Hi Rick,
Thanks a lot for getting back to us so quickly!
-- Yes, this was the first time that we tried to power up the board
-- We tried all different combinations of connections, including various permutations of the hall sensors, phase inputs, and USB cable. At the time of first power up, all motor connections were present. During later attempts, we disconnected and reconnected various combinations of motor connections.
-- At the time of the first attempt, we had the GUI up, though we never touched any of the settings. During subsequent troubleshooting, we disconnected the board from the computer.
Also, it's worth noting that we tried other reasonable/simple things, like different power supplies, monitoring voltage/current with multimeters, loosely monitoring the IC temperature during power up (it gets quite hot, but I suppose it does that during normal operation anyway), etc. We also attempted various grounding schemes. There doesn't appear to be any damage to the board that we can tell.
Thanks again for your time!
Charlie