Our ancient Husqvarna sewing machine got into the Hallowe'en spirit last night after we made a costume. It went "pop" and smoked a lot, then started running on its own!
We pulled off the cover and found it had blown a capactitor:
Apparently the capacitor's job is to be a noise filter for TV/radio interference, and it can be safely removed. I'd still like to replace it, though, in case it also serves other purposes.
Update: The machine works fine after removing this capacitor.