The stepper motor (part #9400) isn't making a full step forward and then goes back on the next beat. The symptoms look rather like you get when the battery gets low but I have this on a test rig and powered by a power supply so it's not that. I have seen other discussions on this same topic elsewhere but none come to any conclusion as to why it would start to behave this way. Have any of you got any ideas or even better, solved this? Secondly, has anyone tried to take one of these things apart? It doesn't look serviceable but as they are as rare as hen's teeth in the marketplace I may as well have a look. Thanks in anticipation.