A Multi Trouble Computer Mouse Repaired
Some time ago my veteran Leadership optical mouse started to work badly. Two basic symptoms: the scroll wheel seemed to be gliding freely, without really driving the expected movement in the screen, and when the left-button was pressed, the screen jumped up and down in an unpredictable manner, making it difficult to position the insertion point in the desired location. Selecting a part of a text became almost impracticable. Over time, its performance got to be worse and worse, until became extremely difficult to use.
It would be simpler and (perhaps) time-saving to throw away the mouse and buy another new one. Ok, it’s a cheap hardware, no problem about. The real problem (at least from my point of view) is that this contributes to increase the technological waste…bad! Just opposite to my ecological thinking. So I decide to fix it, considering that I could learn something with, avoid spending money (even a bit) and give a (even small, but better than nothing) contribution to the health of our planet. No doubt three good reasons!
I had to stop the (important) work being done and disassemble the mouse. Just one screw and it was open.
The first job was to do a general cleaning inside, especially on the optical path (the way between the LED and the optical sensor chip). This can be one of the reasons why the screen jumps.
Then I inspected the scroll wheel. Around the big rigid wheel there was another soft wheel remembering a tire. This “tire” is the soft part that comes in touch with the fingers when turning the wheel.
It was completely oiled, which was the cause of the gliding action over the rigid wheel. Some products are produced with embedded oil, which is “distilled” on its surface over the time. That was the case of this soft wheel oiled, I don’t understand why. It’s nonsense, not applicable to this case and utterly unnecessary. The soft wheel was carefully washed using a detergent and then dried. When installed, it drove the rigid wheel firmly and stable, with no more slipping. The problem is that I know the “tire” still has embedded oil, and in the future it will require another cleaning…
Therefore, the problem still remained, with the screen continuing to jump up and down as the scroll wheel was turned. I observed that the big rigid wheel, by its shaft, drives a second smaller component with the appearance of a potentiometer near the left-click microswitch.
In fact, it is not a potentiometer: it’s a contact set assembly that produce pulses that are sent to the software in order to obtain the scroll effect. I’ve seen on the internet a report saying that this could be an imperfect match between the male axis and the female small wheel. In fact this could happen, but it was not the case here. The component was unsoldered from the PCB and disassembled with the aid of small pliers.
It was all dirty inside. A simple cleaning with ethanol (could be isopropyl alcohol) with the aid of a cotton swab corrected the problem (it’s important to be sure that no lint from the cotton swab remains inside). The moving contacts sliders pressure were slightly reinforced, taking care to not applying too much pressure, which could prematurely wear out the contact set.
The component was assembled again and soldered on the PCB. The screen does not show the uncontrollable jumps anymore when commanded by the scroll wheel.
More problems: when left-clicking, the screen continued to show jumps. There are three microswitches on PCB (of identical type): for left clicking, for right-clicking and for continuous scrolling, that is in this case actuated by pressing down the scroll wheel (instead of turning it).
Pressing gently with a small screwdriver, the left-click microswitch gave a sound different from the other two. And more: required less pressure to be actuated as compared to the other two. So I’ve suspected that it was a problem of mechanical wear, possibly with contact bouncing. According to the literature, this kind of switch is expected to have a useful life of about 1 million mechanical operations. Of course this was not the case – it’s highly unlikely that I have used it this great amount, even over all these years. Obviously the quality of this microswitch is not that great either! As this kind of microswitch is normally difficult to disassemble (or, still worse, to reassemble), I decide to turn the soldering iron on and swap the left-click microswitch with the one used for continuous scrolling (a function that I hardly use). The action corrected this another problem, confirming that the left-click microswitch was not OK (and confirming also the contact bounce problem).
Each plastic pivoting parts in the mouse cover have a kind of tooth, in the point they touch the actuating button of the respective microswitch. The right-click protuberance was OK, as can be seen in the picture below:
On the other hand, the tooth that mechanically drives the left-click microswitch was deformed, causing doubts related to the correct matching to the microswitch actuating button.
Nevertheless, I affixed a plastic foil between the tooth and the microswitch, trying to minimize the problem. I am not shure if this effectively was decisive to correct the problem. As it was said, at this point, with so many problems in a single hardware (i.e. the mouse itself) the things become confusing…
Amazing: what initially seemed to be only two problems just demanded five corrective actions! This sometimes occurs to maintenance people, rendering the things completely confused. And it was occurring with me at that moment! The important thing is that now it is all working fine. And at zero-cost (no component replaced).
One could say: OK, you say no component cost, but have spent time; this is also a cost. I nearly agree, but take into consideration the following: the maintenance work took around only 2 hours of service, I’ve avoided a small trip (consuming gasoline and anyhow time) in order to go downtown to buy another mouse, (i.e. a few dollars saved in my bank account), more experience gotten, all working fine in my computer, a contribution to the environment, much satisfaction to give something useful … and the opportunity to take part of this community. Much more than the initial three good reasons given above. In fact, it’s a remarkable gain. Nothing bad!
This article was prepared for you by Henrique Jorge Guimarães Ulbrich from Curitiba, Brazil. Retired electronics technician. Loves electronics, telecommunications and cars.
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