A horizontal machining center with Fanuc IIM CNC controller alarms PS200 while the X axis returning to the reference point.

After check and found out the decelerate action of zero-return is fine, all parameters relating to it are all right, so this could be “zero-pulse” error.

As the machine is using Heidenhain linear scale, change the EXE601 preposition amplifier, but the problem is still there, so the problem should be from the linear scale.

Take off the linear scale and found it was dirty due to long time using, clean it then test the linear output signal, re-install to the machine then the problem solved.