Right... Exciting update!
Firstly, the sound does work in the cab, if I wait a few seconds and then press the manual reset button on the sound board (works fine on the test bench so must be an issue with the reset kicking in before the power has stabilised) I am going to experiment with delaying the reset pulse on the sound board.
Secondly, the display does in fact work, the fault lies with the CPU board (must be the display RIOT as everything else has been replaced and tested) Massive thanks to @myPinballs for lending me a working CPU board, and thanks to everyone else who offered to help
BTW It is really good fun to play!
Firstly, the sound does work in the cab, if I wait a few seconds and then press the manual reset button on the sound board (works fine on the test bench so must be an issue with the reset kicking in before the power has stabilised) I am going to experiment with delaying the reset pulse on the sound board.
Secondly, the display does in fact work, the fault lies with the CPU board (must be the display RIOT as everything else has been replaced and tested) Massive thanks to @myPinballs for lending me a working CPU board, and thanks to everyone else who offered to help

BTW It is really good fun to play!