Replaced blown fuse and relay board, which was scorched. Power back on and control functions working, but fuse blew again when attempting to cook. Bought a cheap multimeter and tested transformer, high-voltage diode, and magnetron for shorts. All good. Didn’t want to test the 2100V high-voltage capacitor (shocks are not fun), so just bought a new one and a new fuse. Installed and oven fixed.