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I have two stepper motors in parallel on my 3d printer Z axis. The type of motor is Wantal 2,5A 1,8 deg/step and they are both driven by a Polou driver type A4988.

Since I suspected that the Z axis was loosing steps during printing, I swapped the driver around with the X axis where, while printing, it is much easier to see if steps are loosen, simply looking at the result of the printing while progressing.

I detected that the driver on the X axis (ex Z) was the problem because visibly losses steps (the printing was moving away from the original position). Now that I have found out that the problem is the driver I also experienced that the one from X now on Z has been damaged. I think I have a problem on one of the motors on the Z that damage the driver.

How do I check such motors to make sure they are fine without incurring the risk to damage additional drivers?

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Start by checking the stepper coils for shorts. If the motors are of same type, all coils should have pretty much the same resistance. If one coil is shorted (or with very low resistance), for example, then this could possibly fry the driver as well.

Spec sheet says coils should be 1.25Ω, if it is less than that, that could be the problem.

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    \$\begingroup\$ Also check that one coil (black/green) is not shorted to the other coil (blue/red). Also check that neither coil is shorted to the motor casing. All done with an ohm-meter. \$\endgroup\$
    – glen_geek
    Oct 3, 2016 at 14:52

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