"Chris" wrote in message
...

Nah, it was half a stick, well within the pre-programmed range, so
that's not it. In any case, some bit of foil of just the right size
or shape can lead to gradients high enough to get sparks, but this
was not like this. This was some large fraction of the entire current
output of the transformer, like the fireworks you see on youtube when
people have pulled the guts out of the microwave and using it just to
make an arc.

If a thorough cleaning and inspection doesn't resolve the issue, I'd get a
new unit. The potential for damage or injury seems too great.