Thanks Robin, not sure i understand, so is the buzzing/ frying noise when holding ok then? or Have I got problems?

I have basicly had to rewire the driver chip and followed the data sheet and other similar designs but I not sure about the control pin. It sets the chopper for either the 4 phases or on the inhibit wires, could this be causing the noise?

If the noise is ok (typical) then I can increase the vref to gain more current which seems to help with the missing steps at the higher speeds. At the moment its set at 0.5v which i think means I've only got 1amp going to the motor. As it uses 2 L602 output chips I belive it is capable of 4amp but I'm too chicken to just crank it up.

Thanks in advance