Usually a missing ball is from a trough switch not registering. Pull the balls out. Put the game in switch test mode. Drop 1 ball at a time in the outhole and see what happens.

The first ball should trigger trough switch 3 - 2 - 1
Second ball 3 - 2
Third ball 3

or whatever the associated switches are. You get the point. See if one is missing.

Looks light Left trough 58, center trough 57, right trough 56.

No, most likely a wire. You have lost all of the switches in column 5 of the switch matrix.

Game Off - Open the head, go to the CPU board. Locate connector J205 [near bottom] and check wire #5. It is a green wire with a black stripe. It is probably loose. Or the connector itself. First push the connector in and see if it was loose.

Then, with a small flat blade screwdriver like a jeweler's push the wire in so it seems seated.

Turn game on and do the switch test again. This is the easiest of the solutions since the IDC connectors stink and wires do come loose.

It could also be a broken wire going to the first switch in the chain and if something really bad it could be a failure on the CPU for the switch matrix (LM339 chip or something).

But don't panic. The wire is the most common problem.

First do a continuity check from the J205 plug wire 5 to one of the switches where the wire attaches. That let's you know there is no break.

Also do a continuity check from the J205 pin 5 to the chip leg it is supposed to go to. I've had torn traces under a poorly replaced header that didn't cause problems for year.

Yes it could be the 2803 but it also could be a LM339. I'd have to check the schematics to get more specific. Either way clip the cheap chip out and remove clean without damaging the board. Don't try and remove the entire chip at once since you are tossing it anyway. Solder in a socket so you don't heat damage the chip. Double check socket and chip for direction.

Good luck.

Any battery corrosion on the MPU board? If you are not sure, you can post a picture for us.