The LED on the LightningTM II digital servo driver is currently* used as a general diagnostic indicator. During normal operation the LED remains constantly illuminated when the driver is idle, and flickers when the servo is issuing commands. If the LED is not illuminated at all, this indicates a problem, and you may experience problems with communication. Verify the power to the board is connected correctly (connector pins and voltage levels). If the power connection is correct, contact Cambridge Technology for technical support. * Future versions of the firmware might re-define this LED function