Time to troubleshoot.
First step, test the LEDs and confirm the polarity.
- Remove power to the panel -- the multimeter will provide power for this test.
- Set your multimeter to diode test.
- Touch the leads to the LED tabs.
-- If the leads are backward, the LED won't light.
-- If you swap leads and the LED still won't light, either the LED is bad
or you're on the wrong tabs.
-- If you have the correct polarity and the LED is good, it will light dimly. (make a note of the voltage displalyed on the meter)
Next step is to check if the LED is getting enough voltage to forward bias.
- Set the meter to VDC.
- Restore power to the panel.
- Touch the leads to the LED tabs to test how much voltage is dropped across the LED. Compare that voltage to the voltage during the diode test.
-- If the voltage is lower than during the diode test, you need a lower value current limiting resistor so the LED gets enough voltage to forward bias.
Use a calculator like
this one that Zebidee linked earlier.
- Fill in 3 of these 4 values and click on calculate.
- Voltage source = 5v
- Voltage drop from LED = voltage from the diode test
- Current through the LED = usually between 15 and 20 mA
- Resistance = current limiting resistor value
Scott