First I tried replacing the fuse (located waaaaay back and near the top of the housing, accessible by releasing the control panel), but a new one blew immediately when the microwave was tested. The next suggested step was to check the capacitor, which required that the combo oven be removed from the cabinet to access several removable metal panels and shrouds (shut the power to the appliance off at the breaker panel) which must be removed to access the capacitor. I used a pair of insulated needle-nose pliers to short the capacitor before removing it, and got no spark. The multimeter showed an internal short in the capacitor (zero resistance both ways), so I ordered a new capacitor and two fuses. Once they arrived, I installed the new capacitor and swapped in a new fuse, replaced the shrouds, and tested the microwave, which works again! (The turntable drive is dodgy, but that’s another problem for another day...)