[ioaplia]

Hi! I got a primero milling machine with an 4th Axis. Lately while booting I got an error Axis A: Feedback missing. The servodrive is fagor axd 1.15-s0-o-b. I could not find what causes this message in order to solve it. The 4th axis is no longer working.

[joeavaerage]

Hi,
I'm not familiar with Fagor or the particular servo drive, but all servos require feedback, usually in the form of an encoder that feeds back into either the drive or the motion control.
It is by virtue of that feedback that the servo 'knows' where it is. In absence of that signal most servos will drive at full speed one direction or another, a run-away, until it slams into
a stop, often doing damage as a result. As a consequence of the risk most motion controls have a means of detecting the presence or absence of the encoder signal. Should it be absent
it will as a matter of safety shut that axis down altogether.

It sounds like the feedback device, be it a resolver or an encoder is faulty or the wiring is broken/loose. That is where I would start.

Craig