I was having that common problem of the extruder stepper motor, where this stepper motor was oscillating when the head at a certain XY regime. it was creating prints like thisimage.
Suddenly the motor stopped working, so I had to change the extruder cable, and this did not work. so I changed extruder PCB too, and also this repair did not work. I connected the motor to another stepper motor port and it is working. I tried another motor, and the replacement does not work. other elements in the head ( like the heater, thermocouple, fan) are working fine.
Now I think the problem is in the motherboard. my question is how to troubleshoot the motherboard. and if it is difficult to repair it. where I can find an affordable replacement in the US.