Read in Clays WPC repair guide today how he had seen this problem (one coil not firing) fixed by reseating the ribbon cable between CPU board and Power Driver board .

With nothing to lose I gave that a try tonight (reseated both ends) .. powered up and no lights and an error saying Slam Tilt switch stuck on .

Reseated both ends again and now all good, includng the ramp up coil   

Pity I already ordered the parts today , oh well, they'll probably come in handy down the track sometime.