Are you sure that dip switch #6 on the MPU is set to OFF? If it is set to ON, the ball(s) will remain in the saucer at the end of the game, if set to OFF, the balls should kick out at the end of the game.

Check your solenoid expander board for cracked solder joints and burned out lamp.

This. A tell-tale sign that things are not right is the reset sequence at the start of a ball. It should raise all four drop target banks, then drop the inlines one at a time. Any deviation from this, check that solenoid expander and make sure the lamp is working as it needs it for proper loading of the circuit.

Last page of the schematics give indication to the wire colors. See the diagram below for more details:
First digit indicates primary color, second digit indicates stripe/trace color (0 = none, i.e. solid primary color only)

SDB_Wire_Color.PNG

I'm not sure you interpreted what was said correctly. The solenoid expander board is not the same as the solenoid driver board. The solenoid expander board is a tiny board attached to the underside of the playfield, and it just has a relay and a couple of other components on it. If you bought a solenoid driver board, you spent a lot more than you needed to. The solenoid expander board is available from K's Arcade for around $40, but it's usually the solder connections, as previously stated.