I've managed to disassemble the exterior components of a retired Philips Norelco Multigroom (MG7790) which made only a moderate mess with its hair fragments trapped within. In earlier hair clipper teardowns, that was enough for me to access all internal components. However, this unit is IPX7 waterproof which meant everything is inside a clear plastic watertight capsule.

The control circuitry is much more sophisticated than those in the two earlier hair clippers, though I'm not sure why. At the end of the day, this just needs to turn a motor on or off. Perhaps there's battery management as well? The little of blue peeking through various gaps in this enclosure hints at a single lithium-ion battery in a commodity 18650 cylindrical cell form factor.

The motor is genuine Mabuchi! A pioneering giant for small DC motors, I usually encounter knockoffs of popular Mabuchi designs instead of a genuine Mabuchi. Either that, or it's a counterfeiter brazen enough to print the Mabuchi logo on their wares. I'd like to think Philips/Norelco uses the real thing.

The bottom of the clear plastic capsule is sealed with a black plastic plug at the bottom, held in place with four beefy clips. I had hoped to release those clips peacefully, but I shattered some of the clear plastic. The cracks extended past the watertight O-rings, meaning I've managed to destroy its waterproof worthiness.

Not much to lose now! Feeling liberated because I don't have to worry about preserving its watertight seals, I tore apart the retaining mechanism. This clear plastic was interesting: most of it is tough and ductile under stress like a polycarbonate, except infrequent times where it shatters like brittle acrylic. I wish I knew more plastic engineering to better understand this material's behavior.

I thought the black plastic plug at the end was a separate piece of plastic from the structural chassis for all internal components. It turns out to be a single piece, so everything slid out together.

The chip that seems to be in charge is stamped with 10368A F15 H3G7A. A web search found a likely candidate in the Renesas RL78/G12 family of microcontrollers. The R5F10368 variation has 8KB of code flash, no onboard data flash, 768 bytes of RAM. It comes in a 20-pin TSSOP package which matches what's on this board.

If I've correctly identified the controller, it means this is a very software-centric minimalist application because this MCU lacks onboard peripherals befitting the hardware. (Comparison: the MCU in this smoke detector is optimized to be a turnkey smoke detector solution.) There's no obvious motor control peripheral like hardware PWM, though perhaps an offboard MOSFET would suffice as it only needs to turn the motor on/off. There's no explicit lithium-ion battery management capability like a 4056 chip, but there is an A/D converter that would be suitable for monitoring battery voltage.

Speaking of the battery, separating the circuit board from the chassis exposed the battery. The label says:

LG Li-Ion Cylindrical
INR18650S3
2200mAH 3.6V~4.2V
G15 2016.08.12

I retired this trimmer because the motor would stop in the middle of a session, even when fully charged, so I decided the battery has degraded. I thought it might be fun to replace the battery cell and see if that gets it back up and running, hence the concern about trying to preserve the watertight barrier. But as it turned out, I had misdiagnosed the problem.