Based on the above judgment should burst as 250V/8A fuse . After open the cabinet and found that the fuse has indeed burst. Microwave power from circuit theory to analyze the following elements may be damaged : rectifier diodes, high voltage filter capacitor and shunt any damage in one or both bidirectional protection diode capacitance between the high voltage . Remove the bidirectional diode , measured with a multimeter Rx1 block forward and reverse resistance 28.5Ω, explicitly permit has breakdown, to replace the same type of pipe and then boot , microwave start working , but the timer to 23 seconds, just listen to the work of "pop "bang , fuse has been burned. At this end of the tube measured again found damaged, so the suspicion is the rectifier diode soft breakdown and put on the same plow number (HVM12) after pipe failure remains. And high-voltage capacitor leakage is suspected , replace with new capacitance model , the fault persists. Although able to work 23 seconds , but the food is heated in the furnace with no sign that the magnetron does not work, no microwave output , plus there is no doubt the anode voltage . Series resistance measured with a multimeter magnetron anode DC voltage output is 285.3V, high. And then measuring the filament power supply voltage is normal , then the leakage is suspected short circuit between the magnetron pole , but with a multimeter to test the resistance is normal, not a short circuit occurs .PqQservice manual download site

According to circuit analysis, the components can be formed only a short-circuit current of the power transformer . Then , disconnect all loads on the power supply transformer , the power to run 10 minutes without burning phenomenon insurance , temperature is normal, secondary high and low output voltage is normal, disconnect the power measurement at the beginning , the normal resistance of the secondary winding no short circuit turn asked , indicating the power transformer is good, again suspect a problem with the magnetron . Magnetron filament power off , power on, 23 seconds after the "popping sound insurance and are burned . Seen from circuit analysis, this time only the rectifier diode breakdown before the formation of ground -to-ground short-circuit current, but with more than just changing the new rectifier, the fault persists , while replacing the down tube and can normally be used in other machines of the same model , indicating that the problem is not a rectifier diode , after analysis , it may be caused by excessive voltage . Thus, in this rectifier on again an ordinary power rectifier diodes in series , burning phenomenon after power to exclude insurance , but the food inside the microwave heating has not sign this time measured magnetron anode DC voltage is 273.5V, normal . filament power supply voltage is normal , the problem still in the magnetron , the magnetron is not normal because of not generating microwaves .

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