Servo Drive Throwing Alarms — What the Codes Usually Mean

Overcurrent-class alarms (FANUC alarm 8/12, Mitsubishi AL.32, Yaskawa A.10) usually mean a failed power stage inside the amplifier — or a shorted motor/cable that will kill the next amplifier too. A proper bench evaluation isolates which, before you spend anything. Send the alarm code with your unit; it cuts diagnosis time dramatically.

What's usually behind it

Failed IGBT / IPM power module

The classic servo amplifier failure. The intelligent power module shorts, the drive faults instantly at enable or trips the breaker. Replaced with new components, gate drive verified, then powered testing.

DC bus capacitor aging

Aged bus capacitors cause undervoltage alarms, faults under load, and eventually take the power stage with them. Every drive repair we do includes recapping aged electrolytics.

Shorted motor or cable

A motor winding or cable short presents as an amplifier overcurrent. If our evaluation shows your amplifier is healthy, you pay nothing — and you've just saved the next amplifier from the same fate.

Encoder / feedback faults

Feedback alarms can live in the amplifier's encoder interface or in the motor encoder. Bench evaluation tells you which side of the connector the problem is on.

Narrow it down yourself first

Work through these before you pull anything out of the panel. Several of them will tell you the unit is fine and the fault is somewhere else entirely.

□Megger the motor and its cable before condemning the drive. A shorted winding or a cable chafed against the machine frame will destroy a replacement drive exactly as fast as it destroyed the first one.
□Record the alarm code and what the machine was doing when it tripped — during acceleration, at speed, on a hard stop, or only when warm. That distinction separates a power-stage fault from a thermal or feedback fault.
□Check whether the cooling fan still spins freely and whether the heatsink is clogged. If the only fault is a thermal trip, cleaning and a fan may fix it on your bench.
□Confirm incoming line voltage and phase balance. Repeated drive failures on one axis are often a supply or wiring problem the drive is simply reporting.
□Note your parameter set if you have it recorded. Drive parameters normally live in the CNC or the drive's protected storage and our physical repairs do not touch them, but a record is worth having.

What happens if you send it to us

If the checks above point at the unit, this is the sequence it goes through — the same one every time, so nothing gets skipped because a fault looked obvious.

1
Safe intake and bus discharge
Drives arrive holding charge in the DC bus capacitors. The unit is discharged and verified at zero before anything is opened — this is a genuine hazard on any drive with a large capacitor bank, not a formality.
2
Power stage integrity check
The IGBT or power module is checked device by device for shorted and open junctions before power is ever applied. Energising a drive with a shorted power module simply destroys more of it, so this is done cold, first, every time.
3
DC bus and pre-charge inspection
Bus capacitors are assessed for capacitance loss and elevated ESR, and the soft-charge circuit — inrush resistor and its bypass relay or contactor — is checked. A drive that reports undervoltage or trips on power-up very often has a failed pre-charge path rather than a failed power stage.
4
Gate drive and feedback circuitry
Gate driver stages and their isolation are tested, because a partially degraded driver produces asymmetric switching that reads as an intermittent overcurrent fault under load and as a perfectly healthy drive at idle. Encoder and feedback interfaces are checked for the damage a shorted motor cable pushes back into the drive.
5
Thermal path and cooling
Fans, heatsink airflow and thermal interfaces are serviced. A large share of "failed" drives are thermal alarms caused by a seized fan or a heatsink packed with production dust.
6
Powered test under load
The repaired drive is brought up through a controlled power-on and run against a load so the power stage, current regulation and thermal behaviour are proven in operation — not merely confirmed to power up without alarming.