Useful troubleshooting tips for repairing electrical equipment

The most common failures in the electrical circuits of electrical appliances and household appliances:
1) open circuit (resistance of an electric circuit is equal to infinity);
2) a significant increase in resistance;
3) a significant decrease in resistance;
4) short circuit (electrical resistance is close to zero).
Common causes of these malfunctions:
- breakage due to the aging of the elements, the passage of high currents, shock, vibration and corrosion;
- a significant increase in the resistance of electrical circuits compared to the nominal value caused by the aging of the elements, the deterioration of contacts and contact connections, the deviation of the parameters of individual elements;
- a significant decrease in the resistance of electrical circuits compared to the nominal value due to an increase in surface leaks and aging of the elements.
Short circuits are the result of breakdown of insulation, short circuits of conductors and elements on the housing and between each other (for conductors of different polarities and phases).

When troubleshooting, you need to know and be able to use the signs of proper operation of electrical equipment.
They can be divided into two main groups:
active - readings of light and sound signals, signaling devices, triggering of protective equipment, as well as signs detected during measurement by the device;
passive or secondary signs perceived during an external examination of electrical equipment (visual, sound, tactile, olfactory).
Light and sound signals, signaling devices allow you to monitor the status of electrical appliances.
Protective equipment (fuses, maximum or minimum relays, circuit breakers, etc.), when triggered, disconnect electrical circuits from sources of electricity if the disconnected part of the circuit has increased leakage currents, overload currents and short circuits.
In case of malfunctions - such as a break - the protection usually does not work, but its normal state in the presence of a malfunction in the electrical circuit is an indirect indication that the damage has the nature of a break.
Troubleshooting is carried out by directional measurements of the parameters of elements of electrical circuits using portable devices and measuring kits using active features.
When measuring parameters (resistance, current, voltage) of individual elements in electrical circuits (for example, logic control systems, etc.) using portable devices, it is necessary to use the cards of resistance, voltages, currents at the output of individual elements and blocks, given in the instructions for operation of these devices.
When conducting special directional measurements in practice, it is used A number of private troubleshooting methods:
- intermediate measurements, making it possible to sequentially trace the passage of signals through various channels of the system;
- exceptions, allowing through measurements to exclude serviceable parts of the tested circuit and highlight the failed element;
- replacement of blocks (parts), in which the presence of a malfunction is assumed, by the same type, obviously working;
- comparing the test results of the failed circuit with the test results of a working circuit of the same type operated in the same conditions.
In general, troubleshooting consists of the following
stages:
a) the fact of failure of the appliance
by changing active and passive signs of normal operation;
b) analysis of existing signs of malfunctions and comparing them with the possible state of the elements of the appliance;
c) comparing the symptoms of malfunctions indicated in the operating instructions and known from the operating experience with the observed symptoms;
d) the selection of the optimal search sequence and the amount of additional measurements for the examination of elements in which possible malfunctions;
e) sequential measurement;
f) a general assessment of the test results and a conclusion on the most likely causes of a malfunction of the selected element;
g) troubleshooting.
The main causes of malfunctioning electronics are:
- overcurrent;
- overvoltage;
- increased ambient temperature;
- Unacceptable vibration, shock.

In the event of a malfunction or failure of an object (system, device, unit, module, electronic board), it is recommended that the search for a defective electronic component begin after a preliminary check of serviceability:

signal lamps, fuses, switches and other means of switching and protecting the facility;

unit or power supply unit of the object by measuring the voltage at the input and output with a voltmeter;
external devices - sensors, signaling devices, limit switches, monitors, picture tubes, speakers, etc.

After that, it is recommended to check the voltage values ​​or pulse parameters at the test points provided for in the instruction manual.

A further search for the defective item is recommended, taking into account the following instructions:

the principle of operation of the faulty object must be studied and understood;

first, a more complex faulty object is sought, then a simpler one (according to the principle of a system - a block - a node - an element);

the signs of a malfunction are analyzed, assumptions of its causes are put forward, and a verification method is selected;

spot checks of sections and individual elements are carried out, the malfunctions of which are most likely, and their verification takes the least time;

if a faulty element is not detected by spot check, you should go to the search by the exclusion method, moving from the input to the output of the object, or dividing it before the next test into two parts equal to the complexity of the test;

if the malfunction is uncharacteristic, then it is advisable to omit the spot check step and begin the search immediately with the exception method.

It is recommended to introduce and remove removable objects for inspection, replacement with spare parts or searching for defective elements when the power supply is off, especially if there are detachable contact connections.

When examining an object, pay attention

- violations of protective and insulating coatings;

- on discoloration, the presence of darkening, swelling and cracks;

- the serviceability of fixtures, contact surfaces, joints and rations;

- the temperature of the elements (cases, transistors, resistors, diodes, microcircuits, electrolytic capacitors) immediately after turning off the circuit.

It should be remembered that the temperature of the housings during normal operation
should not exceed 45-60 ° С - to the touch (exceeding the temperature above 60 ° С the hand does not tolerate).

Items with flaws detected must be checked first.

The determination of a defective element in an energized object is recommended to be carried out using serviceable extension cords and transitional devices, measuring instruments with high internal resistance and the indications in the documentation about the values ​​and polarity of potentials.

In the absence of the necessary data, the search can be carried out by comparing the areas of stresses on the same elements of a known-good (spare or similar) and faulty objects.

The determination of a faulty element without applying voltage to the object can be carried out by measuring the resistances with an ohmmeter in sections or elements, working capacity
which is in doubt.

If necessary, one or more conclusions of the elements can be disconnected (soldered).

If the element is in good condition (increasing leakage current, decreasing insulation resistance or switching voltage, etc.), it is necessary to measure its basic parameters using conventional or special instruments and test circuits.

In the absence of passport data of the element, the measurement results can be compared with similar data of spare known-good elements.

In the process of searching, checking and replacing faulty elements (especially semiconductor devices) using the most simple means, it is necessary to carefully mark the terminals of the devices.

After the detection of a faulty element, the possible causes of the fault are analyzed, which must be eliminated before replacing it and putting the object into operation.

To increase the reliability of the results, it is recommended to measure the parameters of the elements in a dry room at an air temperature of 20-25 ° C (especially for thermistors, germanium diodes and transistors).

If the measures taken to inspect and verify the malfunctioning object did not lead to the restoration of its operability, and the search for the malfunctioning element did not give a result, the object should be transferred for repair to special workshops.

Independent opening and repair of complex objects based on modern semiconductor elements, in the absence of clear instructions in the instruction manual, is not recommended.