Quoted from texas_compadre:Begging your pardon, but a “stuck” switch is indeed “always closed” until one gets it “unstuck”. I don’t see anything misleading about that.
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He was reading your post literally. There is indeed no such thing as an "always closed" switch. That would basically be a piece of wire. In your case a "normally open" switch was simply stuck closed.
These switches have basically been the same for decades aside from the improvement of rounding the actuator wire where it is above the playfield. That has two effects. The first is the switch allows the ball to roll over more easily; more importantly the round wire holds the switch closed a split second longer giving a better chance to register.
I've never seen a new, uninstalled switch read closed on a meter, but I will assume it was somehow bent or damaged or simply needed to be actuated a few dozen times and broken in by hand to loosen up. Also, a switch that is closed when installed is either not centered in the slot properly and dragging the edge of the playfield or the actuator wire is not adjusted properly. Either way none of these anecdotal findings from your game has anything to do with the problem in this Rush loop.
Microswitches basically have two different ways of adjusting. First is to bend the wire so it sticks up out of the playfield further. Normally this is not recommended because it does NOTHING to make the switch more sensitive. It simply makes the wire stick up further so it gets depressed further (and maybe register an airball as a result). The second way to adjust the switch is to bend the wire (or adjust the switch body position) below the playfield closer to the little button on the switch body. Adjusting it one way or the other here doesn't affect how far the switch sticks up out of the playfield at all. It adjusts the sensitivity of the switch. Adjusting it too far one way and the switch will be always closed. Adjust it too far the other and the switch will not register even if pushed all the way down level with the playfield. Get it just right and the switch will register even on really fast rollovers. Rather than bending, this can more easily be accomplished by loosening the screws and adjusting the position of the switch body itself on switches that have oblong holes.