I have a Emerson MW1119B/W microwave. It has been doing just fine and all of a sudden it has decided not to heat any thing

Hello there,

When your microwave oven starts to zap, then eventually does not heat up, it means there is a problem inside the unit of the microwave. There are some parts to check inside the microwave before you can tell the exact component that is faulty and to know if replacement will do the job for you.

The three (3) main parts to be tested are the power diode, the high voltage capacitor and the magnetron.

But since all other components are working like the fan, light and clock, then it is most likely the magnetron. Here is how to test and replace the magnetron of your microwave.
HOW TO TEST THE MAGNETRON
Before you test this component, make sure your microwave is unplugged, and that you have discharged the capacitor.
There are two tests to conduct in order to determine whether or not a magnetron has become defective. If you receive results other than what are detailed below, you will have to replace your microwave's magnetron. Each test is described for you here:
TEST 1: Locate your magnetron and label each of the wires attached to it so that you know which wires are to be replaced where. Set your ohmmeter to the lowest resistance scale. Take a resistance measurement between each of the magnetron's terminals by touching each probe to one terminal each. Reverse the probes and take a second resistance measurement. Each measurement should read less than one ohm.
TEST 2: Set your ohmmeter to its highest resistance scale. Touch one of the meter's probes to a magnetron terminal. Touch the other probe to the metal magnetron housing. Take special caution to not touch the two probes together. This could result in an inaccurate reading. This test should produce a reading of infinity - indicating an open circuit.
Magnetron replacement
Have a certified and experienced appliance repair technician examine and replace your magnetron. This task is much too dangerous for the average layman to perform on his own.

Hope this helped.

Elect_Comp