Applicable Systems
Series 0i
Series 16/18/21
Alpha
Beta
Symptoms
The CNC system displays alarm 432: n AXIS: CNV. LOWVOLT CON. The converter (power supply module, PSM) has detected that the control power supply voltage has dropped below the minimum threshold. This affects the PSM, PSMR, or beta series SVU.
Possible Causes
- Input control power supply (200V AC at CX1A) voltage sag or interruption
- Internal control power supply circuit failure in the PSM
- Control power supply wiring loose or disconnected at CX1A/CX1B
- Upstream circuit breaker or fuse for the control power tripped
Troubleshooting Steps
- Step 1: Measure the control power supply voltage at the PSM terminals CX1A (200V AC)
Voltage should be within the rated range (200V AC +/-10%, i.e., 180-220V) - Step 2: Inspect the wiring at CX1A and CX1B for tightness
Terminals should be properly torqued; no loose or corroded connections - Step 3: Check the upstream circuit breaker or fuse feeding the control power
Breaker should be closed; fuse should be intact; verify no upstream faults - Step 4: If the voltage is normal but the alarm persists, the internal control power supply circuit in the PSM is faulty
PSM needs repair or replacement
How to Reset
To reset: 1) Restore the control power supply voltage. 2) Press RESET. 3) If the alarm recurs, the PSM is faulty. Caution: Low control voltage can cause erratic behavior in the servo system. Always fix before continuing operation.
Frequently Asked Questions
- Q: What is the difference between the PSM and SVM?
PSM (Power Supply Module) converts the 3-phase input AC to DC for the DC bus, which is shared by all SVM (Servo Amplifier Modules) on the same bus. The PSM also provides control power. If the PSM control power fails, all connected SVMs lose their control power.
- Q: What is CX1A?
CX1A is the connector on the PSM for the 200V AC control power supply input. This is separate from the 3-phase main power input. The control power must be present for the PSM's internal circuits to operate, even before the main contactor closes.
Source: FANUC Series 0i-Mate Maintenance Manual, B-64115EN
Category: PLC & VFD