Fanuc spindle alarm 86 means no one-rotation signal occurred from the SPINDLE sensor at all — the once-per-rev reference never arrives, while the sensor's A/B pulse train may still be working (the spindle shows speed, but orientation, threading and Cs control have no anchor). It is the spindle-sensor member of the ‘Z signal missing’ family, alongside AL-42 (position coder) and the motor-sensor equivalent (alarm 82, which Fanuc's manual references for this code).
The diagnosis — same hunt, one channel
- Sensor parameters (B-65280EN): the declared sensor configuration must match the installed hardware — first suspect after amplifier/parameter work.
- The Z channel specifically: the tell for a ‘no one-rotation signal’ alarm is that only the Z pair has failed — one broken conductor, one bent pin. Check the Z-pair conductors for continuity (both ends disconnected) and the connectors for a single pushed-back pin, while the rest of the cable tests fine.
- The sensor and its ring: a contaminated or damaged index tooth/track on the sensor ring kills only the reference pulse. Inspect the ring; check the sensor gap and signal per its adjustment procedure — unadjustable or absent → replace cable and sensor together.
- Observe directly if equipment allows: a check board or scope on the Z channel while hand-rotating the spindle answers the question in one minute — one clean pulse per rev, or silence.
- The amplifier input — last: a clean pulse arriving at the connector with the alarm persisting is a board-level repair.
Tip: ‘Speed fine, orientation dead’ is this alarm's signature — and one conductor out of the whole cable does it. That is why Fanuc's standing instruction for unadjustable/absent sensor signals is to replace cable AND sensor together: each can hide the other's marginal fault, and the labour to get at them is the same.
Related guides
- Fanuc spindle alarm 42 (position coder Z signal not generated)
- Fanuc spindle alarm 85 (spindle sensor Z in wrong location)
- Fanuc spindle alarm 84 (spindle sensor disconnected)
AL-86 blocking orientation or threading? JJ Automation scopes feedback signals on site in NCR, stocks spindle sensors and cables, and repairs amplifier input stages at component level. WhatsApp us or call +91 88022 12394.