SOmehow, about 5 mins into yesterday's turbo session the cadence sensor's wire managed to wrap itself around the crank. Luckily the wire parted midway and I managed to resplice it by twisting the rlevant bits together. For some reason though the HR was then picking up cadence x 2 and the beeping was driving me nuts
Today, changing cranks, chain, cassette on the runaround, first time doing square taper cranks. All in all very litel drama apart from stripping the first two threads on the LH crank as I'd not retracted the puller enough. Manged to get it past the damaged threads at the second attempt. Most difficult thing was getting the 20-year old locknut off the old cassette. Looking at the freehub, that could do with replacing as well.
All done in about an hour, with the exception of putting the tools away. I was interrupted by shouting from the house, my daughter has managed to break or dislocate her little toe, so she's off to Addenbrookes with the wife while I look after the boy. Unfortunately the minor injuries unit doesn't have x-ray at the weekend.
EDIT: looks like just a dislocation, it was back in place by the time the nurse saw her at Addenbrookes, so just strapped together, no significant swelling either.