If the system has "step" and "direction" input, it is more than likely a stepper, not a servo.
Servo's are merely motors that have an encoder to provide position feedback. In an oversimplifed fashion, If you apply the appropriate power to the terminals, it will run until power is removed. YOu'd have to switch the terminals on a DC motor to change direction - not familair enought with AC to splain how to do direction reversal on one of these.
A stepper is sort of like a "electronic ratchet". Each time to energize a coil, the motor cogs over so many degrees (ala the ratchet concept) as established by the internal design. IF you energize the coils fast enough and in the proper sequence, actual commutation occurs and the armature turns like a motor. Otherwise it will merely tick over a step at a time.
Technically, a simple pushbutton swith can provide the step signals to a stepper control board (needed to provide commutation). A knife or toggle switch could provide the direction input. This would be about as "dumb" as you could get.
YOur photo shows controller cards (not servos) that appear to be PC driven. Unless you're electronically adept, it is not very likely one could make them function in a dumb fashion.