Well, what does a voltage meter say? You can actually measure those pins as soon as 5V is applied. Comparing to the other ones is a good idea.
And ... there's always a chance you Pololu is simply at fault. If all the others work on this axis but not the suspect one, replacing it might be advised. The electronic circuitry for each of the axes is identical, so you can swap stuff as much as you want.
And ... there's always a chance you Pololu is simply at fault. If all the others work on this axis but not the suspect one, replacing it might be advised. The electronic circuitry for each of the axes is identical, so you can swap stuff as much as you want.