ramps 1.4 one motor on Z axis not working correctly (1 reply)

I have a Ramps 1.4 and one of the motors on the Z axis only turns a little when compaired to the other. And neither one of the movements on either motor is smooth. I switch the wires from one motor to the other, and their place on the ramps board and also switched to a known working driver. I also tried moving the little pyrometer on the driver clockwise and counterclockwise, Still the same result. I was testing them with the LCD with the lowest mm/s , and not with Printrun like I plan on doing tonight. Any help is appriciated...
thanks