Diagnosis
Accumulated grease on the cavity ceiling is common. It can drip onto food and, if severe, interfere with the upper heating element or temperature sensor during convection cycles.
How to Fix It
Use a dedicated microwave/oven cleaner or a paste of baking soda and water. Apply to the ceiling and let it sit for 15 minutes. For the CMW-200, you can partially access the area by removing the two screws for the convection fan cover mentioned in . This allows better cleaning access around the fan housing. Wipe clean with a damp cloth. Do not spray liquid directly into the vent or fan openings.
If That Didn't Work
For baked-on carbonized grease, use a plastic scraper or a melamine foam pad (e.g., Mr. Clean Magic Eraser) dampened with the cleaning solution. Gently abrade the surface. Avoid metal scrapers or steel wool.
Heads Up
Never use abrasive cleaners on the microwave waveguide cover (the rectangular mica plate on the side wall). Cleaning it can create holes that lead to arcing and damage the magnetron.