Year: 2025

Introduction

In the realm of modern industrial automation, servo drives, as the core components of precision control systems, play a pivotal role. The VEICHI SD700 series servo drives are highly regarded for their high performance and reliability, finding widespread applications in fields such as CNC machine tools, robots, printing machinery, and packaging equipment. However, various faults may occur during the use of these products, among which the ER.C90 fault is relatively common, manifesting as encoder communication abnormalities. If not addressed promptly, such faults can not only disrupt production processes but also potentially lead to equipment damage or safety hazards.

Based on the detailed version of the VEICHI SD700 servo system manual and practical engineering experience, this article provides an in-depth analysis of the ER.C90 fault and offers a comprehensive and practical guide for diagnosis and troubleshooting. The aim is to assist engineers and technicians in quickly locating problems and enhancing system stability.

Overview of the SD700 Servo System

The VEICHI SD700 series servo drive is a high-performance AC servo system suitable for 200V and 400V voltage classes, supporting servo motors with power ranges from 100W to 7.5kW. This system employs advanced vector control technology, combined with high-resolution encoder feedback, to achieve closed-loop control, ensuring high precision and high dynamic response of the system.

Main Component Names and Functions of the System

• Servo Drive Main Body: Includes a display panel, CHARGE indicator light, and CN series interfaces (such as CN1 control terminals, CN2 encoder interface, and CN7 USB communication terminal). The display panel is used to display status codes, fault codes, and parameter settings.
• Servo Motor: Equipped with incremental or absolute encoders, supporting multi-turn absolute position feedback.
• Encoder: The core feedback component, typically with a resolution of 17 or 24 bits, used to provide motor position and speed information.
• System Block Diagram: The main circuit includes power input, regenerative resistor, and motor output; the control circuit involves PLC upper computers, I/O signals, and communication modules. The SD700 supports multiple communication protocols, such as RS485, CANopen, and EtherCAT, facilitating integration into industrial networks. An example of system composition includes an upper computer (such as a PLC), servo drive, motor, and load, forming a closed-loop control link.

Role of the Encoder in the Servo System

The encoder serves as a bridge connecting mechanical and electrical components, converting the physical motion of the motor into digital signals and providing real-time feedback to the drive. The SD700 servo system mainly uses optical incremental or absolute encoders with resolutions as high as 16,777,216 pulses per revolution (24 bits).

Working Principle of the Encoder

The encoder generates A, B, and Z phase signals (for incremental types) or multi-turn absolute position data (for absolute types) through optical or magnetic grating disks. These signals are transmitted to the drive via the CN2 interface, and the drive calculates the motor position, speed, and torque deviations accordingly to achieve PID closed-loop regulation. If communication is interrupted, the drive cannot obtain accurate feedback, leading to system out-of-control and triggering the ER.C90 fault.

Description of the ER.C90 Fault

The ER.C90 is a specific fault code for the VEICHI SD700 servo drive, displayed on the panel, such as a red LED showing “ER.C90”. This fault is classified as a “Class 1” alarm, meaning “encoder communication fault: disconnection.”

When the drive detects a loss or abnormality in the encoder signal, it immediately stops the motor output and triggers this alarm. Symptoms include:

• The motor fails to start or stops suddenly.
• The system reports an error and cannot enter the enabled state.
• The upper computer monitoring shows zero or abnormal values for position feedback.

Analysis of Fault Causes

The root cause of the ER.C90 fault lies in the interruption of the communication link between the encoder and the drive. The main reasons include:

• Signal wire disconnection or poor connection: Cable breakage due to bending, pulling, or aging during use. Loose or oxidized CN2 plugs can also cause poor contact.
• Incompatible cable specifications: Using non-original cables or improper shielding layers can lead to signal distortion.
• Excessive cable length: Exceeding the recommended length causes significant signal attenuation.
• External interference: Electromagnetic interference from devices such as frequency converters and welding machines. Improper shielding grounding exacerbates the problem.
• Motor or encoder damage: Failure of the internal photoelectric components of the encoder or wear of the motor bearings leading to unstable signals.
• Incorrect parameter settings: Mismatched motor group parameters or incorrect drive power ratings.
• Drive hardware failure: Damage to the communication module on the main board.

