VFD Drives Troubleshooting — real-world interview & field troubleshooting questions with clear, practical answers. Tap any question to open its answer. Showing the first 70 questions free. The complete question bank is available as a PDF below. VFD Power-Up & Startup Faults Q1 The VFD display is completely blank when the main supply is switched ON. What would you check first? Answer Verify the incoming voltage phase-to-phase, input fuses or MCCB, isolator, control power supply, and the drive's DC bus or power-supply indicators. If the correct input voltage reaches the drive but the display remains dead, follow the manufacturer's diagnostic procedure for an internal power-supply fault. Q2 The VFD powers up, but it immediately shows an undervoltage fault. How would you find the cause? Answer Measure the input voltage while the drive is energized and check for a weak supply, loose terminals, blown input fuse, or excessive voltage drop in the feeder. Compare the meas...