A microwave not heating up is caused by one or more of the following -
1) Failed controller board (unlikely if you are getting a clock readout
and you can get the various functions to work, just no heat)
2) Failed door switch
3) Failed thermal fuse, when used
4) Blown power fuse that is dedicated to the microwave circuit
5) Bad diode
6) Bad capacitor
7) Bad magnetron
8) Bad transformer
Door switches insure the microwave circuit will not engage when the
door is open. Slamming the door of the microwave is hard on the switch.
The thermal due is wired into the microwave harness, and is a melting
allow type, based on heat buildup within the oven. Always replace with
a fuse of the same thermal rating.
Hello,
The power fuse is a special type and should only be replaced with that same type and rating. It is easily tested.
The diode is a relatively inexpensive part, and is not easily tested.
If a grumble is heard coming from electrical area of the unit, then the
diode could be shorted.
A shorted capacitor will blow the fuse immediately. And open capacitor will cause a "no heat" condition.
A bad magnetron will also cause a low level hum or grumble from the
transformer. But is may also cause no other identifiable symptom of
failure.
A bad transformer will exhibit a grumble or hum, and may or may not
blow the fuse. But be careful here, the secondary of the transformer
produces very high voltages, up to 2.5Kv. Few people own a meter
capable of measuring such voltages.
Service and repair of microwave ovens is dangerous work. If you don't
know what your doing, DO NOT ATTEMPT TO SERVICE A UNIT WITHOUT
INSTRUCTION.
I hope this helps.
Good luck.
Hi,
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 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.
Good luck again.
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Hi,
Here is a tip that will help you to figure out what is wrong with your Microwave Oven....
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heatman101
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I assume that a bad magnetron could also generate no noise. How would you test for a bad magnetron?
Thanks for your information. It gave me the confidence to attempt a repair of the microwave. When I took the cover off I found an envelope that contained a wiring diagram, electrical schematic and troubleshooting logic diagram. These documents were very useful for troubleshooting. The problem was a bad spade connection on the Primary Switch (upper). The connection must not have been tight because the male spade connector on the switch had tiny metal bumps from arcing. The plastic cover over the female connector was darken by the arcing. After cleaning the spade connector and tightening the female connector the microwave is now working again. Thanks for your help.
The information provided gave me the confidence to undertake the repair of my microwave. My problem was a bad connector on the Primary Switch, which was one of the possible causes identified by the expert.
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