Stannah 400?

My mum's Stannah 400 keeps blowing circuit board fuses.
Replace it and it'll work fine for a random amount of time
The batteries are good and being charged. There are no chafed or broken wires anywhere, carriage, seat or the supply cable.
We've changed the PCB and it still exhibits the problem.
It only blows the fuse on decelerate at the bottom of the track.
I can see no cause for this. Help! Suggestions please