Update.
If I open the normally closed A player relay switch connected to the one point card units (with a piece of paper) then game doesn't bust on 20 but does bust on 30 . So.. this obviously tells me the 10 unit card reels are both OK (as their outputs are connected together) , and yet checking the one point card units they do not have an earth at '2' (or higher) outputs when either reel is on 0 (and all switches on each reel are open at 0 as they should be)