Neil, I'd be interested in your troubleshooting help.
When I blew my board, it took out 2 IGBT's which were dead shorts and would blow the fuse every time the board was powered. I replaced both of them, and looked over the board to see if there were any obvious burned traces or components. The board no longer blows fuses, and when power is turned on I get one beep from the front panel, and the tach display shows 0000. This leads me to believe the ATMEGA is OK and communicating with the front panel, as I understand the beep would continue if the program in the ATMEGA wasn't running.
However, if I try to start the motor using the Start button, nothing happens; and after about 5 seconds the display shows "Err". Hitting Stop clears the "Err", but hitting Start again just repeats the process. So I am assuming that the ATMEGA is trying to start the motor, but is seeing no change from the Hall Effects and is timing out.
My first thought was the IR2103 drivers, but I have replaced all 3 and there is no change. About the only other thing in the path from the ATMEGA to the driver circuitry are the 6N137 optos, I have replacements, but they are not socketed so it will be a bit of a hassle to change. Any ideas?