This may not actually be a 'Mach' problem, more, a computer problem.  On occasion, when I fire up my computer to tinker with my Taig mill I will have no Z axis control... it's just dead.  The Mach DRO shows movement but I don't think the signal is getting to the machine power supply.  Sometimes, rebooting will bring it back, sometimes it takes several reboots.  Last night I gave up after a half dozen reboots.  The diagnostics appear to check out as does the printer port.  I've even tried wiggling the cable to see if I can get it to respond to no avail.

Any thoughts?

Cheers,

Do you have an enable signal for the Z drive from Mach? If you do then a voltmeter would soon tell you if its being applied, same with the Step and Dir signals, you could check to see they are coming out of the port.
Hood

Good idea.  I do have an enable signal from Mach.  I may just have a 'gamy' cable or port.

Thanks!