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!
TA bonus circuit (resized).JPG

K relay circuit (resized).JPG

motor switches and timing (resized).JPG

Thanks for the reply, curriedog. I haven't really checked the player unit connection - I'll do that next time I see the machine. Today, as I was messing with it, I noticed something that may be relevant: As the third ball drains and the bonus stepper solenoid is very weakly trying to fire, I was watching the G relay energize in time with the stepper solenoid. If I pressed the armature on the G relay down with my finger very briefly, so that it stayed in the energized position just a fraction longer, the bonus stepper fired strongly. So I took the G relay apart and really cleaned the contacts on that switch directly before the bonus stepper with my dremel and wire brush until the contacts were shiny - put it back together, made sure the contacts were closing and brushing each other....and no change - the bonus stepper still only gets a very brief pulse to fire. I'm missing something....

Hi CD and Rolf...thanks for chiming in. CD - I have looked at the AX, BX and DX relays as carefully as I can, with magnifying glasses and believe that I have the switches adjusted so that they are working even with the small amount of movement those relays have. But I could always have made a mistake - I'll check them again when I get to the machine. I have checked 1C carefully, and it seems to be good visually...can't remember how carefully I looked at 2B, but I'll check that one too. The G relay is pulsing on and off in time with the bonus solenoids attempts to fire, just getting a really weak signal off the switch on the G relay going up to the solenoid. I do notice that there's a very large arc on motor switch 4D and if I short it while it's firing, a strong signal makes it to the solenoid. I've burnished the contacts on that switch until they're shiny, but could they still be bad? And why all the arcing? I've played with the distance between the contacts, but really close or far apart, doesn't seem to make a difference. So I can make the solenoid fire by either shorting motor 4D or pressing the armature of relay G just a bit while it's firing. I feel like I'm staring right at the problem, but can't see it...

And Rolf...that's an interesting video. The bonus on my machine is maybe 1/3 the speed of the one in the video. I knew that couldn't be right - it just really chugs along very slowly, counting one bonus thousand every time the bonus stepper moves to the next position - maybe slightly faster than once per second. I've touched so many things that it's hard to remember, but I think I had held down the armature of the G relay and that really sped up the bonus stepper's movement. Is the G relay supposed to stay on rather than pulse - is that what you were saying? Because it's definitely pulsing on and off, not locking on. I'm not sure I understand the electrical path if the G relay is supposed to lock on.

It's funny that you mention the P relay - the add player unit doesn't work very well either. I was hoping to wait on that problem, but of course they may be related. I haven't pressed on the armature of the P relay - I'll do that the next time I'm in front of the machine. Unfortunately, I have to travel for the next 5 days or so - won't be able to get to the machine until Wednesday of next week.

I'm starting to dream about it....that can't be good...unless I dream of a solution, of course.

Thanks again for thinking about it with me.

I'll do that, CD. Do you know if that G relay is supposed to stay locked on during the bonus countdown?

Thanks D=G - always a good idea to start with I know. Maybe I missed some contacts on the back side of the stepper units. I know I pulled the bottom board out of the cabinet so I could get to all the relays down there, and the ones in the backbox, though Lord knows, I could have missed a couple. Last problem I had on another machine was solder tabs touching on a motor switch, so I've been watching for those too.

Rolf - I think I remember the bonus countdown happening much faster when I held the G relay armature down, but I've touched so much stuff in there that it's hard to remember. Maybe before I go away, I can swing by and try that once to be sure. If that's the problem, then I'd have to figure out why the G relay is pulsing on and off instead of staying energized through the bonus procedure.

Referring to the image in rolf's post #6 - I'm a little confused by the bonus unit 15th position switches. I'm assuming that the 15th position is the end point that the stepper reaches when it has finished counting down the bonus, not the point at which it starts counting from, which would mean that the 2 bonus unit switches on the schematic (circled in brown) are in the opposite state of what is shown...is that right? If so, how does the G relay get energized?

If I'm wrong about that and the 2 switches are as shown, then I see a path through the "ball return sw", "15th pos. bonus unit sw." and the DX make-break, assuming the DX is energized too. I'm not an expert at reading schematics (obviously)....am I reading that correctly?

Thanks dave and CD. It's always possible those darned DX switches aren't quite right, I'll check that. And now that I know the G relay is supposed to stay locked on, I have something to search for. Yes Dave, I'll check those switches on the back side of the bonus stepper. I can see that if the bonus stepper 15 position switch isn't closed, you lose the circuit for the G relay.

Unfortunately, I'm 350 miles from the machine and won't get to check any of this until next Tuesday. I'm in Pittsburgh right now and going to a place called "Pinball Perfection" tonight to just have some fun.

Thanks for the help so far - I'll let you know what I find on Tuesday. it's a huge help knowing that the G relay is supposed to lock on - that definitely wasn't happening.

Hey guys,
Thank you so much for pointing me in the right direction. It was indeed the 15th pos bonus unit switch that I guess wasn't making contact so the G relay couldn't lock on. I cleaned and gapped the switches back there, and it works now. Makes perfect sense, but I didn't realize that the G relay was supposed to lock on - though maybe it was supposed to pulse, so I was looking for the wrong problem. I'll mark this one as solved.

Now on to the next problem....