I have a Road Kings with seemingly alternating solenoid fuses that blow. This machine is in my work's break room, so I'm never around when it happens.

One of the two fuses will blow, and I'll replace it. I'll then run the system through the coil test five or six times to see if anything's awry. Nothing wrong. I'll play a game. No problems. A couple of days later, I'll hear that the other fuse is blown. If it was the standard solenoid fuse last time, it'll be the special fuse this time.

Now, from my (admittedly apprentice-level) understanding, a fuse will most often blow if a coil is locked on. Coils will lock on if their driving transistor is kept open. A standard solenoid transistor will open if the game tells it to. Assuming that the standard solenoid transistors are all properly functioning, the next logical explanation is that the game is locking one or more coils on at some point, right?

If that's the case, then how does that explain the special solenoid fuse blowing just as randomly? The game doesn't manually fire the kickers or the four jet bumpers during normal gameplay. So, either the game is freaking out and locking on of those coils on at random or we're dealing with two different root causes on two different circuits manifesting themselves as blown fuses.

I'm going to bring in my DMM tomorrow and test all the diodes and transistors involved, but is there something I may be missing about what causes fuses to blow? No coils lock on when I turn the machine on, and I can cycle through the coil test multiple times with no problems.

You might have something here. The machine is turned off and on multiple times during the day. What I may do, while troubleshooting, is to leave a note on the machine asking people to report to me if the coils stop working partially through a game, as opposed to when they first turn on. While diagnosing, if I get no reports of the coils dying in the middle, but only when the game is first turned on, then we may have found our lead.

This current potential root cause aside, it seems better that people turn it on to play it and turn it off when they're done. The issue with leaving the game on is that there's nobody to make sure it's turned off at the end of the day. Do I really want this thing to potentially run 24 hours a day? Over a weekend? Probably not.

I'm having timing/blanking issues with my Taxi at home as well. I really need to try to figure out how this whole thing works. From what I understand, every major controlling chip has a pin that you can ground to reset the whole game. The 555 timer does something with this circuit once the capacitor it pays attention to fills up, correct? That's what allows the system to have a clean boot instead of everything powering on at once.

If that's the case, then it's possible that the 555 timer is going bad, right? I don't know. I'm just guessing right now.

I took another hard look at the MPU board, and found that there's a thin white haze starting at U41 (just underneath where the battery holder used to be) and going all the way down to the bottom of the board. I suspect that this machine used to have a battery holder that someone moved elsewhere after the batteries started leaking. It's possible that this corrosion is finally starting to take its toll.

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