see the troubleshooting section and follow the steps and fix it.
God bless you
If the microwave is sparking or arcing the
waveguide cover might be damaged and shorting out. Try removing the
waveguide cover and see if the problem goes away. If there are any
damaged spots in the microwave ceiling or sidewalls, repair them and
paint them with microwave oven paint. Replace the waveguide cover if it
is burnt or if it will not stay in place.
Microwave Oven Paint
If the microwave is sparking or arcing on the
side walls the paint might have chipped causing pitting in the metal
oven wall. Use microwave safe paint to touch up any bare metal spots.
If the microwave is sparking or arcing near
one of the rack supports, remove the support, repaint any bare metal,
install a new support.