OK, I had a brainwave (or delayed thought..) through the night - the fact that player 1's display only showed 0 instead of 000000 was an issue, i assumed (correctly it seems!) that scores were at least in multiples of 10 - therefore the 0 showing wouldn't work.  Swapping displays, i found that the error must be on the main display board, since changing a 'good' display (000000) with player 1 also caused it to show 0.

I then looked through the manual and worked out how to play multiplayer (i said i was only new to this) and with great joy discovered that players 2,3 and 4 all score perfectly!!!

So, now i shall try and isolate the problem of the missing 5 digits for player one on the main display board....

Thanks for the help again