Check the rollover in the trough. I had a similar problem that happened 50% of the time until I figured it was the rollover wire that wasnt sitting straight in the slot. It would spring back up and the end of the wire would sit on top of the playfield and BLOCK the ball from pushing it down. Therefore the ball would constantly be bouncing back. If this your problem a slight bending of the wire will get it back in place correctly. I hope my crude drawings help show what I’m talking about. PF means playfield on the side view drawings. The last pic shows the wire actually sitting on the playfield when I discovered my problem. It should be adjusted left to stay in the slot to it’s left.

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