I have a game with a magnet grab feature, and once in a while, the magnet simply does not energize. I am positive it is not a switch problem, because the grab sequence has other sounds and animation ... it unfolds correctly except that the magnet itself just isn't energized. And it is worth noting that I never see evidence of a weak magnet. It works perfectly 90% of the time and 10% of the time it doesn't work at all.

Today I realized that these magnets (Bally #20-9247, WMS 22-675T) have a protective thermistor. If the thermistor was flaky... maybe that could explain why the magnet fails to energize some times? But I don't know if it is reasonable for a thermistor to fail in that way.

If not... can a transistor fail in such a way that it won't switch on once in a while? I haven't read about that before, but... maybe?

Assuming the computer is trying to fire the magnet correctly, what else could stop the magnet from energizing only sometimes?

I should do that--but since the problem is intermittent I suppose that test could look OK even if the part was flaky. Maybe I can reproduce a fault by wiggling things.

Unfortunately it doesn't seem to be that simple @tjw998. It could fail on the first grab of the day, or it could fire several times, skip one, and then fire again in the same game. But now that I know the thermistor is in the system I'll have to watch closely again ... maybe my memory is off.

The magnet activity in this game is not super common, and I've not seen my weird problem reported by other users... So if I do see a pattern that suggests thermal protection is active, hopefully it is simply an overly eager thermistor instead of a deeper problem.

A good idea I have yet to try @zigzagzag. I'm honestly not sure what kind of magnet test it has but I will look.

(The game is Shadow... I didn't mention it because the game has a complicated lock sequence which requires a couple of other switches to operate. Lock problems from a failing switch are common and cause a lot of weird problems. For purposes of this discussion I wanted to understand the magnet better and not get sidetracked by the switches, which are all good as far as I can tell.)