The high voltage diode converts the A/C power output of the transformer to D/C, doubling the voltage to nearly 5,000 volts. This high voltage powers the magnetron which emits the energy that cooks the food. If the diode burns out, a lower A/C voltage reaches the magnetron, which is not sufficient to power the magnetron. When the diode fails it is often visibly burned out. If it appears to be good, it can be tested with a volt-Ohm meter capable of testing diodes. High voltage diodes frequently fail and are one of the most common points of failure in a microwave oven. A regular meter with a diode checker will not work to check these diodes. You have to use a meter with a 9 volt battery or put a 9 volt battery in series with the diode to check it.
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If the microwave does not heat, one of the door switches might be defective. Microwave ovens normally have three door switches, if any of them fail the microwave does not turn on and does not heat. Check the switches for continuity with an Ohm meter.
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If the microwave oven doesn't heat the magnetron tube might have burned out. The magnetron uses high voltage, high current DC power to generate the microwave frequency that cooks the food. If the microwave oven is turned on when it is empty this can cause the magnetron to burn out. Once it is burned out it has to be replaced, it's not repairable.
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If the microwave doesn't heat the high voltage capacitor might be defective. The high voltage capacitor works with the high voltage diode to convert the output of the transformer to DC voltage and to double the output voltage. If the capacitor is burned out the entire high voltage circuit stops working properly. The high voltage capacitor can be checked with a special VOM meter which has a capacitance testing capability. Be aware that the high voltage capacitor can retain a charge of more than 3,000 volts and can injure or kill a person if not handled properly. Only trained technicians should perform this type of testing.
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If the microwave does not heat, the high voltage transformer might be burned out. Microwave ovens produce a very high voltage in order to power the magnetron antenna, which emits the energy that cooks the food. When a high voltage transformer fails it will usually arch and have a burning smell.
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If the microwave doesn't heat the thermal fuse may have blown. It can be tested for continuity. Watch our fuse testing video for more information.
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If the microwave doesn't heat the thermoprotector may have tripped. This is a safety device to prevent the microwave from overheating. It can be tested for continuity to see if it's blown.
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If the microwave doesn't heat the main control board may be defective. This is not common. When a microwave doesn't heat the problem is usually a faulty door switch or within the high voltage circuit; either the high voltage capacitor, diode, transformer or magn
The hot surface igniter will not come on - check igniter with a ohm meter,
you should have continuity through the glow bar, the glow bar can also
crack = new igniter time. The glow bar comes on but the main burner will
not light - you should have an amp probe
to check properly, but often this is a hot surface igniter problem. The
hot surface igniter often looses it's ability to get hot enough to open
the gas safety valve. The safety valve can fail, but most times it is
just a bad hot surface igniter. The hot surface igniter can also quit
part way through cooking , in other words the oven may cycle a couple of
times and then it just sits there with the red glow from the igniter.
See this service sheet
for the proper way and amp readings for the hot surface igniter system.
Hot surface igniters do weaken and will eventually generate less heat
than they normally could. When this happens they can still allow
marginally correct current to flow to the oven gas valve for it to open
but not get quite hot enough to ignite the gas burner immediately. When
this happens, gas released into the oven can sometimes build up to the
point where when finally ignited, the amount of gas lit can cause a
small explosion inside the oven or cause an odor of gas with out the
oven working. Yes, your glow bar igniter can glow orange-red and still
be bad!! How a common gas valve works - click here.
Let me know,if needed further assistance.
Hope i helped you.
Thanks for using ' Fixya ' and have a nice day!!
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