Thanks for your help everyone, turned out to be an ASIC chip contact problem. I sorted it by spraying contact cleaner into the ASIC socket (board out of the pin) and then lifting the chip by about 1mm from two corners using a pointed o-ring removal tool, then gently pushing the chip back into place. Repeated a few times and then dried the chip with warm air. Once the board was back in place everything worked again.
Surprising how many issues are cured just by reseating the ASIC.
