Going backwards, can't even get a basic blinky working now

[Demon]

Then it has the mod to address the ETN37 overshoot issue.

No, I meant the PK4 assy number... usually on the label right above "BURxxx". On one of mine it's "10-10094-R2". ...

Mine is up to -R6.

... There's probably no real reason to put a zener on VDD. The overshoot was only on the VPP/MCLR high-voltage generator.

I wasn't really thinking of protecting VDD from the PK4. This was more to protect the circuit from being driven by who-knows-what wall-adapter by a user.

Robert