Mike , what is U20 and how much are they ?

U20 is a ULN2803 Darlington Driver IC and it is situated directly above the plugs on the MPU for the switch looms.

It is also directly in the line of fire for battery corrosion as well as being easily damaged by a minor hickup on the playfield.

Jaycar don't list them I'm afraid but they are available at most electronic wholesalers and the usual pin parts sellers - should only be a few dollars including a socket.