Fanuc 7115 Alarm

This alarm occurs when the FANUC system fails to complete the commanded spindle switching sequence within a pre-determined time limit, or if the magnetic contactors responsible for the switch do not report the correct state.

Once you resolve alarm 7115, take these steps to ensure it never returns.

If you see this message on your screen, the core of the issue is that the CNC control has attempted to change the spindle's speed range (usually by switching between high and low gear), but the process has failed or timed out. The machine is effectively telling you that it cannot safely change the spindle's operating mode, and it has locked itself in a safe state to prevent damage.

If the alarm is accompanied by "AL-15," it specifically points to a switch control failure, suggesting the amplifier itself or the contactor circuit is the bottleneck. How to Reset the 7115 Alarm fanuc 7115 alarm

If a machine builder created a custom macro that executes a DPRNT (Print) function or attempts to write to a PLC address that doesn't exist (e.g., W# instruction with an out-of-range byte), the CNC will halt and display 7115 with a sub-code indicating the illegal offset.

Fix the underlying cause (e.g., replace the 24VDC power supply or the MCC contactor).

Conclusion The Fanuc 7115 alarm points to critical issues in the servo feedback loop or drive system. Systematic troubleshooting — starting with contextual data, inspection, signal monitoring, parameter checks, and component isolation — identifies the root cause while minimizing unnecessary replacements. Repairs typically involve restoring reliable feedback (encoders/cables), addressing amplifier or motor faults, correcting mechanical binding, or fixing parameter/tuning mismatches. Preventative measures such as proper cable routing, grounding, routine inspections, and thermal management reduce recurrence and help maintain consistent CNC performance. This alarm occurs when the FANUC system fails

Measure the output of the 24V power supplies in the electrical cabinet. Even if they show 24V with a multimeter, they may be failing under load. Inspect Spindle Contactors:

The machine builder may have customized the exact logic for spindle switching, but the root causes of this timeout are almost always mechanical or electrical in nature. Here are the most common triggers for the Fanuc 7115 alarm:

Marcus grabbed his multimeter. He measured the resistance across the motor leads and megged the phases to ground. Everything read perfectly balanced—the motor was healthy. He then turned his attention to the auxiliary contactor responsible for the speed transition. There it was: a tiny plastic fragment from a worn-out housing had jammed the relay, preventing it from snapping into high-speed mode. The machine is effectively telling you that it

Look at the modules connected via the FSSB high-speed fiber cables. Ensure the connectors are firmly seated in both the CNC main board and the servo amplifiers. Clean the cable tips with dedicated optical wipes if you suspect oil contamination. Look for sharp bends or kinks that fracture internal glass fibers. 2. Verify Servo Parameters

If the SPM shows a DC link over-current (AL-12) or other failures, it might be causing the switch failure. Summary Table of Potential Issues Common Issue Low/Failing 24VDC Measure under load, replace PSU. Contactors Burnt/Stuck relay Replace contactor/relay. Feedback Switch Misaligned/Dirty sensor Clean and adjust sensor. Wiring Broken wire/Loose terminal Continuity check. Spindle Amp Faulty SPM Test/Replace amplifier. Conclusion

The Fanuc 7115 alarm is classified as a , as its number falls between 1000 and 2000. It originates from the machine tool builder’s logic (PMC) rather than a direct internal fault in the Fanuc drive. However, it is almost always triggered by a fault in the spindle drive system.

In all cases, the underlying issue is a between the machine’s logic processor and the human interface or hardware.