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Tappan Microwave not heating

If your Tappan microwave is not heating, the high-voltage diode is the most likely cause. The diode converts transformer output to the high-voltage DC power the magnetron needs, and a failed diode may look burned or test faulty with a suitable multimeter. Next, check the door switch, since a defective primary, secondary, or monitor switch can prevent the microwave from starting or heating when the door closes. A failed magnetron can also leave the microwave running but not heating food, while an open thermostat may stop voltage from reaching the high-voltage components after overheating. Less common causes include a failed high-voltage capacitor or high-voltage transformer. A transformer failure may produce arcing or a burning smell. Enter your model number to find the exact replacement part for your Tappan microwave. Unplug the microwave before service, and remember that opening the outer cabinet exposes a high-voltage capacitor that can store a lethal charge even after the microwave is unplugged. The capacitor must be properly discharged before interior work. Repairs involving the magnetron, high-voltage diode, high-voltage capacitor, or high-voltage transformer may require a qualified technician, especially if you are not familiar with capacitor discharge procedures.

01 - Tappan Microwave Diode

The 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 to heat the food. If the diode burns out, the magnetron won’t receive enough voltage to operate, preventing the microwave from heating. When the diode fails, it is often visibly burned out. Inspect the diode and if the diode is burned out, replace it. If inspecting the diode proves inconclusive, test it with a multimeter that uses a 9-volt battery or put a 9-volt battery in series with the diode. When the leads are reversed, the diode should only have continuity in one direct...ion. (Warning: The microwave oven can store a lethal amount of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the high running voltage and the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace the diode.)
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02 - Tappan Microwave Door Switch

Most microwaves have three or four door switches. When the microwave door closes, the door switches actuate in sequence to ensure that the door is closed properly. If any of the door switches fails, the microwave will not start or heat. To determine if any of the door switches are defective, use a multimeter to test each of the switches for continuity. If any of the door switches does not have continuity, replace it. (Caution: The microwave oven can store thousands of volts of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the potential for electric shock, it is extremel...y dangerous to replace the electronic components in a microwave. Only a licensed technician should replace a door switch.)
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03 - Tappan Microwave Thermostat

If the microwave overheats, the thermostat trips to cut off voltage to the microwave. If the thermostat is shorted open, it may not allow voltage to reach the high voltage components. To determine if the thermostat is at fault, use a multimeter to test it for electrical continuity. If the thermostat does not have continuity, and it cannot be reset, replace it.
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Highly Likely

04 - Tappan Microwave Magnetron

The magnetron uses high voltage, high current DC power to generate the microwave frequency that cooks the food. If the magnetron burns out, the microwave won’t heat. The magnetron is not repairable—if the magnetron is burned out, you must replace it. (Warning: The microwave oven can store a lethal amount of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the high running voltage and the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace the magnetron.)
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Highly Likely

05 - Tappan Microwave High Voltage Transformer

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 arc and have a burning smell. (Warning: The microwave oven can store a lethal amount of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the high running voltage and the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace the high voltage transformer.)
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Common

06 - Tappan Microwave High Voltage Capacitor

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 will stop working properly, and the microwave won’t heat. To determine if the high voltage capacitor is defective, use a VOM meter with a capacitance testing capability. (“Warning: The microwave oven can store a lethal amount of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the high running voltage and the potential for electric shock, it is extremely dangerou...s to replace the electronic components in a microwave. Only a licensed technician should replace the high voltage capacitor.)
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Common

07 - Tappan Microwave Thermal Fuse

The thermal fuse cuts off power to the microwave if the microwave overheats. To determine if the thermal fuse has blown, use a multimeter to test it for continuity. If the fuse doesn’t have continuity, replace it. The thermal fuse cannot be reset—if the fuse is blown, it must be replaced. (Caution: The microwave oven can store thousands of volts of electricity in its high voltage capacitor, even after the microwave oven has been unplugged. Due to the potential for electric shock, it is extremely dangerous to replace the electronic components in a microwave. Only a licensed technician should replace the thermal fuse.)
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Less Common

Frequently Asked Questions

Why is my Tappan microwave not heating even though it runs?
What should I check first if my Tappan microwave stopped heating or will not turn on?
Can I test the Tappan microwave diode or magnetron with a multimeter?
What should I do if my Tappan microwave sparks, arcs, or smells like burning?
How do I find the correct Tappan microwave replacement part?

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