Steve, I am almost certain that it is not possible to replace just the board, it has to be the complete module, and I am almost certain that the handset if factory set and has to be replaced as well, but I will check tomorrow.
That would make life much easier to me if it was a straight swap of the whole unit as I was concerned I would have to fit heat sinks to the components on the edge of the board
Had to replace the board a couple of years ago on my Powrtouch - it was very easy and took less than 10 minutes. Just remember to label each wire before removing from old unit to ensure you rewire correctly. Alun