I had an issue where the 28BYJ-48 with ULN2003 (as pictured here: Controlling a stepper motor using Stepper library - Photon crashes with 'usage fault') only turned in one direction. I found this topic on the Arduino forum that suggested swapping the middle two pins which got it working perfectly (on 4.8v USB power off VIN of the Photon).
http://forum.arduino.cc/index.php?topic=143276.0
Just in case someone else stumbles across a similar problem!