A faulty door switch may be causing the microwave to blow its fuses.
Other issues could be from the capacitor or diode. After discharging the
capacitor as noted above, the leads can be removed and the capacitor
can be probed with the VOM set to Rx100. Readings should start in the
low ohms and increase toward infinity. To examine the diode, it should
be disconnected from both the capacitor and the appliance. The wires
should be probed with the VOM set to Rx100. One VOM reading should be
infinity and the other in the low ohms. When a microwave activates, but it does not cook anything, there is
likely a disconnect in the internal mechanism of the microwave. Thermal
cutoffs may be the culprit. They are disc-shaped devices that are
connected via a wire. Both thermal cutoffs should be checked at the oven
and the magnetron. The leads should be removed and the terminals probed
with the VOM set to Rx1. The reading should be zero. If it is anything
but zero, the thermal cutoffs should be replaced. Other issues such as
the capacitor, diode, magnetron, or transformer would need be serviced
by a professional. If the microwave cooks the food, but it is either too slow or very
uneven, there may be a problem with the voltage at the outlet that is
supplying the power. If the voltage is less than 115 volts, the problem
is likely with the electrical service or breaker. Another potential
problem is a bad turntable motor. To examine the turntable motor, the
microwave oven must be turned over and the bottom grilled should be
removed. Remove one lead from the motor terminals and probe the
terminals with the VOM set to Rx1. The motor should be replaced if the
reading is infinity.