Could be an issue - but have you tested your voltages? May need to recap it (if caps are circa 1980 it def could use it). and while you are in there add the fuses between the transformer and the bridge rectifiers in the backbox if this work is not already done.

Game won’t start if it doesn’t register 3 balls in the game - so have a look at your ball trough switches. The 40 pin interconnect is also notorious for issues on system 6’s. You can separate and reconnect. If it improves you know you should replace that connector (reseating is not a permanent fix).

Displays you can swap around to see if its a connector or display issue as well.

Also is it going into audit mode (a numeric code in player 1 display)?

Appears to boot. Not to discount a power supply issue - but you have good displays other than 3 and 4. Not sure its related to a game not starting. Need to make sure game knows 3 balls are in it.

My money's on the 40 pin.

Oops double post.

Doubtful on the power supply. With the machine turned off, swap player 1 & 2 with player 3 & 4. Then turn on, see what shows up. I'm thinking bad connectors. If the displays went bad, then you will know because they are now in player 1 & 2.

It appears like the '100s' digit is locked on in player 3 which appears to me to be a display driver board or mpu board issue

Have you separated the 2 boards and reconnected?