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Reviving tired mouse microswitch


Well-known member
I've revived the microswitch in several of my ADB mice without having to replace it. Getting the same replacement can be hard, as the click force should be matched, and of course the shape of the switch must match. The modification involves a slight rewiring and a resistor, so that the normally closed contacts of the switch are used rather than the normally open ones.

I still use my ADB PowerMac as my main machine many hours a day, so I put a lot of wear on the mouse button. As the microswitch wears out, it will sometimes release the button even though I'm still holding it, making dragging really annoying. One day I had the insight that if I rewired it to use the normally closed contacts, the problem would completely be eliminated.

Normally, mice are wired to use a switch that's normally open. When you press it, it closes the contacts connect, and it registers the press. The problem is that any momentary disconnection, due to dirt in the switch, or the spring being weak, can cause the computer to think you released the button.

The other type of switch is normally closed. With this one, when you press the button, the contacts open. While you're holding the button, there's no way they can re-close, even if your pressure changes or your finger moves a bit. The only way for the contacts to reconnect is for the button to be fully released again. At that point, you aren't putting any pressure on the button, so there's no way the normally closed state will ever become momentarily open. So it's totally reliable this way. I'm baffled as to why modern mice still use normally-open switches, since it means they will wear out faster.

I realized today that others may benefit from this modification. I can provide details. As for parts, you need a resistor, 1K (and probably up to at least 10K, so you could just take one from something broken), a soldering iron, and utility knife (to cut a trace on the PCB). I've even done this on an Apple clear USB mouse (the kind without any screws), but the hour or so spent getting it apart and back together wasn't worth it at all.