Recently the foil on my Remington F4790 got a hole in it, it makes the foil and cutter part of the razor unusable. While I placed replacement foils on order, I figured I’d just use the trimmer, but then trimmer stopped working.
Apologies for the poor image quality, they’re screengrabs from a video.
The foil and the cutters pop straight off with a little bit of a pull. Thereafter there are two small screws at the hinge point which can be loosened.
The foil and cutter head then comes out. Take care when reassembling to align the pop-out with the slot on the head.
From here there are 4 screws easily accessible that can be loosened.
A black rubber seal is then visible, which comes off easily to reveal two white plastic mechanisms which are driven by a motor. Align the drive shaft (1) on the motor so that the point is away from the trimmer. Plastic mechanism  can come straight off. Plastic mechanism  drives the trimmer and has a shaft going down. It can now be lifted out.There’s a round rubber seal between the trimmer and the motor housing which must be removed. The trimmer must now be fully extended. With a bit of jiggling the trimmer will come out completely. There is a metal spring near the bottom which might catch, see below.The trimmer is unfortunately a sealed mechanism. The outer casing is two parts which look like they clipped into each other, but looks like some heat was used to ‘seal’ it. Anyway, I pried it apart, because there was nothing left to do. Not too much seemed to break.
When I opened it up it was clogged up with hair preventing it from moving. I cleared all of it up, and the cover fortunately managed to clip back together and seemed to hold.I don’t really know how to disassemble the razor further. There are two screws visible, but loosening them doesn’t achieve anything. Through the clear motor housing other screws can be seen connecting it to the outer case, but no way to access them.
I think the outer case is all just clipped together, but felt nervous in forcing it apart when I still want to use the razor. If my foils don’t make it in the post, then maybe I’ll do it, but for now I can’t see any further way to take the razor apart besides forcing the outer casing apart.