SV0442 DC Link Charge Error fault in Fanuc drive

SV0442 DC Link Charge Error fault in Fanuc drive

Description

SV0442 is a specific power supply fault indicating a failure in the "Pre-Charge" circuit. When a Power Supply Module (PSM) is first turned on, it cannot connect the huge capacitor bank directly to the AC line, or the inrush current would trip the building's breakers. Instead, it routes power through a large ceramic resistor to fill the capacitors slowly (Pre-charge). Once the voltage reaches a certain level, a relay clicks to bypass the resistor for full operation. SV0442 occurs if the DC voltage does not rise fast enough, or if the bypass relay fails to close.

Cause

• Open Resistor: The ceramic pre-charge resistor is burnt out (open circuit). This happens if the machine is cycled on/off rapidly many times.
• Missing Phase: If one phase of the AC input is missing, the capacitors charge too slowly, timing out the logic.
• Leakage: A short circuit or heavy load on the DC link (like a shorted drive connected to the PSM) is draining the power as fast as it tries to charge.
• Relay Failure: The internal relay contacts are carbonized and won't conduct current.

Solution

1. Listen for the Click: Turn on the control. You should hear a distinct click from the PSM about 1-2 seconds after power-up. No click suggests relay logic failure.
2. Check Input: Verify 200VAC is present on all three legs at the top of the PSM.
3. Disconnect DC Link: Remove the heavy metal bus bars connecting the PSM to the other amps. Power up the PSM alone. If SV0442 clears, the problem is a short in one of the other attached drives draining the charge.
4. Replace PSM: The resistor and relay are internal components. While they can be soldered, replacing the PSM is the standard field fix.