Super Chexx uses and solenoid to eject the puck in the game. In the Pro version of the game to solenoid is controlled by 12vdc from the main board at connector P3 between pins 12 and 24.
Using a multi Meter you will see spike in voltage when the board is trying to eject the puck. if you don't have a multi meter to test the eject solenoid you can use a 9 volt battery and some paperclips. See the file below to find out how.