FANUC αi series servo amplifier (SVM, PSM) troubleshooting
FANUC αi servo amplifiers are modular: a power supply module (PSM) feeds a DC link to servo amplifier modules (SVM) and spindle amplifier modules (SPM), all under a FANUC CNC. An alarm shows twice: as a single character on the module’s 7-segment STATUS display and as a servo alarm number on the CNC. Reading both together locates the fault. This record covers the αi series in FANUC maintenance manual B-65285EN/03; the later αi-B and αi-D series have their own manuals and are not covered here.
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How it reports faults
- PSM: on an alarm the ALM LED lights red and the one-digit 7-segment display shows an alarm code. The same code shown as a warning means the alarm condition will follow after a period; the PSM keeps running while the warning is displayed.
- SVM: the STATUS display (7-segment LED) shows the operation status. FANUC’s table maps each SVM display character to an alarm, its major causes and the matching CNC alarm.
- CNC: Series 15i shows servo alarms as SV0xxx (for example SV0436); Series 16i/18i/20i/21i/0i and Power Mate i show a three-digit number (for example 436). Some CNC alarms, such as 436 Soft thermal (OVC), have no amplifier display.
- Newer controls (for example 0i-F) use their own alarm numbering; check the CNC maintenance manual for the control installed.
Fault codes
| Code | Name |
|---|---|
| PSM 1 | Converter: input circuit overcurrent / IPM abnormal (CNC 437, SV0437) |
| PSM 2 | Converter: cooling fan stopped (CNC 443, SV0443) |
| PSM 3 | Converter: main circuit overload (CNC 431, SV0431) |
| PSM 4 | Converter: DC link undervoltage (CNC 433, SV0433) |
| PSM 5 | Converter: DC link precharge failure (CNC 442, SV0442) |
| PSM 6 | Converter: control power supply undervoltage (CNC 432, SV0432) |
| PSM 7 | Converter: DC link overvoltage (CNC 439, SV0439) |
| PSM 8 | Converter: excessive regenerative power (CNC 605, SV0605) |
| PSM A | Converter: radiator cooling fan stopped (CNC 606, SV0606) |
| PSM E | Open phase in the converter main power supply (CNC 607, SV0607) |
| PSM H | Converter: excessive deceleration power (CNC 440, SV0440) |
| SVM 1 | Inverter: internal cooling fan stopped (CNC 444, SV0444) |
| SVM 2 | Inverter: control power supply undervoltage (CNC 434, SV0434) |
| SVM 5 | Inverter: DC link undervoltage (CNC 435, SV0435) |
| SVM 6 | Inverter: overheat (CNC 602, SV0602) |
| SVM F | Inverter: radiator cooling fan stopped (CNC 601, SV0601) |
| SVM P | Communication error between amplifier and module (CNC 604, SV0604) |
| SVM 8 | Inverter: DC link current alarm, L axis (CNC 600, SV0600) |
| SVM 8. | Inverter: IPM alarm, L axis (CNC 449 or 603 for IPM overheat) |
| SVM b | Inverter: motor current alarm, L axis (CNC 438, SV0438); c = M axis, d = N axis |
| SVM U | Inverter: FSSB communication error, COP10B |
| SVM L | Inverter: FSSB communication error, COP10A |
| CNC 436 | Soft thermal (OVC), no amplifier display (SV0436 on 15i) |
| CNC 430 | Servo motor overheat (SV0430 on 15i) |
| CNC 445 | Soft disconnection alarm (SV0445 on 15i) |
Evidence to collect
- Photo of the PSM and SVM STATUS displays at the time of the alarm
- CNC alarm screen and alarm history
- Amplifier and motor specification numbers (A06B-…)
- Which axis (L, M or N) on a multi-axis SVM
- What the machine was doing: power-up, axis motion, decelerating, stopped
Work on fuel trains, burners, pressure vessels and electrical equipment must be done by qualified personnel following the manufacturer’s documentation and local codes. Never bypass a safety device or interlock.