Hello

I have a lathe ( Tsugami NU4B live tool ) fitted with a Fanuc A06B 6078 H112 Spindle servo motor and 0T control. Under MDI, Jog or Auto modes the Spindle is having a seizure.

Symptoms:
The spindle when instructed to move by any input will erratically turn. It jitters back and forwards by about 10 degree increments regardless of inputted spindle speed or direction. Load gauge maxes out due to input RPM and actual RPM being different.
Under no input the spindle moves freely and is not dragging. C axis is not engaged.
No alarms on the control or the spindle drive. A 408 alarm on the control and AL 19 on the driver appeared once but were cleared by a power cycle.

Background:
Purchased working second hand from a big manufacturer that had run the lathe almost every day since new. Meticulously well looked after and there is documented history of servicing down to the smallest washer and fitting. The lathe worked fine once installed and tested in the new location but came to power on today to start its first production and the spindle would not run.

Trouble shooting so far:
Suspected bad motor decoder. Cleaned and gap between encoder and gear tooth wheel checked and set.
Suspected bad spindle decoder. Cleaned and refitted.
Suspected bad cabling between spindle motor, decoders, driver. Re seated every connection. Alarm only shows then cable is not connected.
Parameters checked and updated with the original perimeter backup from new. Including 900 parameter set.
Called Tsugami and Fanuc. Both wanted to sell me new spindle drivers as they had never seen this type of problem.

Questions:
Has anyone seen such behavior from a Fanuc spindle before?
Is the IGBT on the spindle driver easy to access?
Can i run the machine with parameters set to ignore the decoders so i can check for faults.

Tomorrows plan unless someone figures whats i am missing:

Take out the driver and inspect the board. Check fuses and for blown components.
Test every cable connected to the driver with a multi meter.
Check the outputs of the decoders with a scope to see i am getting a signal.
Check that all phases of the motor are working in the correct sequence and cables are connected.

Please help. I am used to problem solving Fanuc hardware but this is driving me and my spindle NUTS!!!

Mike