If an Amana microwave does not heat up, the problem may be with one of these parts: the high-voltage diode, the magnetron tube or the high-voltage transformer. Microwaves can create an electric shock at any time, so use caution when testing any parts.
The high-voltage diode doubles the voltage of the microwave to nearly 5,000 volts by converting A/C power to D/C power. The magnetron, powered by the high-voltage diode, puts out the microwave frequencies that heat food. When the diode burns out, A/C power is directed to the magnetron, which is not strong enough to operate it.
The high-voltage diode can be tested with a volt-Ohm meter powered specifically by a 9-volt battery. If the test shows that the diode is working properly, the magnetron may be burned out and must be replaced. The magnetron can be tested with an Ohmmeter set to the lowest resistance scale.
If the high voltage transformer has burned out, the microwave should have a burning smell. The transformer emits the A/C energy that is converted by the high-voltage diode. If it has burned out, the microwave may arc, causing a fire hazard. Each of these three parts, the diode, magnetron and transformer, should be replaced by an experienced technician.