I have an Interact 4 that I am getting a spindle drive fault. For a time I could reset the controller (Heidenhain 2500) and get the machine to restart. Then I began to have to push the reset on the FAC-IR board to restart. Then the spindle would come on and reach RPM and then coast to a stop. Now all I can get is the spindle drive fault on the controller and the tacho loss LED 11 on the Fac-IR board. Sometimes I also get the inst trip on LED 12. Today we checked the 4 brushes and cleaned the tacho on the spindle drive motor and switched out the FAC-IR board. I understand that the tacho DC voltage on the FAC-IR board should be 120 volts on terminals 6 & 8, But how do you check that? Is that at 4000 RPM? Any help out there?