Somewhere Tormach has a stern warning about blowing drivers, is a stepper is misconnected, but iss a little vague about the specific conditions. I had done all the normal checks,
( phase lead ohms with compensation for meter lead resistance all ok in the .5 ohm area , phase to ground , DC supply voltage .......was 70 DC

Im thinking there was substantial AC superimposed on the DC, picking it up when using the AC scale, what would be normal limit ? Was it 25VAC will check today.

The replacement drivers TMac is suppling for series one blowouts are NOT series three , however the case looks somewhat like series three, in that input power
terminals have no plus or minus but are marked AC

Kirks explanation of the bridge rectifyer explains how this works.

In TMac file TD10173 Driver Replacement instructions for part # PN32793 it explains procedure for reversing rotation,

" Switch A+ with B+ and A- with B- "

I am fairly sure I reversed rotation by just reversng one set of wires only , A+ with A- ( or was it B+ and B- ? ) and it seemed to work could that be a problem?

Would like to know how to check what is + and - on a phase.

Thanks Dave