Diagnostic Steps

Diagnosing the ER.C90 fault requires a systematic approach, starting from simple to complex. Ensure that power is disconnected before operation to avoid the risk of electric shock.

• Preliminary Inspection: Observe the panel display to confirm it is an ER.C90 fault. Use the manual FN000 to view the alarm records.
• Cable Integrity Test: Use a multimeter to measure each signal wire of the CN2 interface to check for continuity and short circuits.
• Connection Inspection: Check the CN2 and motor-end plugs for dust, dirt, or oxidation. Re-plug and test.
• Cable Specification Verification: Measure the cable length and confirm that the model matches the requirements in the manual.
• Interference Investigation: Check the shielding layer grounding and keep away from interference sources. Try adding magnetic rings for filtering.
• Parameter Confirmation: Check parameters such as Pn000 (encoder type) and Pn100 (inertia ratio) for correctness.
• Hardware Testing: Replace with spare cables or motors for testing.
• Advanced Diagnosis: Connect the CN7 USB and use upper computer software to monitor Un003 (rotor position).

Solutions

Provide specific solutions for each cause:

• Disconnection/poor connection: Replace the cable or tighten the plugs.
• Incompatible specifications: Select the correct cable model and shorten the length.
• Excessive cable length: Optimize the layout to reduce the length.
• Interference: Improve grounding and add magnetic rings.
• Hardware damage: Replace the encoder or motor.
• Parameter errors: Reset the Pn parameters and restore factory settings before reconfiguration.
• Drive failure: Contact VEICHI after-sales service to replace the unit.

Preventive Measures

Prevention is better than cure. The following strategies can reduce the incidence of the ER.C90 fault:

• Regular maintenance: Check cables and connections every quarter and clean dust.
• Environmental optimization: Install in ventilated cabinets to avoid high temperatures. Use EMI filters.
• Cable management: Use fixed clips to secure cables and prevent pulling.
• Parameter backup: Use the upper computer to export parameters for easy restoration.
• Training: Train operators on correct installation to avoid misoperations.
• Redundancy design: In critical applications, use dual encoders or wireless feedback.

Case Studies

• Case 1: A printing factory using an SD700 servo drive for roller positioning suddenly encountered an ER.C90 fault, and the motor stopped. Diagnosis revealed a broken A-phase wire of the CN2 interface. Replacing the cable and adding a magnetic ring resolved the issue.
• Case 2: A factory had a welding machine nearby with poor grounding, causing interference. Adding shielding resolved the ER.C90 fault.

Advanced Debugging Techniques

For stubborn faults, use the upper debugging tools in Chapter 14 of the manual:

• Upper computer connection: Connect via the CN7 USB, install the driver, and open the software.
• Real-time monitoring: View Un140 bus voltage and Un003 position feedback.
• Digital oscilloscope: Capture the encoder signal waveform and analyze distortion.
• Auxiliary functions: Perform FN105 vibration initialization and use EASYFFT to eliminate mechanical interference.

Conclusion

Although the ER.C90 fault is common, it can be efficiently resolved through systematic diagnosis and guidance from the manual. The VEICHI SD700 servo system is renowned for its high reliability, and correct maintenance can ensure long-term stable operation. This article provides a comprehensive reference, hoping to be of assistance. For more details, refer to the official manual or contact support.

Abstract
The Leadshine L7 series AC servo drives are crucial components in the field of industrial automation. The startup display sequence reflects the device’s initialization status and operational readiness. This paper provides an in-depth analysis of the phenomenon where users observe a brief display of “1.d002” followed by a switch to “00ST,” indicating a normal initialization process. By interpreting the manual, safety precautions, and incorporating online resources from similar EL7 series, it explores the meanings of display codes, diagnostic methods, potential causes, and optimization strategies, aiming to offer comprehensive guidance to engineers and technicians.

Introduction
In modern industrial automation systems, servo drives play a pivotal role. The Leadshine L7 series AC servo drives utilize the latest DSP from Texas Instruments (TI), featuring high integration and reliability. Users often encounter startup display issues, such as the display showing “1.d002” briefly after power-on, followed by a switch to “00ST.” This paper centers on this phenomenon, conducting a systematic analysis by combining excerpts from the user manual and online resources, aiming to assist users in understanding the technical implications of the display sequence and providing practical diagnostic steps.

