Fagor alarm 4079: ERROR 306: Over-voltage at the power bus (Soft, trigger prior to hardware)
CNC 8055 SERCOS drive error (DDS) · Fagor DDS drives
What it means
Drive software detected the DC bus trending above its soft limit before the hardware threshold trips. PWM is cut (category 0 stop) and the CNC aborts all channels. Treat exactly like the hard overvoltage: verify the ballast/regeneration chain and deceleration profiles.
Likely causes
- Missing or defective internal ballast connection
- External regen resistor open-circuit or undersized
- Aggressive deceleration of high-inertia or vertical axes
- Line voltage spikes on the mains input
Replacement parts
We supply the following units for this alarm — tested, warranty-backed:
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External regenerative resistor
regen-resistor · Common cause
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PS / XPS power supply
power-supply · Check if others ruled out
Need the part urgently?
Send us alarm 4079 with your machine details — typical RFQ turnaround is 24–48h.