Certainly, "Y" has listed the first three steps to follow, UNLESS you are given a list of complaints by the one claiming there is a problem.
Most of my diagnostics are on more complex systems that "Mysteriously start to malfunction for no reason", which occasionally is an acurate statement.
What is very useful is to know what the system should be doing, followed by knowing what it IS doing instead. Often, that knowledge is enough to point toward the portion that is not as it should be. At that point the task is to observe what is no longer delivering the correct function. (The same sequence works for a radio or a hay bailer machine.) The observation portion may take a while, or maybe not.

 

Hi everyone,

I’m still learning the basics of electronics and was wondering when a simple circuit (like an LED circuit) doesn’t work, what’s your usual step-by-step troubleshooting process?

In trouble shooting , The very first is to use two of your senses, sight and smell!
These are thr first self evident clues when finding a problem, if no apparent problem using your senses, then out comes the meter for diagnostic trouble shooting.

 

In trouble shooting , The very first is to use two of your senses, sight and smell!
These are thr first self evident clues when finding a problem, if no apparent problem using your senses, then out comes the meter for diagnostic trouble shooting.

And you can add finger touch. Sense what component is getting too hot by touching with the tip of your finger.
Caution: a really hot device can burn your finger.

 

And you can add finger touch. Sense what component is getting too hot by touching with the tip of your finger.
Caution: a really hot device can burn your finger.

Been there and Done That!. A second degree burn on a fingertip from touching a hot series-pass transistor in a compact power supply mounted in a hard to reach location.

 

And you can add finger touch. Sense what component is getting too hot by touching with the tip of your finger.
Caution: a really hot device can burn your finger.

Most of us (most definitely myself included) have discovered that useful bit of information. But the favorite one I have seen was from one of my students.

A project that they had been given was to design a discrete-transistor differential power amplifier that took a 1 Vpp signal and delivered 5 W to an 8 Ω load. The power supplies were ±30 V supplies (both because that was what we had available in the lab, and because one of the key objectives was to have to deal with power dissipation). We went through how to handle heat dissipation in class, as well as how to read information from the data sheets. They were supplied with lots of 2n3904, 2n3906, 2n3055, and 2n2955 transistors. Not surprisingly, lots of students didn't pay attention and used the small-signal transistors as their output transistors, resulting in a lot of magic smoke filling the lab. Which was fine with me. Even though I was having to buy all the components on my own dime, I was more than willing to keep buying more (and had to make two additional trips to the surplus store to restock) since this is an effective way to learn. I tell students that engineering is both an art and a science. The art is learning from your own mistakes, while the science is learning from the mistakes of others. I had given them the opportunity to practice the science in lecture, if they opted not to, then I had given them the opportunity to practice the art in the lab.

So I wasn't surprised when a student came to me saying that their output transistor was getting really hot. I asked them what transistor they were using for their output stage, expecting them to say either 2n3904 or 2n3905. Instead, they looked at their thumb and said, "2n3055". They had branded the part number into their thumb! So I said, "Well, that's the right transistor, let's go take a look." I don't recall if the problem was that they weren't using a heat sink or whether they weren't using dump resistors. I had given them a selection of both and had chosen the heat sinks such that you needed both. Leaving one or the other (or both) out was a common failing in the early designs.

 

Check first for the most obvious issue:
Fuse? Blown?
LED? Backwards?
Battery? Dead?
Resistor? Too high a value?
These are examples of the above LED circuit someone has already shown. On the subject of the LED being backwards; there are ways to identify which is the Anode and which is the Cathode.

 

In trouble shooting , The very first is to use two of your senses, sight and smell!
These are thr first self evident clues when finding a problem, if no apparent problem using your senses, then out comes the meter for diagnostic trouble shooting.

Yeah that’s true. Burnt smell alone already tells you something’s off before you even grab a meter.

 

First, regarding the possible burned smell, about the diagnostics associated with that sort of problem.
MOST OF THE TIMES, the component that burns up is not the original cause of the problem!!! Most of the time, in fact, almost always, a part overheats because some other part is allowing excess current to flow thru it. So replacing the burned part will simply result in another burned part.

THAT is where some knowledge of how "the system" is supposed to work is very valuable. That knowledge may also include having a schematic of the system and being able to understand what it is supposed to be doing.

The instances where that is not needed are those times when you spot a connection that has come loose, or a wire that has simply broken, probably from excess vibration. Other examples of those kinds of failures include rodent chewing wires and water or other liquids getting into the package. (This does not apply to beginers experimental assemblies.)

Additional diagnostics require knowledge about the failed system's history: Did it EVER function correctly? or was it functioning correctly and then suddenl stopped functioning?? Those two possibilities rquire two very different diagnostic paths. (additional words later, it has gotten quite late here.)