The part(s) or condition(s) listed below for the symptom Microwave is sparking or arcing are ordered from most likely to least likely to occur. Check or test each item, starting with the items at the top of the page.
The waveguide cover might be damaged and shorting out. Try removing the waveguide cover and see if the problem resolves. If the waveguide cover is burnt or will not stay in place, replace it.