After my Remington hair clipper's batteries failed, I had to shop for a replacement. Costco had the Philips Norelco Multigroom (MG7790) on sale and I thought I'd give it a shot. Rather than a single wide fixed-size cutting blade, the Multigroom came with multiple cutting elements to serve different hair cutting/trimming purposes. The tradeoff for this versatility is that the widest flat cutting element is around 2/3 the width of the Remington hair clipper blade. Part of being a smaller and lighter weight device, which I learned to appreciate during its few years of use. I didn't end up using the other cutting elements very much, and the narrower width wasn't a significant detriment in my usage pattern.

After a few years of use, the motor would stop running in the middle of a session even if I fully charge the battery immediately beforehand. The manual claimed a fully charged battery can deliver up to six hours of use, but I couldn't even get ten minutes! I bought a replacement and placed this unit in the teardown waiting list alongside the Conair and Remington hair clippers, where they waited until now.

The two old hair clippers both had a sticker telling us to properly recycle their nickel-cadmium batteries within. There was no such label here telling us of the type of rechargeable batteries used. The power adapter operates at 15V DC, far above the voltage range of any battery pack I would expect to see within. This implies a voltage buck converter in the charging circuit, a level of sophistication I associate with lithium chemistry battery management systems.

An important detail for teardown purposes is at the bottom of multigroom label: "IPX7" followed by a faucet icon. This device is waterproof enough to be rinsed clean under running water and can tolerate being briefly submerged in water if we accidentally drop it in the tub. Waterproofing makes teardowns difficult because the interior may be glued shut and/or buried under epoxy resin. Even if they weren't, a teardown may irreversibly damage the water barrier.

The AC adapter uses this vaguely B-shaped plug that I haven't seen anywhere else, possibly proprietary to Philips/Norelco. Next to the charging port at the base is a Torx-headed screw hidden under a rubber cover. That looks like a good place to start.

The base plate came free easily. Loose fit and no seals meant the waterproof barrier must be further within. Disappointingly, nothing else budged after this plate was removed, so I started looking at the other end.

Different cutting elements can be easily snapped on and off the top. When removed, we can see the motor-driven crank. The manually aptly referred to this as the hair chamber. It's easy to dump out loose hair, but the many small corners meant it takes a lot of work to clear out every little piece. Going in with a cotton swab, I got enough of the corners cleared out to see three small fasteners (combination Torx and flat head) buried underneath.

Releasing those three small self-tapping plastic screws allowed hair chamber disassembly, releasing a lot of trapped hair along the way. Now the guts of the device can slide back and forth around 3-5mm, but not quite freed yet.

The last piece of the interlocking puzzle was the power button, which was held by multiple clips that also served as tabs holding multiple internal elements together. I damaged one clip removing it.

The internals slid out as a single piece enclosed in clear plastic. The motor pokes out the top, a rubber dome on the side pushes on the power switch, and a plug of dark gray plastic sealed the bottom. Numerous rubber O-rings made it clear this was the water barrier. Getting inside non-destructively proved to be a challenge.