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202511-25

Troubleshooting Yaskawa Servo Drive Position Deviation Errors

Position deviation alarms on a Yaskawa servo drive are one of those faults that look “mysterious” from the HMI, but on the plant floor they are very physical: a pick head landing off target, a seal jaw clipping a product, or a robot joint that no longer lines up with its fixture. In practical terms, a position deviation error means the drive does not believe the motor is where the controller says it should be, and the deviation has crossed a trip threshold. From years of commissioning and fixing Yaskawa-based lines in packaging, CNC, and assembly, I have learned that these errors are rarely “just tuning.” They sit at the intersection of feedback integrity, signal quality, mechanics, and drive configuration. The good news is that Yaskawa drives are very transparent if you know how to read their alarms and data, and the same root causes show up again and again. This article walks through how Yaskawa drives think about position deviation, what common symptoms really mean, and a systematic way to troubleshoot and prevent these errors, drawing on published fault-code guides, industrial repair houses, and real-world field experience. What “Position Deviation” Means In A Yaskawa System Servo drives in general regulate torque, speed, and position in a closed loop using feedback devices such as encoders or resolvers. Sources such as BIN95 and InRobots describe the drive as a controller that takes position commands from a PLC or motion controller, compares them against actual position from the encoder, and then drives the motor to reduce the error. Roc Industrial, which specializes in Yaskawa repair, defines position error as the drive’s inability to maintain the commanded position because of feedback, tuning, or parameter issues. In Yaskawa terminology this shows up under several alarm families often labeled as “position error,” “excessive position deviation,” “out-of-control detection,” or “overtravel due to deviation.” Yaskawa fault-code compilations summarized by VIYORK show that: Position and motion deviation alarms such as A.d00–A.d02, A.d30, A.900–A.901, and A.9A0 are triggered when the difference between the commanded and actual position exceeds an allowable range or leads to overtravel. Related alarms like A.C10 indicate out-of-control detection, and A.510 reports overspeed, often appearing alongside deviation problems when the drive cannot track the commanded motion. The exact behavior depends on the series and parameters, but the principle is the same: the drive constantly calculates position error, allows a certain following error band during motion, and trips when that error grows too large for too long. This protects the mechanics and product from uncontrolled motion. To make this concrete, it is useful to frame the key concepts in plain terms. Term In practice on the machine Commanded position Where the PLC or motion controller expects the axis to be, based on its own position calculation. Actual position Where the encoder or resolver says the motor (or load) really is, as measured by the servo drive. Position deviation/error The difference between commanded and actual positions inside the drive. Following error band The window of acceptable deviation during motion before the drive raises a warning or alarm. Position deviation alarm A drive trip because deviation exceeded a threshold, either dynamically or at standstill. A healthy system keeps deviation small and bounded. A drifting or noisy system lets that error accumulate until Yaskawa’s protection logic steps in. How Yaskawa Announces Position Deviation Yaskawa error lists collected and summarized by VIYORK show that deviation-related issues are not represented by a single code but by families of alarms. While you must always check the manual for your specific model, the pattern is consistent. Position deviation alarms A.d00–A.d02 and A.d30 point to excessive position error, often linked with speed limits or motion constraints. Codes A.900–A.901 and A.9A0 are associated with overtravel and position deviations that push the axis beyond its allowed range or limit settings. Alarm A.C10 is an out-of-control detection signal, reported when the drive detects that the servo loop is no longer controlling position adequately. Overspeed error A.510 indicates that the motor is turning faster than the configured maximum speed, which can show up when feedback polarity or scaling is wrong and can coexist with deviation alarms. Alongside these, Yaskawa drives also raise encoder and temperature alarms (for example, encoder faults and overheating coded in the A.810–A.891 and A.861 ranges) that often sit “upstream” of position deviations. An encoder that intermittently fails will not always give you a neat “encoder error only.” Instead, you see position deviation alarms, oscillation, or overspeed, and only occasionally a dedicated encoder alarm. The first pragmatic move on site is simple: write down the exact Yaskawa alarm codes and any axis-common warnings, and check how often they appear in the drive’s history. Industrial Automation Co. emphasizes starting with the code definitions and a structured fault history before you touch wiring or tuning, and that aligns perfectly with what works in the field. What Position Deviation Looks Like On The Floor Although the drive speaks in alphanumeric codes, operators and maintenance techs usually describe the problem in mechanical terms. Several real-world patterns show up repeatedly. On pick-and-place or dispensing equipment, a calibration that starts dead-on begins to drift over a shift. A clean-room pick-and-place example captured by Elektroda shows an axis calibrated at roughly one position slowly ending up close to half an inch off after many continuous cycles, even with stable ambient temperature. Logs revealed that the number of commanded pulses from the controller did not match what the servo drive received, pointing away from “software bug” and toward signal integrity problems. In other cases, the axis runs normally until it approaches a particular position, then the Yaskawa drive trips on position deviation or overspeed just as the motion slows. VIYORK reports low-speed crawling and oscillation when system gain is set too low or too high, and alarm No.16 on some MHMA digital AC servo systems when excessive gain leads to self-excited oscillation. These tuning issues manifest as chattering near the end point and drive trips when deviation spikes. Sometimes the complaint is more basic: “the servo keeps losing position.” Roc Industrial notes that position error often comes with stalling, vibration, or failure to hold a commanded point. Industrial Automation Co. sees similar patterns when encoder feedback is unreliable or when communication between controller and drive is unstable. Finally, in harsh environments the position deviation may be the last thing you see before more dramatic failures. Industrial Monitor Direct describes Yaskawa SGDH drives that repeatedly trip on overcurrent (A.10) due to motor shorts caused by oil and vapor ingress. In those plants, damaged internal components and repeat trips are the visible symptom of an underlying environmental and motor-insulation problem. Even when the drive still moves the axis, accumulated damage and unstable current can show up first as poor positioning. Understanding which of these patterns you are facing is critical, because the root causes and priorities are very different. Root Causes: Electrical, Mechanical, And Configuration Command And Feedback Mismatch From Noise In modern Yaskawa systems using pulse-train or similar position commands, the drive expects precise, noise-free pulses. The Elektroda case showed a clear mismatch between pulses sent by the controller and pulses counted by the Yaskawa drive, with one experienced practitioner claiming that the overwhelming majority of such drift cases they see are caused by AC mains noise coupling into the pulse wiring. When electrical noise corrupts the pulse train, two things happen. The controller believes the axis is at the “correct” position based on the pulses it issued. The drive’s internal position counter, however, misses or miscounts pulses and ends up with a different coordinate. The drive then raises position deviation alarms or you see gradual drift that you cannot explain by mechanics or temperature. The same thread and other industrial guidance recommend a classic set of noise-mitigation measures: install an AC line noise filter on the panel supply, physically separate AC power and low-level DC or pulse cables, keep pulse