by Cre8ivdsgn » Tue Oct 16, 2012 12:19 pm
Try looking to see if one of the connections are not made. Or perhaps the output of the driver is not working on one of the phases. We (royal "we")see exactly this kind of thing when a wire harness is worn out and one of the four conductors going to the stepper motor fatigues and breaks.
Its possible the motor might be mis-wired. Drivers can be labelled for connections A, B, C, D or A, A-bar, B, B-bar (I don't know how to "over" line versus underline but the symbology is A, NOT A, B, NOT B). So the two phases (typically) are A,B and C,D (or of course A, A-bar and B,B-bar). If you use a meter, each complete phase will be the max reasistance (below 20 ohms or so) you find across a pair of wires. I spell it out this way because you can have six and eight wire motors as well (well, with the eight wire motors you will end up with four pairs and then you need to figure out if you want torque or speed optimized motor performance to determine the wiring order). With four-wire motors there are no choices to make and this method works.
For eight wire motors, you really need to find the exact wire color codes given by the manufacturer of the motor for best results. (Oriental drove me nuts for a while when I tried to use "common sense" to figure out the pairings, but a color change from what I expected had me chasing my tail.)
If the motor is running the wrong direction, simply swap the wires on ONE of the phases. And document it!!!
Disclaimer - its been many years since I gave this much thought. Someone can improve on this I'm sure.