After looking over the electronics of my retired Philips Sonicare HX686P electric toothbrush, I unsoldered the main circuit board from the actuator, battery, and charging coil so I could remove it from the black plastic chassis.

Separating the main circuit board from the rest of the device also meant I could get good pictures both front and back.

I was surprised to see that there were a handful of surface-mounted components on the back. They couldn't fit everything on one side.

The "pressing too hard" sensor's flexible printed circuit strip is directly soldered to the back of the main board. I see ten soldering points, two per wire except for the left-most where four of them are connected to a single wire. This is consistent with power/ground/clock/data or some similar variation thereof.

On my previous Sonicare HX6530 teardown, my next step was taking the brush motor actuator apart. It was an instructive process, but a destructive one. Since the actuator in this HX686P is nearly identical, I doubt I'll learn much from taking this one apart. It's also in better shape, as it lacks the rust and deposits of water intrusion. I can keep it intact while hoping a project idea would arise. What would I do with it? I'm not sure! Recently, Hackaday featured somebody turning their old electric toothbrush into a tiny sander. The Hackaday writer Al Williams correctly pointed out this control board has a lot of features unsuitable to sanding. For example each session only runs for two minutes, with a small beep every 30 seconds. If we want to run it as a sander, we might be better off building our own control circuit for the actuator.

Sander or not, reusing the actuator will be best done with my own control circuit. I don't know how to do that, but maybe this is a good opportunity to learn! I now have components on hand to support such a learning exploration: circuit boards with existing implementation, a disassembled actuator where I can test the coil by itself, and I have an intact actuator for potential application. And any knowledge I gain could continue to be useful in the future, because I'm still using a Sonicare every evening for my dental hygiene routine and it's just a matter of time before I have additional retired toothbrushes to play with. Toothbrushes, and their associated charging bases.