runs as short as feasible, twist the CW and CCW pairs, and use shielded cable with proper single-point grounding. Ferrite beads on noisy lines can also damp high-frequency interference. Industrial Automation Co. adds that communication faults in general should be approached systematically by checking cables, verifying protocol parameters, and ruling out EMI sources before replacing hardware. In practice, when I see a clean mechanical system with gradual drift and Yaskawa deviation alarms, I treat signal integrity as the prime suspect before reaching for the gain parameters. Feedback Device And Encoder Issues Encoder and resolver problems are a classic source of position deviation. VIYORK’s Yaskawa fault-code summaries list entire ranges of encoder-related alarms, covering wiring faults, data errors, calibration issues, low encoder-battery voltage, and communication failures between encoder and drive. Industrial Automation Co. stresses that encoder feedback errors can arise from loose or broken connections, mechanical misalignment of the encoder, or damage to the encoder itself. Mitchell Electronics, which focuses on servo motor troubleshooting, adds that damaged encoder cables, connectors, or disks manifest as positioning errors and unstable motion. In the field, an encoder that is starting to fail does not always produce a neat, repeatable encoder alarm. Instead you may see intermittent position trips, random overspeed alarms, or a motor that occasionally “jumps” while the commanded trajectory is smooth. If the encoder is shaft-mounted or uses a coupling, any slip on that coupling will cause the encoder to report a position that differs from the actual load. Feedback polarity is another source of trouble. VIYORK notes that incorrect speed-feedback polarity, or miswired encoder phases, can lead to stalling and erratic motion; swapping encoder lines or Hall signals and confirming the 5 V encoder supply and reference are standard corrective actions. Whenever I face unexplained position deviation alarms, one of my first tests after mechanical inspection is to examine the encoder wiring and connectors under magnification, pull on each conductor, and verify the encoder supply voltage and ground reference right at the motor. Mechanical Slip And Misalignment No amount of tuning can overcome mechanics that move independently of the motor. THM Huade describes servo motor alignment as the precise matching of the motor shaft to the driven load, warning that misalignment causes vibration, heat, premature bearing wear, torque loss, and poorer positioning accuracy. They also point out that misalignment symptoms include unusual noise, excessive vibration, overheating of the motor housing, and reduced positioning accuracy. Electroda practitioners remind us that belt slip, loose couplings, worn pulleys, and weak return springs can all cause the tool point to drift away from its nominal zero position over many cycles. This is particularly insidious when the mechanism settles in a new “soft zero” without obvious noise or alarms until the deviation accumulates to the trip threshold. The solution is mechanical discipline. THM Huade recommends shutting down and electrically isolating the system, cleaning and leveling mounting surfaces so the motor is not distorted, using proper alignment tools to correct angular and parallel misalignment, verifying that flexible couplings are correctly sized and installed, then retesting at low speed and recalibrating while monitoring vibration. Even in smaller systems, the principle holds. A comment from an Ikon flybarless discussion on RC helicopters emphasizes physically adjusting servo arms to align travel instead of relying solely on electronic trim. In industrial terms, that translates to centering mechanics and coupling positions first, then using software offsets sparingly. If your axis only hits its mark with large electronic offsets, you have mechanical trouble waiting to happen. Tuning And Servo Loop Dynamics Poor tuning can turn a marginal system into one that constantly trips on position deviation. VIYORK’s examples with MHMA digital AC servos illustrate two extremes. With gain set too high, the system experiences self-excited oscillation at power-on and raises alarm No.16. With gain set too low, the motor “crawls” at very low speed, alternating speed-up and slow-down cycles instead of moving smoothly. PMD’s discussion of common motion problems explains that dynamic tracking error, not just final position error, matters in many applications. High servo gains reduce tracking error but increase the risk of oscillation; lower gains improve stability but allow more position lag, especially during acceleration and deceleration. Advanced techniques such as velocity and acceleration feedforward, cascaded position and velocity loops, and carefully chosen sampling times help reduce tracking error, but the fundamentals still apply: you must tune the system aggressively enough to follow the commanded path without exciting resonances. Yaskawa drives often provide auto-tuning and vibration-suppression functions, which can help, but they assume that mechanics and wiring are sound. VIYORK notes that vibration-related alarms and auto-adjustment errors are often hints that mechanical rigidity is insufficient or that couplings and mounting need improvement, not that you should blindly raise or lower gains. A practical rule I use is simple. If the axis drifts slowly and quietly, look at noise, feedback, and mechanics first. If it chatters, hums, or oscillates near the end of the move and trips on deviation or overspeed, then bring tuning and mechanical stiffness to the front of the investigation. Power Quality, Grounding, And Drive Health Multiple sources, including BIN95 and InRobots, emphasize that overheating, power quality issues, and poor grounding are among the most common causes of servo drive failures. Overvoltage and undervoltage alarms, overcurrent trips, and internal power-supply faults can all show up in Yaskawa’s main-circuit and power-supply alarm ranges summarized by VIYORK. Industrial Automation Co. notes that overvoltage can be caused by a supply that is too high or by regenerative energy raising the DC-bus voltage during aggressive deceleration. Their recommendation is to verify supply voltage, consider installing a braking resistor, and optimize deceleration. Undervoltage errors are typically linked to drops in input power, failing power supply components, or loose wiring. From a position-deviation standpoint, unstable power and poor grounding do two things. They create intermittent resets and brownouts that cause axes to stop mid-travel and lose their position reference. They also increase electrical noise and stress on internal components, which then feed back into feedback and communication problems. InRobots points out that more than a third of servo drive failures stem from poor ventilation or blocked filters, which is a simple maintenance issue. They recommend keeping drive cabinets clean, monitoring temperature, maintaining fans, and replacing them periodically. When you see a Yaskawa position deviation error combined with power, temperature, or axis-common alarms, treat the electrical environment as seriously as the motion control. Harsh Environments, Motor Shorts, And Repeat Faults Industrial Monitor Direct describes a tough case in harsh, oily, high-temperature environments using Yaskawa SGDH drives. In these applications, motor shorts caused by oil and steam penetrating through motor shaft seals and housings led to repeated overcurrent alarms (A.10) and burnt ceramic resistors inside the drive. Standard line-side fuses and surge suppressors could not protect the drive from fault currents originating at the motor. Their root cause analysis highlights two key points. The motor insulation and sealing were not matched to the real environment, and operators repeatedly reset overcurrent alarms without addressing the cause, allowing damage to escalate. Their recommendations are very pragmatic. Mechanically, install proper shaft seals on all motors to prevent oil ingress, consider low positive-pressure kits around three psi in heavy vapor or oil-mist environments, and verify that motor environmental ratings truly match on-site conditions. Electrically and procedurally, treat overcurrent alarms like A.10 as serious events that cannot be simply cleared. Use the HMI to enforce lockouts after a fault, remove the operator’s ability to endlessly reset critical alarms, and track fault frequency, allowing only a limited number of resets per drive per day. They also explicitly warn against inserting extra fuses between the drive