You're going a little too far, check the easy stuff first. I'm assuming you have checked to make sure the wires are still soldered well on (and the little wires into the coil are as well). The coils are daisy chained to three circuits, each circuit having a fuse. Given all other coils work, check the daisy chain, as it might be that the last coil that works, has a broken wire from that working coil to the non-working one.

Above that, I had this exact same problem, and it turned out to be something in the connection between the ribbon cable. I had it twice, and both times reseating the ribbon from the cpu to driver, and the long one from the cpu all the way across to the DMD (not sure which one it was exactly) solved it each time. I eventually replaced the ribbon cables, and haven't had an issue since.

Above those first easy things, then measure the coil resistance, and the transistor for that coil. The values for the transistor should be between .4-.6, anything open or shorted indicates an issue, but if it locked on, it should have taken out the fuse, and you would have seen/smelled something.