I write root cause because more than one existed yet solving them made no permanent correction.

My Z axis from time to time would not raise, hence, scratched surfaces and broken end mills followed by vulgar words would come to pass.  First cause was faulty wiring.  I replace the shipped cable with opens in the wire with my own.  Worked for a while.  Second cause was the screws becoming loose for the motor shaft coupler.  Tighten it down and the CNC3040 Z axis worked again for a while.  All the prior bagging of the axis from the first cause eventually loosed/stripped the screws.

Finally, the darn machine Z just went kaput, no power at all.  Cracked the controller case open and seen the YOOCNC board for Z axis did not power its LEDs.  Removed card and look at each component.  Voila!!  The LM317 regulator surface mount package, now get this, not a cold solder joint, there was NO SOLDER AT ALL for one of the legs.  I nearly flipped.  So much rework time and router bits biting the dust just because lack of solder.

The thing ran for a year before I found this out.  Added the solder and now works flawlessly in the realm of CNC3040.  Operational for 1 year by means of close proximity of one piece of metal to another  

Is there a specific place on the forum to add to CNC3040 trouble shooting?