In the middle of buggering about with the encoder circuit, the Y axis stopped responding to the controller. The controller doesn't know any different, as it has no visibility of the actual position of the table. Oh, wait a minute.....
But sure enough, the step signals were getting to the control terminals of the servo drive (easy to check with a DMM), the ballscrew was being held on position, yet it wasn't moving in response to the step signals. WTF???
So clearly, as the servo was in control, there was no issue with the PSU or motor connections and the drive hadn't popped.
This has happened before on a couple of occasions. The last time was a few weeks ago on the X axis. When I connected up the diagnostics / programming cable on that occasion, I found that the PID settings etc had changed and the reason the thing wasn't responding to the step/dir inputs was because it had also magically changed the control mode to RS232 all by itself. I had left it on step/dir mode and it had been running for months like that, so it clearly has a mind of its own. I'm not sure I approve of that.
Let's have a look:
Got the progarmming / diagnostics cable connected up and the software running. Sure enough, the DMM software reported some funky new settings and RS232 mode. No wonder it wasn't responding to the step/dir signals. Here's a screenshot:
And here's the X axis in comparison - the way they should both be:
No, simply connecting up the diagnostics lead doesn't force it into RS232 mode. Let's just say this is fucking shit. How often is it going to randomly decide to change its settings without telling anyone?
I know these DYN drives are closer to hobby quality rather than industrial but FFS, get your act together, DMM !!