A common issue on Gottlieb "Scan" type bonus collect is the Run out switch on the Bonus unit. This is the leaf switch that rides on the outer edge of the bakelite cam. They sometimes don't stay "Closed" during the entire cycle of the bonus scanning. I have found this sometimes to be the condition of the center bearing that the shaft goes through of the cam. If it can wiggle around a lot, this will cause issues as it moves in a circle. Here is another discussion from a while back:

https://pinside.com/pinball/forum/topic/hot-shot-bonus-reset-issues

For reference. At the top, you will see what silences the Knocker during coin drop (NC on W). The rest is the bonus collect scan step up circuit. "C" is Add bonus unit relay. "Q" is Ball Return control Relay. Second snip is the bonus unit step up circuit. When it detects a DT down, it should pause and score, then step to the next DT.

HS Bonus (resized).JPG

HS Bonus SU (resized).JPG

The flux in normal rosin core solder is enough to do the job. The problem is you need more heat. Either a solder station turned all the way up, or a good old Weller Solder GUN. With enough heat, you can zip through the whole playfield in no time as long as you scratch off the old corrosion first. I just use a triangular needle file to get between the socket and the bracket. For the tip, just drag a flat needle file across it.

Watch the score motor during the process. Watch for blue sparks on contacts. That may lead you to the ones that might need attention.

Some spark no matter what. But often, excessive sparking leads you to a problem.

If the bonus unit is scanning properly, it could also be the switches at each DT if you can find some kind of consistency. Try one entire bank over and over and narrow down from there.

The new black jumper wire looks fine. I think it is the original cotton jumper that looks suspicious us.

If you have some, Solder wick makes a great replacement.

Rolf,

When I said 2 cycles per rotation, what l meant was that the stepper is symmetrical. The 15 steps are duplicated. One bonus collect cycle uses one half the unit. The next collect process uses the other half.

Your purple highlighted circuit is the hold circuit for J. At the start of a score motor cycle, if a DT is detected, the J relay is pulled in. Then, the hold circuit insures the J relay stays in as the stepper is advanced to the next rivet position.

Someone may have adjusted the blades in such a way that the relay would not open completely. Therefore, their fix for their error may have been a heavier spring.

How does that spring compare to other relays?