Hi. This is my first post. I decided to join because I feel I'm at a loss for what to do with a problem I'm having with my Williams Skylab EM machine and I'm hoping someone here can help me. The machine is basically working well. I've been working for the last 2 weeks on cleaning up the machine and getting everything to work. The problem is the ball count display (ball index) does not work correctly some of the time. I've had it work well for 6 ball cycles of 5 balls each. Then, on the 7th time in a row, it doesn't work. When I say doesn't work, I mean that the ball count initializes correctly every time you start a game, i.e. 5 balls indicated. When a ball drains, the ball count is supposed to decrement until all 5 balls have been played then it's "GAME OVER". However, somewhat randomly, the ball will drain but the count will not decrement. It may take one or several ball drains to get it to decrement. I have seemed to make the problem better by adjusting a couple switches on the score motor, but it's still not working completely. The problem seems to be that the ball count reset coil is not getting a pulse. I've lubricated the ball count unit and I believe that it is working ok, but it's, sometimes, not getting a coil drive pulse, for some reason. I feel like this is probably a timing issue with switch adjustments on the score motor, but I'm not sure. I've looked at all of the relays involved in the circuit (I know about), cleaned all of the switch contacts and verified they are open when they should be and closed when they should be. I have the schematic and owner's manual. I'm pretty new to pin repair, but I'm an electrical engineer and understand schematics, etc, although I'm far from a qualified EM machine tech. I should mention that there are no problems when the machine initializes. If there are balls still play, the machine will decrement to zero then increment back up to 5 reliably when you hit the reset button on the front. The ball count has been working for quite a while with no problems. The problems started after I began troubleshooting a different problem. (problem was too many bonus lights were turning on after the SKYLAB targets were all hit. Should only be 2 lights) I fixed that problem then other ones popped up. I suppose that I may be causing the problems myself from the cleaning and adjusting I'm doing, but I'm not sure how. I appreciate any help you can give me. It's starting to get a little frustrating.

Mark, that's an excellent suggestion. I've looked at and cleaned all of those switches and I adjusted the cam switch 2A. However, I don't know if I adjusted it in the right way. I think I made the gap larger when the switch is open, but, because timing here may be a problem, maybe I should have made the gap more narrow???? I'll look at it again, but I like your suggestion. It really feels like there is a timing problem that, somewhat randomly, doesn't send a pulse to the ball index reset coil. Thanks for the suggestion.

OK, an update. I tried the clip lead bypass idea from MarkG. The results were not conclusive. I first bypassed the cam switch 2A. This resulted in a good ball count decrement every time. Ah-ha, I thought I found the problem. I tried adjusting the cam switch 2A multiple times, getting the open switch gap as close as possible. I got it so close that I started to be impacted by switch bounce (I think) and was now getting multiple decrements instead of just one. Opening the gap, slightly resulted in the same problem as before. So, I then decided to bypass the switch on the ball index relay. Again, this resulted in a good decrement every time. I found that when starting a new game, it would increment up to 5 then back off to 4 when the game started, but the decrements after that were consistent. I suppose the decrement from 5 to 4 at the start was an artifact of bypassing the switch on the ball index relay. Next, I bypassed the switch on the outhole relay. This resulted is multiple decrements, i.e. 2 or more decrements at a time. The number of decrements was not consistent. This is probably an artifact of bypassing the switch which I did not investigate. I think the fact that bypassing either the cam switch or the ball index switch results in good operation confirms that it's some kind of "timing" problem in the system. I began to wonder if the problem was the circuit which turns on the ball index coil is turning off too quickly, therefore not allowing the cam switch to pulse the ball count reset coil. I started to look at this last night, but started to get tired. I did adjust one switch in the ball count reset coil circuit, but that did not change the performance. I have not had time to go to the auto parts store and pick up a couple tail light bulbs (MarkG). I may be able to do that today. I've been putting of another (non-pinball) that I need to spend some time on today, but I have some time this afternoon I can spend on the machine. If I can get to the store, I will pick up the bulbs and give that idea a try. Appreciate the help so far. Any other thoughts would be appreciated also. Thanks.

Currieddog, thanks for the advice. I will check that out today. Also, I've noticed a symptom that may shed some light on the problem. It seems that the games tend to work correctly every other game. In other words, If I get through 5 balls in a game with no ball index decrement problems, the next game will not work correctly. The 3rd game will work correctly. In general, every other game works. So, after a game completed, I took a sharpie and marked a line on each of the cam wheels. What I discovered is that when the game starts with the marks in that same position the ball decrement does not work. I can do a couple things that make the score motor run then hit the reset button and the game starts with the marks on a different position and the game will then work correctly. The only difference, as far as I know, is that the switches on the score motor are on a different detent on the cam wheel. I haven't noticed any differences in the detents, but I haven't really looked at them. I admit that I haven't done enough testing to say definitely that this is happening, but I've noticed for some time that every other game seems to work ok. I didn't give it much thought because I didn't think there could be any difference, but now that I've marked the cam wheels, I think there may be. Could something like this be the cause of my problem? Thoughts? Thanks.

update: I found that when the game initializes with the sharpie marks horizontal (as I drew them initially), the game will not count down correctly. However, if I turn the cam switch by hand, it starts to rotate on it's own then stops. At that point, the ball count down will work correctly. It almost seems that the game isn't initializing correctly. The score motor needs to turn for about another half turn (estimated) before the game starts. I haven't looked where the marks go to when it works correctly. When you initialize a new game, what stops the score motor from running? Also, I looked at the detents in the cam rotors and I don't see anything different about them. The problem seems to be the score motor stops too early. Not really sure what problems that causes to make the ball count decrement not work, but it seems to. Thoughts?

Hope everyone had a great Christmas. MarkG, thanks for your thoughts. I was also thinking about the reset relay. However, I had a bit of a Christmas miracle of sorts. I had removed all of the screws holding the score motor to the cabinet board (not sure what it’s called) so that I could better see the switches. It has the hinge, but it was still difficult for me to really see the switches, spacing, contacts, ect. Anyway, I was holding the score motor in my hand about 5-6 inches above the board and I dropped it. No apparent damage. I eventually put it back down after a small adjustment on one switch (can’t remember which one) and then tested the game. The ball index decrement worked perfectly. I’ve now played the game many times and it works reliably. The funny thing was that my original problem was that the bonus lights, when initiated by the S-K-Y-L-A-B lights, wasn’t working correctly. It is supposed to give you 2 bonus lights, but it was frequently giving a lot more. Well I fixed that initial problem, but, then, more just kept coming. That problem came back. The good news was that all the time I spent running down that problem allowed, earlier, allowed me to fix if pretty fast this time. Not sure why it stopped working correctly, but then I don’t know why the ball index problem went away. May be tied to me dropping the score motor, that’s my best guess. Anyway, as of now, the machine is working correctly and I hope it stays that way. Can’t believe how many hours I’ve put into this machine, but I’ve learned a lot and it’s working. Thanks to everyone for all of the comments and help. It really helped me out and gave me some directions to look at. I bought my son a Williams Grand Prix game a few years ago and now it’s not working properly. He wants me to come over and fix it. Not sure I’m up for it (haha). Hopefully, it will go a lot faster this time around.

Best Regards…….