[raymo]

Thank you all for your help. I don't know if the mount is still under warranty; I'll have to find out. The freeze up has happened during
each of the last four sessions. I don't think that the power supply
is to blame; there is no interruption to the light in the controller,
and the scope keeps tracking perfectly. It only happens when I am
using the motors manually for guiding or slewing. When it freezes,
it keeps tracking, and the only way you can change anything is to
switch the mount off. It is reminiscent of when a computer freezes
and all you can do is switch off and reboot.
raymo