[Elecraft] KPA3 D10 Blown. Causes?

[Geoff Wolf AB3LS]

Was running the CQ WPX CW contest here on 20 meters after a normal transmit
cycle, the radio unkeyed and immediately everything was very quiet. All of
the signals dropped in strength by about 7 S Units.

I tried keying up again but this time I wasn't getting any power out and a
high current warning from the radio.

I dropped the power from 100W down to 12W. As soon as the relay kicked to
switch to the LPA, the receive was working fine again. I'm getting the full
~10W out of the LPA.

So... I pulled out the KPA3 and quickly noticed that D10 is blown.

Other than just a normal diode failure, could there be any suspect external
causes for this? I'm not very good at schematics. What is the purpose of
this diode?

73
DE AB3LS