Thanks KiwiJochen.

I've had another more detailed look at the Service Menu and it looks like I've no signal.
It tells me that 8 Satellites were found, but the S/N on all of them is 00.0. PRN (whatever that is) varies between 2 and 31, but S/N is zero across the board.The Almanac and Gyro settings were as you said they should be.

Can anyone give me any pointers on how to change the antenna or any idea what it's likely to cost?

Finally, the OS is 4-1/00. Is this the latest version? I've seen reference on the forum to 4-1/100, but not 00.

Thanks for the help. Much appreciated.