Fanuc spindle alarm 70 occurs only on machines with Dual Check Safety, and means the spindle amplifier's connection status does not match the hardware setting — the safety function's picture of how the amplifier is connected disagrees with what it actually finds. The redundant safety channel verifies the drive configuration at start-up; a mismatch stops the machine before anything can run with an unverified safety chain.
When it appears
Almost always after configuration work: an amplifier replaced or moved, FSSB order changed, boards swapped, safety hardware settings edited, or a control replaced/reloaded. On an untouched running machine it points at failing hardware losing its configuration.
Fanuc's two steps, expanded
- Check the Spindle Amplifier connection and its setting. Verify the amplifier is connected exactly as the safety configuration expects: correct FSSB position/axis assignment, correct amplifier model for the configuration, and the Dual Check Safety hardware settings matching the actual installation. After an amplifier swap, confirm the replacement is the exact specification — a near-match model changes the connection signature and trips AL-70 (the safety cousin of the AL-14 mixed-board trap).
- Replace the CPU card or the amplifier's control PCB — only once the configuration is verified correct: then one of the two ends of the check is misreading. Board-level repair or exact-spec exchange, followed by a verified safety-function test — on Dual Check Safety systems ‘the alarm went away’ is not sufficient acceptance.
Tip: AL-70 right after any hardware/config change → the change is the cause; re-verify the configuration on paper before replacing anything. Out of nowhere → hardware; check the alarm history for companion self-test codes (AL-16, AL-74/75) that name the failing side.
Related guides
- Fanuc spindle alarm 69 (safety speed with guard open)
- Fanuc spindle alarm 71 (safety parameter error)
- Fanuc αi drive alarms — PSM, SVM & SPM codes
AL-70 after an amplifier swap — or on an untouched machine? JJ Automation verifies Dual Check Safety configurations, supplies exact-spec exchange amplifiers, and repairs control boards with verified safety-function testing. On-site diagnosis in NCR. WhatsApp us or call +91 88022 12394.