Allen-Bradley Kinetix 5700 servo drive alarm FLT S43: FDBK LOSS FL (Feedback Signal Loss, factory limit)
Fault FLT S43 – FDBK LOSS FL on an Allen-Bradley Kinetix 5700 is Feedback Signal Loss (factory limit): the detected voltage levels of the A/B channel signals from the feedback device fell below the factory limit. It applies to all compatible feedback devices except DSL encoders; the sub-code shows which feedback channel reported it.
Diagnose this with AI
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When it happens
- At power-up or enable, with an open or missing feedback conductor
- In motion, when a cable in a carrier breaks intermittently
- At random, when noise or poor grounding corrupts the signal
Likely causes and checks
1Feedback wiring open, shorted or missing
- Points to it
- Fault every time; after a cable change or connector work.
- Check
- Verify the motor feedback wiring is not open, shorted or missing, checking continuity end to end with power off.
2Noise from poor shielding or routing
- Points to it
- Intermittent faults, more with nearby drives switching.
- Check
- Use shielded cables, check shield terminations and route feedback away from noise sources.
3System grounding problem
- Points to it
- Several axes affected; panel bonding poor.
- Check
- Check system grounds and bonding.
4Motor or encoder failure
- Points to it
- Wiring and grounding check good; fault follows the motor.
- Check
- Replace the motor or encoder.
Telling it apart
- FLT S43 (FL) trips at the factory limit; FLT S44 (UL) at a user-set limit. Both are A/B signal-level faults on non-DSL devices.
- FLT S45 – FDBK COMM FL is the data-loss fault for DSL and Hiperface serial feedback; FLT S47 is an internal feedback device failure; INIT FLT M03 – MTR ENC STARTUP is a failure to start communication at initialization.
Evidence to collect
- Full LCD text and the sub-code (feedback channel)
- Feedback type and cable catalog number
- Continuity results and shield termination photos
- Whether the fault follows the motor when swapped
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