I had this problem on a old Bally Playboy, If I remember correctly the ball will kick out at start up. what is happening is when you end bal 1 its not seeing that has happened so check the Outhole switch but in my case it was the female connector at the MPU. I to had installed a new MPU on those old Bally's you really have to check that the connectors are good. when the ball drains wiggle the wires a little bit on the MPU I think its the J@ connector for the outhole check your schmatics to double check.

J2

should have said J2

Was it the connector on the MPU?

there is a small fuse on the power driver board check it for your displays if you changed this board it may be a larger fuse, ether way if its bad no displays. Is the game booting up? Remove the back glass and watch the flashes on the MPU if you are not getting 7 the game is not booting up so no displays no start. If that's the case and the fuses are good check your voltages. Did you rebuild/replace the power supply board?