Test the remaining devices.
This post is part of a series describing the generic, high-level troubleshooting process.
What is Troubleshooting?
Simplified Troubleshooting Overview
Step 1. Understand the correct inputs and outputs of the “black box.”
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 10. Repair/Replace faulty device(s).
Step 11. Fully test the system.
Step 9. Test the remaining devices.
In this step, we will basically repeat all of the steps, just on a smaller scale.
If the device is simple, like a switch or relay, you will run through the steps fast. What is the resistance with the contacts closed? What is the resistance with the contacts open? Do the contacts open and close?
If the device is complicated, like a PLC, circuit board, IC, etc., you will need to treat this item like a new “black box” and go through all of the steps. This is where it can get complicated. You could save a lot of time by “throwing parts at it”… If a spare is available, replace it. If it fixes the problem, you can decide if you will just leave the spare in place, or fix the original. If it doesn’t fix the issue, just put the original back in, and move on the the next item.
If you need to troubleshoot and/or repair an item like a circuit board, the same steps apply, but it is much more difficult and is well beyond the scope of the high-level blog.
Test each device, one at a time, until you find the faulty component(s).