Interesting that you mention HVAC. I have had my furnace control board fail last month. The failure was in the power relay gating the power to the blower moto

Interesting that you mention HVAC. I have had my furnace control board fail last month. The failure was in the power relay gating the power to the blower motor (which is a pretty hefty 1kW load). The relay had melted to a lump of charred plastic, and the circuit board around the relay pins turned into a hole. I guess no matter which way it failed there would've been no serious consequences (blower motor stuck on) so I classified the incident as "neat." :-)