After some further questioning, my wife divulged that she had been cooking some 5 medium sized sweet potatoes (aka yams), which as you know are quite firm initially and probably don't have a huge amount of water, nor radio penetrability. So I think the volume of potato and time of cooking (around 10 minutes) overtaxed the capabilities of this 1.1cu ft P.O.S. from FoShan. But to play devils advocate
I think most microwaves today would choke on this as well, and there is no way to know what is inside unless I bring a screwdriver to the store.
Likely almost every microwave, electric tea kettle, toaster, mixer and other kitchen or small home appliance is made in a place like Factory City China and just designed and branded for what we consider non-Chinese brands.
http://youtu.be/xMm-YMO5H7oAnyways if it starts happening on more "easy" cooking situations and less time, I think it's safe to say the device will have to be tossed. Which begs the question, how do you know if a Magnetron starts to go bad? Is there any test that is easy to conduct? What about the transformer heating? Is this a symptom of another faulty component or the transformer itself? And even if we have a definite diagnosis of the problem, since a new one is $80 is it economically feasible to even bother fixing up a piece of crap like this, or buy a new one every 3-5 years?