Hi. I've been working on my ever misbehaving Williams Skylab EM machine. I think I found one of the problems that's been aggravating me for some time. Now, I'm down to, hopefully, the last problem. It's one that's doesn't happen very often, thanks to my lack of expertise with this game. Just a little background. The Skylab machine has 5 captive balls in the center. They can move around a "track" when you hit either side of the track, which is like a large upside down "U". When you get all 5 balls to one side of the "U", which is indicated by a red arrow pointer, you score an additional ball. The problem is that I typically, but not always, get more than one ball awarded. Just now, I was on my 3rd ball, of 5, and scored the extra ball. The ball count went up to 5 from 2. Looking at the schematic, it's not clear to me how the captive ball logic works and how it pulses the credit up coil. I know there are switches in the captive ball track that detect how many balls are on one side of the "U". From that, it turns on the correct indicator light (new game) for the side with the least amount of balls. One of the switches tells the machine that 5 balls are all on one side. If 5 balls are one a side AND the indicator light for that side is on, an extra ball is awarded. I would appreciate any insight to what any of you may have on how this works and where the problem may lie. Thanks.

OK, I have an update. I didn't see in the schematic that the credit/add-a-ball adjustment had 2 separate outcomes (2 sides of the adjustment switch, 3 possible positions), one for spacelab special and one for rocket special. The outcomes for these 2 specials is different depending on where you put the 3 position switch. Anyway, there is a path, through that adjustment, to power the ball count step up coil. This was the path I was looking for, but didn't see earlier. The path to pulse the ball count step up relay goes through the captive ball switches and the rocket special relay. I cleaned the contacts on the rocket relay and made a slight adjustment. I also cleaned the captive ball switches as well as a switch on the score motor. Afterwards, I played the game with the glass off and "manually" forced the captive balls to move from one side to the other in order to trigger the ball count step up. After several iterations, I could not get the ball count to increase past 1 ball, as it is supposed to. I'm hoping that this has fixed the problem. It's difficult for me to consistently get 5 balls on one side. I'm just as likely to move a ball in either direction, so when I move one over to the "correct" side, my next attempt will move that ball back to the "incorrect" side. The ball centers, at the bottom of the "U" are only about 1 1/2 inches apart, so it takes more skill than I have to be able to move a ball in the direction I want it to go consistently. Keeping my fingers crossed that I've solved the problem. In a related note, 3 have 3 EM pinball machines, 2 Gottlieb wedge heads and this Williams Skylab. I find that the Skylab is, by far, the more difficult machine. The minimum score to win a game is 111,000. In order to get there, you almost have to win at least one extra ball and maximize your bonus when the ball drains. Pretty difficult for me to do. This machine is a little faster than the others also. Best regards to all.