Extruder won't turn, even when connected to different stepper

I have a Taz6, and recently my extruder stopped working. I know that it won’t turn when not hot, so all the testing I’ve been doing has been with a heated hot end (about 150degrees).

I was able to attach the extruder stepper connector to the Y stepper, and that stepper wouldn’t work. Then, I was able to attach the Y stepper connector to the extruder stepper, and then that stepper turned. To me, that means that the stepper itself is fine, and somewhere in the wiring harness, one or more of the wires that go to the extruder connector have a fault.

I’m not sure what my next troubleshooting step is. Should I be checking voltages on the main board? What should those voltages be? Thanks!

Could be the harness, but it could also be a blown stepper driver on the circuit board. I would make sure everything is connected back as normal, then open the electronics box and swap the Y harness and the extruder harness. Then try driving the extruder motor by moving the Y axis. If that works, it would indicate that the harness to the extruder motor is good and it’s the stepper driver that is bad. Could also plug the Y harness into the extruder connector on the board and if you can’t move the Y motor by calling for extruder movement that would be a second indication that the extruder stepper driver chip is bad.

If you swap the extruder harness to the Y connector at the board and it still doesn’t work that would indicate that the problem is in the harness somewhere, since you know the extruder motor is good and you know that the Y stepper driver is good.

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Swapping the two 4-pin connectors on the RAMBo let the extruder stepper turn (while using the controls to move the “Y axis”), and the Y harness wouldn’t (while using the controls to turn the “extruder”) So, nothing is wrong with the wiring harness - it sounds like a busted stepper driver, like you suggested.

It looks like the fix is to just replace the entire RAMBo, at this point?

Yeah, sounds like you need a new Rambo board.