I figured it out…
One has to remove the outer frame/trim of the entire microwave oven then remove the 2 screws at the top of the control panel to gain access to the electrical components inside. On my old GE model, one did not have to remove the trim - the panel would tilt down by removing 2 screws on the left side of the control panel.
With this Whirlpool model (RM278BXV-4), one has to remove 5 screws (3 on top + 1 screw on each of the sides) securing the outer trim frame then take the 2 screws on top of the control panel.
By the way, the reason why the microwave had no power at all was a burnt fuse (250V, 20A) inside the unit (about $1.00).
I hope this helps someone in the future.
Cheers! 