-- An earlier test subtituted 1500W toaster at transformer
primary--unit ran normally (toaster elements heated) but then shutdown
at the same point in the cycle as it had been doing with normal
transformer, magnetron, capacitor load.

--Disconnected transformers primary for test you suggested. Units
shutdown pattern was unchanged--ie shutdown about 40 seconds into the
cook cycle.

--The schemetic shows one relay located on the relay board that
controls power to the primary side of the transformer. I can hear it
tripping, interrupting the cook cycle--prior to it tripping though
there are one or two noises in that general area that may be other
relays activating.

--Both control and relay circuit boards appear normal from the top--no
discolored parts, no odors, loose wires etc.