LG microwave will not run

Microwave blows fuse when enter for heating. When plugged in, all accessory equipment works. As soon as enter heat cycle the fuse blows. When plugged in I have checked voltage to transformer and get 0 reading. Had service tech come out and he said it must be megatron, which should be under warranty. I replaced megatron and no change. In the process I have replaced megatron, transformer, capacitor, and door switches.

My guess is that it is in the control panel and that I should stop trying to repair. However, I would like a second opinion!

A follow up to my post. I unplugged power to transformer and turned the microwave to heating. I thought that it was heating. So I now have to retest all of those down stream things that I thought that I had tested and replaced.:o