Toemat Labs

Fixing the Logitech MX Master Scroll Wheel

I've had the Logitech MX Master mouse for 1 week and I already believe it's one of the best mice since the esteemed MX518. It also already stopped working.

Well, not completely. It's actually only one feature that stopped working. But it's the feature I found most interesting – the mode shifting scroll wheel.

But before we get into that, lets have a look at the device overall.

Quick Review

Logitech MX Master, still assembled

Here's the MX Master – a wireless, rechargeable mouse that can connect to either an included USB dongle or via Bluetooth.

The physical design is great. The construction feels solid and it has a nice weight to it. I'm a fan of the aesthetic too – the bronze and black color scheme looks sophisticated (as opposed to how edgy many of the gaming mice look).

I even like the configuration software, "Logitech Options", which is saying a lot because normally peripheral software is terrible (looking at you, Razer...) and I do my best to avoid installing it.

But my favorite feature is something I didn't expect. It's called SmartShift and it works like this: Normally the scroll wheel has the clicky/ratcheting feel that most mice have but if you flick the wheel quickly the ratcheting disengages and the wheel spins freely, automatically reengaging when the wheel is stopped.

This makes scrolling through long documents really easy. It was weird the first day or so, but I quickly began to love it. Then it stopped working.

The Problem

On the fifth day of use the scroll wheel started feeling strange. It was loose, as if it was stuck between ratcheting and free-spinning modes and it no longer seemed to be able to switch modes at all.

Seems like a common problem, but I couldn't find any solutions.

Disassembly

Opening this thing up requires a Torx T5 driver (try this if you don't have one) for the two exposed screws and a phillips driver for four screws hidden under the large plastic feet/pads.

MX Master, disassembly

With the screws out the top half easily pops off.

MX Master, split open

MX Master, scroll wheel assembly

Okay getting closer. It's a really interesting mechanism they've come up with to do the mode shift.

In the photo above you can see the lever that, when relaxed, puts pressure on the inside of the wheel creating the ratcheting action. When the lever is pressed it disengages with the wheel, freeing it to spin easily.

Above is a slow motion playback of what actually happens when the mode shift is activated. The motor spins that little cam from one position (where it doesn't press the lever) to another (where it does press the lever).

It took some time to figure out what really was causing the problem, but it came down to this:

Sometimes the motor would overshoot when changing modes, then it would get stuck and be unable to un-stuck itself.

The solution

Why was it able to get stuck? From what I can tell, the actual spinning part attached to the motor had worked its way up the motor shaft and eventually made it to where it was out of alignment with it's end stops.

Which means, fortunetely, the fix is really easy! You just have to push that piece back down on the shaft of the motor. Hopefully the above photo explains it.

Either way, check out this video where I explain the actual fix:

How long will it stay fixed? I have no idea, but I'll post an update right here if I have to fix it again.

I hope this helped you! Let me know if it helped by leaving a comment below, and thanks for stopping by! 🖱🎆

Update 1 (5/24/16): It's been over a week of use, still working correctly. I'll update again if the issue returns.

Update 2 (6/14/16): It came back today. Same issue. So, it worked right for about a month. At least it only takes a few minutes to open up and fix. Still really like the mouse.

Thomas Renck

I make things. Sometimes I un-make things. Most of the time I write code and teach on intentionality in design.

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