Troubleshooting Techniques

The art of troubleshooting is not limited solely to electrical or electronic systems. In the broad sense,
troubleshooting is a process by which acquired knowledge and experience are used to localize a problem and offer or implement a solution.
There are many reasons why the simplest electrical circuit might not be operating correctly.
  • A connection may be open;
  • the measuring instruments may need calibration;
  • the power supply may not be on or may have been connected incorrectly to the circuit;
  • an element may not be performing correctly due to earlier damage or poor manufacturing;
  • a fuse may have blown;
  • and so on.
Unfortunately, a defined sequence of steps does not exist for identifying the wide range of problems that can surface in an electrical system. It is only through experience and a clear understanding of the basic laws of electric circuits that you can become proficient at quickly locating the cause of an erroneous output. It should be fairly obvious, however, that the first step in checking a network or identifying a problem area is to have some idea of the expected voltage and current levels.
Fig. 1: A malfunctioning network.
For instance, the circuit in Fig. 1 should have a current in the low milliampere range, with the majority of the supply voltage across the 8 kΩ resistor. However, as indicated in Fig. 1,
$$V_{R1} = V_{R2} = 0 V$$
$$V_a = 20 V$$
Since $V = IR$, the results immediately suggest that $I = 0 A$ and an open circuit exists in the circuit. The fact that $V_a = 20 V$ immediately tells us that the connections are true from the ground of the supply to point a. The open circuit must therefore exist between $R_1$ and $R_2$ or at the ground connection of $R_2$. An open circuit at either point results in $I = 0 A$ and the readings obtained previously.
Occasionally, the problem may be difficult to diagnose. You've checked all the elements, and all the connections appear tight. The supply is on and set at the proper level; the meters appear to be functioning correctly. In situations such as this, experience becomes a key factor. Perhaps you can recall when a recent check of a resistor revealed that the internal connection (not externally visible) was a "make or break" situation or that the resistor was damaged earlier by excessive current levels, so its actual resistance was much lower than called for by the color code.
Recheck the supply! Perhaps the terminal voltage was set correctly, but the current control knob was left in the zero or minimum position. Is the ground connection stable? The questions that arise may seem endless. However, as you gain experience, you will be able to localize problems more rapidly. Of course, the more complicated the system, the longer is the list of possibilities, but it is often possible to identify a particular area of the system that is behaving improperly before checking individual elements.

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