Servo Drive Repair: Symptoms, Fault Codes, and When to Fix vs. Replace

Your servo drive is down. Your line is stopped. Every hour costs you money. Whether it's a Yaskawa Sigma-7 throwing an A.820, a Fanuc alpha-i SVM with SV0447, or an Allen-Bradley Kinetix 5500 stuck on E07 — Flexa Systems repairs it at component level, with a 2-year warranty, and ships back to you anywhere in the US. Rush 24–72 hour turnaround available.

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A servo drive failure stops motion. On a CNC machine, a packaging line, a robotic cell, or an assembly station — when the servo amplifier goes down, everything it controls goes with it. And unlike a VFD fault that often announces itself with gradual degradation, servo drive failures tend to be sudden: one power cycle it runs, the next it doesn't.

This guide covers the full picture — how to diagnose a servo drive failure, what the fault codes mean across the major brands, and how to make a rational repair vs. replace decision. Whether you're running Yaskawa, Fanuc, Siemens, Allen-Bradley Kinetix, or Mitsubishi, the failure modes and decision framework are largely the same.

What a Servo Drive Actually Does (and Why It Fails)

A servo drive — also called a servo amplifier or servo controller — takes a position or velocity command from a motion controller (PLC, CNC, robot controller) and converts it into precisely controlled current to a servo motor. The drive closes a feedback loop: it reads encoder position thousands of times per second and continuously adjusts motor current to match the commanded position or speed.

That continuous, high-frequency switching is exactly what makes servo drives more demanding than general-purpose VFDs. The IGBT power stage switches at 4–16 kHz, generating significant heat. The control circuitry processes high-speed encoder signals with microvolt-level precision. The communication interface handles real-time motion data with microsecond-level timing. Each of these subsystems has a failure mode — and each produces recognizable symptoms.

The 7 Most Common Servo Drive Failure Modes

1. IGBT Power Stage Failure

The IGBT (Insulated Gate Bipolar Transistor) module is the component that actually switches current to the motor. It's under the most thermal and electrical stress of any part in the drive. IGBT failure is the most common reason a servo drive completely stops producing output — and the most common reason a drive appears "dead" on power-up with a fault that won't clear.

IGBT failure has two primary causes:

• Overvoltage: Fast deceleration generates regenerative energy that spikes the DC bus. If the shunt (dynamic braking) resistor is undersized, bus voltage exceeds the IGBT breakdown threshold — typically 600V on a 480V drive. The IGBT fails in a short circuit, which usually blows the DC bus fuse and sometimes damages gate driver components.
• Thermal degradation: Running at or above rated current in high ambient temperatures accelerates thermal cycling damage. The bond wires inside the IGBT module fatigue and eventually fail — first intermittently (random overcurrent faults under load), then permanently.

Symptoms: Drive powers up but faults immediately on enable. No motor current on any phase. Blown DC bus fuse. Burnt smell from drive enclosure. Fault codes indicating hardware overcurrent.

2. DC Bus Capacitor Degradation

The DC bus electrolytic capacitors store energy and filter voltage ripple on the rectified DC supply. They degrade slowly over years — capacitance drops, equivalent series resistance (ESR) rises — until the drive can no longer maintain stable bus voltage during load transients.

Degraded capacitors cause a pattern of problems that's easy to misdiagnose: the drive appears to work normally at light loads but faults during acceleration or heavy cutting. Intermittent DC bus undervoltage faults. Drive that works fine after being powered off for a day but fails again under production load. These symptoms often get attributed to the power supply or incoming line quality — when the capacitors on the bench are the real problem.

Symptoms: Intermittent undervoltage faults under load. Drive works fine on initial power-up but faults after 20–30 minutes. Random shutdowns that clear after a cool-down period.

3. Encoder Feedback Circuit Failure

Modern servo drives use high-resolution encoders — 17-bit to 23-bit absolute encoders on current Yaskawa, Fanuc, and Siemens drives — that communicate via proprietary serial protocols (EnDat, Hiperface, BiSS-C, serial incremental). The feedback receiver circuit on the drive board must maintain signal integrity at high data rates.

