It’s a bummer that this batch has issues, but the good news is that a new board from the new batch does seem to be a reliable fix so at least we have a solution.
It’s the stepper motor driver chip which is the chip with a heat-sink closest to where the stepper motor plugs in. I’ve found that it takes quite a while (like two minutes of heat) to get them to work reliably.
Yeah, if I get time i’ll get the second new board out to check that one too, but I think I don’t think i’ve seen someone complain about a replacement board being bad yet, which is a good sign.
Ah, i’m could to get a magnifying glass out and have a look at the mine, see if I can see anything 
They are back to not working… installing the new board today
You can try loosen the bolts holding the motors to the sled a little. Maybe the motor are a little out of alignment and binding up?
Dano
So I saw earlier @bar said that the no response on the z-axis motors had to do with heat. That must be why when I leave it powered up for a few hours that it starts working.
P.S. I do have a new board I just have not installed it yet