and motor, because this can interfere with the drive’s internal short-circuit protection and make failures worse. They also note that upgrading from older SGDH units to Sigma-5 SGDV drives improved short-circuit protection logic and provided clearer fault indication through codes such as A.100. Combined with shaft sealing and stricter alarm handling, some sites reportedly reduced Yaskawa servo-drive failure rates by more than eighty percent. While these are overcurrent cases rather than “pure” position deviation alarms, in practice the same harsh conditions that damage insulation also corrode connectors, contaminate encoders, and create intermittent faults that first appear as positioning issues. Treat the mechanical and environmental root causes with the same seriousness you give to the electrical ones. A Step-By-Step Troubleshooting Workflow Begin With Safety And Fault Information Before touching a Yaskawa drive, follow the safety practices outlined by BIN95, Yaskawa’s general troubleshooting guides, and others. Lock out and tag out the machine. Wait for DC bus capacitors to discharge fully, which can take several minutes. Use insulated tools and appropriate PPE, and do not megger-test a motor with the drive still connected. Then capture information. Note the exact Yaskawa alarm codes, any axis-common warnings, and the context: whether the trip happens at startup, during motion, at stop, or randomly. Check the drive’s fault history if available, as InRobots and Industrial Automation Co. suggest, to look for patterns rather than isolated events. A recurring pair of alarms, such as an encoder warning followed by position deviation, points you toward feedback; a pattern of undervoltage and deviation alarms during peak load points you toward power. Distinguish Drift, Offset, And Following Error Clarifying how the axis misbehaves helps narrow the list quickly. If the axis starts correctly but gradually moves off target over hundreds of cycles while the environment is stable, as in the Elektroda pick-and-place case, noise and mechanical slip are prime suspects. If the axis is consistently off by the same distance after every move, especially after power cycling, you are likely dealing with a homing, reference, or scaling issue, or with mechanical zero shifting. If the axis tracks acceptably until heavy acceleration, deceleration, or near a specific setpoint, and then trips with a sharp position deviation or overspeed alarm, tuning, mechanical resonance, or travel limits are in play. PMD emphasizes that dynamic tracking error during motion can matter more than final settling error. Many Yaskawa position deviation faults are triggered dynamically during demanding parts of the profile, not after everything has come to rest. Perform A Mechanical Walk-Down With power off and the system safely isolated, inspect the mechanics end to end. Check that the motor is firmly mounted and that the base or machine frame is not cracked or warped. Verify couplings, keyways, and clamping hubs are tight and show no fretting or shine that would indicate slip. Inspect belts and pulleys for wear, missing teeth, or contamination; a belt that jumps a tooth will give you a substantial position error in a single cycle. THM Huade recommends cleaning and leveling the mounting surfaces, correcting angular and parallel misalignment using proper tools, and verifying that flexible couplings are correctly sized. If the axis has a home sensor or mechanical hard stop, confirm that it has not physically shifted. Use alignment marks, dial indicators, or laser tools where appropriate. If you can release the motor mechanically and move the axis by hand, feel for tight spots, play, or backlash. Any intermittent resistance or slack can translate directly to varying position deviation under servo control. Verify Encoder And Feedback Path Next, focus on the encoder. Inspect connectors on both the motor and drive for contamination, loose pins, or bent contacts. Gentle tugging on each conductor can reveal broken strands crimped into a terminal. Mitchell Electronics recommends checking the power supply at the motor terminals with a multimeter to ensure the encoder’s supply voltage and ground are within specification and stable. If your Yaskawa drive is showing explicit encoder-related alarms like Alarm No.22, or encoder backup and communication faults in the A.810–A.891 and A.C20–A.CC0 ranges summarized by VIYORK, prioritize encoder troubleshooting. Verify the encoder type and wiring match the drive configuration. If possible, view encoder position counts while manually moving the axis slowly; jittering or discontinuous counts are a red flag. When stalling or unstable motion is accompanied by signs of incorrect feedback polarity, VIYORK suggests swapping feedback lines such as tachometer or encoder phases and confirming the encoder supply and ground reference are correct. Always document the original wiring before making changes. Investigate Command Signals And Noise If the encoder and mechanics check out, return to the command side. In pulse-train systems, use the controller’s diagnostics to verify that it is outputting pulses in the expected direction and quantity. Then examine cable routing. Separate AC mains and motor power cables from low-level command and feedback cables as much as possible. Avoid running them in the same conduit or bundle. The Elektroda practitioner’s experience that most drift cases stem from AC noise is worth taking seriously. Install an AC line noise filter on the control panel supply if one is not present. Use twisted pairs for CW and CCW or pulse and direction signals. Replace any generic unshielded cable with shielded cable rated for industrial motion control and ground the shield at a single point as recommended. Ferrite beads or cores on noisy lines can help suppress high-frequency interference. Industrial Automation Co. also recommends checking communication cables and connectors on digital networks and ensuring protocol and parameter settings match between drive and controller. After making these changes, repeat a long run under the same conditions that previously produced drift and compare the results. Elektroda suggests logging commanded versus received pulses over several hundred cycles, then repeating the test after noise-mitigation steps to confirm improvement. Review Drive Parameters And Control Mode Once wiring and mechanics are under control, turn to configuration. Yaskawa drives expose numerous parameters that govern control mode, pulse formats, maximum speeds, and gains. VIYORK highlights practical examples. In position-control mode, if the controller sends pulse and direction signals but the motor turns only one way for both forward and reverse, the drive may still be set for quadrature A/B input. They note that setting parameter No42 to select pulse and direction mode resolves this in affected systems. They also show that excessively high gain parameters such as N.10, N.11, and N.12 in some Yaskawa digital AC servo systems cause self-excited oscillation and alarm No.16. Reducing gain removes the oscillation. Conversely, gains set too low produce low-speed crawling behavior, with the motor speeding up and slowing down at very low speeds. In these cases, increasing gain or enabling automatic gain adjustment helps. Industrial Automation Co. and MroElectric recommend using the drive’s tuning tools and configuration software to review maximum speed limits, acceleration and deceleration profiles, and motion limits. Misconfigured maximum speed parameters can lead to overspeed alarms like A.510, and poorly chosen limits can interact with deviation detection thresholds to create false trips. Where possible, back up current parameter sets, then compare them against known-good configurations or factory defaults. Restore parameters that are clearly out of range or inconsistent with the motor and mechanics. Check Power Quality And Grounding At this point, if position deviation alarms persist, re-examine power and grounding. BIN95 and InRobots both stress that voltage fluctuations, loose connections, and poor grounding are major contributors to servo drive issues. Verify that input voltage to the Yaskawa drive matches its nameplate and is stable under load. Look for signs of overheating around terminals and contactors. Tighten all power and control terminals to the manufacturer’s recommended torque, as BIN95 suggests. Inspect grounding conductors for corrosion or looseness; InRobots notes that grounding resistance should remain low, with one ohm or less as a typical good target. If overvoltage alarms are present, follow Industrial Automation Co.’s guidance by checking