Hopefully this can be useful to Geekhack folks, as well as random googlers.
Most Logitech mice use Omron D2FC series switches, which after a pretty short time develop what's been affectionately referred to as the "double click issue". Most of the fixes I've seen involve taking the switch apart and bending the leaf spring back into shape.
But, that's just going to cause it to break again, and repeat the process.
I can't be bothered with all that noise. I have the tools and the knowledge to do something better. I'm going to just replace the switches! And I'm gonna show you how!
This is more or less the same for all Logitech mice, the exact tear-down procedure is different though. I'm using a Logitech M705 Marathon Mouse.
The switches I ordered are a tad.. overkill. The operating force of the original Omron switches is 0.7N (1/2 a pound), so if you ever felt your mouse was just too light, these might be the switches for you. You can look around the Mouser website and see if you can find another switch with similar operating force, they just need to be the same size really.
The switches I settled with were
Cherry DG13series. The exact one requires an operating force of 1.4N (1 pound) and is rated for a minimum of 1 million operations mechanically.
While you're at it, pick up some
Spudgers and
Solder Wick (if you don't have/want a desoldering iron).
Mouser order in hand, time to open your mouse. Each mouse is a little different. But they seem to all involve removing the feet, and poking through the lable in the battery compartment.
Be careful of little wiring harnesses if you have forward/back buttons (1)! And remove any wiring harnesses for laser assemblies (2).
It took me a while to figure this out, but you need to slide out this piece in order to remove the scroll wheel mechanism. Not sure how many mice this is used on.. Also be careful of two very tiny springs that hold up the front end.
Now, remove the screws that hold down the circuit board and disconnect the battery wires. Set the rest of the mouse somewhere safe.
Logitech neglected to put a connector on the hidden special button! Doh! Wonder what this little switch does (1)? Anyway, warm up your soldering iron and start removing one of the two switches. Pay close attention to the orientation of the switch! The new one must go in the same way!
Proper tools make for light work! I have a Hakko 472 desoldering iron that did this in a few seconds. If you can pick one of these up cheaply, it makes taking stuff apart a lot easier and more fun!
Bye bye Omron switch
Solder in the new Cherry switch! I have a very old Ungar 9100 soldering iron that, again makes light work of this. So glad I picked that up on Ebay!
Repeat these steps for both switches. MAKE SURE YOU PUT THEM IN THE RIGHT WAY!
New Cherry switches installed!
Now, just look at the dissasembally instructions in reverse order and put your mouse back together!
Hope this helps someone!