After some frustration my 3D printer is back up and running again. I thought this deserved it's own post rather than simply updating the previous one.
In the end the problem turned out to be the 'quick connect' fitting on the end of the control cables to the extruder stepper motor. These connectors are designed to squeeze on to the end of an electrical cable and have a cutting edge that cuts through the plastic coating on the wire to make a contact with the metal underneath. Apparently mine had vibrated loose so one of the coils on the stepper motor was not getting driven - thus resulting in it not turning correctly.
NOTE I have to point out that the technical support from Solidoodle was excellent. I was a little concerned about how long it took me to get the first response but I hadn't realised it was Thanksgiving in the US so to get support over the holiday weekend at all was very much appreciated. The support people I spoke to were very helpful and walked through the troubleshooting steps to get me back up and running again.
As I mentioned at the end of the last post I don't think 3D printing is quite up to consumer 'plug and play' standards just yet although it is getting closer and closer all the time. If you do intend to buy a 3D printer it helps to have a basic understanding of the components in the printer, know your way around a multimeter and be prepared to pull things apart to fix them (or at least have a friend who can do these things and is willing to help you).
This process has also been a good experience in teaching (or more to the point, reminding) me to be more patient when doing any sort of fault testing. When you are in a hurry, impatient or frustrated by a problem it is very easy to overlook the basics. In this case I automatically assumed the problem must have been in the more complex parts and forgot to check the basics (in other words, I didn't test my underlying assumptions). I was ready to order a complete replacement print head when the problem was actually a 5c connector (that didn't even need to be replaced). I am kicking myself that I didn't test the cables as my very first step before being reminded by the helpful support person - it would have saved me a lot of time and effort. On the upside, I now know a lot more about the internal workings of the printer than I did before which will come in useful in the future.
I still strongly recommend the Solidoodle printer as a budget friendly 3D printer if you don't want to go the DIY route. With the recent work on a high resolution profile for the printer it becomes an even more attractive solution.
Now that I've got the basics going (a Raspberry Pi case is printing out next to me as I type this) I can start experimenting with designs in OpenSCAD to test the limitations of what I really wanted the printer for - mechanical components for robotics. Expect to hear more in the near future!