SV0362 Avalanche Diode Alarm (Pulsecoder) fault in Fanuc drive

SV0362 Avalanche Diode Alarm (Pulsecoder) fault in Fanuc drive

Description

SV0362 is a highly technical alarm indicating an internal hardware protection trip within the Absolute Pulse Coder. The encoder contains an "Avalanche Diode" (Zener diode) designed to absorb high-voltage spikes and protect the sensitive memory chips. If this diode conducts for too long or fails (short circuits), the encoder sends the SV0362 status bit. It typically means the encoder has been subjected to a massive electrical surge.

Cause

• Welding on Machine: Arc welding on the machine chassis without properly grounding the workpiece close to the weld. The current travels through the bearings and encoder ground.
• Lightning Strike: A power surge that bypassed the main input filters.
• Short Circuit: A catastrophic short in the feedback cable connecting 24V or motor power to the 5V encoder lines.

Solution

1. Replace Motor/Encoder: Once the avalanche diode has tripped or burned, the encoder is permanently compromised. It cannot be reset.
2. Inspect Grounding: Before installing the new motor, verify the machine's earth ground integrity to prevent recurrence.
3. Check Cable: Ensure the feedback cable doesn't have melted insulation that caused the voltage injection.