There are 2 moments where I know the game will always auto launch and that's if

1) Switch 56 "Ball shooter" is closed while ball is in play.

2) If a trough switch remains closed after feeding the ball shooter, it will feed again and automatically shoot the balls.

When the ball launches, do you hear the casting reel sound effect ? If the trough switches are closed and it kicks the balls you wont hear that sound effect. Also , the plunger will still be "charged" and pressing the cast button will make the reel sound effect , and activate the plunger even without a ball in the lane. Only when pressing cast does it make the sound effect.

You rebuilt this machine, did you change any switches ? Did you verify that the pinout of the switches you changed were the same as the original ones ?

This a crap shoot , but you've swapped all these boards .. Have you tried a different ribbon cable? It has to be something that remained behind during your tests.. The wiring , the switches, the ribbon cable.. I re-wired the 3 trough switches mixing the wires , but the game doesn't seem to care if trough 1 is wired as trough 2 and etc.. it only reacts if a ball is out but a switch remained closed. I had an issue in the past where jet bumpers would close when the others we struck.. turned out the vibrations alone from hitting one bumper was enough to close the leaf switch on other bumpers , causing them to close. I wonder if something similar might happen, where as it kicks out the ball, vibrations make another trough switch close and the game then launches it..

I read the other thread that was posted by creepykenny and tried just that. I disconnected the ball shooter lane switch 56 and it behaves exactly like that. When the ball is fed it is autolaunched. Then it passes long cast switch and the plunger triggers again. At this point I grabbed the ball and placed it back in the shooter lane and nothing happens, obviously , because it doesn't know the ball is there.

Go in switch test , place a ball in the shooter lane and move it a little. You say you issue happens most of the time , so moving the ball around in there might show you a dead spot where the actuator is down , but not closing the switch...

Well, your issue definitely isn't from the boards since you changed them. It has to be the wiring, nothing else.. In my machine the second I unplug 56 , I get the exact behavior you mention, auto launch without the reel sound. I would really check the wiring on 56 and all the switches in column 5 and row 6.

How often does it happen ? Every 1st ball ? Every 2nd ? Is there a moment it doesn't happen?

If I had the machine in hand , I would disconnect that switch , run wires to the outside of the playfield to a switch I manually control and hold it closed as I start a game. If the issue persists, I would focus on all switches in the column / row.

You test the switch with a multimeter or with the switch test from the settings menu ?

I would do the test with the actual wires that are on switch 56 at first , white blue and green black. Or I would tap from the right outlane for white-blue and left sling for green black. The diode should have the gray band on the green black side. I know I keep mentioning switches and their pinout, but there was a case where the issue was exactly that, the pinout of the switch was different than usual and was overlooked for a while. Also , you didn't answer on how often it happens? Does it not happen at times ?

Start a game, the ball auto launches.
Press the cast button, does the plunger kick again, with no ball in the shooter lane?

Then, intercept the ball in play and place it back in the shooter lane, what happens? Does the ball stay there or does it get launched again?

It had to be switch 56, so for anyone with similar issues, even if switch 56 seems good, the auto launching issue comes from that switch alone.

Glad it's fixed and that the real reason (the routing of the new playfield) was identified.

Gone fishin!