deceleration rates and considering a braking resistor sized correctly for the application. If undervoltage alarms appear, suspect upstream transformers, power supplies, or loose mains wiring. Run Controlled Test Moves And Trend Error With the mechanical, feedback, command, and power elements addressed, perform controlled test moves. Start at reduced speed and load, logging position error, motor current, and any vibration or noise. Gradually increase speed and load toward production levels. PMD recommends analyzing dynamic tracking error rather than only final position. Observe whether deviation spikes during acceleration, deceleration, or near particular positions. Use the drive’s diagnostic plotting or waveform tools if available. In some cases, adding modest velocity or acceleration feedforward, where supported, can reduce tracking error without compromising stability, but this should be done methodically and within the manufacturer’s tuning framework. If the axis passes low-speed and low-load tests but fails at full production speeds with clean mechanics and wiring, you may be approaching the limits of the motor-drive-load combination, and derating or mechanical redesign might be necessary. Decide When To Repair Or Replace If position deviation errors remain after systematic checks, consider the health of the drive and motor. BIN95 notes that typical servo drive life expectancy is about eight to fifteen years under normal conditions, with better environments and preventive maintenance pushing drives toward the upper end. InRobots warns that neglecting maintenance leads to overheating failures and repair costs several times higher than proactive care. Roc Industrial outlines a repair process for Yaskawa servo drives that includes detailed evaluation, component-level repairs, and full-load testing under simulated real-world conditions. They highlight their ability to handle position error calibration and other complex faults and note that all repairs are backed by comprehensive warranties. Field repair by in-house technicians is reasonable for tasks such as fan replacement, cleaning, terminal re-torquing, and parameter restoration, especially when those technicians are ESD-trained and have the right tools, as BIN95 and Mitchell suggest. However, they also caution that severe symptoms such as burned or cracked PCBs, persistent or cryptic faults after basic checks, or a lack of access to OEM diagnostic software are signals to engage the manufacturer or a certified service center. Preventing Position Deviation Problems Before They Start Position deviation problems are often late-stage symptoms of issues that could have been caught during routine maintenance. Several sources converge on the same theme: structured preventive and predictive maintenance greatly reduces servo problems. BIN95 and InRobots both recommend regular inspections and cleaning of servo drives and control cabinets, monitoring temperature, tightening terminals, and logging faults for trend analysis. InRobots adds specific guidance on fan and capacitor maintenance, including typical fan replacement intervals and capacitor life, and notes that keeping drive temperature below around one hundred thirty degrees Fahrenheit is a practical guideline. ACS Industrial emphasizes daily visual checks and listening for unusual noise, weekly cleaning and connection checks, monthly lubrication and performance testing where applicable, and periodic professional maintenance by experts who can detect subtle problems and optimize settings. CMIndustrySupply encourages routine verification of servo drive accuracy to catch drift or degradation before it causes downtime, and reminds machine builders that servo drives are robust and efficient when properly maintained but vulnerable to contamination and misalignment. Industrial Monitor Direct’s experience with Yaskawa SGDH drives in harsh environments underlines the importance of matching motor and drive environmental ratings to the actual site conditions, adding shaft sealing or pressurization as needed, and enforcing disciplined alarm handling. Their data showing more than eighty percent reduction in failure rates after combining environmental sealing with strict alarm strategies is a compelling case for investing in prevention. From a controls perspective, PMD’s discussion of tracking error and servo dynamics highlights the benefit of revisiting tuning and motion profiles periodically as mechanical conditions change. Tightening mechanics without adjusting gains, or vice versa, can inadvertently push the system toward the edge of stability. In my own practice, the lines that stay out of trouble are the ones where maintenance treats drives and motors as critical assets, not black boxes. Cabinets stay clean, logs are reviewed, fans get replaced before they seize, encoder batteries are changed on schedule, and position deviation alarms are treated as early warnings rather than nuisances to be reset. When To Call For Help There is a point where continuing to chase a position deviation problem on your own costs more than bringing in specialized help. Mitchell Electronics recommends consulting manufacturer documentation and technical support whenever systematic checks of power, connections, feedback, controller settings, mechanical components, load, and environment do not resolve the issue. Industrial Automation Co. and Roc Industrial both stress that when basic troubleshooting has been exhausted, providing detailed information to the drive manufacturer or repair center accelerates diagnosis. That information includes the exact Yaskawa model and firmware, alarm codes and fault history, operating conditions, and any changes recently made to the system. You should strongly consider external help when position deviation alarms persist despite a clean mechanical, electrical, and parameter review; when the drive shows internal system alarms indicating possible hardware faults; when PCBs show visible damage; or when your team lacks access to model-specific tuning and diagnostic tools. Outsourcing at that point is usually far cheaper than extended downtime and repeated part swapping. Short FAQ Can I just increase the Yaskawa position deviation limit so the alarm goes away? Raising deviation limits without fixing the underlying cause is risky. VIYORK’s code summaries and Industrial Automation Co.’s guidance both imply that deviation and overspeed alarms protect you from real mechanical, electrical, or configuration issues. Raising thresholds may stop nuisance trips briefly but can allow damaging conditions to continue unchecked. It is better to use the alarm as a diagnostic clue and correct the root cause, then, if appropriate, fine-tune limits within the ranges recommended by Yaskawa. Do position deviation errors always mean the drive is bad? No. Roc Industrial explicitly notes that position error is usually related to feedback, tuning, or parameter problems. Many cases are resolved by fixing encoders, wiring, mechanics, noise, or improper configuration. Only when those are ruled out and the drive still misbehaves, especially in combination with internal fault codes and visible damage, should you suspect the drive electronics themselves. Should I add fuses between the Yaskawa drive and motor to protect against faults? Industrial Monitor Direct specifically warns against inserting extra fuses between a Yaskawa servo drive and motor. Doing so can interfere with the drive’s internal short-circuit protection and can make faults more severe. The safer approach is to rely on the drive’s built-in protection, make sure its parameters are set according to Yaskawa’s recommendations, and address the root causes of faults such as environmental contamination and motor insulation breakdown. In the end, a Yaskawa position deviation alarm is not just a code on a keypad; it is the drive telling you something in your system is no longer under tight control. If you treat that alarm as a partner rather than a nuisance and work through mechanics, feedback, signals, and configuration in a disciplined way, you can usually bring the axis back into line and keep it there for years. References https://www.plctalk.net/forums/threads/servos-keeps-losing-position.143016/ https://www.viyorktech.com/what-are-the-common-fault-codes-of-yaskawa-servo-drives.html https://cmindustrysupply.com/blogs/servo-drive-maintenance-how-to-prevent-problems-before-they-happen https://www.elektroda.com/rtvforum/topic4141045.html https://www.mitchell-electronics.com/8-tips-for-troubleshooting-servo-motor-problems/ https://www.rocindustrial.com/repair-page/servo-drive-position-error-calibration-for-yaskawa https://thmhuade.com/how-to-fix-servo-motor-alignment-issues/ https://www.yaskawa.com/about-us/contact-us?_com_yaskawa_contact_us_contactUsActionPortlet_selectedDocumentId=MTN-5UDT6W&_com_yaskawa_contact_us_contactUsActionPortlet_safetyText=true https://blog.acsindustrial.com/servo-motors/extend-lifespan-performance-preventive-maintenance-strategies-servo-motors/ https://forum.arduino.cc/t/servo-not-going-to-the-right-position/1056444

