mystic line extra ball design flaw
discovered by ernie hite

After ernie's rather brilliant diagnoses, we looked at how to fix the problem (well, resurrect the lie that single stepping to "extra" is gtting you closer to getting the extra ball).

There's a few options, but some require adding switches, modifying cams, or changing the odds. There is one fix that just requires a little rewiring, which is the one that is recommended.

super 7
extra ball step up circuit

Suggested fix

This fix takes advantage of the fact that switch 6A/6B is really not needed in the single step circuit. As mentioned earlier (see, you should have read the circuit theory section), it is there to keep the multiple step circuit from passing pulses when it shouldn't.

So the fix is to move 6A/6B to where it still keeps the multistep circuit happy, but doesn't inhibit the single step. That means moving the switch into the blue path, and there is only one place you can do that so it works all the time - wire #78 between the start relay and the 16 pulse cams.


  1. look in the manual to see if switch 6A or 6B opens the extra ball circuit. You need to look on the control unit switch chart. Whichever it is, that's the switch we are talking about when referring to 6A/6B below (in other words, you aren't going to mess with both 6A and 6B...just the one that is doing extra balls).

  2. remove the wires from CU cam switch 6A/6B and connect them together (highlighted at top right of schem)

  3. connect two new wires (tan highlight) to switch 6A/6B and run them to either the 16 pulse cams or the start relay. The start relay is probably easier to get to, so we'll use that. And be the wires along the harnesses and tie them down - there's lots of moving parts in the head!

  4. disconnect wire #78 from the start relay and connect it to one of the wires going to 6A/6B. Connect the other wire to 6A/6B back onto the start relay where #78 was.

You've now inserted 6A/6B in the circuit as shown in the highlighted circle. It does it's job blocking the 50V when it should, and doesn't affect 8A.

How could this happen?

This bug was in multiple games spanning several years. Either nobody noticed, or nobody cared (especially since it doesn't really matter).

Ernie said that someone had tried to fix his machine by swapping the switches between cam 3 and cam 6. Unfortunately, the cam 3 lobe didn't rise early enough either, so the attempt failed.

intro | timing cams | why it doesn't matter