I've been working on a Target Alpha for a friend - the machine was in storage for years and didn't work at all so I did all the grunt work - cleaning score reels, de-gunking steppers, cleaning and adjusting switch contacts, checking for touching solder tabs/wires, etc. Got it partially working but there are still a couple problems. One of which I could use some help on: I have it set on 3 balls right now, and the bonus scores correctly after the first two balls drain (1,000 for each drop target down) and I can hear the solenoid on the bonus stepper on the underside of the pf chugging away as it checks for bonus. But after the last ball drains, and I'm supposed to get double bonus, the solenoid is only getting a weak signal to fire, so isn't firing long or hard enough to advance the bonus stepper...so the stepper just stays in the same position. I can see the solenoid trying to fire - it moves very slightly every time the G relay pulls in, but not enough to actually complete its movement. Is this a timing issue as a switch somewhere isn't staying closed long enough to give it a full pulse? (The bonus stepper is clean and moving freely, by the way. Also, all the switch dogs on the score motor are in the correct positions and none of the actuator arms look bent or abnormal.)
I'm looking at the schematic, and who knows if I'm reading it correctly, but it looks like the switches involved are Motor 4A, Motor 4D, Motor 2D, Motor 3B, K and G. The bonus scores correctly on the first 2 balls, so I'll assume G is working correctly, and indeed I can see it pulling in each time the solenoid fires (or should fire). The K is also energized on the third ball (as the "Double Bonus" light comes on), so the K switch is open. I don't understand what else (other than the K switch) changes when the double bonus is active. I closed the gaps a bit on the score motor switches I pointed out, hoping that they would stay closed just a bit longer - but no change.
I was checking voltage pulses with 2 12-volt car light bulbs in series hooked into various places, but I'm not sure how to interpret the results. The bulbs pulse brightly every place I've checked except for the actual "add bonus unit" solenoid - where the bulbs barely light, which makes sense since the solenoid isn't getting enough juice to fire. But why?
Also, the machine is about 15 miles away in an arcade, so it will take me a bit to get there and check out any ideas or answer questions you may have - but I'll get there! Thanks for your help!