I've owned several of these toothbrushes - it's worth pointing out that they work just fine with 3rd party heads with no chips in them. At least, the 2 models I

I've owned several of these toothbrushes - it's worth pointing out that they work just fine with 3rd party heads with no chips in them. At least, the 2 models I've owned do. Something bizarre I noticed about these Philips toothbrushes is that they fail on a reliable schedule. I owned 3 of the "4100" model and they all failed after exactly 13 months! What's crazier, is that they all failed in the exact same place. There's a metal piece that protrudes outside of the case where the heads attach. Inside the case, this piece clamps to the part that creates the vibrations using a single screw through a cast zinc/nickel block. On _all_ of my brushes, this block cracked right through the screw hole. What's cool is that the vibration motor uses a magnet of similar strength of hard drive magnets, so now I have some nice strong magnets on my refrigerator.