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Heidenhain Controller
Servo/Axis · Intermediate · 30-120 minutes
HEIDENHAIN 231-C4A0 - C4A0 Inverter is not active
The TNC control cannot establish proper communication with or activate the specified inverter module. This is most commonly caused by power supply issues, communication interface failures, or hardware defects in the inverter itself. The control monitors inverter readiness and will not permit axis operation until all configured inverters report active status.
231-C4A0
HEIDENHAIN 231-C4A0 - C4A0 Inverter is not active
C4A0 Inverter is not active
The named inverter is not active. Typical reasons are that the charging or main contactor on the supply unit has not closed, the safety relay is off, or the PWM bus cable is interrupted.
Root Cause Summary
The TNC control cannot establish proper communication with or activate the specified inverter module. This is most commonly caused by power supply issues, communication interface failures, or hardware defects in the inverter itself. The control monitors inverter readiness and will not permit axis operation until all configured inverters report active status.
Safety
- Refer to Heidenhain service manual
- Ensure qualified technician performs repairs
Causes and Fixes
- 1
Measure 24V at Inverter Terminals
Use multimeter to check voltage at X122 connector pins for 24V supply. Verify voltage is between 22-28V DC under load. Check both supply and ground connections for security.
Ensure proper lockout/tagout procedures before accessing electrical connections. Hazardous voltage present.
- 2
Check Circuit Breakers and Fuses
Verify all 24V DC supply fuses in the cabinet are intact. Check circuit breaker states for 24V power supply feeding the drive system. Reset any tripped breakers after investigating cause.
On multi-inverter systems, check if other inverters on same 24V rail are functioning - helps isolate supply vs. module issue.
- 3
Inspect Power Supply Loading
Check 24V power supply load indicator. If supply is overloaded or in current limit, voltage will drop. Verify total current draw does not exceed supply rating (typically 10A or 20A units).
- 4
Verify Enable Signal Path
Check continuity of enable signal from UM (Unit for Monitoring) X122 to inverter enable input. Signal must be present for inverter to activate. Trace through any safety relays in enable chain.
The enable signal path includes E-STOP circuit - verify X122 pin assignments match your machine's safety configuration.
Call a technician if:
- ·PWM bus cable replacement required
- ·Inverter hardware replacement needed
- ·High voltage measurements required
Prevention
- Regular inspection of safety circuit connections
- Periodic PWM bus cable inspection
- Environmental protection for motor connections
Common Mistakes
- Ignoring safety circuit status before troubleshooting
- Not verifying contactor auxiliary contacts
- Assuming cable is good without electrical testing
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Always verify with your machine manual or a certified technician before performing service procedures.