Meaning of the indication
The DC bus rose above its permitted boundary, usually from regenerated energy, high input line, short decel time, brake path failure or DC-bus measurement issue.
Checking order
- Confirm whether F5 occurs only during deceleration or also at idle/power-up.
- Record input voltage and machine/load condition.
- Lengthen decel ramp as a controlled diagnostic where process-safe.
- Inspect dynamic brake resistor, brake wiring and brake-chopper evidence where fitted.
- Review DC bus history and fault queue before board replacement.
Suspect areas
Short rampHigh inertiaBrake resistorBrake chopperHigh line voltageDC bus sensing