The circuit diagram of the microwave oven can be known from the above circuit diagram. The high-voltage diode has a high conduction threshold voltage. If the normal resistance of the internal battery with a battery voltage of 1.5V is used to measure the forward resistance, the resistance value may be large. If you don’t move, you can’t judge whether it is good or bad. Therefore, you should use the R×10k block of the multimeter with the internal battery larger than 6V, preferably 9~15V. The measured forward resistance is normally about 20-300kΩ; the reverse resistance is gigantic. If measured with a megohmmeter, the forward resistance is normally less than 2kΩ; the reverse resistance is infinite. If there is no such instrument, it can also be measured by the R×1k block of the ordinary multimeter. However, it is necessary to connect the 6~9V battery in series on a test lead and then measure it. When the battery is connected in series, the red test pen is connected to the positive battery, and the negative battery is used as the original. The red test pen is used for measurement. Do not short-circuit the two measuring ends during measurement, and do not measure high-voltage diodes or other components whose internal resistance is abnormal (too small) to avoid damage to the hands over the head; for safety reasons, a suitable current limiting resistor can also be connected in series. reuse. For the measurement resistance judgment standard, refer to the value of the normal high voltage diode measured by the same method. Of course, it is more convenient to judge according to the general experience, and most of them are reliable. As long as the reverse resistance is infinite, the forward resistance is not infinite or large (the needle is deflected by a certain angle, not micro-motion), indicating that the diode is basically good. For some asymmetric protection diodes used in microwave ovens, they can be measured in 10k steps, and their normal forward and reverse resistances should be infinite.
The repairer disassembles the microwave oven and disconnects the power supply. In order to prevent: high voltage capacitors from having high voltage, it is necessary to discharge them. This is necessary from a safety point of view, but generally there is a 10M9 resistor inside the high voltage capacitor, so it is used. When the X10K file of the pointer multimeter is measured, the pointer of the watch is not stopped at the 欧姆 of the ohm scale tick mark after the detection of the charge and discharge at the time of the interrogation measurement, but refers to the 1K position of the tick mark 1: that is, the capacitance The resistance is 10M2 (measured with the MF47 meter), which means that the capacitor is good, and most maintenance personnel are easily mistaken for capacitor leakage.
When performing microwave capacitor repair, if you need to check the internal circuit, you should usually remove the microwave after power off. After disassembling the machine, first use a plastic insulated handle screwdriver to short-circuit the high-voltage capacitors at both ends to avoid accidental electric shock during the maintenance of the microwave oven. This is because after the microwave oven is powered off, there may still be a higher voltage on the high-voltage capacitor, especially in the furnace that is short-circuited. Do not think that it is safe after power-off. If the parts need to be disassembled or replaced during the maintenance of the microwave oven, the original position of the removed parts should be remembered one by one when disassembling, especially the parts of the safety mechanism and high-voltage circuit should be taken seriously, and should be placed after disassembly. Well, avoid losing, causing unnecessary trouble; reinstalling should be accurately reset one by one, and tighten each fastening screw and other fasteners, do not install wrong, or miss the small parts that are easily overlooked such as installing washers. If you need to replace parts, please pay attention to the original model parts. If not, replace it with a similar replacement.
1. Check the appearance of the microwave oven before servicing. If the furnace door is found to be deformed, the sealing surface of the furnace door is defective, uneven, and the cavity is desoldered, etc., these places should be repaired first and then turned on.
2. After the microwave oven is turned off, there may still be a high voltage on the high-voltage capacitor. Therefore, when inspecting or replacing parts, you must use a screwdriver with an insulating handle to make one end of the high-voltage capacitor (that is, the end connected to the diode) and the microwave oven case. Short-circuit discharge to prevent electric shock from injuring people.
3. In the case of the microwave oven being turned on, high voltage and large current are present in the high voltage winding of the high voltage transformer, the magnet filament and the circuit at both ends of the capacitor. Therefore, when starting up, do not check and repair these parts under normal circumstances. For testing, it is necessary to specifically prevent electric shock. When replacing parts, turn off the power and replace the capacitor before discharging.
Post time: Aug-18-2018