Stepper motors. Wrong direction. Please help!!!

Hello everyone,

I assembled my reprap from parts that i bought 5 months ago. It worked well in the first 4 month. My reprap's Z axis is actuated by 2 stepper motor LDO-42STH47-1684A as shown in attached file.

The problem is now the right one sometime rotates in the opposite direction with the left one or not rotate at all. Especially, when i were trying to do the Z offset. I tried to re-wire the motor, actually, i re-wired all the electronics parts but the result is still the same. Is it because of the motor or the wiring or the coding in Arduino processor? I have tried to fix this problem for nearly a month.

Please help me. I am so depressed right now.

Since both motors are normally wired in parallel and thus always move the same. I would guess you have a broken wire on the right one. (or the plug is falling out, or dry solder joint on the plug)

@Dust: Thank you so much. You are a lifesaver.

I triple checked the wires and it fell out as your suggestion. Thank you.