25-11-25

202511-25

Yaskawa Servo Drive Alarm Reset: Step-by-Step Procedures

Yaskawa servo drives sit right in the critical path of motion on CNC machines, robots, and automated lines. When a servo alarm pops up, the plant does not care whether it is an A.71 overload or an A.30 regenerative fault. What everyone sees is a machine that just stopped making parts. As someone who spends a lot of time in hot panels and cramped machine bases, I can say that how you reset a Yaskawa alarm matters just as much as how fast you reset it. Done correctly, you clear the fault, protect the hardware, and keep the line stable. Done carelessly, you turn a simple alarm into a cooked motor, a blown drive, or a safety incident. This article walks through practical, field-tested procedures for resetting Yaskawa servo drive alarms. It focuses on what to do before you hit reset, the different ways you can reset alarms, and how to handle some of the more common Yaskawa alarm families. The guidance draws on Yaskawa’s own safety notes, third‑party troubleshooting resources, and real‑world alarm lists for Yaskawa servo and robot drives, and it is written for technicians and engineers who actually work on the floor. Safety And Documentation Come First Before touching a servo drive, you should be on the same page as Yaskawa’s own safety guidance. The official FAQs and technical notes around servo alarm reset are very clear: their advice is only an addition to the product manuals, not a replacement. They explicitly state that users must read and understand the product instruction manual before installing, servicing, or operating any Yaskawa product. They also emphasize that only qualified personnel should install, operate, or maintain the drive, and they remind you that incorrect work exposes you to high voltages and potential serious injury or death. In practice, that means you should treat any alarm reset procedure as part of a controlled maintenance task, not as a button‑mashing exercise. Lockout and tagout of upstream power, verifying the DC bus has discharged, and following the warnings and cautions in the official manual are not optional. The FAQ material also notes that documentation and FAQs cannot cover every wiring variant and machine configuration, so you should always cross‑check against the specific servo model manual and the machine builder’s documentation. The legal language may feel dry, but it reflects a simple reality. Yaskawa drives sit on dangerous DC buses and can move heavy equipment instantly once an alarm disappears. Do not attempt any deeper reset method if you are not trained and authorized to work at that level. How Yaskawa Servo Alarms And Resets Work A Yaskawa servo drive constantly monitors current, DC bus voltage, heatsink temperature, encoder feedback, and internal logic. When it detects an abnormal condition, it raises an alarm code on the display or robot teach pendant and asserts a servo alarm output. A common convention is an ALM output that goes active when a fault exists. At the same time, an alarm history buffer usually captures the last several alarms. One servo alarm guide notes histories on the order of ten entries, which is enough to see whether you are dealing with a one‑off event or a repeating pattern. On the input side, many servo systems provide an /ALM‑RST (alarm reset) input. Once the root cause is fixed, you can assert this input from a pushbutton or PLC output to clear resettable alarms. That same alarm guide warns that certain encoder related alarms do not clear through /ALM‑RST and require cycling control power instead. It also notes that resetting without removing the cause can leave the motor running under fault conditions and can damage the servo system. That aligns with Yaskawa’s own advice and is the main reason a disciplined procedure matters. Alarm codes themselves follow a structured pattern. In Yaskawa robot servo drivers, for example, codes like A.02, A.04, A.05, A.71, A.72, and many others map to specific failures such as parameter errors, capacity mismatches, overloads, regenerative circuit issues, DC bus faults, or encoder problems. Cross‑vendor guides show similar families across brands: power anomalies, overcurrent and thermal protection, mechanical overload or stall, feedback errors, communication faults, parameter or memory issues, and main power stage failures. Understanding which family a particular Yaskawa alarm belongs to is the foundation for choosing the right reset strategy. A Structured Workflow Before You Press Reset On a busy line, the temptation is to clear the alarm and “see if it comes back.” Every reliable servo troubleshooting reference warns against that habit. A servo alarm article aimed at general drives states that you should never clear an alarm before understanding it and that you should record the exact code and machine state, then consult the model‑specific manual. A troubleshooting guide from an industrial repair house reinforces the same pattern: focus on concrete symptoms and codes first, work external causes, and only then decide whether you are resetting, repairing, or replacing hardware. In practical terms, a disciplined workflow for Yaskawa servo alarms looks like this. Step 1: Capture The Alarm And Context The first step is to read and record the alarm exactly as the drive reports it. That means the full alphanumeric code, any additional LED behavior, and what the machine was doing at the time. A resource that catalogs Yaskawa robot servo alarms shows codes such as A.02 for user parameter failure due to abnormal memory data, A.05 for servo motor and servo drive capacity mismatch, A.71 for high‑load overload, A.72 for low‑load overload during continuous operation above rated torque, and so on. The difference between, say, A.71 and A.72 matters when you decide whether to adjust duty cycle, mechanical design, or both. Along with the code, note the axis, direction of motion, commanded speed or torque, and whether the alarm occurred during acceleration, steady state, deceleration, or at power‑on. The MRO Electric troubleshooting article on Yaskawa drives emphasizes that fault logs and alarm histories are key for seeing repeated patterns and verifying that an issue is solved rather than just cleared temporarily. Step 2: Check Power, Wiring, And Mechanical Load The next step is to check for external causes, because multiple independent sources stress that many servo drive faults trace back to power quality, wiring, and mechanical issues rather than failed electronics. A servo alarm overview points to power anomalies such as unstable supply, overvoltage or undervoltage, and poor power‑line connections as primary alarm triggers. Another guide notes that undervoltage alarms often result from supply dips, missing phases, blown fuses or contactors, or loose mains terminals. For Yaskawa robot alarms like A.40 (main circuit DC overvoltage) and A.41 (main circuit DC low voltage), this is exactly where you should look. At the same time, inspect the mechanical side. A servo drive failure guide notes that mechanical problems such as wear, looseness, or jamming in connected machinery can increase load or resistance and cause overload alarms. Yaskawa robot codes A.71 and A.72 explicitly reflect overload conditions, where torque exceeds the rating for a certain interval or under sustained operation. Removing belts or uncoupling the load to see whether the motor and drive run cleanly is a standard way to separate mechanical from electrical causes, and it is recommended in troubleshooting articles for both Yaskawa and other brands. Step 3: Inspect Motor And Feedback Motor problems can masquerade as drive faults. Field experience shared by repair specialists indicates that output short alarms and overcurrent alarms often come back to damaged or intermittently grounding motor cables. A drive error summary for Yaskawa SGDH notes A.C as output short circuit and A.E as overvoltage, and independent repair notes mention cable damage and grounded motors as frequent root causes for such alarms. Use insulation tests and resistance checks where appropriate to confirm that motor windings are not shorted to ground and that phase resistances are balanced. For encoder related Yaskawa codes such as A.81 (absolute encoder backup battery power loss), A.83 (battery voltage drop), A.82 (encoder memory checksum error), A.84 (abnormal encoder data), A.85 (encoder overspeed at power‑on), and A.86 (encoder internal temperature too high), focus on battery condition, connector integrity, cable routing, and environmental conditions around the encoder. A servo alarm list also mentions AC8 as absolute encoder clear abnormality or incorrect multi‑rotation limit, and codes A.C9, A.CA, and A.Cb as communication or parameter failures between servo and encoder. For these alarms, replacing a weak battery, reseating encoder connectors, verifying encoder parameters, and re‑establishing the absolute position are the actions to perform before attempting a reset. Step 4: Review Parameters And Commands Parameter and command issues are another major root cause. The Yaskawa robot alarm list includes parameter‑related faults such as A.02 for user parameter failure due to abnormal EEPROM data and A.04 for parameter settings outside allowable range. It also lists A.03 for abnormal detection in the main circuit decoder or power circuit. In practice, that means you should verify that key parameters for motor model, ratings, limits, and control mode match both the motor nameplate and the machine builder’s documentation. A multi‑brand alarm guide advises backing up parameter sets, using vendor initialization or reset functions where available, and then restoring only necessary values to avoid rewriting read‑only or unsupported items. For Yaskawa drives, that translates to capturing the existing parameter set before making changes and avoiding random edits in an attempt to clear a stubborn alarm. On the command side, several Yaskawa robot alarms relate to input quality, such as A.b1 for speed command A/D converter fault, A.b2 for torque command A/D converter fault, and A.bF as a general system alarm. If these codes appear, you should confirm the integrity and scaling of analog signals or fieldbus commands, not just reset and hope the drive “forgets” the problem. Step 5: Choose The Correct Reset Method Only after the root cause has been addressed should you reset the alarm. A general servo alarm article outlines a safe baseline procedure: power off the drive in a controlled way, review alarm information against the code list, troubleshoot based on the cause, confirm that the fault is eliminated, then power on again and check for remaining alarms. If alarms persist on power‑up, it suggests using brand‑specific reset methods such as a manual reset key on the drive, a reset command from the controller, or built‑in automatic reset modes after fault clearance. Different reset mechanisms have different implications. Some are gentle and fully controlled by the PLC or robot controller. Others, such as power cycling, stress components and can even be involved in causing certain faults. The rest of this article looks at those methods in more detail. Common Reset Methods On Yaskawa Servo Drives Servo alarm references and vendor FAQs describe several ways alarms are typically reset. Yaskawa’s own FAQ material around servo alarm reset focuses largely on safety and qualified personnel, but cross‑referencing with servo drive alarm guides and encoder reset procedures makes it clear what practitioners actually use on the floor. Panel Or Operator Based Reset Many servo systems allow alarms to be reset directly from an operator panel. A servo alarm article that describes a generic servo system notes that alarms can be reset by pressing the up and down keys simultaneously on the panel operator. While that example is associated with a particular servo brand, the pattern is similar on many Yaskawa‑based systems where the front‑mounted digital operator or the robot teach pendant includes a reset or clear function. The advantage of a panel reset is that it is quick and does not require rewiring or PLC logic changes. It also tends to respect whatever interlocks the manufacturer has built into the operator. The downside is that it is easy for operators to press the panel reset without recording the alarm code or verifying that the root cause has been removed. If you rely heavily on panel‑side resets, build a discipline that requires technicians to log the code and conditions before clearing the alarm and to check the alarm history afterward. Digital Input Alarm Reset (/ALM‑RST) A more controlled approach is to wire a dedicated reset input from your safety‑approved control system. The servo alarm guide that discusses ALM and /ALM‑RST shows this pattern clearly. Once the alarm condition is eliminated, asserting /ALM‑RST allows the drive to clear faults that are designed to be resettable. This is typically wired to a PLC output, panel pushbutton, or robot controller output, and the machine sequence logic decides when it is safe to issue a reset. The benefit is that you can coordinate alarm reset with other actions, such as verifying that e‑stops are released, guards are closed, and axes are in a safe position. However, the same source warns that encoder‑related alarms often ignore /ALM‑RST and only clear when control power is cycled. Another limitation is that the reset input can be overused: poorly written PLC code that automatically pulses reset as soon as an alarm appears can mask serious problems and create repeating, hard‑to‑trace fault cycles. In a well‑designed cell, the reset input is only activated as part of a deliberate recovery sequence that mirrors the steps laid out earlier. Power Cycling And Automatic Reset Power cycling is the blunt instrument of servo resets. The general servo alarm reset article notes that, after the root cause is fixed, you can power the drive off and then back on to clear many alarms. Several Yaskawa‑focused troubleshooting guides also assume that once wiring or load issues are corrected, a power cycle will return the drive to a ready state. There are two problems with leaning on this too heavily. First, frequent on and off switching stresses the surge current limiter and main power circuitry. Yaskawa robot alarm A.74, defined as surge current limiter overload due to frequent switching of the main power supply, exists for exactly that reason. Second, power cycling often removes valuable evidence. Some drives clear parts of their alarm history or detailed diagnostics at power‑off, leaving you with only the current code but not the sequence that led up to it. Automatic reset modes are another variant. Some servo drives, once configured, can attempt an automatic reset of certain transient alarms. A cross‑vendor guide mentions such capabilities generically but stresses that you must review the drive manual to understand which alarms can be safely auto‑reset and under what conditions. For safety‑critical axes or heavy mechanical loads, relying on automatic reset can be risky unless the system integrator has designed the entire sequence around it. Special Procedures For Absolute Encoder Alarms (A.00, A.81 And Related) Absolute encoder alarms deserve their own treatment because they affect position data and homing behavior. A detailed article from Precision Zone describes a method, specifically named Method 2, for clearing A.00 or A.81 alarms on Yaskawa Sigma I servo drives with 12‑bit absolute encoders when the standard method fails. According to that description, this method applies to motors whose nameplate starts with SGMG and includes a trailing W after the kilowatt rating, indicating a 12‑bit absolute encoder. The procedure as explained begins with prerequisites. Before attempting the reset, you must confirm that the battery, encoder, and encoder cable are in good condition. Precision Zone notes that you need a push‑button box wired into the CN2 connector cable, and they mention that they sell a kit or can modify the cable in‑house if the user cannot solder the pushbutton. With the motor connected, you power on the drive and let it run for about three minutes, which allows the drive and encoder logic to stabilize. Then you press and hold the added pushbutton for at least three seconds, with the recommendation to hold it for roughly fifteen to thirty seconds to improve the success rate. After that, you power cycle the drive and check whether the alarm has cleared and whether the motor can be jogged normally. Precision Zone reports that it is common for this reset not to work the first time and advises repeating the procedure three to four times if necessary. If the alarm is still present after several attempts, their guidance is to short‑circuit terminals P and S for at least five minutes, then repeat the same procedure again. In most cases, they state, this clears the alarm. If