Understand the correct inputs and outputs of the “black box.”
This post is part of a series describing the generic, high-level troubleshooting process.
Previous Posts:
What is Troubleshooting?
Simplified Troubleshooting Overview
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Step 2. Determine which output(s) are incorrect.
Step 3. Figure out which input(s) affect that output(s).
Step 4. Verify that those inputs are as expected.
Step 5. Analyze the path(s) from input(s) to output(s).
Step 6. Check all connections.
Step 7. What are the devices in those path(s) that change the data?
Step 8. Eliminate the devices that could not cause this output.
Step 9. Test the remaining devices.
Step 10. Repair/Replace faulty device(s).
Step 11. Fully test the system.
Step 1. Understand the correct inputs and outputs of the “black box.”
The first step when beginning troubleshooting, is to get a firm understanding of how the equipment is supposed to function. If you don’t know what it is supposed to do, then you won’t recognize when it is not doing what it is supposed to. Don’t worry about the inner workings just yet, that will come, for now, consider it a “black box,” figure out what it does before you figure out how it does it.
This seems obvious, but I have watched others, and myself, dive head first into trying to fix a problem before knowing anything about the equipment. Not taking the time to learn about the equipment, or assuming that you understand it, can cause a lot of frustration and lost time chasing ghosts. I personally have spent hours chasing problems and pulling my hair out, only to finally realize that the section I was troubleshooting was doing exactly what it was designed to do. My desire to fix it fast, caused me to skip this step and I completely wasted that time as a result.
- What are the input(s) to the box?
- What should they look like?
- Where do they come from?
- Are they user inputs, or are they outputs from other boxes?
- What are the output(s) from the box?
- What should they look like?
- Where do they go?
- Is it a screen, lights, bells, etc., or is the output an input to another box?
This step is also critical when assisting someone else who is stuck in their troubleshooting. My experience has shown that often when I jump in to help someone who has been working on an issue for a while, that as I ask questions about how it is supposed to work, it triggers a thought in their own mind about where the problem could be, something that they had not thought of before, probably because they hadn’t taken the time to fully understand the “black box.” Often this leads them to finding the problem that has been alluding them, without me ever even completing Step 1 for myself.