What’s the full spec of the lift? Hinge, sliding rail?
coms link is also needed for these and is supplied via a pick up on the rail, check the charge strip/coms strip and pick ups, if you have one? Try cleaning the copper strip and check the condition of the brushes
if this link is lost at the point where the power swivel needs the signal it won’t work, check for the coms voltage at the top of the rail with the chair loaded
if I was attending site I’d start by checking the motor runs? Then move onto the p/s board by swapping it out with a known working board, then the trigger system for the relative systems, in this case the coms system, the supply to it and finally the main board, start with the cheap options before throwing the big bucks item at it
