How to hook up an oscilloscope to a stepper motor driver?

[cvriv]

I have this 3D printer that I assembled and the z-axis refuses to move. I know the steppers are good. I think it's the mainboard. I want to hook up the oscilloscope to see what the z-axis pins on the board are doing, but first want to hook up the oscilloscope to the y-axis pins because the y-axis works fine. I want to know what a working axis looks like first.

They are four wire steppers and I know that red and blue(A and A') is one coil and green and black(B and B') is another coil. I hooked the osc from ground to the red pin. When I try and move the y stepper, I get some activity on the oscilloscope but can't good a good visual of the waveform. If I try to scale it just disappears off screen and can only get it back if I hit the auto button.

I'm doing a lot wrong here. Can someone please advise? Thanks.

Do I hook the osc up to red and blue? I somehow think that's not a good idea. I dont know.

[james_s]

Four wire motors are driven by a pair of H-bridges, look up the datasheet for the driver ICs being used. You can scope any one of the four wires relative to ground and you should see something however stepper motors are inductive and there is also magnetic coupling between the windings so you're likely to see a whole lot of noise and ringing. Better may be to look at the signals going *in* to the drive ICs and check the power rails. If the signals going in look good, the ICs have power, and there is not an open circuit between the IC and the motor and the motor is not running then the IC is likely bad.

[rstofer]

You can set up your scope to do A-B or differential measurements.  Be sure to remove both ground clips so they aren't dangling where they shouldn't be and to prevent an operator induced 'oopsie'.

You will get a trace going both above and below the 0V line as the polarity of the winding changes.