Everything seems to work except there is no heating. Disconnected the high voltage section and monitored the 120vAC coming to board and it was good. Ohm checked the magnetron 170Mohms and 160Mohms from chasis to terminals and .12 ohms across terminals. Using an analog meter the resistance across each of the HV diodes are 60Kohms in one direction and ~infinite in the other. With a digital meter there are 125Mohms and 9Mohms. On the heat sink the bridge resistance between + and - was ~ 24K ohms. The gate to collector resistance was 38Kohms and the gate to emitter ohms was 10Kohms on thermistor? It appears the most likely part is the control board unless there is some other way to reset the controls. The micro switches checked good with the door opened or closed. What is that two pin connector at the bottom of the microwave that is not connected to anything?

see this causes and fix it. God bless you
Diode 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.

Door Switch 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.

Magnetron 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.

High Voltage Capacitor 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.

High Voltage Transformer 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.

Thermal Fuse 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.
Thermoprotector 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.

Main Control Board 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 within the high voltage circuit; either the high voltage capacitor, diode, transformer or magnetron.

Does it make any extra sounds that it didn't use to? This would indicate something shorted in the high voltage doubleing section. If not, probably a bad magnetron or door switch.

9 times out of 10 this is usually this is a bad magnetron, the other time is sometimes a bad high voltage diode. See components section. Many thing can do this but, common things are....loose high voltage wire.....poor solder joint on board.....magnetron.....power relay..... Q - The microwave display counts down and the inside light is on, but nothing is heating and the fan is not running.
A - This most commonly is a bad door switch, other possible problems are a faulty relay or solder joint on the power module, but a bad door switch is most common.

When the microwave sounds okay, but there's no heat, one of the internal door switches, the high voltage circuitry, or the circuit board may have a problem. To resolve this problem, you need the assistance of a qualified appliance repair technician.
If it is under warranty you are golden. If not, you should get an estimate, as many new microwaves are now in the 50 dollar to 99 dollar range

Q - The microwave makes a loud "hum or buzz" noise but will not heat up the food?
A - 9 times out of 10 this is usually this is a bad magnetron, the other time is sometimes a bad high voltage diode. See components section.
Q - My microwave is running and sounds like it is working but will not heat up anything.
A - Many thing can do this but, common things are....loose high voltage wire.....poor solder joint on board.....magnetron.....power relay.....
 Q - The microwave display counts down and the inside light is on,  but nothing is heating and the fan is not running.
A - This most commonly is a bad door switch, other possible problems are a faulty relay or solder joint on the power module, but a bad door switch is most common.
Q - The fan in my microwave oven is not running will this hurt my microwave?
A - YES, the fan cools the magnetron and electronics, take the microwave in for service, most fans are not too expensive to replace.
Q - My microwave blows the fuse inside itself as soon as I push the start button.
A - Usually a shorted high voltage capacitor...see components section.

Is the unit under warranty? If not, you can try to remove the cover and see if there is a blown fuse in the section that powers the Magnetron. How old is the unit? Typically, no heating of food, indicates a bad Magnetron (tube).

Good Luck,

- Jim

Magnatron is suspect. Need to put a voltmeter on it and see if the input (primary) side to the high-voltage transformer (big heavy iron thing in there) is getting 120Vac. Don't touch the other (high voltage) side of this transformer. If the power is there, you are looking at replacing the magnatron. Its affordable if you do it yourself - buy the part on EBAY - lookup "universal magnatron"

Magnatron is suspect. Need to put a voltmeter and see if the input (primary) side to the high-voltage transformer (big heavy iron thing in there) is getting 120Vac. Don't touch the other (high voltage) side of this transformer. If the power is there, you are looking at replacing the magnatron. Its affordable if you do it yourself - buy the part on EBAY - lookup "universal magnatron"

Magnatron is suspect. Need to put a voltmeter and see if the input (primary) side to the high-voltage transformer (big heavy iron thing in there) is getting 120Vac. Don't touch the other (high voltage) side of this transformer. If the power is there, you are looking at replacing the magnatron. Its affordable if you do it yourself - buy the part on EBAY - lookup "universal magnatron"

check high voltage section, check magneatron, diodes, etc.