Microwave (inside on right hand

Question

Microwave (inside on right hand side wall) has a plastic cover. Behind this cover while popping popcorn there was bright yellow/red flashing/light, it started to melted the plastic cover within seconds. ??? No ideaI would like to see a set of schematics to know what i am looking at before bringing in in for repairs. This microwave was only purchased April 1, 2006. I am not happy.