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FANUC Controller
Power Supply · Advanced · 1-2 hours
Fanuc Alarm 433 - DC Bus Overvoltage
Fanuc alarm 433 indicates the DC link voltage in the servo amplifier module (SVM) has dropped below the acceptable threshold, typically below 270VDC for 200V class or 540VDC for 400V class systems. This is caused by insufficient input AC voltage, failing DC link capacitors, regenerative discharge resistor issues, or power supply module malfunction. The alarm protects the servo system from operating under low voltage conditions that could damage components or cause erratic axis motion.
433
Fanuc Alarm 433 - DC Bus Overvoltage
CNV DC Link Overvoltage
Communication error: cnv dc link overvoltage. Data transfer between devices has failed or timed out.
Root Cause Summary
Fanuc alarm 433 indicates the DC link voltage in the servo amplifier module (SVM) has dropped below the acceptable threshold, typically below 270VDC for 200V class or 540VDC for 400V class systems. This is caused by insufficient input AC voltage, failing DC link capacitors, regenerative discharge resistor issues, or power supply module malfunction. The alarm protects the servo system from operating under low voltage conditions that could damage components or cause erratic axis motion.
Safety
- High voltage - extreme caution
- Lock out power
Causes and Fixes
- 1
Check input AC voltage at the PSM terminals using a multimeter. Verify 200VAC class systems have 200-230VAC ±10% or 400VAC class have 380-480VAC ±10% across all three phases (R-S-T). Check for phase imbalance exceeding 2%.
HIGH VOLTAGE: Use proper PPE and lockout/tagout procedures. Only qualified personnel should access power terminals.
- 2
Navigate to DIAGNOSIS > SERVO > DC LINK or check parameter #3196 (DC link voltage monitor) to read actual DC link voltage. Compare to specification: 200V class = 280-310VDC nominal, 400V class = 560-620VDC nominal. Alarm triggers typically at <270VDC or <540VDC respectively.
- 3
Inspect all input power connections at the PSM: AC input terminals, MC contactor output, and circuit breakers. Check for loose terminals, burned contacts, or corroded connections. Verify fuses (if equipped) are intact and rated correctly.
- 4
Check PSM LED indicators: CHG (charge) LED should be solid green during normal operation. If CHG LED is off or red, or if ALM (alarm) LED is lit, replace the PSM. Verify PSM fan operation and check for overheating or capacitor bulging.
Call a technician if:
- ·DC link capacitor replacement needed
- ·Power supply module replacement required
- ·Insulation breakdown detected
- ·Voltage measurements exceed safe limits
Prevention
- Install AC line reactors to reduce voltage spikes
- Implement gradual acceleration/deceleration profiles
- Schedule preventive maintenance for DC link capacitors every 5-7 years
- Monitor regenerative power consumption during program optimization
Common Mistakes
- Ignoring AC input voltage quality issues
- Attempting to repair servo amplifier modules in-house
- Not properly discharging DC link capacitors before service
- Overlooking regenerative unit capacity when modifying machine programs
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