I pulled the az motor control box apart again, checked all cables for firm contact, loosened off the slip clutch nut, reassembled and...
It seems to be working again.
So, admittedly, there may be some intermittent problem there, but I will hold off sending it away for now!
Luke did say many of these type of problems (this happens a lot ??) are caused by faulty cable, often from the Hand Controller.
Thanks to everybody for their input.
The weather will, no doubt, now return to its normal crappy mode.