Fanuc alarm 129: ABNORMAL POWER SUPPLY (AMPn)
30i/31i/32i system alarm · Fanuc 30i/31i/32i-B
What it means
The CNC detected a voltage drop or abnormality in the 24V control power feeding a unit on the FSSB line (amplifier or SDU variant). Communication on the fibre itself may be fine - the downstream unit browned out. Check the supply voltage and wiring to the affected unit, and look for input-voltage sag caused by surge current at power-up.
Likely causes
- Undersized or failing 24V DC power supply for the drive section
- Loose or corroded power connector on the amplifier/SDU
- Input voltage drop due to surge current or unstable shop supply
Need the part urgently?
Send us alarm 129 with your machine details — typical RFQ turnaround is 24–48h.