Fanuc spindle alarm 69 can only occur on machines using Dual Check Safety. It fires when, in safety signal mode C — that is, after a guard-open request has been entered so the operator can open the door — the spindle motor's rotation speed exceeds the permitted safety speed. With the guard open (or opening), the machine is only allowed to turn the spindle at a strictly limited speed; the redundant safety channel watches, and AL-69 means the spindle went faster than the door-open limit allows. This is a safety-function alarm — respect it accordingly: it exists so a spindle cannot spin at cutting speed next to an operator's hands.
Fanuc's three checks
- (a) If the guard is open — observe the safety speed. The operational cause: something commanded more than the door-open limit while in mode C — an operator override, a program still issuing an S-command, or a warm-up/jog habit that exceeds the limit with the door open. Verify what speed was actually commanded at the moment of the alarm and keep door-open operation within the limit. If the machine's workflow genuinely requires higher speed with the guard open, that is a conversation about the machine's safety concept — not a parameter to quietly raise.
- (b) Check the safety speed parameter. The configured safety speed must match the machine builder's risk assessment. Wrong after a parameter restore or retrofit → restore the builder's documented value — from the machine's own backup or the builder's sheet. Both redundant channels' settings must agree; mismatched safety parameters themselves cause trouble on Dual Check Safety systems.
- (c) Replace the Spindle Amplifier control PCB. If commanded speed was genuinely within limits and parameters are correct, the safety monitoring itself is misjudging — the speed-monitoring circuit on the control board. Because this is the safety channel, the repair must be verified properly: board-level repair or exchange, followed by a documented safety-function test (guard-open speed monitoring re-tested), not just ‘alarm gone’.
Tip: Establish the facts in this order — what speed was COMMANDED, what the PARAMETER allows, what the MONITOR measured. Commanded too high → operational discipline/program fix. Parameter wrong → restore the builder's value with documentation. Both correct but the alarm fires → the monitor — hardware. Never respond to AL-69 by raising the safety speed to ‘make it work’: that limit is the difference between an alarm and an accident report, and on Dual Check Safety machines it is part of the machine's certified safety concept.
Diagnosis checklist (in order)
- Confirm the machine runs Dual Check Safety and was in mode C (guard-open request active) at the trip.
- Determine the commanded spindle speed at that moment — program, MDI, or override.
- Verify the safety speed parameter against the builder's documented value (machine's own backup).
- Commanded and parameter both correct → control PCB safety-monitoring repair/exchange + verified safety-function test.
- Recurring operational trips → fix the program/workflow so door-open operation stays within the limit.
Related guides
- Fanuc spindle alarm 16 (Dual Check Safety RAM error)
- Fanuc spindle alarm 37 (E-stop deceleration supervision)
- Fanuc αi drive alarms — PSM, SVM & SPM codes explained
AL-69 with correct commands and parameters? JJ Automation repairs spindle amplifier control boards — including safety monitoring circuits — at component level, with verified safety-function testing before dispatch. On-site diagnosis in NCR. WhatsApp us or call +91 88022 12394.