Erik.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.