Investigate these three areas if your microwave won't heat
diode is an electronic component that readily passes current in one
direction only and blocks the flow of current in the opposing
direction. If your microwave's diode has become defective, your
microwave will not heat and you will hear a buzzing noise. Test the
diode to determine if this is the cause of your problem. Replace it if
it is defective.
Testing a diode
NOTE: Before you test your diode, make sure your microwave is unplugged, and that you discharge the microwave's capacitor.
it is shorted or open, a defective diode will most likely show some
sign of defect. Defective diodes will usually emit an electrical
burning smell, signifying its defectiveness. Also, it may have split in
two, or it may exhibit a burned crack, or possibly even a blistered
A shorted diode is indicated by a loud humming noise from
the high voltage transformer, and no heat produced when a cook cycle is
initiated. Whereas little or no heat produced in your microwave, with
an absence of a humming noise is indicative of an open diode. In either
case, the diode has to be replaced.
With your microwave
unplugged, and your capacitor discharged, use extreme caution to remove
the lead that leads to the capacitor. You can leave the ground
connection attached. The side of the diode that goes to the ground is
usually marked with a dot, stripe, or arrow. Set your ohmmeter to R x
10,000 or higher. Touch the positive meter probe to the anode and the
negative meter probe to the cathode to measure the resistance across
the diode terminals. Remember that the cathode is on the side that goes
to the ground, which is often marked by a dot, stripe, or an arrow.
normal diode, that is a non-defective diode, will read anywhere from
50,000 to 200,000 ohms. Differences in microwave make and model account
for this large range in resistance readings.
Reverse the meter
probes and measure resistance while touching the positive probe to the
cathode and the negative probe to the anode. Reversing the probes like
this should result in a reading of infinity. Unless a bleeder resistor
is present. The presence of a bleeder resistor would produce a reading
of the value of the resistor.
High Voltage Capacitor
capacitor is an electrical device which stores electricity. A defective
capacitor may be why your microwave is not heating but you are hearing
a buzzing or humming noise. The capacitor will have to be tested to
determine if this is the cause of your problem. A defective capacitor
will have to be replaced before your microwave will work again. Make
sure you discharge the capacitor before you test it, though.
defective magnetron is the third possible cause of why your microwave
is not heating, but you can hear a buzzing noise. Test your microwave's
magnetron. Replace it if it is defective.
Testing a magnetron
NOTE: Before you test this component, make sure your microwave is unplugged, and that you have discharged the capacitor.
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.
Read the tips on the below links on how to replace your microwave oven's diode and how to discharge the capacitor.
I hope the above is helpful.