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A 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.
Whether 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 spot.
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.
A 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
A 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.
A 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.
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
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
Read the tips on the below links on how to replace your microwave oven's diode ad how to discharge the capacitor.
I hope the above is helpful.
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