The collect bonus sequence is kicked off by the Ball Return switch (slate-black wire to black-yellow wire) in the outhole. Maybe that's gapped too close?

/Mark

Hi Petermunro
You say "Ball-Return-Switch (Outhole-Switch) is wide open" - I suspect "my encircled orange with questionsmarks" switch is adjusted tight - just a bit of vibration and the switch faulty closes (?).
The schematics tells us "G-Relay has 4 (Type) A switches - means 4 Normally-Open-Switches --- the relay has no "Type B is Normally-Closed-Switch" - has no "Type C is threebladed Make-and-Brake-Switch". Find in Your pin this switch (questionmarks) and inspect it - gapped tight ? doghair crap of wire ? (on the solder-lug-side).

If "No luck": I suggest You make You an SteveFury-Test-Light made of two 12Volt-Car-Bulbs put one behind the other - see here: https://pinside.com/pinball/forum/topic/reading-gottlieb-schematics#post-2634425 --- then hook the Test-Light up as shown in the JPG here - have long wires on the Test-Light so You can take it through the open coin-door out into the open - lay the Test-Light on the apron (put a sheet of paper first on the apron (for guaranteed insulation)). Then play many games - question: When the fault starts to happen - DOES the Test-Light light up - telling us "The G-Relay has pulled-in" ? Greetings Rolf

0Solar-City-Work-02 (resized).jpg

Hi Petermunro
a small chance is: The fault happens but the G-Relay is not pulling-in. I want to learn: Does the G-Relay pulls when the fault happens ?
If "Yes": We have an detailled look on "what can make the G-Relay to pull-in (?)".
If "No": We must look other places.
It is getting late here in Switzerland (south of Germany) - I must go to sleep - this (really) is my last post for today. Greetings Rolf

Can you elaborate? How did you rule that out?

The Bonus Score Control/G relay has two normally open switches in its circuit:
Solar City Bonus Score Control relay (resized).jpg
Closing either one of the switches in the red boxes can cause the Bonus Score Control/G relay to fire and the bonus to be added. Ordinarily the Ball Return switch fires the Bonus Score Control/G relay through the upper red path. Once it fires the G relay adds a lock in circuit to hold itself on through the lower red path by closing the normally open G switch.

Chances are that one of those two switches is closing while the ball is in play, due to mechanical vibrations, and firing the G relay. The Ball Return switch is mounted on the playfield and is subjected to some of the vibrations of the flippers, pop bumpers, resetting targets, etc. The G relay switch may be subject to the same playfield vibrations if the G relay is mounted on the playfield. If it's mounted to the bottom of the cabinet it's less likely to be getting excess vibrations.

Try starting a game, launching a ball, adding some bonus points and then removing the ball before it drains. The game will think you're still playing. Then gently thump the playfield with your fist in various places to see if you can get the bonus to collect. That would prove the mechanical vibration theory.

Then you could try slipping a piece of folded paper between the contacts of the two switches in the red boxes (one at a time) to see if that makes the problem go away. That might tell you which switch is the culprit. Also carefully check that there aren't solder tabs, loose wires or other conductors near those two switches that might be shorting even if the contacts aren't touching.

/Mark