VFD Control Board Failure
6 Oct 2026
A variable-frequency drive that trips, will not start or shows a fault code often has a failed board rather than a failed motor. Finding which board, and which stage on it, is what makes repair possible.
Two boards, two kinds of fault
A drive usually has a control board, which holds the logic and communications, and a power board, which holds the rectifier, DC bus and output stage. Control-board faults tend to show as startup, display or communication problems. Power-stage faults show as trips, blown fuses and damaged switching devices.
Frequent failures
Ageing DC-bus capacitors, failed gate drivers, damaged output transistors, faulty current sensors and failed switch-mode supplies are typical. Heat and dust are common underlying causes, and a failed cooling fan accelerates all of them.
What a good diagnosis looks for
Diagnosis checks the power supply to the control board, the gate drive signals and the condition of the power devices. It looks for the reason a part failed, such as a failed fan, a motor insulation problem or a bad supply, so the repair is not undone by the same cause.
Safety
Drives hold dangerous voltage in their DC bus after power is removed. Boards are discharged and handled with care. Do not open a drive on site unless you are qualified to.
Repair and testing
Repair replaces failed power devices, drivers and capacitors and addresses damaged traces. The board is tested for rails and gate signals and, where practical, run under load before return. Repair does not include functional-safety re-certification.
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