Hello friend, greetings before placing the magnetron, you have to check the high-voltage part, for example, the capacitor measures it with a multimeter in continuity. If you give any reading it is crusado, the strange thing is that most of the times the capacitor enters shortly it melts or open the ac input fuse but still measure it if it is okay to place another diode of another microwave that you have and tests if it follows the same do not hesitate to change the transformer greetings this failure almost always causes the capacitor, diode or traffic test as I commented and Comment greetings. Atte Hector of Venezuela