Servo Drive Fundamentals

Basic Principles

Servo drives drive servo motors to achieve precise motion by receiving command signals from an upper-level controller. The fundamental principles include triple-loop control (position loop, speed loop, and current loop), with PID algorithms at the core.

L7 Series Characteristics

The L7 series belongs to AC servo drives, supporting 220VAC input and a wide power range. The manual emphasizes that improper operation can lead to severe consequences, and users must adhere to safety precautions.

Key Components and Initialization

The key components of a servo system include the drive, motor, and encoder. The drive integrates a DSP processor, and the initialization process involves self-tests, parameter loading, and status monitoring.

Display Panel Basics

The display panel employs a seven-segment LED digital tube, supporting status display, parameter settings, and alarm prompts. Understanding these codes is crucial for diagnosing device status.

Control Modes and Parameter Settings

Servo drives offer control modes including position, speed, and torque modes. Parameter settings are achieved through panel buttons or MotionStudio software.

Safety Guidelines

The manual stresses that product storage and transportation must comply with environmental conditions, and user modifications will void the warranty.

Overview of the L7 Series

Product Features and Updates

The Leadshine L7 series is a fully digital AC servo drive, utilizing TI DSP, supporting stiffness tables, inertia identification, and vibration suppression. The version has evolved from V1.00 to V2.10 with continuous updates.

Application Areas and Manual Structure

The L7 series finds wide applications in PLC control, robotic arms, and other fields. The manual structure covers the preface, safety matters, specifications, installation, wiring, commissioning, and maintenance.

Wiring and Version Descriptions

Wiring includes power, motor, encoder, and I/O ports. The version description indicates program compatibility and content updates.

Display Panel in Detail

Operation Interface and Key Functions

The L7 drive’s operation interface consists of a 6-digit LED digital tube and 5 keys for status display and parameter settings.

Initialization and Monitoring Mode Codes

Upon power-on, the panel first displays initialization codes. “1.d002” may be a custom or transient display, and switching to “00ST” indicates a standby state. Monitoring mode codes include position deviation, motor speed, etc.

Alarm Code Interpretation

Alarm codes start with “Er,” and the absence of “Er” indicates normal operation.

Diagnostic Analysis

Core Phenomenon Interpretation

The display showing “1.d002” briefly followed by a switch to “00ST” is a normal sequence. The initialization process includes self-tests and parameter loading.

Potential Causes Explored

Potential causes include normal boot-up, configuration influences, and external factors.

Diagnostic Steps and Methods

Diagnostic steps include checking the display history, software verification, and factory reset.

Troubleshooting

Non-Normal Situation Exclusion Methods

If non-normal, exclusion methods include power supply checks, wiring verification, parameter resets, and software tuning.

Common Faults and Solutions

Common faults such as overcurrent and overload are unrelated to the display sequence.

Applications and Optimization

Case Studies: CNC Machine Tools and Robotic Arms

Case 1: A CNC machine tool uses the L7 to control axes, and a normal startup sequence ensures precision. Case 2: A robotic arm in bus mode uses EtherCAT synchronization to avoid delays.

Optimization Strategies and Future Trends

Optimization strategies include adjusting control modes and vibration suppression. Future trends involve integrating AI tuning.

Conclusion
The transition from “1.d002” to “00ST” indicates a normal state. Mastering diagnostic methods can enhance application efficiency. It is recommended to refer to the manual and technical support to ensure stable system operation.

The EST900 series inverter from Yiste, as a high-performance vector inverter, is widely applied in the control and speed regulation of three-phase asynchronous motors. This article, based on the official manual, will elaborate in detail on its operation panel functions, parameter setting methods, external terminal control and speed regulation implementation, as well as handling measures for common fault codes, helping users quickly master the usage skills.

I. Introduction to Operation Panel Functions and Parameter Settings

(A) Overview of Operation Panel Functions

The EST900 series inverter comes standard with an LED operation panel, which offers a variety of functions:

• Status Monitoring: It can display key information such as operating frequency, current, voltage, and fault codes in real time.
• Parameter Setting: It supports viewing and modifying functional parameters.
• Operation Control: Control commands such as start, stop, and forward/reverse rotation can be executed through the panel.
• Indicator Lights: It is equipped with indicator lights including RUN (operation), LOCAL/REMOT (control source), FWD/REV (direction), and TUNE/TC (tuning/torque/fault), which visually reflect the equipment status.