Feedback circuit failures can be in the encoder itself, the feedback cable, the connector, or the receiver circuit on the drive. Identifying which requires careful isolation — many drives returned to repair shops for "feedback failure" have a cable or connector problem, not a drive failure. But when the drive's feedback receiver IC fails, the symptom is the same: a feedback loss fault that doesn't clear even with a known-good encoder and cable.

Symptoms: Feedback loss or encoder error fault that doesn't clear with new cable/encoder. Drive enables but immediately trips on position error. Position count erratic or frozen at one value.

4. Gate Driver Circuit Failure

The gate driver circuit is the interface between the low-voltage control board and the high-voltage IGBT power stage. It amplifies the control signals to the level needed to switch the IGBT gates reliably and provides isolation between the two voltage domains. Gate driver failures are often secondary — caused by an IGBT failure that sends a voltage spike back through the gate driver circuit.

A failed gate driver produces one of two results: the IGBT on that phase never switches (producing phase loss and position error), or the IGBT switches uncontrollably (producing overcurrent). In multi-axis drives, a gate driver failure on one axis can affect the other axes through shared bus voltage.

Symptoms: Phase-specific overcurrent faults. Motor produces unusual noise or vibration at low speed (torque ripple from asymmetric phase current). Drive enables but motor runs rough or stalls under light load.

5. Communication and Fieldbus Interface Failure

Servo drives communicate with the motion controller via various fieldbuses: EtherNet/IP, EtherCAT, PROFINET, MECHATROLINK-III, SERCOS III, or analog ±10V with pulse/direction. The communication interface — a dedicated processor and hardware on most drives — can fail independently of the power stage.

Communication failures are particularly frustrating because the drive may appear electrically healthy — all power rails correct, no thermal damage, no blown components — but refuses to establish communication or drops the network intermittently. This failure mode often gets attributed to the controller or network infrastructure before the drive interface itself is investigated.

Symptoms: Drive not visible on network despite correct IP/node configuration. Communication drops at random intervals. Drive establishes communication but fails to respond to motion commands. Fieldbus faults on the controller side that point to a specific axis.

6. Control Power Supply Failure

The internal power supply on a servo drive generates multiple low-voltage rails for the control board, encoder supply, fan, and safety circuits. These supplies use switching regulators and linear regulators that can fail from age, thermal stress, or input voltage transients.

A failed control supply produces a range of symptoms depending on which rail is affected: complete power loss with no display, erratic faults that change character over time, encoder supply dropout that looks like an encoder failure, or safety circuit issues that prevent enable.

Symptoms: Drive completely dead despite correct input power. Display flickers or shows incomplete characters. Drive faults intermittently with different fault codes on each occurrence. Fan not running despite drive being powered.

7. Overtemperature and Thermal Management Failure

Servo drives generate significant heat — particularly in high-duty-cycle applications like continuous cutting operations or high-inertia motion profiles. Most drives have a heat sink thermistor that monitors IGBT temperature and triggers a fault before thermal damage occurs. When the cooling system fails — clogged heat sink fins, failed cooling fan, blocked ventilation path — the thermistor trips and the drive faults on overtemperature.

The fault itself is protective, but repeated thermal cycling accelerates component aging. A drive that has been running hot for months before the fault finally triggers has often degraded its capacitors and gate drivers in the process. When we see a drive with a history of overtemperature faults, we inspect the entire power stage — not just the thermal management system.

Symptoms: Overtemperature fault on the drive display. Fault occurs after a consistent run time. Drive runs normally after cooling down. Heat sink noticeably hot to the touch when running.

Fault Code Reference: Major Servo Drive Brands

Fault code numbering varies significantly between manufacturers. Here are the most common fault codes for the five major servo drive platforms in North American industrial applications:

Yaskawa Sigma-7, Sigma-5, Sigma-II Servo Amplifiers

Fanuc Alpha-i, Beta-i, and αiS Series Servo Amplifiers

Siemens SINAMICS S120, S110, and SIMODRIVE 611

Allen-Bradley Kinetix 5500, 5700, and 6500

Mitsubishi MR-J4, MR-J3, and MR-E Series

Line down right now? Skip to the bottom — request a quote here or call (254) 254-0005. Rush 24–72hr turnaround available. We ship back to all 50 states.

