A growing library of technical articles covering common fault patterns, diagnostic procedures, and maintenance best practices for industrial automation equipment.
Fault Pattern Guides
DC Bus Overvoltage Faults
Causes, diagnosis flow, and resolution for OV/overvoltage faults on variable frequency drives. Covers regenerative energy, deceleration ramps, and braking resistor sizing.
Output Overcurrent (OC) Faults
Distinguishing between genuine overcurrent, earth faults, and IGBT short-circuits. Measurement procedures for output phase-to-phase and phase-to-ground resistance.
Earth Fault / Ground Fault Detection
How VFDs detect earth faults, why motor cable length matters, and step-by-step megger testing procedures at the drive output terminals.
Encoder Feedback Errors
Diagnosing encoder communication loss, ABZ signal integrity, battery backup for absolute encoders, and cable shield grounding best practices.
Communication Timeout Faults
Profinet, EtherCAT, and Modbus TCP timeout diagnosis. Network topology checks, switch configuration, and cable certification procedures.
Safety Circuit Diagnostics
Understanding safety relay feedback circuits, dual-channel monitoring, light curtain alignment, and e-stop chain troubleshooting.
Thermal Overload Faults
Drive vs motor thermal models, I²t calculations, ambient temperature derating, and cooling fan inspection procedures.
Power Supply Diagnostics
24V DC rail troubleshooting, ripple measurement, load distribution analysis, and SMPS component-level fault identification.
Motor Phase Loss Detection
Three-phase supply monitoring, single-phasing risks, contactor contact inspection, and phase rotation verification.
Manufacturer Guides
Siemens SINAMICS Fault Code Map
Overview of Fxxxxx fault code structure, alarm classes, and reaction patterns across G120, S120, and S210 series.
ABB ACS Drives — Error Code Families
Understanding the ACS580/ACS880 fault hierarchy, fault word structure, and parameter-level diagnostic access.
Lenze i-Series Error Structure
Decoding Lenze i550/i700 E-xxxx codes, diagnostic LED patterns, and keypad navigation for fault history.
Yaskawa GA700 / GA500 Faults
Dot-format fault codes (A.xxx, E.xxx, L.xxx), alarm vs fault distinction, and auto-reset configuration.
Danfoss VLT Alarm Reference
Alarm/Warning numbering system, alarm log access via LCP keypad, and extended status word decoding.
Fanuc CNC Alarm Categories
SV (servo), PS (power supply), SP (spindle), OT (overheat), and IO alarm groups with PMC diagnostic ladder access.
Best Practices
Before You Start a Repair
- Record the exact error code, any sub-codes, and the sequence in which faults appeared
- Check the equipment’s built-in fault history log — most modern drives and PLCs store the last 8–32 faults with timestamps
- Note the operating conditions when the fault occurred (load level, speed, ambient temperature)
- Always apply LOTO before opening any cabinet or disconnecting wiring
- Verify DC bus capacitors are discharged before touching power stage components
Measurement Safety
- Use instruments rated for the voltage category of the circuit (CAT III for industrial distribution, CAT IV for supply origin)
- On VFDs: always measure DC bus voltage before assuming the unit is de-energized — capacitors can hold lethal charge for 10+ minutes after power-off
- Never disconnect encoder cables while the servo drive is enabled — this can cause uncontrolled motion
- When megger-testing motor insulation, disconnect the drive output first to protect IGBTs