An odd assortment of things are wrong on this TSPP pinball machine. Are they related? Let’s look into what’s wrong and where we should look to fix things?

This has now turned into a multi-part series where I also discover some other issues:

So here’s the take-away from the first 5 parts of this series.

Everything was basically inter-related (except I believe the slingshot and pop bumper coils were separate failures). The trouble with the ball trough opto led to the failure of the shooter lane coil. When the ball trough opto started failing, it signaled false switch closings, tricking the game into thinking balls were moving through the trough and causing the VUK to try to clear a problem, which caused multiple balls to go into the shooter lane. This happened faster than the auto-plunger could handle and once X number of balls went in there, the plunger could not clear them, and eventually the MPU sent too many “fire-the-coil” signals and blew the driver transistor — interesting that it blew the driver transistor before it melted the coil — I suspect either (or both) can happen in this circumstance.

What’s interesting about this, is that this problem could be compensated for by software. It’s also possible the other coil failures are the result of a similar characteristic: Not having a certain timeout or duty-cycle enforced on coils. Meaning… the software could check to make sure that if a coil is firing too much (say x amount of times in y time), that it knows there’s some kind or problem and then put the game into some sort of error state rather than blow the coil or the drivers. I know in some later games this happens… when errors are encountered, the game just stops trying to fire coils rather than blow them.

This obviously isn’t the case in some of these 2000-era Stern games. I’ve noticed this on several titles including WPT and NBA as well.

Unfortunately, there’s not likely to be a software fix available, so what is important is to keep an eye on game behavior and try to catch switch malfunctions before they blow things. Had I been told about the shooter lane situation earlier, I could have fixed the opto before it blew the driver transistor on the SDB.