You have checked the motor is wired correctly?

Disconnect the motor wiring at the EM806, and using a multimeter, check for continuity between the wires you have connected to A+ & A-, B+ & B- (both readings should be very similar), then check there is no continuity between any of the A & B terminals, and also between A & Gnd, and B & Gnd.

If both A & B coil resistances are not similar, test again directly at the motor wiring.
Or if you have continuity where you should not have continuity, then you need to work out where the short is, at which point I would start by disconnecting the motor wires one at a time and checking continuity each time. Ideally keep the multimeter connected, in case you disturb the short while disconnecting something else, so you'll know what you last moved when the short cleared.