I would try just working with the pump with no controller, the pump is not meant for continuous use but for the purpose of testing, for a short time it will be much easier to find the problem with no controller attached and working with just the pump. I would check that collar, the drive unit should spin freely in one direction and not so easily in the other. Basically, they don't ship a pump without a test run so it had to work before it left. The controller gets a check on an oscilliscope but it is possible for something to be missed their but it hasn't happened yet on a 6091. I think that a loose part or something resulting from shipping would be the most likely cause.