alarms persist even after shorting P and S and repeating the steps, they recommend contacting their technical support for further troubleshooting. This is a specialized method, and it is important to highlight what it implies. Clearing A.81 and similar absolute encoder alarms does not magically restore position data. By definition, an absolute encoder backup battery power loss erases stored position. That means after such a reset, you must follow the robot or machine builder’s procedure to re‑establish the machine’s reference and any multi‑turn limits, and you must update any safety‑related position checks that rely on the encoder’s absolute counts. Handling Common Yaskawa Alarm Groups Once you understand the categories and reset options, it becomes easier to decide how to respond to specific Yaskawa alarm codes. The following sections group several common robot and servo alarms by their nature and summarize the primary corrective focus once the alarm appears. Parameter And Combination Alarms Alarms such as A.02, A.03, and A.04 revolve around parameters and internal data validity. The Yaskawa robot alarm list describes A.02 as user parameter failure due to abnormal EEPROM data and A.04 as user parameter settings outside the allowable range. A.03 relates to abnormal detection in the main circuit decoder or power circuit. When these alarms occur, resetting alone is meaningless. The correct approach is to check whether recent parameter changes were made, compare the current parameter set to a known good backup, and restore or correct values as required. The multi‑vendor alarm guide’s advice to back up parameters and to avoid editing read‑only items is especially relevant here. A.05 flags a servo motor and servo drive capacity mismatch. The alarm list describes this as a combination alarm where the drive and motor capacities do not match. In practice, you should verify model numbers, ratings, and encoder types against the drive’s allowable combinations. Clearing the alarm will not fix a genuinely mismatched pair. Overload, Overcurrent, And Thermal Alarms Overload and thermal alarms protect the motor and drive from sustained stress. Yaskawa robot alarms A.71 and A.72 cover high‑load overload and low‑load overload under continuous high torque respectively. Alarm A.10 signals overcurrent through the IGBT radiator that causes overheating, and A.7A is defined as servo radiator overheating. A separate servo alarm guide notes that drive heatsink overtemperature in some vendors occurs around 239°F for certain frames and around 257°F for larger ones; the exact values for Yaskawa drives are model dependent and found in the official manuals, but the practical implications are similar. For these alarms, recommended responses include reducing the mechanical load, adjusting duty cycle, checking for binding or misalignment, and improving cabinet ventilation and drive cooling. Cleaning filters and heatsinks, ensuring fans actually run, spacing drives so that airflow is not obstructed, and checking ambient temperature inside the enclosure are all part of the reset‑before‑restart process. Only after temperatures are back in range and loads have been corrected should you reset and test. Treating overload or thermal alarms as a nuisance and repeatedly resetting them guarantees premature failures. Regenerative And Braking Alarms Regenerative and braking alarms occur when the system cannot safely dissipate energy returned from the load. The Yaskawa robot list defines A.30 as regenerative circuit or resistor failure and A.32 as regenerative overload when returned energy exceeds resistor capacity. It lists A.73 as dynamic brake overload when rotating energy exceeds brake resistance and A.74 as surge current limiter overload due to frequent switching of the main power supply. For A.30 and A.32, standard recommendations include inspecting the regenerative resistor, verifying wiring, and replacing components if they are damaged or undersized. A cross‑vendor alarm guide notes that overvoltage and regenerative faults often follow rapid deceleration of high‑inertia loads or overhauling axes, and that properly sizing the braking resistor and softening decel ramps eliminated most trips on a packaging line in one documented case. For A.73, you should examine the dynamic brake circuit and the mechanical deceleration profile. Alarm A.74 is essentially a warning that frequent on and off switching is overstressing the surge limiter, which brings us back to the earlier point that power cycling is not a harmless reset method. DC Bus, Power Supply, And Communication Alarms DC bus and power supply alarms highlight upstream issues. A.40 represents main circuit DC overvoltage, while A.41 is main circuit DC low voltage. A.F1 indicates a power line under‑phase where one supply phase is missing. CPF00 is described as an operator–servo transmission error, indicating a communication fault between operator and drive. In response, check input voltage with a meter under load, inspect mains terminals for looseness or discoloration, verify fuses and contactors, and correct any missing phase conditions. For CPF00 and similar communication alarms, you should examine operator and encoder communication cables and connectors, check node addresses and baud rates where fieldbus is involved, and ensure proper termination. A servo alarm article notes that RS‑485 Modbus links can run to about 4,000 ft when wired and terminated correctly, but that long runs require careful shielding and routing to avoid noise‑induced communication faults. Encoder, Battery, And Feedback Alarms Encoder and battery alarms require both electrical and data‑integrity responses. As already mentioned, A.81 and A.83 point to absolute encoder backup battery loss or low voltage, A.82 and A.84 indicate encoder memory or data errors, A.85 flags encoder overspeed at power‑on, and A.86 reports encoder internal temperature too high. Alarm AC8 indicates absolute encoder clear abnormality or incorrect multi‑rotation limit setting, and A.C9, A.CA, and A.Cb cover communication failure between servo and encoder, encoder parameter failure, and encoder feedback error or incorrect communication content respectively. Recommended steps, drawn from the Yaskawa robot alarm list and servo alarm guides, include replacing low or depleted batteries, checking encoder wiring and connectors for looseness or damage, verifying encoder parameters and multi‑rotation limits, and re‑establishing the absolute position if data has been erased. Where encoders are mounted in hot environments, you should also verify that ambient temperature is within specification and that no external heat sources are driving the encoder beyond its thermal limits. Resetting these alarms without fixing the underlying electrical or configuration problem can lead to repeat faults and loss of positional trust. Motion And Command Alarms Finally, motion and command related alarms tell you that something about the commanded movement or position error is outside the drive’s limits. Yaskawa robot alarm A.51 signals motor overspeed, while A.C1 indicates servo overspeed with the motor out of control. Alarm A.d0 flags position error pulse overflow where deviation exceeds parameter Pn505. Together with A.b1 and A.b2, which reflect speed and torque command A/D converter faults, and A.bF, which is a general system alarm, these codes point toward either overly aggressive motion profiles, incorrect tuning, or deeper system faults. The Yaskawa servo troubleshooting article from MRO Electric notes that positioning errors, oscillations, and overshoot are often tied to feedback problems, incorrect PID tuning, or mechanical wear and misalignment. On the reset side, you should first adjust motion profiles to reasonable acceleration and speed, inspect gears and couplings for backlash or play, and verify tuning parameters. Only then should you clear these alarms and execute low‑speed test moves while watching for residual oscillation or following error. Example Alarm Codes And Reset Focus The table below summarizes several of the Yaskawa robot servo alarm codes mentioned earlier and highlights the primary focus before performing a reset. The descriptions are paraphrased from the Yaskawa robot alarm list and related servo alarm guides. Alarm code Category and meaning (per published lists) Reset focus after root cause is addressed A.02 User parameter failure due to abnormal EEPROM data Compare parameters to a known good backup, correct corrupted or out‑of‑range values, then reset A.04 User parameter settings outside allowable range Bring parameters back into allowable ranges, avoid unsupported combinations, then reset