(B) Factory Parameter Settings

During debugging or when parameters are in disarray, a factory reset operation can be performed:

• Steps:
  • Enter the FP – 01 parameter.
  • Set it to 1 (restore factory parameters, excluding motor parameters).
  • Press the ENTER key to confirm.
  • Wait for the display to restore, indicating parameter initialization is complete.
• Notes:
  • FP – 01 = 2 can clear fault records and other information.
  • FP – 01 = 4 can back up the current parameters.
  • FP – 01 = 501 can restore the backed-up parameters.

(C) Password Setting and Clearing

To prevent misoperation, a user password can be set:

• Setting a Password:
  • Enter FP – 00 and set it to a non-zero value (e.g., 1234).
  • After exiting, the password needs to be entered when accessing parameters again.
• Clearing a Password:
  • Set FP – 00 to 0.

(D) Parameter Access Restrictions

Parameter access can be restricted in the following ways:

• Parameter Group Display Control:
  • Set the FP – 02 parameter to control whether Group A and Group U parameters are displayed.
  • For example, setting it to “11” can hide some parameter groups to prevent mismodification.
• Prohibition of Modification during Operation:
  • Some parameters marked with “★” cannot be modified during operation and need to be set after shutdown.

II. External Terminal Forward/Reverse Rotation Control and Potentiometer Speed Regulation

(A) External Terminal Forward/Reverse Rotation Control

• Wiring Terminals:
  • D11: Forward rotation (FWD)
  • D12: Reverse rotation (REV)
  • COM: Digital input common terminal
• Parameter Settings:
  | Parameter Code | Name | Setting Value | Description |
  | —- | —- | —- | —- |
  | F0 – 02 | Operation Command Selection | 1 | Terminal control |
  | F4 – 00 | D11 Function Selection | 1 | Forward rotation |
  | F4 – 01 | D12 Function Selection | 2 | Reverse rotation |
  | F4 – 11 | Terminal Command Mode | 0 | Two-wire type 1 |
• Note: If a three-wire control system is used, set F4 – 11 = 2 or 3 and cooperate with other DI terminals.

(B) External Potentiometer Speed Regulation

• Wiring Terminals:
  • +10V: Positive pole of potentiometer power supply
  • GND: Negative pole of potentiometer power supply
  • A11: Analog voltage input (0 – 10V)
• Parameter Settings:
  | Parameter Code | Name | Setting Value | Description |
  | —- | —- | —- | —- |
  | F0 – 03 | Main Frequency Command Selection | 2 | A11 |
  | F4 – 13~F4 – 16 | A11 Curve Settings | Adjust according to actual conditions | Minimum/maximum input corresponds to frequency |
• Tip: It is recommended that the potentiometer resistance be between 1kΩ and 5kΩ to ensure that the current does not exceed 10mA.

III. Common Fault Codes and Handling Methods

The EST900 series inverter has a comprehensive fault diagnosis function. The following are common faults and their handling methods:

(A) Overcurrent Faults

(B) Overvoltage Faults

(C) Other Common Faults

(D) Fault Reset Methods

• Press the STOP/RESET key on the panel.
• Set a DI terminal to the “Fault Reset” function (F4 – xx = 9).
• Write “2000H = 7” through communication.
• Power off and restart (wait for more than 10 minutes).

IV. Conclusion

The Yiste EST900 series inverter is powerful and flexible in operation, capable of adapting to various industrial scenarios. Through the introduction in this article, users can master the following key contents:

• Basic usage methods of the operation panel and parameter setting skills.
• How to control and regulate the speed of the motor using external terminals and a potentiometer.
• Diagnostic ideas and handling skills for common faults.
• Effective use of password management and parameter protection mechanisms.
  During actual use, it is recommended that users strictly follow the manual specifications for wiring and parameter setting, and regularly carry out maintenance work to ensure the long-term stable operation of the equipment.

