Put your multimeter on AC voltage, then insert the meter leads in the J6 socket of the rectifier board where the two blue wires are. It doesn't matter which way around you put the meter leads.
The voltage you read across those blue wires should be around 14.2VAC - this is the transformer voltage that delivers the 12 volts for the system.
If you measure close to this voltage, then there is a problem at the BR1 bridge rectifier on the rectifier board.

Pull the F3 fuse off the rectifier board and remeasure that transformer output. That bridge rectifier might have an internal short which could be pulling the transformer voltage down. Those transformers are generally tanks.

By the way, are you running the game from 120VAC wall power while the transformer is wired for 220VAC input?

I would disconnect the transformer from the rectifier board (isolate everything off the transformer) and measure all the transformer output winding voltages. Then you'll have a better idea.