No, very sensible question!

The circuit I have assembled is precisely as advertised here: http://telescope.marford.me.uk/Proje...controller.htm .

You will see that I am using a 16 pin L293D, where VS is pin 8, and this is what is connected directly to the battery positive. So there should be lots of power available to the L293D.

I think it is unlikely to be a failed L293D either, since the circuit actually contains two PICs driving two seperate L293Ds (with slightly different programming), and both of them display the same problem. This circuit is advertised as a working stepper motor driver, but I am coming to the conclusion that maybe it is not!