Geoff,
I'm sad to say I'm in the same boat. Seems to be losing the plot multiple times a session, making it very difficult to complete a 3 star alignment. I've tried a battery (17AH starter pack) and 12V3A regulated power supply, so I'm pretty sure it isn't power. MInd you the power plug socket appears very insubstantial - a little wiggle is enough to cause a power reset on my mount.
I thought it might have been cord between the Synscan handset and mount, but can't really reproduce the problem. When it does lock and I power off and reboot, usually get the "Unable to connect with m.c. - stand-alone mode" error.
I got mine through Andrews (who were fantastic actually - hope they're just as good when I phone up about this). Wondering where yours came from?
Rob