The capacitor in the foot control in the newer (late 1970's to 80's) 800's to 1000's models has to be replaced, or the machine will just sputter.
I just found out that the thermal switch we've been replacing in the old carbon pile Bernina foot controls is no longer available. When that's gone, it'a fire hazard. We've had a couple ladies bring the foot control that's been melted to the carpet, and they had to cut the carpet to bring it in. When the foot control gets over-heated, the thermal switch's purpose is to shut it off, like a fuse.