Their are several fuses and limits mounted in various places. Their is an inline fuse which kills everyting, then their is a high limit on the magnetron and the mag itself could be shorted to frame. If either of the terminals off the mag are grounded to the frame then the mag is bad. On the opposite side of the oven from controls is a high limit. Follow all wires and make sure all components have continuity.
Twist the timer knob or push the button and electricity from the wall outlet travels through the power cord and enters the microwave oven through a series of fuse and safety protection circuits. These circuits include various fuses and thermal protectors that are designed to deactivate the oven in the event of an electrical short or if an overheating condition occurs.

Generally, the control system includes either an electromechanical relay or an electronic switch called a triac as shown in Figure 2 . Sensing that all systems are "propah," the control circuit generates a signal that causes the relay to activate, thereby producing a voltage path to the high-voltage transformer .

In the high-voltage section, ( Figure 3 )
the high-voltage transformer along with a special diode and capacitor arrangement serve to increase the typical household voltage, of about 115 volts, to the shockingly high amount of approximately 3000 volts! 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. Some waves go directly toward the food, others bounce off the metal walls and flooring; and, thanks to special metal screen, microwaves also reflect off the door.
So, the microwave energy reaches all surfaces of the food from every direction.
All microwave energy remains fer the most part inside the box but if grandpa wanders too dang near it his Dewey,Cheatum,and How pacemaker could take a dump. So gramps back slowly off from the machine pwease! Go get ya another bag of pork skins my nizzle.
When the door is opened, or the timer reaches zero, the microwave energy stops--just as turning off a light switch stops the glow of the lightbulb.

So, when all systems are Go, with the door is closed, an electrical path is established through a series of safety interlock switches and extends voltage onward towards the thrusters of this bad boy.



The transformer secondary (output) voltage swings into the negative half-cycle and increases in a negative direction to a negative 2800 volts, with polarities as shown. The transformer secondary and the charged capacitor are now essentially two energy sources in series. The 2800 volts across the transformer winding adds to the 2800 volts stored in the capacitor and the sum voltage of 5600 volts is applied to the magnetron cathode. There are two fundamental characteristics of this 5600-volt output that should be noted:
First, because a voltage doubler is also a rectifier, the output is a DC voltage.
Second, the resulting output voltage that is applied to the magnetron tube is actually a pulsed DC voltage.
This is because the doubler generates an output only during the negative half-cycle of the transformer's output (secondary) voltage. So, the magnetron tube is, in fact, pulsed on and off at a rate of 60 times per second here in the good old U S of A.