How to repair the broken microwave oven in rainy days?

1. magnetron

Under normal circumstances, the resistance of the filament is less than 1ω, and the resistance between the filament and the shell is ∞, so the magnetic steel should not crack. Magnetron is damaged, some of which are manifested by open circuit at both ends of filament, some of which are characterized by conduction from both ends to the shell to form a channel, and some of which cannot be measured directly. The phenomena caused by magnetron damage are: the microwave oven runs quietly, does not generate heat, or burns out the power supply insurance, high voltage insurance, high voltage diode and so on.

2. High voltage diode

Under normal circumstances, measured by multimeter Rx 10k, it is conducted in the forward direction (with a certain resistance, about 150K Ohms) and turned off in the reverse direction (with infinite resistance); It is impossible to measure forward and reverse resistance with other electrical isolation grids. The damage of high voltage diode is mostly breakdown, that is, both positive and negative directions are conductive. The fault phenomena caused by the damage of high-voltage diode are: burning high-voltage fuse, or microwave oven running without heating, microwave running without heating, and noise increasing.

3. High voltage capacitor

The capacitance is between 0.8 UF and 1.2 UF, and the resistance between the two ends of the capacitor and the shell is ∞, and a 9MQ resistor is connected in parallel. Under normal circumstances, the pointer multimeter is placed at Rx 10k, and the two probes are respectively connected to the two poles of the high voltage capacitor. At first, there was a certain resistance value, but it was not high, and then it gradually rose to about 9MQ. In actual maintenance, the faults of high-voltage capacitors are relatively low. The common damage forms are pole pieces or insulating wood on fire, and some are failure or breakdown. The phenomena caused by the damage of high-voltage capacitor include: burning power fuse or high-voltage fuse, microwave oven running without heating, etc.

4. High voltage transformer

Under normal circumstances, the primary winding resistance is about1.5 ~ 3Ω, the secondary winding resistance is about100 ~ 200Ω, the filament winding resistance is less than1Ω, and the resistance of each winding to the core is ∞. The damage of high voltage transformer is mostly short circuit between turns of high voltage winding. The phenomena caused by the damage are: increased running current, peculiar smell, or smoke when running without heating.

5. Mechanical timer/fire selector

When it is normal, measure the resistance at both ends of the motor, rotate the time knob clockwise, and the contacts of the timing switch are connected. When the motor rotates, the fire contact opens and closes. The contact of timing switch is damaged, resulting in the whole machine not working; The contact of the fire switch is damaged, which causes the microwave oven to run without heating; The damage of the motor causes the microwave oven to run without heating, or to run without heating or stopping.

6. Door switch

The door switch contains several touch switches. Normally, when the switch is closed, there are tiny contacts to change the sound. After the damage, the faults are: the whole machine does not work, the operation does not heat up, and the power supply fuse is blown when the door is opened.

7. Thermal relay

Also known as thermal isolation switch, temperature limit switch, thermal switch, etc. It belongs to automatic reset thermal protection element. Put the multimeter on the RxlO block and connect the two probes to the two terminals of the thermal isolating switch respectively. The resistance should be 0 Ω at room temperature, infinite when it reaches its marked value at high temperature, and automatically becomes 0 Ω when the temperature drops by a certain value. After the thermal relay is damaged, the relay with the same specifications and parameters should be replaced. If the temperature is too low, it will cause false protection. If the temperature of the label is too high, the purpose of protection will not be achieved.

8. Bidirectional diode

Put the pointer multimeter in Rxl0k position, connect two probes to the two poles of the bidirectional diode respectively, and the forward and reverse resistances should be infinite. The breakdown and leakage of bidirectional diodes generally lead to the microwave oven not heating or fusing the power supply. If there is no such pipe during the inspection, it can also be removed. After removal, it will not affect the work of the circuit, but it will lose the function of high voltage and overvoltage protection.

Second, common faults

1. There is no response when power is applied, and the safety tube is in good condition.

Mechanically controlled microwave oven: mechanical timer and magnetron temperature limiter can be checked. Computer-controlled microwave oven: observe the safety tube of the computer board, and check the power transformer and magnetron temperature limit protector on the computer board. After troubleshooting, the safety tube tester can be replaced.

2. There is no response when the power is turned on, and the fuse is blown.

Check the door switch, microwave high voltage system (high voltage transformer, high voltage diode, magnetron and high voltage capacitor), fan motor and turntable motor. After troubleshooting, the safety tube tester can be replaced.

Check the high-voltage transformer mainly to observe whether the primary winding and high-voltage winding are burnt or not, and whether the insulating paint is burnt or not.

3. Burn the power fuse repeatedly

Check the door switch and high-voltage transformer first, and then check other devices in the microwave system, such as high-voltage diodes, high-voltage capacitors, bidirectional diodes, magnetrons, etc.

It can run, but the microwave oven is not heated.

Firstly, whether there is power supply on the primary side of high voltage transformer is measured, and then the maintenance range is determined according to the measurement results. If it is measured that there is no AC220V power supply in the primary of the high voltage transformer, the microwave oven is mechanically controlled, so check the timer and door switch; When the computer controls the microwave oven, check the door switch, computer board fire relay and drive transistor. If AC220V power supply is detected at the primary of the high voltage transformer, check the high voltage transformer, high voltage fuse, high voltage diode and protection diode.

If the microwave oven is not heated, the noise will increase or the vibration will be great. Focus on microwave systems, such as high-voltage diodes, high-voltage transformers, high-voltage capacitors, bidirectional diodes, magnetrons, etc.

6. Microwave heating is slow, and the firepower is obviously less than before. This kind of fault is usually the aging of magnetron, and a few are the poor contact of power control selector switch or power relay.

7. If the barbecue grill is not heated, check whether the barbecue grill has AC220V power supply. If the power supply is normal, replace the barbecue tube; If there is no power supply voltage, check the barbecue control circuit, such as barbecue temperature limit protector and barbecue switch. For computer-controlled microwave ovens, check the barbecue relay and drive transistor.

8. After starting the machine, the inner container is ignited. Under the condition of confirming that the user has never used metal utensils, check whether the mica sheet is burnt and whether the inner container is too wet.

9. Start or stop key failure

Generally found in computer-controlled microwave ovens, check the membrane switch.

10. There is a display when the computer microwave oven is powered on, but the door switch and the switch on the panel are not started.

1 1. Sometimes it doesn't start, sometimes it automatically switches functions, and the buzzer rings by mistake.

Measure the +5V, reset and clock oscillation pin voltages of CPU, and replace the crystal.

12. Tray does not work

Check the pallet synchronous motor and its power supply voltage when the shaft and track are normal.

13. The fan motor does not work.

Check the fan motor and power supply.

14. After opening the oven door, the motor of the oven panel still rotates.

Computer-controlled microwave oven, check the main relay and control transistor on the computer board; Mechanically control the microwave oven and check the oven door switch.

15. Without stopping the heating of the mechanical microwave oven, check whether the timing motor is damaged, whether the rotating shaft of the timing button adheres to the panel, and whether the power supply of the timing motor is normal.

Timer motors can be divided into AC220V and AC50V. If the fan motor is damaged, the timer motor will stall.