How do protection diodes get damaged?

[duck_arse]

Frankly, though, you got lucky that the diode failed to short.  The couple that I've seen just exploded and left the reverse power free to plow through the rest of the circuit popping electros and frying chips.

I thought this too, until I re-read it. I actually thought he was lucky the 1n914 went short. I've seen from a 1n400x in a boss dd-something which didn't go short, and just kept conducting, heating, burning. that pedal was shot completely in the end.