Diagnosing a Fanuc
Servo Amplifier Alarm

An alarm points to a symptom, not always a failed part

When a Fanuc alarm stops a machine, the instinct is to order a new amplifier. Sometimes that's right. But servo alarms are raised by protective functions that also trip on causes outside the amplifier: a damaged motor cable, a failing motor, a feedback problem, or poor incoming power. Diagnosing in order, before ordering, saves both money and a second round of downtime.

This guide covers the practical sequence: identify what you have, read the alarm by category, check the usual suspects, and then match an A06B amplifier replacement exactly if the amplifier is confirmed as the fault.

Know which unit is alarming before you read the code

Many Fanuc drive systems are built from separate modules in a row, and each does a different job. Reading the alarm from the wrong module sends diagnosis down the wrong path. On modular amplifier systems you will typically find these three roles:

Each module carries a nameplate with its full A06B ordering number and specification. Record it exactly before you do anything else, because it is the key to a correct replacement later. Older and stand-alone amplifier styles are laid out differently, so check the actual unit rather than assuming the module structure above.

Work from the alarm category to the likely cause

Alarms are shown on the CNC screen and usually as a status indicator on the amplifier itself. The exact code and its meaning depend on the amplifier series, so always confirm it against the maintenance manual for your specific units. As a general guide, most servo and amplifier alarms fall into a handful of categories:

A useful test, where the manual allows it: if an alarm follows a motor or cable when you swap it to another axis, the amplifier is probably not the cause. Follow the manufacturer's procedure for any swap test.

Rule out the cheap causes first

Safety: servo amplifiers store energy in the DC link after power is removed. Follow your lockout/tagout procedure and the manufacturer's discharge and wait-time instructions before touching any module, and have the work done by qualified personnel.

Match the full ordering number, not just the family

If the amplifier is confirmed as failed, the replacement has to match the original closely. Two units from the same family can differ in current rating, axis configuration, or interface, and a near match is not a safe substitute.

Use the complete A06B number

Compare the full ordering number from the nameplate, including any suffix, rather than just the series or the first digits. If you only have a partial number or the label is damaged, send IAC the model details and photos of the unit and we can help identify it.

Check how it connects to the rest of the system

Confirm the replacement's current rating suits the motor it drives, and that its interface to the controller and neighboring modules matches the original. Where you're substituting a different but compatible model rather than an identical one, IAC's cross-reference can help compare them, and an engineer should confirm the fit against manufacturer documentation.

Plan for parameters and commissioning

Some replacements need parameters restored or checked after installation. Having the parameter backup from earlier makes this a short job instead of a long one.

IAC stocks Fanuc A06B amplifiers

IAC carries Fanuc A06B servo and spindle amplifier modules and can cross-reference a unit against the nameplate information you have. If you aren't sure which module is at fault, send the alarm details and nameplate numbers and we'll help narrow it down before you order.

Warranty and verification

Every component IAC ships carries a 2-year in-service warranty — twice the industry standard for refurbished industrial parts. Components are functionally tested before they leave the warehouse.

Same-day shipping

In-stock parts ordered before 4:00 PM Eastern ship same day. For urgent needs, call (877) 727-8757 during business hours — quote turnaround is typically under five minutes. You can also submit a part number via the quote form ↗ or email sales@iac.us.com.