A diagnostic tree is a method that anyone can use to create structure when diagnosing a problem. It helps you plot your progress throughout your diagnostic journey and it gives you reference points that you can look back on. They come in all shapes and sizes, just like the problems that they can help you solve.
At New Manhattan, our team uses diagnostic trees for all sorts of projects we do, from mechanical R&D and prototyping to Web Development and electrical diagnostics. Of all types of projects, diagnostic trees present themselves most useful when faced with an electrical issue because of its complexity and lack of visual confirmation. An electrical circuit is a lot like a stream of water. It begins at the main point, travels along a specific path, performs a duty, and eventually ends back in a larger body of water. But if there is a blockage in the circuit (or river) beginning to solve that problem may seem overwhelming when looking at the circuit as a whole. That’s where building a diagnostic tree comes in.
For example, power and ground are essential to any electrical circuit operation, so it's a pretty safe bet that if things aren't working, check power! It is amazing how many times something as simple as a loss of power or ground is the main culprit. This is the reason why when you call tech support, they usually start by asking “Did you check if it was plugged in?” Start simple, then move up in complexity.
Common points of failure are components or loads within the circuit. Wires going to and from those components, or the part itself. Any place there is a connection is another opportunity for something to go wrong. Check the wiring to and from the part, and the connections directly on it. If they test ok, swap out the component with a known working part for a quick test. Even though I am not particularly a fan of “part swapping,” if you have an extra one laying around, it may speed up diagnostic time.
If the problem you are experiencing changes, then great! You’re getting somewhere.
But if it doesn't, still write down what you have done on a piece of paper, put the circuit back to where you had it before you conducted your experiment, and continue downstream until you find another suspect. Here is an example of how I layout diagnostic trees, but they come in all shapes and sizes.
Compiling a list of the tests you conducted gives your diagnostic process structure, even if you did not find a change in behavior after making changes. I find that when writing down your ideas about possible problems, it opens up your mind to thinking abstractly about an issue instead of what is directly in front of you. This abstract frame of mind is helpful when diagnosing very difficult and eluding issues. Also, if it becomes a multi-day diagnostic process, you have a reference to refer back to if you forget what you have already tested.
As a self-proclaimed maker, diagnostic trees have been an absolute must when diagnosing those pesky electrical gremlins that plague any awesome project. Trust me they will happen, and this tactic for conquering those annoying electrical problems will pay off by reducing your diagnostic time and saving your sanity.