Kinetix 5700 FLT S43 FDBK LOSS FL: what to check first?

Question

I'm getting a FLT S43 FDBK LOSS FL fault on my Kinetix 5700 servo drive. It happens intermittently during motion. What should I check first?

Top answer · Written by InduQT from the fault guide and manufacturer manuals cited below · Oct 28, 2026

The FLT S43 FDBK LOSS FL fault on a Kinetix 5700 servo drive indicates that the detected voltage levels of the A/B channel signals from the feedback device fell below the factory limit. This fault applies to all compatible feedback devices except DSL encoders. It can occur at power-up, during motion, or randomly due to various issues.

Likely causes and checks

1Feedback wiring open, shorted or missing

Points to it: This is the most common cause, especially if the fault occurs every time or after recent cable work. The feedback conductor may be physically damaged or disconnected.
Check: Verify the motor feedback wiring is not open, shorted, or missing by checking continuity end-to-end with power off.

2Noise from poor shielding or routing

Points to it: Intermittent faults, especially when other drives are switching nearby, often point to electrical noise corrupting the feedback signal.
Check: Use shielded cables, check shield terminations, and route feedback cables away from noise sources.

3System grounding problem

Points to it: If multiple axes are affected or panel bonding seems poor, a system grounding issue could be causing signal corruption.
Check: Check system grounds and bonding.

4Motor or encoder failure

Points to it: If wiring and grounding checks are good, the fault might be due to an internal failure of the motor's encoder.
Check: Replace the motor or encoder.

Next check: Given the intermittent nature of the fault during motion, I would first check for noise from poor shielding or routing, as well as thoroughly inspect the feedback wiring for any intermittent breaks or loose connections.

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