VFD and Servo Drive Failures: Common Fault Codes and What Is Repairable

Most variable frequency drive (VFD) and servo drive failures come from a small set of causes: failed power semiconductors (IGBTs), aged DC bus capacitors, cooling fans, overvoltage from braking, and encoder or feedback faults. The fault code on the drive tells you which part of that chain tripped, but not always whether the drive itself is damaged. Before you replace or repair a drive, check the motor, the cable and the supply, because a drive that failed because of them will fail again. Most drive faults that do sit inside the drive are repairable. Automa.Net lists repair companies for VFDs, frequency converters, servo drives and servo motors by brand, among more than 120 repair companies worldwide (October 2026).

What Fails Inside a Drive

Capacitor ageing deserves a special mention. A drive that has been on a shelf for years can fail on its first power-up because its capacitors need reforming. Ask the supplier of a stored spare whether it was reformed, or have it done before installation. We cover storage of spares in managing industrial inventory for legacy machines.

Common Fault Codes and What They Mean

Every manufacturer uses its own numbering, so always look up the exact code in the drive's manual. The families of faults are the same across brands:

• Overcurrent. The output current exceeded the drive's limit. Siemens SINAMICS reports power unit overcurrent as F30001; Allen-Bradley PowerFlex 4 and 40 drives show F12 (HW OverCurrent). Causes range from too short an acceleration time and a mechanically blocked load to a shorted motor winding, a damaged cable or a failed IGBT.
• Overvoltage. The DC bus voltage rose too high, usually during fast deceleration of a high-inertia load when there is no braking resistor or it is undersized. It can also come from supply spikes. PowerFlex 4 and 40 drives show F5.
• Undervoltage. The DC bus voltage dropped: a supply dip, a missing phase, a failed input rectifier or aged capacitors. PowerFlex 4 and 40 drives show F4.
• Ground fault. Current is leaking to earth, most often through damaged motor insulation or a cable. Check the motor and cable with an insulation tester before suspecting the drive.
• Overtemperature. The heatsink or the power module is too hot: a failed fan, a blocked filter, a hot cabinet or a sustained overload.
• Encoder or feedback fault (servo). The drive lost or does not trust the position signal: a damaged encoder cable or connector, interference, a failed encoder in the motor or a damaged encoder interface in the drive.

If the code points to the motor side (ground fault, overcurrent at start, encoder fault), disconnect the motor and test it and the cable before replacing the drive. A healthy drive connected to a shorted motor will be damaged again within seconds.

What to Check Before You Send a Drive for Repair

1. Read and note the fault code and the fault history. Most drives keep the last several faults with time stamps.
2. Measure the motor insulation and the cable. A ground fault or a phase-to-phase short in the motor explains most repeated overcurrent faults.
3. Check the supply: all three phases present and balanced, no tripped fuse on one phase.
4. Check cooling: fan running, filters clean, cabinet temperature within the drive's rating.
5. Check the parameters if the fault appeared after a change: acceleration and deceleration times, motor data and current limits.
6. Back up the parameters before the drive leaves the machine, so a repaired or replacement drive can be set up quickly.

If all of that is clean and the fault stays, the problem is inside the drive. You can repair it or buy a replacement; if you consider a refurbished unit, read whether refurbished industrial electronics are worth it.

Servo Motors: Repairable Too

Servo motors fail mostly through encoders, bearings, and windings or magnets damaged by overheating. Bearings and many encoder faults are repaired routinely; an encoder replacement needs alignment to the rotor, which specialised repair companies do with the right equipment. Severe winding damage or demagnetised rotors are the cases where a replacement motor is usually the better choice.

Repair, Exchange or Replace

The general decision is laid out in our repair or replace guide for PLCs, drives and HMI panels; for drives, a few points weigh most. Repairing a drive keeps the same model, the same dimensions and the same firmware, so it drops back into the machine with its saved parameters. That matters most for discontinued drive series, where a new model of a different size or generation can mean re-engineering the cabinet and re-commissioning. If the line cannot wait, ask the repair company about an exchange unit: a repaired drive of the same part number shipped straight away. If the drive has failed repeatedly and the series is long discontinued, plan an upgrade while repairs are still possible; our guide to managing obsolete industrial spare parts covers that planning.

Getting a Drive Repair Quote

A repair company quotes faster and more accurately when the request includes the full part number from the nameplate, the number of units, the fault code and when it occurs, what you have already checked, and photos of the nameplate and any visible damage. A description like "F30001 overcurrent right after start-up, motor and cable checked, insulation fine" can be quoted; "drive broken" cannot. What happens after that, from diagnosis to warranty, is described in how industrial electronics repair works, and how to compare repair companies in our 10-point checklist for choosing a repair company.

With Automa.Net repair services you filter repair companies by category (VFDs and frequency converters, or servo drives and servo motors) and by the brand on the nameplate, such as Siemens, ABB, Schneider Electric, Mitsubishi Electric, Omron, Lenze or Bosch Rexroth. Each company card shows the usual repair time, the warranty and service options such as express repair. You send one request to up to 100 companies, with photos attached, and each replies to your email. If you would rather buy the drive, search its part number in AutomaSEARCH for new, surplus and refurbished stock.

Frequently Asked Questions

What causes overcurrent faults on a VFD?

Too short an acceleration time, a blocked or overloaded machine, a shorted motor winding, a damaged motor cable or a failed IGBT in the drive. Disconnect and test the motor and cable before blaming the drive.

What does Siemens fault F30001 mean?

F30001 on SINAMICS drives is a power unit overcurrent fault. Check the motor, the cable and the acceleration settings first. If the fault appears with the motor disconnected or immediately at power-up, the power section of the drive is likely damaged.

Why does my drive trip on overvoltage when stopping?

The motor feeds energy back into the drive during deceleration, raising the DC bus voltage. Lengthen the deceleration time, or fit or check the braking resistor and chopper.

Can a VFD with blown IGBTs be repaired?

Yes. Repair companies replace the IGBT modules and the gate drive components, and usually check the capacitors and fans at the same time. The repaired drive should then be tested under load.

Is it worth repairing a servo motor?

Usually yes for encoder and bearing faults, which are common and repairable. Severe winding damage or a demagnetised rotor often makes a replacement motor the better choice.

How long does a drive repair take?

Repair companies state a usual repair time, from up to 3 days to a month or more, and confirm the time for your drive when they reply. Express repair and exchange units are the fastest options for a stopped line.