Galvanometer motor SC17 15K

Hi, I am now experimenting projected laser by using galvanometer motor (SC17 15K). This galvo is connected to Arduino Uno and 2 DAC shields in order to get analog output for both mirrors (x and y). When I try to connect each shield separatedly, all can work well. As I stacked the shield, one of the mirrors cannot turn. Is there anything I should check regarding to this case?