If any optically isolated input on the controller is not working, follow the steps below to identify the cause.

Step 1: Check Ground Side Continuity

Using a multimeter, check continuity between the black connector and the marked pin of the optocoupler input that is not working.

If there is no continuity, the possible causes are:

• The optocoupler is not plugged in correctly

• The PCB track has been damaged

Step 2: Measure Input Signal Voltage

Connect a 5 V to 24 V signal to the input being tested.

Measure the voltage at the marked test points.

• Expected voltage: ~1.1 V

If this voltage is not present, possible causes are:

• The optocoupler is not plugged in correctly

• The PCB track has been damaged

• The resistor associated with the optocoupler is damaged

Step 3: Measure Output Signal Voltage

With no signal connected to the input:

• Measure the voltage at the marked test points

• Expected voltage: ~3.1 V

With a 5 V to 24 V signal connected to the input:

• Measure the voltage at the same points

• Expected voltage: ~0.14 V

If these voltages are not seen, possible causes are:

• The optocoupler is not plugged in correctly

• The optocoupler is damaged

• The PCB track has been damaged