Mach3 fails to send signals to axes

[Doddy]

I'm only dipping my toe in this, I've no experience of the ESS (but assume it's an "Ethernet Smooth Stepper"?). Probably a longer long shot than Robs.

I've been able to reproduce the issue consistently.

Good - if you can reproduce, you can diagnose.

I recorded the operation starting at the beginning of the code recording the sequence of moves and each time the Z failed to move. Then I re-ran the code and found that the Z failed to move at the same instructions during the second run. I was also able to identify that the failure is not a dependency of the previous XY location prior to the failure.

I'm guessing you've examine the GCode, and with experience of previous failure you're confident that it's not the GCode itself that's at fault?, if so we don't need to know too much of what's going wrong. Although... clutching at straws here (and this is just cause/effect analysis) - worth checking the integrity of the wiring from the ESS outputs to the drivers (though process: a short on e.g. Y-DIR to Z-PULSE could mean that you lose Z only if the last direction that the Y axis travelled was in one direction - in the other direction Z would be unaffected). Long shot, but explains the observation.

This tells me that it is an issue with either MACH3 or with the communications to the control box.

Possibly - I'd be checking CPU utilisation on the host machine just to take it off the table. Mach3 and its trajectory planner are, irregardless of anything else, well proven.

At one point I received an ESS buffering error which leads me to believe that there is an issue with the ESS driver that communicates with the control box or the ESS board itself.

Possibly - hence the above utilisation check. Here's a question. And this is from my inexperience with ESS. Do you have a dedicated ethernet link from the PC to the ESS?, if not, is there a chance that you're getting congestion on the network? (running Wireshark in promiscuous mode may help to understand traffic flow on a given interface). This WOULDN'T explain the apparent repeatability though. So I'm not sold on this.

I'm curious with your wording - is the ESS inside the control box, co-located with the drivers?

Faced with this problem I'd be measuring the step pulse-train on one axis on a scope - but that's an obvious test if you have a scope - my guess that level of diagnostics is not on the table for you?