What is SV0385 Serial data error (external) on Fanuc CNC controller?

When configuring a position detector, communication stops and communication data from the position detector cannot be received. Typical position detectors include optical scales, magnetic scales, external rotary encoders, and others. The position detector signals are accessed into the servo amplifier via the position detector interface unit (SDU).

Why does the SV0385 alarm occur?
The SV0385 alarm is related to the communication of the position detector, including:
1. Position detector feedback cable disconnection
2. Position detector feedback cable interference
3. Position detector failure, and it is also recommended to check the system parameters and other hardware related to servo feedback data:
4. Check the system parameters related to the full closed loop, and the position detector interface unit (separate position detection interface unit) (SDU).
5. Check amplifier communication fiber optic cables
6. Check servo amplifier hardware

How to Solve SV0385 Alarm
First of all, you need to gradually narrow the focus on the location of the fault, follow the first easy to difficult, first software and then hardware principle.
1. Troubleshooting system parameters
2. Check amplifier hardware
3. Check the SDU hardware
Secondly, you can clear the fault point by parameter setting item by item shielding.
1. First change to semi-closed loop, shield the position detector, test whether the position detector failure
2. Modify the FSSB parameters, shield the SDU, test whether it is SDU hardware failure.
Of course, if you have spare parts, you can confirm the failure point by hardware replacement method, you need to pay attention to use the same specification hardware.
1. Replace the position detector
2. Replace the position detector feedback cable
3. Replace the fiber optic cable from SDU to the system, step by step