Opto's if none is found when you fire the circuit up it maybe because they require some voltage
Cheers, I did check the outputs when the onboard processor was controlling the motors and could see the logic highs and lows on the step and dir. pins, but when I tryed to inject a signal in to it my self nothing happened. I was just wondering if anyone knew if the enable pin can completely switch off the chip? as the board is double sided and very crowded it is difficult to see what is going on. (and after the last one went bang , I'm not keen to randomly test points) I was hoping that the enable switch is also controlled by the processor, which would explain why the motors wont work when I try to control them.

They go bang because of excessive current not voltage...usually if upper and lower devices in the bridge are 'on' simultaneously... 40v across .5 ohms = 80A peak, 3200W instantaneously.... your PSU will do that for a few 100uS no problem!
Looks like I must have shorted something whist I was trying to get it to work. Is this driver set up usually Ok?

P.S if you are throwing them away KIP, my bin has plenty of space