So the question that I struggle with is how did preheating the bed and then starting a print zap the board?
Just for shirts and giggles, I checked the board while attempting to preheat via the control panel. When heating the extruder (which does work) there's a green pilot LED next to the transistor near the screw terminals. Not so when heating the bed, and assuming the board also has a pilot LED for that function as well, it would suggest that the transistor or other wiring is booked.
I'm wondering if this would be considered a warranty issue, given I've done nothing to cause damage to the unit and all other functions - including heating the extruder - work properly.