Fanuc spindle alarm 75 occurs only with Dual Check Safety, and means an error occurred in the CRC test — the checksum verification of the safety function's program/data storage failed. Where AL-74 says the safety processor itself failed its test, AL-75 says the code and data it runs on no longer verify — corrupted storage on the amplifier's control board. The safety channel refuses to execute unverified code, and rightly so.
Fanuc's remedy — with the practical preamble
The manual: replace the Spindle Amplifier or its control printed-circuit board. As with its siblings, a short preamble costs nothing:
- One clean power cycle — rule out a single marginal boot (a power dip mid-check). Repeats are real.
- Reseat the control-board faceplate — the standing rule of this series.
- History check: AL-75 alongside AL-74/AL-16 or the ordinary self-test codes (AL-13, AL-18 sum check) confirms the board's memory environment is failing broadly — repair, don't retry.
- After a lightning/surge event: corrupted storage is a classic surge signature — have the control supply rails checked at the same repair; the flash is rarely the only casualty.
The repair, done properly
Board-level repair (storage device, its supply, aged joints — sometimes reflashable with the correct software series/edition) or an exact-specification exchange board. Software series/edition must match the unit and configuration, or AL-75 gets traded for AL-14/AL-70. Acceptance for any safety-chain repair: a documented safety-function test, not just a clean boot.
Related guides
- Fanuc spindle alarm 74 (CPU test failed)
- Fanuc spindle alarm 32 (LSI memory abnormal)
- Fanuc αi drive alarms — PSM, SVM & SPM codes