Control board dead after a storm or power surge: what to check and what to tell the customer

Surges usually damage the input section of a board: a protective varistor (MOV) shorts and the board fuse opens, or the power supply fails. Sometimes the surge enters through a signal or communication line instead. Check the supply and the board's input fuse, look for burn marks near the power input, and test loads before installing a new board.

Single source ~45 min moderateBrands: All

Before you start

Verify the receptacle and circuit before blaming the appliance; storms also damage house wiring and breakers.
Never bypass a blown fuse with wire or a resistor.
Inverter boards: discharge and measure the DC bus before touching.

Diagnostic steps

Unlock all 8 steps with expected values

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