I've been searching a solution to this issue, found very old threads but no one seams to have solved the mistery.

Since I'm not the only one with this problem, I will try to solve it with you help

The problem:

. Ball release coil acts strange, it should stay open for about 1sec to allow the ball go into shooter lane, but what it does is going on and off very quick for 2 or 3 times, clak!clak!clak!, so the ball had no time to go into shooter lane.

. Game registers random switches activated, that causes the game to think you already shoot the ball into game, scoring, activating game modes....

What I already did:
...........................

. Check for bad switches.
. Check for broken wires.
. Resolder optos and opto-boards
. Hit the playfield many times to see if some switch is registering because vibration (no one does)
. Replaced CPU and Driver board with two working ones from my other Gottlieb pinball.
. Verified and adjusted +5V for the CPU
. Cleaned and adjusted the ball trough switches
. Reatached all the ground connectors inside cabinet (no ground mod yet)

What I've found:
.......................

If I disconnect the cueball motor, the game works flauless 100% of the time, we already played the game for 2 hours with 0 problems.

When motor is running is goes smooth, no grinding noises, it moves correctly side to side.

Since the motor is what starts all the problems, I'm trying to understand what causes the CPU to go crazy, I've been checking the CPU +5V when the motor is running and never goes less than +5V, its stable at +5.07V.

I'm starting to think that the motor is causing problems with the PS, maybe its sending noise, asking too much to the transformer....

Since coils and motor are both getting juice from the 50VAC part of the transformer, maybe the motor is asking too much current, and the release coil cannot get enough power to move completely, causing the coil to stutter (similar to weak flippers problem), thats one problem, but it does not explain the random switches activated :/

Clues:
........

. Motor runs at 50VAC directly from the transfo, same connector used by the 48V bridge (coils)
. Both Motor and ball release coil are controlled by U4 at Driver Board.

Any ideas about where to start to check the motor issue?