Monty Python flying circus free play how to switch off / coin mech not working

[Grandzizi]

I have just bought a Monty Python flying circus machine. However, it's in free play mode and the coin mech rejects 90% of all coins. I'd like to switch off free play and need some ideas on the coin mech. It seems to be the coin checker that is rejecting pretty much everything. Every now and again it will accept a coin. I've checked the dip switches for the free play but with no joy. It seems there are no bank 1 switches there are only serial ports.. Is this a hard coded option only changeable by programming? Will I need to replace the entire coin mech?