I was noodling around with my HD-1410 keyer while tuning up my Eico
720. Then the AC power had a brownout, and a bright orange flash and
loud pop came out of the keyer. Opening it up reveals that Q7 is now a
bunch of little pieces of burnt plastic. The keyer beeps the internal
sidetone but now no longer keys the transmitter.

About a quarter century ago when I built the keyer, I remember
something similar happening (except I think it failed shorted), and I
seem to recall that Q7 is just a NPN maybe HV transistor, probably
something like a MSA42. Can someone confirm this?

Tim.