1. Introduction

In industrial automation systems, frequency inverters are the key components for controlling motor speed and torque. The operational stability of an inverter directly determines the reliability of an entire production line. Among numerous industrial drive products, the Emerson EV2000 series is well recognized for its robust performance, precise vector control, and adaptability to a wide range of applications — from pumps and fans to textile machines and conveyors.

However, during field operation or long-term use, some users may encounter a display message reading “P.oFF” on the inverter’s LED panel.
At first glance, this may look like a severe fault such as a power module failure or control board defect.
In reality, “P.oFF” is not a typical fault alarm, but rather a protective shutdown state known as “Undervoltage Lockout (LU).”

This article provides a comprehensive technical analysis of the P.oFF condition in the Emerson EV2000 inverter.
It integrates official documentation, field diagnostic data, and maintenance experience to explain its causes, triggering mechanism, troubleshooting methods, and preventive measures.

2. Technical Definition of P.oFF

According to the official EV2000 User Manual:

“When the DC bus voltage drops below the undervoltage threshold, the inverter outputs a protection signal and displays ‘P.oFF’ on the LED panel.”

This statement reveals the essence of the fault:
P.oFF occurs when the inverter’s internal DC bus voltage (DC link voltage) falls below a safe limit.

Normally, the rectifier circuit inside the EV2000 converts three-phase AC power (380V ±10%) into DC voltage of approximately 540–620 VDC.
When the input power drops, the rectifier is damaged, the DC bus capacitors age, or the braking unit malfunctions, the DC voltage may fall below the predefined undervoltage threshold (around 300 VDC).
At that point, the inverter automatically enters a protective lockout to prevent unstable operation or component damage.

It is important to note that unlike “E” code faults (such as E001 – overcurrent, E002 – overvoltage), P.oFF does not trigger a trip alarm.
Instead, the inverter temporarily disables output until the voltage returns to normal.

3. Electrical Mechanism Behind the P.oFF State

To fully understand this phenomenon, we must look into the EV2000’s main power structure.

3.1 Composition of the Main Circuit

The inverter’s main power path includes the following key components:

• Input terminals (R, S, T): three-phase AC supply
• Rectifier bridge module: converts AC to DC
• DC bus capacitors: stabilize and filter DC voltage
• Braking unit and resistor: absorb regenerative energy from motor deceleration
• IGBT inverter bridge: converts DC back into PWM-controlled AC output

3.2 How Undervoltage Lockout Is Triggered

The control board constantly monitors the DC bus voltage.
When it detects a voltage lower than the threshold (typically around 300–320 VDC), it executes the following logic sequence:

1. Disables IGBT outputs — halting motor operation
2. Displays “P.oFF” on the panel
3. Waits in standby mode until the DC bus recovers above the normal level (typically >380 VDC)

This mechanism is a preventive protection system designed to shield the inverter from grid voltage sags, capacitor discharges, or transient faults.
Thus, P.oFF is not an error; it is an intentional safety lock.

4. Root Causes of the P.oFF Condition

From field experience and manual analysis, the following are the most common reasons for P.oFF to appear.

(1) Input Power Problems

• Voltage imbalance between the three input phases (>3%)
• Mains voltage below 320V AC or fluctuating severely
• Loose power terminals or poor contact
• Excessive line voltage drop due to long cable runs

These account for nearly half of all P.oFF cases and are primarily related to unstable supply power.

(2) Faulty Rectifier Module

A damaged or open diode inside the rectifier bridge reduces the DC bus voltage, often accompanied by audible hum or irregular current flow.

(3) Aged or Leaky DC Capacitors

Over time, electrolytic capacitors lose capacitance and their internal ESR increases.
This weakens their ability to smooth the DC voltage, resulting in a temporary drop when load or braking energy fluctuates — enough to trigger an undervoltage lock.

In units running for 3–5 years, this is one of the most frequent root causes.

(4) Braking Circuit Malfunction

A shorted braking unit or resistor constantly discharges the DC bus, causing the voltage to collapse.
To verify, disconnect the braking circuit and power on again — if P.oFF disappears, the issue lies in that circuit.

(5) Momentary Power Interruptions

Factories with welding machines, compressors, or heavy inductive loads can experience grid sags.
If the inverter’s “Ride-through” (instantaneous power-loss recovery) function is disabled, any short voltage dip may cause P.oFF.

