Tiny Encoder and Bringing an Old Mouse Back to Life

I think the vast majority of people reading this have used a computer mouse. Like any device, mice sometimes break, but sometimes you can give them a second life.


When a mouse breaks, most users simply buy a new, more modern model. But sometimes you get used to something and don't want to replace it with something new, even if it's more modern. That's what happened to me.

My first "mouse" wasn't the classic tailed kind, but one built into a laptop, just like the one shown in this photo (taken from here). But I found the trackball rather awkward to use. It got dirty quickly, so I always kept a bottle of alcohol and a piece of cotton wool on my desk. My first actual mouse was also a ball mouse, a Mitsumi, which got clogged up too, though not nearly as often.


I can't remember what came next, though at one point I tried an A4tech wireless mouse that used an IR link. 5 GHz? Ha, 320 THz :)
I wasn't too keen on that mouse, and then I came across the WOP-35, which I first got to know almost 20 years ago and still use to this day.
No, not that very first one, but my third. There were three generations of this mouse, all sharing the WOP-35 (SWOP-35) model name, but with some differences:
First version — PS/2 connection only
Second version — USB connection, with a USB-to-PS/2 adapter included (not to be confused with a converter)
Third version — USB connection only.

This mouse turned out to be incredibly comfortable for me: two scroll wheels, five buttons, and I especially like the large side buttons.

But in reality, there were many more differences between them. The first version worked perfectly for me with Windows 2000, and then XP, until I installed the first service pack. After that, the cursor started to jitter a little and sometimes move across the screen on its own, which was a bit annoying.
Some time later, I spotted the second version in a store, bought it, plugged it in, and the cursor stopped drifting.
After I installed the second service pack, the jittery cursor problem came back. In 2009, I bought the third version and swapped it in. After that, everything worked perfectly, and I've been using this very mouse ever since — for more than 10 years now.

Some might ask what was so great about a mouse with a jittery cursor. Honestly, I didn't pay much attention to it, because the comfort of using it outweighed that drawback.


Then, many years later, when the encoder started acting up, my first thought was to take one from the old mouse, which is exactly what I did. A few more years passed, and that one started to fail too. Then I thought, why not use the encoder from the very first mouse, especially since there's hardly anything left to plug it into anyway?
And this is where I was in for a surprise: it turned out the first version had an optical encoder, and I'd simply forgotten about it. This is a great example of cost-cutting and simplification in practice, because an optical encoder is practically immortal.
Also, the stepped rotation here isn't produced by the encoder's spring, but by spring-loaded pins and a small gear on the scroll wheel's axle.


The second and third versions came with ordinary encoders, which were the ones that eventually failed.


At one point, I settled for just cleaning the encoder and lubricating it with technical petroleum jelly. That helped, but the little "fingers" in the contact group gradually started to wear down, and I figured it would probably be easier to replace the encoders themselves.

I went to AliExpress, found a suitable listing that included 10 pieces, ordered them, and received them. The count checks out, although while preparing this review I noticed that some of the encoders have a smooth metal casing, while others have a matte finish.


The seller offers encoders from 5 to 13 mm tall, as well as a listing with five sizes, two pieces of each.


It's very easy to determine the height of the encoder you need: the stated size is the distance from the center of the hole to the circuit board, or to the molded tabs that rest against the board. In my case, I needed 7 mm-tall encoders, and that's exactly what I got.


Nothing unusual on the outside—just ordinary little encoders.


There's grease inside, so hopefully they'll last a reasonably long time. Either way, I now have spares—the main thing is remembering where I put them :)


The rest is straightforward: desolder the old encoders, but do it carefully. The circuit boards in my mice, for example, are made of phenolic laminate, and the traces can easily come off.


While we're at it, let's compare the originals with the ones I bought.
The originals are at the top, the new ones at the bottom, and the disassembled original is on the right.


It turned out that the encoders in the old mice had different diameters. The new one is on the left; the ones from the second and third versions (or the third and second) are in the middle and on the right.


Carefully solder the new encoders in place, making sure they're straight. Sometimes the roller shaft can have a little play. If that happens, you can push a piece of ordinary thread into the hole and then insert the shaft; that will take up the slack.


And that's it. Check that everything works, then screw the mouse back together.
The keyboard on the left in the photo is also an A4tech. I got it to replace my old Logitech Ultra-X, and after a year of use I can say that the Ultra-X is much better—but unfortunately, you can't buy one anymore.


Conclusions.
The encoders work, at least the pair I installed. Subjectively, they turn a little more smoothly; the originals had more distinct detents. Sometimes an encoder lands between detents. I wouldn't say it's annoying, but I do notice it.

In short, I'm happy with them so far. Time will tell how they hold up.

It occurred to me much later that I could have used an encoder like this in my soldering station instead of the large, bulky standard one. If I remember correctly, that was exactly what I didn't like about it at the time. And in terms of reliability, a “mouse” encoder would certainly be just as reliable. The only catch is that I'd have needed to add a separate button, since this one is just an encoder.

That's all for today. I hope this information was useful and helps you save your old “rodents” :)