My WOZ had a flipper coil lock on and overheat. A replacement coil did they same thing. It turned out the thing that controls the coil was bad - I think it was a transistor on a main board. I had to send the main board to JJP for repair. I know JJPs are way different from Stern's but you might have the same sort of problem. At any rate have a hand on the power switch when you boot it up.