5. Systematic Troubleshooting Process

To effectively diagnose and repair the P.oFF issue, engineers can follow a step-by-step workflow:

Step 1 – Observe the Symptom

• Panel displays “P.oFF”
• No “E” fault code is present
• Motor stops automatically
• After a few minutes, the inverter may restart on its own

If these conditions match, the inverter is in undervoltage lockout mode.

Step 2 – Measure Input Power

Use a multimeter to measure R–S–T line voltages:

• Normal range: 380–440 V
• Below 360 V or phase difference >10 V → adjust power source or connections

Step 3 – Measure DC Bus Voltage

Check voltage across (+) and (–) terminals:

• Normal: 540–620 VDC
• Below 300 VDC → rectifier or capacitor failure

Step 4 – Isolate the Braking Circuit

Disconnect the braking resistor/unit and test again.
If the problem disappears, replace or repair the braking components.

Step 5 – Test the DC Capacitors

After power-off, measure capacitance and discharge rate:

• If voltage drops to zero within a few seconds, leakage is severe
• Replace if measured capacitance is <70% of rated value

Step 6 – Verify Control Power

Check auxiliary voltages (P24, +10V, +5V).
Low control supply may cause false P.oFF detection.

6. Repair and Recovery Procedures

Once the root cause has been identified, proceed with the following repair actions:

1. Stabilize Power Supply
   • Re-tighten input terminals
   • Ensure voltage balance across all three phases
   • Install an AC reactor or voltage stabilizer if necessary
2. Replace Faulty Components
   • Replace aged electrolytic capacitors as a set
   • Replace damaged rectifier modules with same-rated units
3. Inspect Braking Circuit
   • Measure P–PR resistance for shorts
   • Ensure thermal relay contacts (TH1, TH2) are functioning
4. Enable Ride-through Function
   The EV2000 allows short-duration undervoltage ride-through; enabling this can prevent false P.oFF triggers caused by brief voltage dips.
5. Recommission and Verify
   • Power up and observe DC voltage stability
   • Run at light load for 10 minutes, then gradually increase load
   • Once the display shows “RDY”, the inverter is ready for normal operation

7. Preventive and Optimization Measures

To avoid recurring undervoltage lockouts, adopt the following best practices:

7.1 Power-Side Protection

• Use proper circuit breakers or fuses rated for inverter service
• Add a DC reactor for harmonic suppression and voltage stabilization
• Use thicker power cables if installation distance is long

7.2 Environmental Control

• Maintain cabinet temperature below 40°C
• Ensure clean airflow; avoid dust, oil, or moisture buildup
• Regularly clean cooling fans and filters

7.3 Periodic Maintenance

• Measure DC bus voltage and capacitor health yearly
• Replace capacitors after ~3 years of continuous operation
• Test rectifier module every 5 years or after heavy load operation

7.4 Parameter Optimization

• Set appropriate acceleration/deceleration times to avoid current spikes
• Enable AVR (Automatic Voltage Regulation) and Current Limit functions
• Review output terminal settings in parameter group F7 to prevent incorrect logic assignments

8. Case Study: Intermittent P.oFF on a 22kW Fan Drive

Background:
A 22kW EV2000 inverter controlling a centrifugal fan exhibited intermittent P.oFF shutdowns after six months of operation.

Symptoms:

• Occurred around 45 Hz operation
• The inverter automatically recovered after a few minutes
• Mains voltage appeared normal

Diagnosis:

• DC bus voltage fluctuated between 520–550V with periodic dips
• Two electrolytic capacitors found bulging and degraded
• Replaced capacitors → inverter operated normally

Conclusion:
The failure was caused by aged capacitors reducing DC storage capacity, resulting in transient undervoltage.
This is a classic “aging-induced P.oFF” scenario.

9. Conclusion

The P.oFF message on Emerson EV2000 inverters is not a random or critical failure, but a designed protective feature to safeguard the drive system when DC bus voltage drops abnormally.

Understanding its mechanism helps engineers correctly differentiate between true hardware faults and temporary protective lockouts.
By following a structured diagnostic approach — from input power verification to capacitor and braking circuit inspection — technicians can quickly restore normal operation.

Furthermore, implementing preventive maintenance and enabling built-in functions such as ride-through and AVR can significantly enhance long-term reliability.

