Troubleshooting GE Profile microwave. Display was powered up and everything normal until I tried to defrost a frozen item. Microwave emitted a louder than normal hum as it began to heat then the line fuse blew after a few seconds. I have tested the HV Cap, the HV Diode and the Magnetron. All appear to be good. I have tested the door switches and they appear good. Tested the HV Transformer and the resistance across the primary appears good. Trying to decide if the transformer is bad though and need some advice. The primary has 3 leads. A red lead that goes to one side of the monitor interlock switch and a low power relay, a blue lead that goes to the HV Fuse and a hi power relay, and set of black leads that go to the monitor interlock switch, primary interlock switch and thermal cutouts. I have discovered that if I unplug the black lead from the transformer, start a cooking function, the loud buzzing is not present and the fuse does not blow. I had placed a cup of water in the microwave and interestingly enough the water was warm after 30 seconds. When I plug the black lead back into the transformer the problem reappears, loud hum and the fuse blows. Any suggestions?