Before You Send the Drive for Repair: What to Check First

A significant percentage of servo drive faults — especially communication faults, feedback faults, and enable faults — have external causes that are faster and cheaper to fix than a drive repair. Before shipping the drive, run through this checklist:

1. Verify input power: Check all three phases at the drive's L1/L2/L3 terminals under load. Phase loss — even a sag on one phase during motor acceleration — causes DC bus faults that look like drive failures. A single blown fuse upstream can cause a complete drive failure symptom.
2. Check the feedback cable: Encoder cables fail more often than encoder drives. Inspect the full cable run for crush damage, tight bends, frayed shields, and corroded connector pins. For absolute encoders, verify battery voltage if applicable (typically 3V lithium, Yaskawa and Fanuc both use this).
3. Verify the safety circuit: Safe Torque Off (STO), Emergency Stop, and enable signals must all be satisfied before the drive will output. Check each interlock signal at the drive terminals with a meter — don't assume. A missing +24V on an STO input looks exactly like a dead drive.
4. Check the shunt (dynamic braking) resistor: Measure resistance across the regenerative resistor terminals. An open-circuit shunt causes overvoltage faults during every deceleration. A shorted shunt causes the braking transistor to overheat and fail. Both look like drive faults on the display but are actually external components.
5. Inspect the drive environment: Overtemperature faults are sometimes mechanical — a cooling fan that stopped, heat sink fins packed with coolant mist or dust, a vent blocked by cable bundle. Check before concluding there's an electronics failure.
6. Document all fault codes and the conditions that trigger them: A fault that only occurs during axis acceleration tells a different story than one that appears at power-up. Write down the exact fault code, the sequence of events, and any changes that preceded the first fault. This information significantly reduces diagnostic time at the repair shop.

Repair vs. Replace: The Decision Framework

The repair vs. replace decision on a servo drive is not a question of economics alone. Lead time and reprogramming complexity are often the deciding factors — especially on older equipment.

When Repair Is Clearly the Right Choice

• The drive is discontinued or has long lead times. Yaskawa SGDA, SGDE, SGDB series; Fanuc Alpha-i and αiS SVM modules; Siemens SIMODRIVE 611; Allen-Bradley Kinetix 300 — all discontinued or allocation-limited. Sourcing a replacement can take 6–16 weeks. Component-level repair typically takes 5–10 business days.
• The replacement requires reprogramming. A new drive always requires parameter entry. On complex multi-axis systems with custom tuning, this is hours or days of commissioning time — and carries risk if the original parameters weren't documented. Repair returns the same drive with all parameters intact.
• The repair cost is less than 50% of replacement. At this level, repair delivers substantially the same function at half the cost, with a warranty. There is no rational argument for replacement.
• Only one component has failed. A single failed IGBT module or capacitor bank in an otherwise healthy drive is a straightforward component-level repair. Replacing the entire drive for one failed component is unnecessary.

When Replacement Makes More Sense

• The drive has multiple simultaneous failures across different subsystems. A drive with a failed IGBT, failed control board, and failed feedback circuit has typically experienced a catastrophic event (power surge, severe overvoltage). Repair cost approaches replacement cost, and the underlying cause needs to be addressed regardless.
• The drive platform is being migrated as part of a planned upgrade. If the machine is being converted to a new control system in the next 12 months, repair may not be the best investment unless downtime cost demands it immediately.
• The repair-to-replacement cost ratio exceeds 70%. At this level, the economics of repair become harder to justify unless the lead time or reprogramming complexity tips the balance.

The Lead Time Factor — Often Overlooked

The most underestimated factor in the repair vs. replace decision is lead time on the replacement unit. For current-production drives like a Yaskawa SGD7S or Siemens S120 power module, availability is usually 2–4 weeks from authorized distributors. For discontinued or allocation-constrained units, it can be 8–20 weeks — sometimes longer.

At Flexa Systems, standard servo drive repair turnaround is 5–10 business days from receipt. Rush service is 24–72 hours. Against a 12-week replacement lead time on a production-critical axis, the economics of repair — even at 60% of replacement cost — are clear.

