Look under the playfield. There's a switch that senses when there's a ball in the outhole. Then the ball ejects, and it passes another switch on the way to the shooter trough. My guesses are: a) that switch is bad or b) the ball isn't pushing the little wire thing down far enough to trigger the switch or c) there's a bad solder joint at the switch or d) the wire from that switch to the ball count relay is bad.

I would start with b. Find the switch and try pushing it and seeing if your ball count increments.

mark

When you put it into 2-player mode, does it switch back and forth between players? Or does it stay on player one? If it switches from 1 to 2, does it also just stay on ball one for both players? Does this game score a bonus at the end of each ball?

My Fan-Tas-Tic and my Big Shot and my friend's Card Whiz that I fixed all have a switch after the one that ends the ball. It's under the channel that goes from the eject hole to the shooting lane. All three of those machines had the same issue as yours at one time or another, and all three times it was that switch. This is not the same as the outhole (ball eject) switch, and it's not the one in the shooting lane. It's a rollover in the trough after the eject hole.

Since we don't have a schematic, I can't be sure without a pic, but...

The only em I have worked on lately that didn't have that switch is my DIng Dong, but it's a single player with no bonus.

Dang... can you post the pics?

First off, you shouldn't use a screwdriver to do that. Push the thing like the coil would.
Second, it looks like you've found it. It looks like there's a latch relay--that's the one at a right angle, I think (others can chime in). That's probly what fires for player two's balls to increment. And it looks from the second pic like the 3rd switch from the left should be making contact at the same time as the others. If you don't already have a switch adjusting tool, order one tonight.

@Jeff: You're right... I didn't have my specs on when i was looking at the pic. Ok... I have a new wild theory. I think there's a switch on the score motor that's related to incrementing the ball count. Look for the same colored wires on cam three (I think) on the score motor. I was just reading about a Williams machine from the same era having the same issue, and it was switch on the score motor. I think when you short those two switches and get it to increment, you're doing what the switch on the score motor should be doing.

Jeff, I think you're on to something here.