We use technical and security cookies and, only if you accept, analytics with no cross-site tracking. More in the Cookie policy and Privacy policy.
We use first-party cookies and technical storage to make the site work, Google reCAPTCHA security technology and, only if you accept, Vercel analytics (no cookies, no cross-site tracking). You can accept or reject analytics; both options are equivalent and you can change your choice at any time. More info: Cookie policy, Privacy policy, Legal notice and Terms and conditions.
A group of initialisation alarms for the fibre optic servo bus: the control cannot complete the amplifier recognition, or what it finds does not match what its parameters declare. The axes do not enable and the machine does not come ready. It is diagnosed at start-up, because start-up is when the bus is configured.
For reference only: alarms change with the manufacturer, the control and the machine PLC. Check the full code in the official manual before doing anything. Legal notice.
Always, if it persists after a restart.
Reset/reboot after correcting wiring or FSSB configuration.
Choose the manual matching your control series, software version and machine builder. A support portal is a starting point; it does not establish applicability to every model.
At power-up the control walks the fibre optic chain asking who is there: it counts the devices, works out their type and their order, and with that information, cross-checked against the axis configuration parameters, decides which logical axis belongs to which physical amplifier. That process has timings and checks. If a device does not answer within the allowed time, there is a timeout. If a device answers but enters an error state, initialisation aborts. And if the number or order of what it finds does not match what the parameters declare, the control cannot make the assignment and reports an incorrect configuration. The distinction between those three matters a great deal, because they point at different places: a timeout points at a device that does not start up or a broken link; an error state points at an amplifier that has diagnosed itself as faulty; and a configuration mismatch points at parameters, which is what happens after restoring somebody else's backup or changing an amplifier for one of a different size. There is also a sequencing factor: if the amplifiers take longer to power up than the control takes to ask, recognition fails even though everything is healthy, and that is the classic case of the machine that starts sometimes and not others.
In order, from the fastest and cheapest check to the most expensive.
01Note the exact number and which axes are left out
Within this group, the number separates timeout from device error and from incorrect configuration, and that distinction is half the diagnosis. Also note which axes do not come ready and what order they sit in along the chain.
02Do a full, orderly power cycle
Power down by the procedure, wait for the time the builder specifies and power up. If the problem was the supply sequence, it starts correctly. If it comes back exactly the same, it is a hard fault and you have to look at the hardware or the parameters.
03Reconstruct what was done beforehand
An amplifier change, a parameter restore, work in the cabinet, adding an axis, installing an accessory. A bus configuration failure appearing with no prior intervention is rare; with a prior intervention, it is what you would expect.
04Do not handle the fibre
Optical links are not unplugged with the equipment energised, are not bent below their minimum radius, and are not cleaned just any old way. If you suspect the optical wiring, it is a maintenance job with the machine locked out and with proper equipment.
05Let maintenance read the amplifier status
Each amplifier's indicators say whether it has supply, whether it sees the bus and whether it has gone into error. Reading them means opening the cabinet, so electrical maintenance does it. It is the information that locates where the chain breaks.
06If it is configuration, restore from the machine's own backup
Assigning axes to the bus is specific to each machine. It is restored from its own backup, not from a sister machine's, and with a copy of the current state taken first. Afterwards the axes have to be validated one by one, moving them slowly and checking that each axis name moves the correct axis: a crossed assignment is dangerous.
Amplifier supply sequencing and timing, or a degraded optical link. It is confirmed by the intermittency being confined to start-up. It is worth resolving early: this symptom usually ends in a hard stoppage.
The declared configuration no longer matches the hardware. Confirm it by comparing the installed model against what the parameters show. It needs the configuration adjusted with the builder's documentation and the axes validated afterwards.
A break in the link at one specific point, or an intermediate amplifier with no supply. It is confirmed by the order of the missing axes. Maintenance locates it by reading the indicators from the first absent axis onwards.
A parameter backup including the axis configuration, dated and tied to the machine serial number. A record of every amplifier replacement, with the model removed and the model fitted. Respect for the fibre routing and bend radius in every intervention, with a photo of the inside of the cabinet taken first. Thermal control and cleaning of the cabinet. And axis-by-axis validation after any change to the bus configuration, before the machine goes back into production.
Fanuc detects initialization/configuration failure of the FSSB servo bus between CNC and amplifiers. It is an alarm from the Servo / ejes area, and in the catalog it is listed as “FSSB: timeout, error mode or incorrect configuration”. On the machine you notice it like this: The servos do not enable, Alarm when starting, One or more amplifiers do not appear on the FSSB.
On the shop floor it almost always comes from one of these causes: FSSB optical cable, Incorrect number of amplifiers, Axis setting incomplete, Amplifier without power or damaged. Rule out the most likely one on your machine first, before touching parameters or swapping anything.
Reset/reboot after correcting wiring or FSSB configuration. Resetting without fixing the cause first only hides the problem: FSSB 5134/5135/5137-5139 trips again and, in the meantime, you keep working with the machine in bad shape.
With the machine stopped and in a safe state, start with these checks: Write down exact FSSB number, Check the amplifier LEDs, Do not change the axis setting without a backup. That alone will tell you whether it is the program or whether you need to raise a maintenance job.
With FSSB 5134/5135/5137-5139 active, avoid this: Do not bypass safety devices, Do not manipulate energized electrical cabinet, Do not continue producing if the alarm reappears. Skipping any of these points is what turns a minor stop into an expensive breakdown.
Always, if it persists after a restart. If you are not sure how far it goes, stop the machine and report it: a repeat alarm always works out cheaper than a crash.
It is critical: there is a real risk of damage to the machine, the tool or a person. Leave the machine stopped, do not keep resetting it to see if it goes away, and call maintenance before producing again. Guidance reference. Always confirm the full text in the exact machine/control manual.
List of G and M Codes for CNC Programming. Search and filter ISO commands by control, machine or function.
CNC IDE: editing with G/M tooltips, line inspector, conversion between controls and 2D/3D toolpath.
Estimate CNC turning and milling cycle time from G-code. Calculate parts per hour with a breakdown of cutting, rapids, canned cycles and tool changes.
