Hi Matt,

I didn't look up the pin numbers but assumed you are talking about the two which drive the stepper motor. They are the open collector (sink to ground) outputs, so if you have hash on the high side of both phases of the waveform that would be consistent with a poor connection (open circuit) in the path from the power supply to the motor's common pin, where the windings are joined.

A poor solder or broken (stressed) motor winding wire would do that, as would a crack in the foil. Move your scope probe to this terminal and toward battery source to find where the voltage drop is occurring. Having the magnetic load of the rotor would have but a subtle effect on the waveform at the driver terminals.


--
Art Benstein near Baltimore

Without geometry, life is pointless.