I can see the damage on your picture of the motor drive speed controller, this is "usually" cause of a dead unit.
It's a minor part but i usually also replace the switching ic and FSD ic at the same time.
Boards are difficult to source, especially working ones which are rare i believe, i suspect Stu if he had one spare wouldn't let it go as he uses them for his own customers units ?
I do get one in ten approx, which may have gone to far - they explode and are not possible to repair ecenomically.
Another note, is one of the Ic's is now manufacturer obsolete - so when stocks are depleted that's it... i have suffered with fake ic's in the past so only use a known established uk supplier.