Servo Drive Repair for All Major Brands

We perform component-level servo drive repair for the full range of industrial servo amplifiers. Browse our servo drive inventory — tested units available to ship while yours is being repaired.

• Yaskawa servo drives: Sigma-7 (SGD7S), Sigma-5 (SGDV), Sigma-II (SGDH), Sigma-I (SGDA/SGDB/SGDE), Cacr series
• Fanuc servo amplifiers: Alpha-i SVM, Beta-i SVM, αiS servo amplifier modules, αCi series — all spindle and feed axis amplifiers
• Siemens servo drives: SINAMICS S120 (Motor Modules, Single Motor Modules, Double Motor Modules), SINAMICS S110, SIMODRIVE 611D/611U/611A
• Allen-Bradley Kinetix servo drives: Kinetix 300 (2097), Kinetix 350 (2097-LM), Kinetix 5100 (2198-E), Kinetix 5500 (2198-H), Kinetix 5700 (2198-D), Kinetix 6500 (2094-AMP), Ultra3000
• Mitsubishi servo drives: MR-J4, MR-J3, MR-J2-Super, MR-E series servo amplifiers
• Bosch Rexroth: IndraDrive C/M/CS/Mi, Eco Drive, DKC series
• Lenze: i700, 9400 Servo Drive, 8400, EVS series
• Parker: Compax3, ViX, ACR series

Don't see your model? Contact us with your model number — this list covers our most common repairs, not the full scope of what we work on. If you need a tested spare unit while yours is in repair, check our servo drive inventory for in-stock units ready to ship same day.

Servo Drive Repair in Lewisville TX — Ships to All 50 States

Flexa Systems is based in Lewisville, TX (Dallas-Fort Worth metro). If you're in Dallas, Fort Worth, Irving, Denton, Plano, Carrollton, McKinney, Frisco, Arlington, Garland, Richardson, or anywhere in DFW — drop off in person by appointment. Same-day diagnostic evaluation available for local customers with production-critical situations.

Outside Texas? We repair servo drives for facilities in all 50 states — California, Ohio, Michigan, Illinois, Pennsylvania, Georgia, North Carolina, Florida, New York, Washington, and everywhere in between. Return shipping is included in every repair. Standard turnaround: 5–10 business days. Rush turnaround: 24–72 hours.

• ✔ Free diagnostic evaluation — you pay nothing unless you approve the quote
• ✔ 2-year warranty on every repair — best in the industry
• ✔ Component-level repair — not board swap, not parts replacement
• ✔ Rush 24–72hr service for production-critical downtime
• ✔ All program and parameter data preserved — no reprogramming after receipt
• ✔ Written repair report on every job — what failed, why, what was done
• ✔ Ships nationwide — return shipping included, all 50 states

We've repaired servo drives for automotive plants in Michigan, food processing facilities in California, packaging lines in Ohio, CNC job shops in North Carolina, and industrial facilities across Texas — including customers who found us after a local shop said their unit was "not repairable." Don't scrap a drive until you've had it evaluated at component level.

Need a Spare Unit While Yours Is Being Repaired?

If your line can't wait 5–10 days for the repair, we also stock tested servo drives ready to ship same day. Swap in the spare, keep production running, send us the failed unit on your schedule.

• Allen-Bradley Kinetix servo drives in stock — Kinetix 300, 350, 5100, 5500, 5700
• Yaskawa servo amplifiers in stock — Sigma-5, Sigma-7, Sigma-II series
• Mitsubishi MR-J series in stock — MR-J2, MR-J3, MR-J4
• Siemens SINAMICS in stock — S120, S110 Motor Modules
• Browse full servo drive inventory →

All units are tested, cleaned, and ship with a warranty. Contact us with your model number and we'll confirm availability and pricing within 4 hours.

Get Your Servo Drive Repaired — Free Quote, Fast Turnaround

Submit your brand, model number, and fault code. We respond within 4 business hours with a repair estimate and turnaround time. Evaluation is always free — you pay nothing unless you approve the repair.

→ Request a free servo drive repair quote  |  Call (254) 254-0005

Rush 24–72 hour service available. Serving Lewisville TX, Dallas-Fort Worth, and all 50 states. 2-year warranty. Free return shipping. No fix, no charge.