Odd Turret Rotation Fault

[magno_grail]

Turret works fine initially but after a couple hours, mostly with the same tool (ball mill profiling) I try to do a tool change. The carriage comes in and the head moves slightly then get the turret rotation fault 115. I can then do a Zero Single Axis on Z and the carriage pulls back and rotates around to tool #1. So obviously no problem with the motor. Tried increasing the time delay for rotation but no change. When the tool tray is rotating I can see the index mark momentarily changing from 0 to 1 at each tool position and when the tray reaches tool #1 the tool 1 index changes to 1.
Any ideas on what to look for? Maybe put a meter on the motor to see if it is getting power at the tool change.
1991 VF-1