As the design philosophy of Emerson EV2000 suggests:

“Reliability is not accidental — it begins with every small detail of protection.”

From Overheated IGBT Modules to Full System Recovery

1. Introduction

In modern screw air compressors, the variable frequency drive (VFD) is the core component responsible for controlling motor speed and optimizing power consumption.
The Chmairss VGS30A compressor, equipped with a 22 kW VEMC inverter, uses variable-speed control to maintain constant discharge pressure while achieving high energy efficiency.

However, after long-term operation, one of the most common issues that field engineers encounter is the “Err14 – Module Overheat” fault on the VEMC inverter.
This error not only causes system shutdown but also indicates potential thermal imbalance or hardware degradation inside the inverter.

This article provides a comprehensive technical explanation and a complete repair workflow — from understanding the root cause of Err14, diagnosing the issue step-by-step, to repairing and preventing future failures. It is based on real-world field data from a VGS30A compressor maintenance case.

2. Fault Symptoms and Display Information

(1) On the Main Control Panel (HMI)

The compressor controller repeatedly shows the following message:

STATE: MOTOR INV FAULT
CODE: 00014

Multiple entries appear in the fault history list (024–028), all labeled “MOTOR INV FAULT.”

(2) On the VEMC Inverter Panel

The inverter LED display reads:

Err14

The red alarm indicator is on, and the motor cannot start.
Once the contactor closes, the inverter trips immediately.

(3) PLC and System Reaction

The PLC detects the inverter fault signal and sends a stop command to the entire compressor.
Frequency display freezes at 0.0 Hz, power output shows 0.0 kW, and total run time stops accumulating.

3. Understanding the “Err14” Code — Module Overheat Fault

According to VEMC documentation:

Err14 = Module Overheat Fault (IGBT Overtemperature)

The inverter continuously monitors the IGBT module temperature via an NTC thermistor attached to the power module.
This analog signal is converted to a voltage and fed to the control CPU through an A/D converter.

• Normal temperature range: 25 °C – 75 °C
• Warning level: ~85 °C
• Trip threshold: ~95 °C

If the module temperature exceeds the limit or the temperature signal becomes abnormal (open circuit, short circuit, or unrealistic value), the inverter will immediately shut down to protect the IGBT module. The control CPU disables PWM output and reports Err14.

4. Common Root Causes of Err14

Based on maintenance experience and field diagnostics, there are five main categories of causes for Err14:

5. Step-by-Step Diagnostic Procedure

Step 1 – Inspect the Cooling Fan and Air Duct

1. Power on the inverter and check whether the internal cooling fan starts automatically.
2. If the fan does not spin, measure the voltage at the fan terminals (usually DC 12 V or DC 24 V).
   • Voltage present but fan not spinning → fan motor failure.
   • No voltage → main control board output failure.
3. Clean the air duct, dust filter, and heat-sink fins thoroughly.

Step 2 – Check Cabinet Temperature

• Use an infrared thermometer to measure temperature inside the control cabinet.
• If it exceeds 45 °C, install additional exhaust fans or ventilation openings.
• Avoid placing the cabinet near heat sources (e.g., compressor discharge pipe).

Step 3 – Test the NTC Thermistor

1. Power off and wait at least 10 minutes for discharge.
2. Remove the drive or power board.
3. Measure resistance between NTC terminals (typically around 10 kΩ at 25 °C).
4. Heat the sensor slightly with a hot-air gun — the resistance should decrease with rising temperature.
5. If resistance is fixed or open circuit → replace the thermistor.

Step 4 – Check the IGBT Power Module

1. Use a multimeter diode-test function to check each phase (U, V, W) to positive/negative bus.
2. Any shorted or low-resistance reading (< 0.3 Ω) indicates IGBT damage.
3. Verify that the power module is tightly clamped to the heat sink.
4. Reapply high-quality thermal grease (e.g., Dow Corning 340) if dried or cracked.

Step 5 – Check the Control Board Temperature Circuit

If all above components are normal but Err14 remains:

• Inspect connector pins (often CN6 or CN8) for oxidation or loose contact.
• Use an oscilloscope to observe temperature signal voltage (should decrease gradually as temperature rises).
• Constant 0 V or 5 V output → indicates A/D converter or amplifier failure.
• Replace the entire driver/control board if signal circuit is defective.

