Fuse Blows Once "Start" is Pushed

Microwave Repair
,
1

Jenn Air Microwave (M166). Replaced fuse and plugged it back in. Timer display came back on and interior light worked when door opened. I pressed "Start", and fuse blew again.

Did a little research and found out that it may be the magnetron or transformer.

  1. Am I on the right track?
  2. If correct, how do I determine which is the bad item?
  3. Read that you must discharge the capacitor before replacing parts. How do I accomplish this?

TIA