JIM HOLSONBACK wrote in a message to ALL:

 JH> Speaking of sparks and smoke - trying to microwave some "baked
 JH> potatoes" this evening.  Saw sparks up on the wall of the thing,
 JH> heard some accompanying "Poof" types of noises, and turned the
 JH> thing off. 

Working my way through this pile of repair FAQs I've downloaded,  it says here:

*  Arcing in oven chamber:  clean oven chamber and waveguide thoroughly. 
Replace carbonized or damaged waveguide cover.  Smooth rough metal edges. 
Touch up the interior paint.

It promises details further along,  I'll post 'em if I run across them...

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