can mach3 burnout transistors on a CNC control board?

[Robin Hewitt]

I may be teaching Granny how to suck eggs here, but that's never stopped me before

Catastrophic transistor failure in CNC is usually down to an inductive load.

eg: An NPN transistor sinks a coil to ground and current starts to flow. The transistor switches off but the current doesn't want to stop flowing.

Ohms Law V=I*R

You have current from the inductance. The resistance from the switched off transistor is enormous so the Volts become even more enormous. The breakdown voltage of the transistor is exceeded. Pop.

The solution is a diode across the inductive load so the unwanted current goes through the diode back to the top of the coil. Round and round the coil it goes until resistance takes care of it.

If transistors start going pop check the diodes across your inductive loads.

Slightly trickier to wire if you are driving the coil in both directions but there will be a circuit diagram showing where to put the diodes somewhere.