ge micro JES65T 011 start pushed,loud hum&fuse blows

When micro is started theres a loud hum and 3 seconds later the line fuse blows, When I removed the primary leads from transformer control board, fan,turntable and light ran fine until I shut it off. I have tested the transformer, the cap and hv diode and the magnetron multiple times and they all seem to check out good . I even checked the diode by using a 9volt battery in series . What am I missing ?? Thanks, Steve