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Press and hold the Reset button on the operator box and observe the K1 LED. Then release the Reset button and observe the K1 LED.
If the light only stays on when the button is pressed: There is a loose coil wire, short, or the K1 has malfunctioned.
If the light never comes on: Go back to the previous troubleshooting topics to ensure your machine is receiving power. See Machine Won't Power On - 770MX