Switched on guiding and went for 4 min shots - 100% failed with DEC runaways, grr. Looks like the mount is going back to the shop -again....[/quote]
I have reread this a couple of times, I am wondering, are you hot plugging the autoguider cable? that could cause a runaway, do you need to put the controller into, for example, photo mode or similar? are there additional steps that need to happen when autoguiding?
These are only guesses, I am trying to troubleshoot as I would with the Gemini system.
I also did some Googling on the Sphinx mount, the specs say the mount has Servo motors, I asume that you have Firmware version 1.2 build 24 or above, I note that it introduced backlash compensation and autoguider port control. There is also a Yahoo Group
http://groups.yahoo.com/group/Vixen_Sphinx that you might want to post the question to.
I don't know if I can much more than that.
JohnG