Fagor alarm 4077: ERROR 304: Over-voltage at the power bus detected by the power supply module
CNC 8055 SERCOS drive error (DDS) · Fagor DDS drives
What it means
The power supply module itself measured DC bus overvoltage (as opposed to the drive's own detection). PWM is cut (category 0 stop); the CNC drops enables and aborts all channels. Inspect the regeneration path and wiring with the supply disconnected.
Likely causes
- Internal ballast bridge/connector missing or loose
- External regen resistor not connected or open
- Burned-out ballast resistor
- Bus bar connections loose
Triage note: Related: E215 (hard, drive-side) and E306 (soft, drive-side).
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 4077 with your machine details — typical RFQ turnaround is 24–48h.