Finishing up on an Gottlieb AAB machine. All scoring operates perfectly, however upon startup the game randomly resets to 5 balls, or 4 or 3. Each game it could be one of these ball counts. Would this issue be directly related to the wiper disc on the BCU?

Yes, I disassembled and cleaned the BCU. I see the reset bank sometimes kicks twice while the BCU is resetting back to ball 5. In the attached schematic image, is this the correct path I should check for the pulse being sent to the BCU?

IMG_20180305_0001 copy (resized).jpg

Hello Rolf,
I've checked both paths and the switch contacts appear to be ok. However, looking closer at the BCU wipers, I've noticed significant wear to the tips. The attached video shows the BCU upon reset. When it advances it sometimes has a small electrical arch at the black conductor rivet. When the disc stops at that point, it is at ball 4. When it resumes one step past that, it is on ball 5. This side of the BCU plate is high power, so could the defective wiper tips be causing the failure to properly advance to ball 5 repeatedly?

www.flickr.com/photos/151944058@N08/

Many thanks

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Ya, I'm on the hunt for replacements as we speak.

By high power, I am referring to the white, red, and black conductors shown on the BCU plate. This is where the wiper finger is arching at times as shown in the video. (Black conductor position)

Hello Rolf,
I've checked the path as highlighted in post #11 and don't see anything that looks odd. What I am seeing is, sometimes as the reset relay bank resets one second before the score motor stops, ball 4 will light. When the reset bank resets at the same time as the score motor stopping, ball 5 will light.

So what would cause the reset bank to fire periodically at different times?

Also, the black conductor on the BCU goes to the "ball adjustment" position for 5 balls. The white also goes to the "ball adjustment" for 3 balls. The orange green goes to the "point score" adjustment as well as the "zero position" switch. The red yellow goes back to score motor 3B.

Many thanks,
Ken

Here are 2 quick videos of the test light and score motor revolution. The first shows the score motor turning 360 degrees and stepping the BCU to ball 5.
https://flic.kr/p/25oEbHS

Also, at 1A the correct color is Green Yellow. Schematic may have looked like Orange Yellow.

IMG_20180305_0001 (resized).jpg

2nd video showing the score motor turning 1/3 revolution and stepping to ball 4.

https://flic.kr/p/HjC4y3

I am noticing the score motor randomly turns 1/3, 2/3, and complete revolution when starting a new game.

Rolf,

Thank you for your help. I'll have to dig deeper into this. Occasionally the score motor will continually spin, and the knocker will continually fire. The score reels all do reset properly. I will follow your advice and keep record of where the score motor stops.

Ken

Thanks, that's my feeling right now. I did replace the wipers, but am seeing scorching taking place on the new wiper. I'll remove the plate and replace the rivets.
I'm curious why these were so badly worn. Looks more like it was caused electrically.

Troubleshooting is currently on hold due to sending the BCU contact plate out for replacement rivets. I was told by "Steve", that these Add A Ball games are notorious for burning up the wipers on the last 2 positions, because that circuit is what trips the reset bank.