I powered the pi with USB and sent 12v to the 12v switch port. Whoops.

[obscenic]

I powered the pi with USB and sent 12v to the 12v switch port (NMEA2K). I just did it for testing (for an entire day of sailing) ... And of course shutdown worked but power-on doesn't work.  Then I noticed the big warning in the documentation...

Have I done irreparable damage?

[Adrian]

I don't think that your MacArthur HAT got damaged. What warning are you referring to?

[obscenic]

I don't think that your MacArthur HAT got damaged. What warning are you referring to?

https://macarthur-hat-documentation.read...power.html

Has a big yellow warning: "Do not power the Raspberry Pi using the USB-C power supply (5V) and the MacArthur HAT power module (12V) at the same time."

Technically I didn't do that,, but I did send 12 volts to the 12 volt switch line whilst powering via 5 volt USB.

[Adrian]

12V on those pins is valid, even when MacArthur HAT is powered from to Pi. For example it's required for Seatalk1 or MAIANA.