6. Case Study — Actual Field Repair of a VGS30A Compressor

Equipment details:

• Model: Chmairss VGS30A
• Inverter: VEMC 22 kW
• Total runtime: 7 303 hours
• Ambient temperature: ~38 °C
• Fault: Err14 appears within seconds after startup; fan not rotating

Inspection and Findings

After cleaning and replacing the fan, the inverter started normally.
After 30 minutes of continuous operation, module temperature stabilized at 58 °C, confirming successful repair.

7. Electrical and Thermal Theory Behind Err14

(1) Power Loss and Junction Temperature

The IGBT’s heat generation consists of conduction and switching losses:
[
P_{loss} = V_{CE} \times I_C + \tfrac{1}{2}V_{CE} I_C f_{sw} (t_{on}+t_{off})
]
If heat cannot be transferred efficiently to the heat sink, junction temperature (Tj) rises sharply, increasing conduction loss — a positive feedback that can lead to thermal runaway and module destruction.

(2) Importance of Thermal Interface

The thermal resistance (Rθjc) between IGBT and heat sink determines how quickly heat is removed.
Dried or aged thermal compound increases resistance several times, leading to localized hot spots even when load current is normal.

(3) Protection Logic Inside VEMC Drive

The inverter CPU continuously samples the temperature signal:

• Below 0.45 V (≈ 95 °C): trigger Err14 and shut down PWM output.
• Above 0.55 V (≈ 85 °C): allow reset condition.
• Open circuit: immediate fault lockout, manual reset required.

8. Preventive Maintenance Recommendations

Regular maintenance can extend inverter lifetime by 30–50 %, reduce downtime, and prevent expensive module failures.

9. Temporary Reset for Diagnostic Verification

If you suspect a false alarm:

1. Power off and wait at least 10 minutes for cooling.
2. Power on and press STOP/RESET.
3. If Err14 reappears immediately → likely sensor or circuit fault.
4. If it occurs after several minutes of operation → genuine overheating issue.

10. Troubleshooting Flow (Text Version)

Err14 Detected →
   ↓
Check Cooling Fan Running?
   ├─ No → Measure fan supply → replace fan if needed
   └─ Yes →
         ↓
Is Ambient Temperature >45°C?
         ├─ Yes → Improve ventilation
         └─ No →
               ↓
Measure NTC Thermistor Resistance
               ├─ Abnormal → Replace NTC
               └─ Normal →
                     ↓
Inspect IGBT Module & Thermal Grease
                     ├─ Abnormal → Reapply grease / replace module
                     └─ Normal →
                           ↓
Replace Driver Board (temperature circuit failure)

11. Practical Notes and Safety Reminders

• Always discharge DC bus capacitors before touching power terminals (wait >10 minutes).
• When replacing thermal grease, ensure no air gaps between module and heat sink.
• If replacing the IGBT module, apply torque evenly and use original insulation pads.
• Keep cabinet filters clean and avoid placing the compressor near exhaust heat or walls.
• Use infrared thermometer to monitor heat sink temperature during first startup after repair.

12. Lessons Learned

This case of the Chmairss VGS30A compressor with VEMC inverter Err14 demonstrates the critical role of thermal management in power electronics.
Although the message “Module Overheat” seems simple, it reflects a complex interaction between cooling airflow, thermal interface condition, and signal detection circuits.

Field statistics show:

• About 70 % of Err14 faults are resolved by cleaning the cooling path, replacing fans, or re-greasing the module.
• The remaining 30 % involve circuit faults or component failures (NTC or driver board).

Understanding these mechanisms allows engineers to diagnose quickly, repair efficiently, and reduce costly downtime.

13. Conclusion

The Err14 (Module Overheat) fault is not merely an alarm — it is the inverter’s self-protection mechanism preventing irreversible IGBT damage.
Proper analysis requires both electrical and thermal reasoning.
By following the structured diagnostic steps in this guide — inspecting the fan, air duct, thermistor, power module, and control board — maintenance engineers can isolate the root cause systematically.

Regular preventive maintenance, good ventilation, and periodic internal cleaning are the best strategies to ensure long-term reliability of VEMC inverters in air compressor applications.