What causes FANUC alarm 5139?

Machine system or function indicated by the alarm name has detected a fault. Control parameter or configuration error related to the alarm condition. Hardware component fault on the CNC or machine. Part program error or illegal operation for the indicated function. Machine interlock or safety condition not satisfied.

How do I fix FANUC alarm 5139?

1. Note the alarm number and check the Fanuc alarm screen for any sub-code or additional details. 2. Identify the specific machine system or function from the alarm name. 3. Power cycle the machine to clear transient faults. 4. Consult the Fanuc parameter or operator manual for alarm 5139 specific remedy. 5. Contact Fanuc service if the alarm persists after basic troubleshooting.

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FANUC Controller

Servo/Axis · Intermediate · 30-90 minutes

Alarm 5139

Fanuc Alarm 5139 - FSSB: ERROR

Alarm 5139 indicates a communication failure on the FSSB (Fanuc Serial Servo Bus) network between the CNC and servo amplifiers. This is typically caused by damaged/loose optical fiber cables, amplifier power issues, incorrect FSSB parameter settings (especially parameters 8000-8015 series), or defective optical interface boards on the amplifier or CNC side.

FANUCServo/AxisIntermediate30-90 minutes

5139

Fanuc Alarm 5139 - FSSB: ERROR

SYSTEM ALARM 5139

Root Cause Summary

Alarm 5139 indicates a communication failure on the FSSB (Fanuc Serial Servo Bus) network between the CNC and servo amplifiers. This is typically caused by damaged/loose optical fiber cables, amplifier power issues, incorrect FSSB parameter settings (especially parameters 8000-8015 series), or defective optical interface boards on the amplifier or CNC side.

Causes and Fixes

1
Power down CNC and amplifiers. Inspect all optical fiber cables for visible damage, excessive bending, or pinching. Check fiber bend radius is greater than 30mm throughout cable run.
Do not look directly into fiber optic connectors - can cause eye damage from laser diodes
2
Disconnect and reconnect all FSSB optical fiber connectors at both CNC (JD1A/JD1B) and amplifier ends (CN1/CN2). Clean connector ferrules with lint-free cloth and optical-grade isopropyl alcohol. Ensure positive click when reconnecting.
3
Check amplifier FSSB LED indicators. Normal operation shows CN1 LED (orange) ON steady and CN2 LED (orange) ON steady for mid-bus amplifiers. First amplifier CN1 only, last amplifier CN2 only. Flashing or OFF indicates communication loss at that point.
4
If damage found, replace optical fiber cables with FANUC genuine parts (A660-20xx series). Verify FSSB loop topology: CNC JD1A > AMP1 CN1 > AMP1 CN2 > AMP2 CN1... > LAST_AMP CN2 > CNC JD1B forms complete loop.

DIY Feasiblehigh confidence

Call a technician if:

·CNC FSSB board replacement required
·Multiple amplifier failures
·Persistent alarm after all troubleshooting steps

Prevention

Protect fiber cables from damage with proper routing
Perform regular FSSB communication diagnostics
Keep spare fiber cables in stock
Document FSSB parameter settings for backup

Common Mistakes

Looking into fiber optic cables
Using non-Fanuc fiber cables
Ignoring proper fiber bend radius
Not cleaning connectors before reconnection
Powering up in wrong sequence

Related Alarms

5138 5140 5141 401 402

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Always verify with your machine manual or a certified technician before performing service procedures.