Well - after all the fuss and mess; the real cause was after all..... a bad resistor. I had intended to use 1K resistors for the the transistor bias resistors on the relay, valve, and lamp driver circuits. They did all come from the same package.

The resistor for the relay driver was a 1R (1 ohm) resistor instead of 1K (1000 ohms) and was badly overloading the output on the PIC, causing it to malfunction. I finally determined there was a serious issue when I felt the PIC chip, and the 5V regulator both getting VERY WARM when the relay output was active.

After changing the resistor, the circuit works fine, without any extra choke coils or capacitors, and nothing gets warm.

The resistor was correctly marked as a 1R resistor (by color bands) but was in a package with 1K resistors so (like a dummy) I did not look closely at it before soldering it in.

Live and learn. Thanks again for the ideas, I really appreciate it and am glad to have found a place to discuss these projects!

Later,
David