Using the block-sequential method for troubleshooting electrical circuits

What is a block? A certain device or part of the circuit selected by us, having the so-called “input” and “output” for signal transmission, and the input “power”.
Consider a simple circuit where, as such, there is no control signal, its function is performed by directly turning on the power to the executing mechanism (output device).
Further, in this case, the concepts of “input” and “output” will be applied to the transmission of the supply voltage.
Any device in itself can be thought of as a separate unit. For example, we inserted the plug into a power outlet, made an “input”, and at the “output” we get the result: we watch TV, the iron is heating, the music sounds, etc.

Take, for example, a lamp - a night lamp with rotating light filters and a 12-volt incandescent lamp. We divide the object, for convenience, into separate blocks.
The first is the power cord with fuses. After the fuses: “output” of 1 unit - “input” of 2 units.
The second is the power supply. After it: “exit” 2 blocks - “entrance” 3 blocks.
The third is the central block, most often consists of several objects - blocks. In our case, there are two of them. The backlight unit and the motor unit. Each has its own “entrance”.
There are no "exits", since they have the final devices of the object, this is an electric lamp and an electric motor. We begin the verification of the object with logical reasoning.
If in one of the final blocks there are signs of the presence of supply voltage, then we conclude that it comes from the power supply to the next block and presumably has the proper value.
Next, check the power supply to each end unit. Let's say the night light was buzzing, but not lit. Power comes to both end blocks. We check the lamp for an open, in our case, the open is confirmed.
We give an example from practice and on its basis we consider possible malfunctions along the entire circuit. The engine does not spin, the lamp does not light.
We already checked the lamp, it is faulty. Note: A break at the lamp can be located not only on the filament, but also in the base, when it cannot be visually detected.
Electric motor

We look at the electric motor. Instrument (multimeter) shows an open winding. This case is well suited as an example, but in real life this rarely happens.
We assume the reason. If two units of one block fail, then you need to look for a common cause that affects them. There are quite a few possible common reasons to come up with, but the real one is most likely one. This is an increased mains voltage.
A sharp surge in voltage is accompanied by a short-term increase in current, the fuses do not have time to blow out, and the weak winding and, moreover, the filament of the electric lamp cannot withstand and burn out in their most vulnerable "thin" places.
Simultaneous breakage is excluded, since the lead-out conductors of the lamp and the motor of the winding and its connections cannot have the same "bad" spots.
This indicates a rather long increased voltage and that protective measures in the form of fuse-links (fuses) are not always able to prevent such deplorable results of a voltage mismatch.
Next, go back. If, when checking at the inputs of the last lamp and engine blocks, we did not find the supply voltage, but at all the previous ones, then we look at the power supply.
In our case, the power supply consists of a power transformer with two windings: a primary voltage of 220 volts, a secondary voltage of 12 volts.
Transformer

What can happen to a transformer? Open circuit or interturn circuit.
There are two real reasons: increased voltage on the winding 220 volts or a large load on the winding 12 volts (We will not assume factory defects anywhere, although this is a fairly common occurrence, you just need to remember this.).
The transformer could suffer the same fate. An increased load on the secondary winding may occur from a short circuit of an electric motor or a short circuit in its circuits and lamp circuits. In this case, the current increases both in the secondary and in the primary winding to a value at which the winding simply burns out again in a weak place. This whole thing is accompanied by a poisonous haze.
In this case, we did not talk about fuses. Most likely, they would have fulfilled their function if no one had put “bugs” in their place.
With this word, I always have associations with the music of youth. I still listen to “Beatles” (BEETLES), but in those days I trudged more often and with great pleasure. Then another rock and roll “AC / DC” (alternating current / direct current) appeared on the ear. Have you noticed a steady craving for electricity?
Move on. Suppose that we detected a voltage loss before the power supply, after the fuses. We check the integrity of the inserts by the device for an open. If the fuses are intact, then the matter is in the power cable.

In conclusion, I would like to tell you about a rather important observation. A person who has impressive knowledge and extensive experience in the field of electrical engineering, electromechanics, radio mechanics, etc., does not use his abilities as often as one might suppose.
If we conduct a statistical analysis, it turns out that out of a certain amount, for example, faulty household appliances, more than 50% will have breakdowns of small complexity.
If we compare with our block diagram, then the malfunctions would be located no further than the power supply from the plug, which may well be corrected even by a beginner.
This suggests that the average stock of knowledge in our profession is much higher than the average need for this knowledge, but you need to remember that it is impossible to use this freebie, that is, you need to know almost everything in the area in which you work.
At some stage of training, but rather in practice, you will find that you easily solve problems that you haven’t hoped to solve.
This is a very encouraging factor, if you like it, then go ahead.