Stage Stall Problem

The ? axis has stalled. The stage may have been obstructed.

The ? axis has failed and has shut down. There may be a mechanical/electrical problem with the stage.

This article should only be applied to Pre 2020 Machines

The LED Status of Encoder read head (Applies to the Renishaw encoder system on Excel XYZ stages and Vertex Z stage only):

Green throughout the travel when crossing the reference mark towards the negative direction it will blink red and when crossing the reference mark towards the positive direction it will blink off (no color).
RED color throughout travel means it is not counting and the read head needs to be realigned.
ORANGE color throughout travel means the encoder counts are weak and the read head needs to be realigned.

Procedures

Power the machine on. E-Stop is not pressed:

If the Z stage is not holding its position (the Z stage will fall), meaning the Z motor has no power. This cause may be from the amp board to the Z motor, including every cable in the middle that connects them.
If the Z stage holds its position barely meaning a small force will push it out of holding, then you may need a new motor.
If the Z stage holds its position very strongly meaning there is too much resistance force for the Z motor to push through. There might be other issues such as lead screws losing their coating so that at some spots it is very tough to move. Usually, that happens on the top of the travel where it binds the most.

Swap the Z breakout board with a new one to see if it reads or swap it with the X/Y breakout board from the same machine to see if the problem follows the breakout board if you do not have a spare part.
If no readings from the above step, then swap the Z encoder cable between the Z breakout board and the Logic board with a new cable to see if it reads or if you do not have a spare cable, grab the cable from either X/Y stage for testing.
If still no readings, then the problem is either the logic board or the encoder itself, replace them one by one to see if the linear, rotary, and index reads.

All four components in the encoder line ( encoder, breakout board, encoder cable, and logic board) need to be checked once a time with a spare/new part because the Z components on a Vertex are different than X/Y.

Move the Z stage up and down around the index mark, the index mark should not move at all. If it moves, adjust the index mark first so that when moving from positive direction to negative direction the LED on the encoder flashes red.
If not repeating, swap the Z breakout board with a new one, test again in Alpha Tune.
If the problem still exists, replace the encoder.

Perform the Alpha Tune Test
Find the encoder resolution from Micro-Vu product specifications. (E.g. scale resolution 0.1um for Excel 501UC).
For the linear encoder, encoder counts between both ends of rulers times the encoder resolution should be equal to the distance measured by the ruler.
For the rotary encoder, the total rotary encoder count divided by the count/revolution (from Alpha define), times the leads(also from Alpha define) should be equal to the distance measured by the ruler and linear encoder reading too.