I tried shielding the control board with aluminum foil to isolate any
stray RF--no change in unit response.

A spare microwave I recently purchased for parts to fix the Sharp has
two thermal cutout switches--the R1810 doesn't according to the
schematic we discussed. Still looking for the thermistor. Contacted the
company repair reps--no response yet.

This unit fits as a built-in wall unit in our Foretravel RV--if not for
that, it would be in the trash can.