A.05 Servo motor and servo drive capacity mismatch Verify motor and drive model compatibility and ratings, correct any mismatch before resetting A.10 Overcurrent through the IGBT radiator causing overheating Inspect for shorts on motor side, excessive load, and inadequate cooling, fix issues, then reset A.71 High‑load overload where torque exceeds rating for several seconds or tens of seconds Reduce peak load, adjust mechanical design or duty cycle, then reset and test under controlled conditions A.72 Low‑load overload under continuous operation above rated torque De‑rate continuous load, review cycle times and duty, verify motor sizing, then reset A.7A Servo radiator overheating Improve ventilation, clean heatsinks and filters, verify fan operation and ambient temperature, then reset A.30 Regenerative circuit or resistor failure Inspect and, if needed, replace regenerative resistor and wiring, then reset and test decel moves A.32 Regenerative overload where returned energy exceeds resistor capacity Increase resistor capacity or soften decel ramps, then reset and validate with worst‑case moves A.73 Dynamic brake overload when rotating energy exceeds brake resistance Review braking method and mechanical inertia, correct any mismatches, then reset A.74 Surge current limiter overload due to frequent ON/OFF switching of main power Reduce power cycling frequency, correct start/stop logic, allow rest time, then reset A.40 Main circuit DC overvoltage Check line overvoltage and regenerative events, verify braking resistor, correct issues, then reset A.41 Main circuit DC low voltage Diagnose supply dips, missing phases, loose terminals, or blown fuses, fix them, then reset A.F1 Power line under‑phase (one supply phase not connected) Restore full three‑phase supply with correct wiring and fusing before any reset CPF00 Operator–servo transmission error Check operator and communication cable connections and settings, correct faults, then reset A.81 Absolute encoder backup battery power loss, position data erased Replace battery, re‑establish reference position and multi‑turn data, then reset using the prescribed method A.83 Absolute encoder battery voltage drop Replace weak battery, confirm voltage, and only then reset A.82 Encoder memory checksum error Inspect encoder and cable, replace if faulty, and re‑initialize encoder data before reset A.84 Abnormal encoder data Troubleshoot cabling, connectors, and encoder, correct faults, then reset and re‑home as required A.85 Encoder overspeed at power‑on Review mechanical coupling and startup sequence, correct causes of overspeed, then reset A.86 Encoder internal temperature too high Improve cooling around the encoder or reduce thermal load, allow temperature to drop, then reset AC8 Absolute encoder clear abnormality or incorrect multi‑rotation limit setting Verify and correct encoder clear process and multi‑rotation parameters, then reset and re‑home A.C9 Communication failure between servo and encoder Reseat connectors, correct wiring and shielding, and verify configuration before resetting A.CA Encoder parameter failure Correct encoder parameter settings and restore valid data prior to reset A.Cb Encoder feedback error or incorrect communication content Fix wiring, shielding, or encoder hardware, then reset and verify stable motion A.b1 Speed command input A/D converter fault Check command signal source and wiring, correct electrical issues, then reset A.b2 Torque command input A/D converter fault As with A.b1, inspect torque signal path, correct faults, then reset A.bF General system alarm indicating a servo failure Use alarm history and diagnostics to identify specific cause, correct it, then reset A.51 Motor overspeed Reduce commanded speed and adjust profiles, check for mechanical over‑run, then reset A.C1 Servo overspeed, motor out of control Investigate feedback, tuning, and mechanical coupling, correct issues, then reset cautiously A.d0 Position error pulse overflow where deviation exceeds Pn505 Adjust tuning and motion profile, check for mechanical binding or backlash, then reset and test Using Alarm History And Documentation To Stay Ahead Servo alarm references and troubleshooting guides repeatedly emphasize the value of alarm history. The servo alarm article that discusses ALM and alarm history notes that systems typically store the most recent alarms, making it possible to see whether you are dealing with a one‑time event or a pattern. The general servo troubleshooting workflow from Industrial Automation Co and the Yaskawa‑focused guide from MRO Electric both push the same point: document what you see and what you do. In practical terms, that means recording alarm codes, axis, time, operating mode, and corrective actions, and periodically reviewing that log. If you notice repeated A.30 and A.32 regenerative alarms on the same axis during deceleration, that is a strong signal to revisit braking resistor sizing and decel ramps instead of continuing to reset. If you see A.81 and A.83 absolute encoder battery alarms recurring more frequently than expected, it is time to inspect battery quality, environment, and maintenance intervals. Preventive measures recommended in servo alarm guides include routine inspection of terminals and connectors for looseness, periodic insulation resistance checks on motors and cables, cleaning cabinets, backing up parameter sets after commissioning, and keeping copies of relevant Yaskawa manuals with the machine. These actions do not eliminate alarms, but they reduce the number of surprises and make reset decisions more informed. Short FAQ Q: Is it safe to just power cycle a Yaskawa servo drive when an alarm appears? A: Power cycling is a valid reset method but should not be your first move. Alarm guides warn that frequent on and off switching can overload surge limiters, which is exactly what Yaskawa alarm A.74 represents. More importantly, cycling power without understanding the code discards context and may leave serious issues unresolved. You should capture the alarm, correct the root cause, and then use a controlled reset method, whether that is a panel reset, /ALM‑RST input, or a single power cycle. Q: Do I always need to re‑home after clearing an encoder battery alarm like A.81? A: The Yaskawa robot alarm list notes that A.81 indicates absolute encoder backup battery power loss and that position data is erased. That means you should expect to re‑establish the machine reference or home position and verify multi‑turn limits after clearing the alarm. Skipping that step can leave safety zones and position‑based logic relying on invalid data. Q: When should I stop troubleshooting and involve Yaskawa or a repair provider? A: If alarms indicate internal hardware failure, if the same alarm returns quickly after proper corrective actions, or if specialized procedures like the absolute encoder reset method from Precision Zone fail to clear A.00 or A.81, it is time to involve the OEM or a qualified repair provider. Many drives store fault histories and provide detailed diagnostics that specialist technicians can interpret more effectively, and repair services often back their work with multi‑year warranties, which is cheaper than repeated unscheduled downtime. At the end of the day, resetting a Yaskawa servo alarm is not about finding the fastest way to turn a red light green. It is about understanding what the drive is telling you, fixing the underlying problem, and then using the right reset method so the machine goes back into production safely and stays there. That is how you keep both the plant and the servo packs happy. References https://admisiones.unicah.edu/uploaded-files/FJIXOM/9OK169/YaskawaV1000ManualFaultCodes.pdf http://www.chem.cmu.edu/groups/bier/procedure_files/mac/Yaskawa_J7-Drive_Manual.pdf https://engineering.purdue.edu/ece477/Archive/2016/Fall/477grp5/Files/docs/final%20datasheets/servo%20packs.pdf https://people.wallawalla.edu/~ralph.stirling/classes/engr480/docs/Motoman/dx100_operator_155507-1CD.pdf https://www.justanswer.com/computer/icz5c-customer-yaskawa-servo-drive.html https://okplazas.com/blog/yaskawa-robot-servo-driver-alarm-codes-and-troubleshooting-methods.html https://precisionzone.com/how-to-reset-12-bit-absolute-encoder-for-yaskawa-sigma-1-drives-method-2/ https://www.sahinbearing.com/blog/servo-motor-alarm-list-meanings-and-correction-settings https://www.yaskawa.com/about-us/contact-us?_com_yaskawa_contact_us_contactUsActionPortlet_selectedDocumentId=DRV-5NSKGT&_com_yaskawa_contact_us_contactUsActionPortlet_safetyText=true https://www.amikong.com/Blog/n/servo-drive-alarm-code-guide

25-11-25

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