I retired & took apart my Philips Sonicare HX6530 after it had slowly degraded over years. So slowly I didn't realize until I was reminded by a newer unit: "Hey, this is what a Sonicare clean should feel like!"

I replaced it with this HX686P, which has also been recently retired due to degradation. But this one degraded overnight instead of gradually. Literally: one evening it felt fine, the next night "hey, what's wrong with this thing?" My first thought was that I had accidentally triggered the "Easy-Start" feature, which introduced newcomers to Sonicare clean by starting easy and ramping up strength over time. I verified Easy-Start was not active, and ran out of ideas on why it might have suddenly weakened. Oh well, time for a new one and tearing down this one.

The manual for this HX686P explicitly stated it can be disassembled for battery disposal so I tried pushing on the metal toothbrush stem. Unlike attempts with the HX6530, I was successful popping this core loose. In addition to seeing if I can find any obvious signs of why it failed, I'll be looking for physical implementation of some new features:

  • It works with newer brush heads to keep a usage count and notifying me when it's time to replace the brush.

  • It detects when we're pushing too hard for effective brushing, telling us to back off.

Comparing HX686P and HX6530 side by side, the mechanical components appear nearly identical.

There's a loop of fiber-reinforced tape that would be useless for holding the metal assembly in place. I think it exists to hold the RFID antenna wire.

Peeling off the tape confirms there isn't anything else underneath other than the RFID antenna wire. It also confirms the clips + welded system is still here. When I saw the welds on the old HX6530 I had wondered if it was a hack on top of an original clip-based design. Since it's still here after several generations, I assume clips+weld is a belt-and-suspenders system to hold the mechanical actuator chassis together.

Here's the other end of the RFID counter system, at the base of the brush head.

It was glued in place and impossible to remove non-destrutively, so I destroyed an old brush head for a closer look. The small chip is connected to a coil of wire that would sit aligned with the coil visible inside the toothbrush handle. I've read that people have tried to reverse-engineer this system.

Relative to the older Sonicare, another new component is this chip and capacitor sitting on a little segment of flexible printed circuit. Why are they here and what are they doing?

A hypothesis surfaced when looking at the side view: this chip is sitting above the gap between the electromagnet and permanent magnet, ideally placed to sense brush actuator lever motion. I think this is a sensor that feeds into the "is the user pushing too hard on the brush?" feature. To test this hypothesis, I peeled off the sensor which was held by double-sided tape. Once it was bent away, the "pushing too hard" alarm feature stopped working.

Another observation: The gap is noticeably larger here on the HX686P than on the older HX6530, but I'm not sure if that signified anything. On the other hand, the lack of water intrusion is certainly a good thing.

Until I decide to start destructively cut things away, I could only lift the circuit board a tiny bit. Peeking underneath, I don't see any signs of a connector for the flexible board implying it's soldered directly to the bottom of the circuit board. Before I try to get a better look at the bottom, there are plenty of interesting things up top.