Monday, March 31, 2014

Fixing broken mouse button on a Logitech M705 Marathon mouse (cordless) - Logitech M705 Marathon mouse taken apart

Some weeks ago I fixed my Logitech LX6 mouse, this week came time to fix my Logitech M705 Marathon mouse.

I knew it was coming... some months ago the M705 started to make unexpected double-click, and today it reached the "can't stand it no more" level :-)

The plan is the same as for the LX6 fixing... but this time I used a dremel to loose less time in desoldering/removing the switches.

I must say that the disassembly of Logitech product is always interesting, I think them are very well engineered.

Here we go with some detailed photos of the Logitech M705 internals.

First, there are the screws, 5 screw to be precise.
1 screw directly visible on the right,
2 screws under the sticker inside the battery holder,
2 screws under the big mouse feet on the left (in the photo you can see the hole for the already removed screws)

Now you can open the mouse

The assembly of the free spinning wheel is very well done!
Wheel, please, look to the left... look to the right.

And here is the mechanism that switch from free-spinning, to the classical click-spinning.
When you push the button on the mouse, there is a tiny hook that engage the notch inside the wheel.

Here the hook is engaging the notch, and the wheel is in the classical click-spinning mode.

In this other image the hook is disengaged, and the mouse is in free spinning mode.
It's just a 1mm difference... but the free spinning wheel is amazingly useful (especially when you are a software developer and need to scroll trough thousand on lines of code :-) )

Another view of the wheel, and the switch.
The broken one is the switch of the left mouse button.

Now came to the interesting part: how do we remove the wheel assembly?
It turned out there there is a tiny plastic pin that hold it in place.
If you remove this pin... will be able to lift and remove the wheel assembly!

Yeah, now I can have a better look at the circuit board...
...and establish that the board is still firmly locked to the case.

There are 4 more screws to remove...

...but first you need to take care of these 2 tiny spring, they will keep the wheel stright, so don't loose them.
They are just placed in their hole, so gently lift hem and put them in a safe place.

I use some tiny neodymium magnet to hold all the different screws/spring in a safe place.

Then get a tiny screwdriver, and remove these 4 screws: you'll find out that these screws are STRONGLY tightened to the board.

After removing these screws, and some more plastic, you can observe some switches in not wildly used form factor, it's interesting....

Finally I can remove he main board... opps...
I thought I can remove it, but ther is more under the board: there is a tiny circuit for the hidden thumb mouse button.

 Some other screws to remove...

Then remove this piece of plastic...

 and unhook the last piece of circuit from the case.

 Eureka: Finally free!
 The M705 main circuit board in all it's glory!

Now it's just the same old story:
  1. Desolder the the old broken switch.
    (typically this is a sequence of: cut, heat, push, pull, heat again, cut, use your light saber.... until you get the switch out without breaking the main board)
  2. Resolder a new working switch.

With this particular switch I've had some issue: 1 of the 3 pin war very stiff, I had to pull a lot.
Even after desoldering and cleaning the board, it's been a complex job to push the new switch in it's place.
I had the feeling that I've been very near to the breaking point of the copper under the board.
Anyway, I've eventually been able to replace the broken switch with a working one.

A final note: if you, like me, are thinking about using a dremel to speed up the "broken switch removing" part, here is what happened to me...

By not having a welder tip specific for desoldering, the only working way I found for removing a mouse switch is by breaking it in 3 part, and desolder them individually.
This time I tried to use a dremel to break the switch in 3 part more easly and less aburptly than by using a nipper.

For the most part, the idea worked out well... but you need to pay attention when you have a 10'000 rpm spinning diamond coated 120 grit burs.
If you loose control of it, you may end up with something like this, look at the 4 tiny smd resistors/capacitors in this image, just under the broken switch:

Here is a bigger image.
I nearly ripped off a capacitor, and damaged the soldering on the two nearby resistors/capacitors.

Another image or the scraped smd components.

After all, I've been very lucky, the mouse still seem to works perfectly.
Probably there still is enough tin on the side and maybe under the smd capacitor.

But still, sometime, I look at my mouse and I ask myself: how much will it last now? :-)


  1. As a production repair line tech in the 80's repairing buckets of boards per day, I hate to see parts destroyed in the name of removal. Always preferred finesse. Any small soldering iron, along with some de-soldering braid can remove those three connections in a jiffy. De-soldering braid, if you're not familiar, it a fine copper mesh braid infused with some rosin to attract all the solder to itself, effectively cleaning the board of 95% of the solder. The trick is to lay the braid against the joint, then apply heat to the braid. The old soldering rule is "the solder flows to where the heat goes" is true and the copper braid sucks up the solder. Try that or my favorite, a vacuum "solder sucker" pen. I could yank a 32 pin EEPROM chip in about a minute. Although, most of those were socketed.

    1. Thanks for your suggestion.
      In fact some months ago I bought both a desoldering braid, and a vacuum "solder sucker" pen. (I don't want to find myself again at cursing a pcb to unsolder a switch...)
      The next time I'll try both method (and I'll even try to combine them) :-)

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  3. Thanks to your article I could repair my mouse.
    in Turkey

    1. I fixed my mouse, thank you for your informations. :) :) :) :)

  4. Спасибо за полную разборку!

  5. That plastic pin to telase the wheel mechanism and where the springs go :-) was just what needed to know. Mouse is as good as new again with new switches. Thanks

  6. hi... i have the same mouse and it fell on one of the side buttons (backward button).. and it's constantly pressed, i opened it up and the small square switch is broken, any idea how to fix it/or where can i get such part ?

    1. I bought some compatible switch on ebay: