I can vary the voltage because I am using a MAAS lab bench power supply that changes mains into DC 3-18V variable which then supplies the M2. Does your tester tell you the ramp time for the various voltages or does it just tell you the correct voltage is on the correct pin? I have a fluke that is more than capable of telling me the voltage on any of the pins to .01v not just light up an LED. I belive to test the supply any further would need a scope with multiple traces that would let me know what was going live and when. I tested the board with different ATX power supplies to see if I could replicate the problem with different brands. These ranged from a cheap £25 with a case to an expensive £150 Server hot swap power supply. The reason I could do this is because I am an HP/Compaq A+ hardware engineer so I have free access to all the bits.