LED won't turn on

The LED string is made of four LEDs in series and requires approximately 24V DC across the digital output and 0V (GND) to illuminate.

Safety first

Work only if you're qualified to test live circuits. If you're unsure, power down and ask an electrician. When measuring voltages use a properly rated digital multimeter and take all safety precautions.

Wiring convention:

• White wire → 0V (GND)
• Red wire → digital output (DO)

To test a digital output without the LEDs connected: remove the LED load, set your multimeter to DC volts, and measure between the digital-output terminal (for example D01) and 0V while the output is activated. You should read approximately 24V (nominal).

On the digital-output terminal, verify that the terminal screw clamps the inner conductor and not the cable jacket. Make sure there are no frayed strands or poor crimps. If needed, strip a little more insulation and reterminate for a reliable connection.

---