My wife found a video that showed the upper micro-switch being the culprit. This model had 3 safety switches to ensure the door was closed before cooking. After purchasing a bit to take out two security screws, I removed the oven, then the switch. I could see that the switch look visibly burnt and it failed a continuity test using my ohm meter. I ordered a new switch that arrived 2 days later. Popped in the new switch, placed the outside cover back on (to act as a microwave shield and without screws) to test it with a cup of water. It heated fine, so reinstalled the screws and all is good now.