I am helping a friend but I hit a wall.
I replaced the bad coil on the left sling shot of a bally zip a doo because it was shot, and the game shut down every time the ball hit the left sling. But it still doing the same thing. The right one works fine. What would cause this? I have no schematic and I don't know where to look next

It goes dark.
You can start a new game if you press the button. Otherwise it is dead
It did just burn a wire going to the game over relay the last time I pressed it so once I fix that maybe it was the problem

I just fixed it today, and yes, it was a shorted coil issue, and an over fused issue, and a couple fuses were soldered in to broken fuse sockets.
So it runs fine, although the ball count lights don't work. The bulbs are good, and the 1st light flickers when you start a game, but does not stay lit.
The machine counts balls fine, and ends after 5, but the lights don't come on to indicate.

I don't think so, looks like the wires run direct to the ball count unit.

So bulbs are good. Contacts are good. I tested continuity from the count reel to the socket, and that's good too. The 1st ball light flicks on for a sec right at the beginning and goes out.
Shit. I just realized what it is. It's the game over/start relay latch contact spacing. I was typin in all the stuff I checked, then I was watching the score moter as I started the game. The light flickered for a second when the second reel tripped the game over /game start relay latch. So I lifted the contact on the second cam to make it active, and sure enough. As long as I held it, activating the start half of the relay latch, the ball light was on. It's like one CH too much gap that when latched it doesn't touch, but if energized it does.
Thanks to everyone who chimed in to help.

Now here's an interesting phenomenon. When the 10pt reel scores once, the 100pt coil is energized and hums. Then the second time the 10pt reel gets energized both it and the hundred pt reel score advance. So for every second hit of a 10pt target you get an additional 100.
What could cause that? Bad spacing on the 10's advance so it always thinks it's at 9?

On both the first and second player too.

I'm thinking the 100 reel doesn't score every time, because the coil just locks on, then lets go the next time you hit a point. so its basically going through half the scoring action each time.
I am going to stick my head in the machine again this weekend. I had hoped I might have had some traction on the forum for a possible starting point.

So every time the 00-90 unit advances one, the coil for the 100pt score locks on, thus energizing the coil on the 100pt reel. then when the 00-90 unit moves 1 more time it releases. so the issue is why does the 00-90 unit cause the 100pt relay to energize?

I just tried to isolate the issue a bit. When the 00-90 unit advances, and the 100's coil locks, I started to lift the spider contacts on the 00-99 unit. There is a portion of the 00-99 wheel where if I lift either the outside ring of rivets contact or the second inner ring of contacts, it releases. so I masked the section of the reel on the outside rivets (basically covered about 10 of them with tape, and it played perfectly for the player 1. when I tried on player 2 it would score for the 10's but would never roll over the 100's.

Ill try what you suggested to see what happens. so block the pos 9 on both the 1st and second player reels on the 10's reel?

I covered all the contacts on the P1 & P2 10's score reel, and it made no difference at all.

I have looked at those but I don't think that's it. It boots up at zero. No coil lock. It's not till you hit the first 10pt target that it does the 100pt coil energize, then I noticed it won't even score 100pt target, till you hit a 10pt again to release it.

Jones plugs are in the right spots.
If I take the spider off the 00-90 unit it works without issue.
On the outer ring, every second pin in this stretch is connected, and seems to be the reason the 100's reel coil locks on, because if I lift the spider off that outer contact it releases.
I drew the wire path in for clarity.image.jpg