Fully test the system.

Repair/Replace faulty device(s).

Test the remaining devices.

Eliminate the devices that could not cause this output.

Eliminate the devices that could not cause this output.

Check all connections.

Analyze the path(s) from input(s) to output(s).

Verify that those inputs are as expected.

Figure out which input(s) affect that output(s).

Determine which output(s) are incorrect.

Understand the correct inputs and outputs of the “black box.”

Effective troubleshooting is 60% science, 40% art, and 50% luck. You will need to draw from your training, your experience, and your gut feeling.

To most people, equipment (of whatever kind, from a light switch, to an assembly line, to your smart phone) is just a “Black Box”…