Tornado A50 - 1001 SPINDLE MONITOR OFF WHEN COMMAND alarm :-(

Hi all,
I have a Tornado A50 with a 21i-T controller. For the most part it’s been smooth sailing since buying it from new. Last week, it had been running fine all morning and all of a sudden, after pressing cycle start, it started fine, but 5 seconds in, it alarmed out with “1001 SPINDLE MONITOR OFF WHEN COMMAND”.

I could press reset and the alarm disappeared, rewind the program and start again, but the same thing happens. The spindle will start up, but alarm out after a few seconds. All axes work fine. I’ve put it into MDI mode and just given it the command to spindle start, to see if it alarms out and it does within 5 or so seconds. No other alarms or errors. I’ve shut the machine down for half an hour and restarted it, and it boots up fine without any alarms or errors as it normally does. But alarms out as soon as the spindle starts. The belt that runs from the spindle to the small encoder box is intact (hoping that it may have just thrown a belt).

Has anyone encountered this before? Any advice or suggestions would be greatly appreciated.

Cheers.