Fanuc alarm 971: NMI OCCURRED IN SLC
PMC/I-O Link alarm · Fanuc Power Mate
What it means
A non-maskable interrupt was generated because the serial link controller (SLC) driving the I/O Link detected a disconnection or fatal link error. In practical terms the I/O Link dropped out mid-operation: a slave lost power, a link cable opened, or the link transceiver failed. All PMC I/O over the affected line stops.
Likely causes
- I/O Link slave powered down or 24V supply to it lost
- Open, shorted or unplugged I/O Link cable (JA7B/JD1A chain)
- Failed I/O Link transceiver on master or slave
- Excessive link length / missing termination per build rules
Triage note: Trace the I/O Link chain and check every slave's power LED; the last unit still answering is next to the break.
Replacement parts
We supply the following units for this alarm — tested, warranty-backed:
- Request a quote →
I/O Link cable (fibre or twisted pair per installation)
i-o-unit · Common cause
- Request a quote →
Affected I/O Unit (e.g. A03B-08xx / Operator panel I/O)
i-o-unit · Common cause
Need the part urgently?
Send us alarm 971 with your machine details — typical RFQ turnaround is 24–48h.