Update - The machine is working to a point. I'll add a tutorial on how to rebuild a "match unit". It plays like a dream but has one small problem - It plays a 5 ball game across all four players. Here's what I mean ;

Press  the credit button for a 1 player game - resets perfectly, and serves BALL 1.
Plays ball 1. Ball drains.
Advances to Ball 2, but the player unit advances 5 times and now the game scores on player 2 !
Plays ball 2. Ball drains.
Advances to Ball 3, but the player unit advances 5 times and now the game scores on player 3 !
Plays ball 3. Ball drains.
Advances to Ball 4, but the player unit advances 5 times and now the game scores on player 4 !
Plays ball 4. Ball drains.
Advances to Ball 5, but the player unit advances 5 times and now the game scores on player 1 !
Plays ball 5. Ball drains.
Game Over

The machine does exactly the same on a 2 or 3 player game. It is acting as if every game is a "four player game". The game plays exactly as it should if you play a 4 player game.

I think the issue is either the coin unit or AX. I will retest tonight