•Go from the simple to the complex. Make the simple tests first. Do not try anything complex and complicated until you have ruled out the simple and obvious.
•Do not make more than one change at a time. If you do, and one of the changes corrects the problem, you have no way of knowing which change actually fixed the problem. Make one change, test the change, and then, if necessary, make the next change.
•Do not neglect the obvious. Small things can cause big problems. Check plugs, connectors, cables, and so on.
•Keep a record of the tests you have completed. Record your tests and results, and keep an historical record of the problem, in case it reappears.
