I believe that the HV transformer on the microwave is defective. It has blown the internal fuse a couple times. Do you have any info on what the resistance on the primary side of the transformer should be?
Answer Tom, The basic resistance on the high voltage transformer is as follows: primaty winding is less than 1 ohm resistance. The secondary winding is usually 50 to 120 ohms resistance. and the filament winding is less than 1 ohm resistance. Don't forget to check each terminal to chassis ground for a possible shorted winding. The resistance t the magnetron should be less than 1 ohm resistance, across the terminals, and an "open circuit between each terminal and chasis ground. Thanks