SV0365 LED Error (Pulse Coder) fault in Fanuc drive

SV0365 LED Error (Pulse Coder) fault in Fanuc drive

Description

The SV0365 alarm is specific to the internal optics of the encoder. Inside a Fanuc Pulsecoder, there is a glass disk with microscopic gratings and an LED light source that shines through these gratings onto a photo-receptor. This creates the pulses that the computer counts. SV0365 (LED Error) means the intensity of the light received by the photo-sensor has dropped below a critical level. Essentially, the encoder is "going blind." This is usually a hard failure of the feedback device.

Cause

The environment is the biggest enemy of optical encoders.

• LED Aging: Like any light bulb, the LED inside the encoder dims over time (10-15 years). Eventually, it becomes too dim to read the disk.
• Vibration: Heavy milling vibration can cause the filament or bond wires in the LED to fracture.
• Contamination: If the O-ring seal on the red cap of the motor fails, oil mist or coolant can enter the encoder. This oil coats the glass disk or the LED lens, diffusing the light and triggering the error.
• Cable Voltage Drop: If the 5V supply to the encoder drops to 4.5V due to a long or damaged cable, the LED will dim physically.

Solution

This is almost always a hardware replacement scenario.

1. Cable Verification: Before condemning the motor, check the 5V supply at the encoder connector. If it is low, fix the cable or power supply.
2. Clean the Encoder (Risky): Some technicians attempt to open the encoder, remove the glass disk, and clean it with alcohol. Warning: This requires re-aligning the disk to micron precision. If you move the read-head, the motor will lose commutation and may run away or shake violently. This is not recommended for field service.
3. Replace Pulsecoder: The standard repair is to replace the Pulse Coder unit. Note that after replacement, you will lose the Home Position and must perform a Reference Return setup (see SV0300).