Generally, the control system includes either an electromechanical relay or an electronic switch called a triac. The microwave energy is transmitted into a metal channel called a waveguide, which feeds the energy into the cooking area where it encounters the slowly revolving metal blades of the stirrer blade. Some models use a type of rotating antenna while others rotate the food through the waves of energy on a revolving carousel. In any case, the effect is to evenly disperse the microwave energy throughout all areas of the cooking compartment. So, the microwave energy reaches all surfaces of the food from every direction.
All microwave energy remains inside the cooking cavity.
Bad interlock switches or door misalignment can cause fuses to blow or no operation when the start button is pressed. Replace carbonized or damaged waveguide cover. Smooth rough metal edges. Touch up interior paint. Thus, replacement should be considered seriously before sinking a large investment into an older oven.