Need Help!- Zaxis tach gen disconnect alarm

[JOC]

How do I determine if my problem is with the tach gen or servo board? All connections are solid. Board is Fanuc A20b 1001 0770 04B servo is AC Fanuc "red cap". Are schematics available? Any test I can perform w/o-scope etc?

[Al_The_Man]

The Red Cap, (AC servo's) do not usually use a DC tach in the sense the DC ones did, at least I have never come across a AC motor that uses a tach?
The encoder usually performs all position and commutation duties.
Al.

[JOC]

Hi Al,
Thanks for the reply. There is an encoder on the end of the servo. On the screen it is displayed as tach gen. disconnect. however when X comes up it refers to a pulsecoder disconnect?

[Al_The_Man]

It is more likely you have a problem either with the encoder or the cable.
First measure the continuity through to each end of the cable.
Al.

[JOC]

Had checked all wiring and connectors. Continuity checked OK. Do you know of any checks I can perform to prove out the encoder?