grbl 1.1 dual axis

I'm trying to get dual y axis working with a Protoneer Rpi CNC shield v2.60. No matter what I try I am unable to get the second y motor to move.

The developer says this board uses the same pinout as the v3.51 board.

I did notice that the dir and step pins are reversed in cpu_map.h but switching them made no difference. I traced the paths on the board and confirmed the A-axis is indeed on A3/A4.

#define ENABLE_DUAL_AXIS
#define DUAL_AXIS_SELECT Y_AXIS
#define DUAL_AXIS_CONFIG_PROTONEER_V3_51

Any ideas?

Thanks,
Duane