Extruder_2 Stepper Motor does not work I have a FlashForge Creator Pro. It is equipped with the board revision V SF7.7.

My Right extruder prints great, however, the left does not work at all. I have tried to diagnose the cause, but at this point, I feel all the mechanicals are working and it's coming down to logic boards. I don't know what and how to test these. The main problem is like this:


When I order to Load/Unload Filament the motor does not advance
When printing from the left extruder, filament does not come out.


I have done the following tests:


The hotend works and the nozzle is clear. I can push filament through when it is hot.
Teeth are in great shape, unclogged and perfectly aligned with the "V" on the guide wheel.
The Stepper motor is functional. I can perform the LED test on both pairs of leads and 3V LED lights are up when the motor is turned.
The Stepper cable is OK. I tested continuity on all 4 wires and they are fine.
The Connectors are fine and well-seated.
Voltage to Stepper Driver board: 5.0V when the machine is powered ON


I have however encountered these tests that seemed to show a fail:


When I set the left extruder to "Unload Filament" the voltage across both pairs of leads is 0V


How can I continue troubleshooting and fixing the machine?
The next logical step is to swap the working board with the one that powers the misbehaving motor. If this fixes the motor but makes the other one stop working, it hints that the stepper driver board might be broken. If it does not fix the motor but the right motor works again, while the left is not, then the motors or the board controlling the stepper drivers might be broken.

As changing the driver boards did (as OP said) swap the problem from the left to the right extruder, it is extremely likely that the board that was originally left is defective in some way.

Getting a replacement part might be in order, and until then, running with a single extruder.