I like a good challenge, but my Grand Prix has just about got me whipped. I’ve been working on it off and on for six months, and it’s about 90 percent functional. That’s the good news, because when I started it was totally dead.

The bad news is it still exhibits crazy, intermittent issues. Sometimes it won’t fire the ball release coil at the beginning of a game or between balls. The top eject hole sometimes steps up the right bonus ladder more than the expected two steps. The right eject hole doesn’t always kick out the ball. The most aggravating issue is the unreliable way it steps up the ball in play. Sometimes it steps up correctly, sometimes 2 balls, sometimes not at all.

I have read all the Grand Prix and stepper related posts I could find on pinside and the old RGP newsgroup. I’ve pulled the playfield and bottom panel multiple times. I’ve examined every relay and score motor switch, only cleaning and adjusting when obviously necessary. I have disassembled and rebuilt both bonus steppers, the coin unit, and the ball count unit. I’ve poured over the schematic and feel like I have checked and tried to adjust anything that might relate to any of the odd behaviors.

Because the issues are inconsistent, I figured there was something intermittent going on, like a shorted switch or wire, or a mis-adjusted switch. But I’m at the point where I’m about ready to throw in the towel and start on another project. I hate to admit defeat – even temporarily - but I am at a loss as to what to try next. I also know Grand Prix is a complicated EM and prone to issues, but my experience with EMs tells me once they’re adjusted and set up right, they’re pretty reliable.

So I guess this is my final plea – is there anybody out there with a creative suggestion that doesn’t involve a sledgehammer? Thanks in advance for your help!

Funky-I tried decreasing the spring tension on the ball count unit by unwinding one turn; it had no effect. The finger contacts and rivets on both bonus steppers look to be making good contact; I had cleaned both and lightly lubed the rivets with Super Lube. Here’s the one thing that I have noticed with the bonus steppers that is odd: usually the 5k lamp on the right bonus ladder is lit at the start of each ball, the left is not. Which is correct? I have also noticed that on the left bonus stepper, I can manually cause the gear to step up another half turn after it has been counted down to zero; in other words, the switches on the left bonus unit have already been activated and I can still manually get the gear to move slightly by depressing the reset plunger. On the right bonus stepper, it seems to be prevented from moving by the thick metal pin on the gear that butts up against the stepper bracket when it has been reset. I didn’t consider this an issue – in my mind the stepper should stop decrementing when that switch stack is “activated”.

eded-like you are thinking, I had previously checked that the ball count unit stepped up properly when I manually activated the coil plunger, and it was. In fact, I couldn’t get it to step up more than one ball at a time manually. And I’ve been careful to only play a single player game, and verified that the player stepper is not moving during game play.

Howard-I haven’t used a bulb tester, but have examined motor switch 4A and the m/b switch on the outhole relay (multiple times). I’ve actually checked all the score motor switches, and all the relay switches on the bottom panel multiple times, with the panel removed.

So maybe this is another clue… I mentioned earlier that it seems strange that on game start up, when the ball release coil doesn’t fire, the 5k lamp on the right bonus ladder is lit and no lamps on the left ladder are lit. If I manually step down the rt bonus ladder so that no lamps are lit, then manually activate the outhole switch, the ball release coil fires and the ball count steps up one. For balls 2 thru 5, points must be scored before that works (which I would expect to prevent zero score balls). I’m now assuming that at the beginning of each ball both bonus ladders should be at zero, NOT 5k?? If that’s true, then I guess the problem originates with whatever is stepping up the right 5k bonus. I had already checked for closed playfield switches, so something else must be stepping that right bonus up?