The simplest ways to check the health of electrical radio elements

Checking wire and wire-free resistors

To check wired and wireless resistors with constant and variable resistance, it is necessary to do the following: make an external examination; check the operation of the variable resistor actuator and the condition of its parts; by marking and dimensions, determine the nominal value of the resistance, the permissible dissipation power and the accuracy class; measure the actual resistance value with an ohmmeter and determine the deviation from the nominal value; for variable resistors, also measure the smoothness of the change in resistance as the slider moves. The resistor is in operation if there is no mechanical damage, the value of its resistance is within the permissible limits of this accuracy class, and the contact of the slider with the conductive layer is constant and reliable.

Checking capacitors of all types

Electrical faults include: failure of capacitors; short circuit of plates; change in nominal capacity beyond the permissible deviation due to aging of the dielectric, moisture ingress, overheating, deformation; increase in leakage current due to deterioration of the insulation. Complete or partial loss of capacity of electrolytic capacitors occurs as a result of drying of the electrolyte.

The simplest way to check the serviceability of a capacitor is an external inspection, during which mechanical damage is detected. If no defects are found during the external inspection, an electrical inspection is carried out. It includes: checking for short circuit, for breakdown, for the integrity of the conclusions, checking the leakage current (insulation resistance), measuring the capacity. In the absence of a special device, the capacity can be checked in other ways, depending on the capacity of the capacitors.

Large capacitors (1 μF and more) are checked with a probe (ohmmeter), connecting it to the terminals of the capacitor. If the capacitor is in good condition, the needle of the device slowly returns to its original position. If the leak is large, the needle of the device will not return to its original position.

Medium capacitors (from 500 pF to 1 μF) are checked using telephones and a current source connected in series to the terminals of the capacitor. With a working capacitor, at the moment of closing the circuit, a click is heard in the telephones.

Small capacitors (up to 500 pF) are tested in a high frequency current circuit. A capacitor is connected between the antenna and the receiver. If the reception volume does not decrease, there are no wire breaks.

Checking the inductors

Functionality check inductors begins with an external review, during which they are convinced of the health of the frame, the screen, the conclusions; in the correctness and reliability of the connections of all parts of the coil with each other; in the absence of visible breaks in wires, short circuits, damage to insulation and coatings. Particular attention should be paid to areas of carbonization of the insulation, frame, blackening or melting of the filling.

Electrical testing of inductors includes an open test, short circuit detection and determination of the condition of the winding insulation. The open circuit check is done with a probe. An increase in resistance means an open or poor contact on one or more wires. A decrease in resistance indicates the presence of a short-circuit break. When the terminals are short-circuited, the resistance is zero.

For a more accurate representation of the coil fault, you should measuring inductance… In conclusion, it is recommended to check the operability of the coil in the same known working device for which it is intended.

Inspection of power transformers, transformers and low frequency chokes

In design and manufacturing technology, power transformers, transformers and low frequency electric chokes they have a lot in common. Both consist of coils made with insulated wire and a core. Malfunctions of transformers and low-frequency chokes are divided into mechanical and electrical.

Mechanical damage includes: breakage of the screen, core, wires, frame and fittings; electrical failures — breaks in the coils; short circuits between winding turns; short circuit of the winding to the body, core, screen or armature; breakdown between windings, to the body or between turns of a winding; reduction of insulation resistance; local overheating.

Checking the serviceability of transformers and low-frequency chokes begins with an external check. During it, all visible mechanical defects are identified and removed. Checking for a short circuit between the windings, between the windings and the housing is carried out with an ohmmeter. The device is connected between the terminals of different windings, as well as between one of the terminals and the housing. The insulation resistance is also checked, which should be at least 100 megohms for sealed transformers and at least tens of megohms for unsealed ones.

The most difficult turn-by-turn closing test. There are several known methods for testing transformers.

1. Measurement of the ohmic resistance of the winding and comparison of the results with the passport data. (The method is simple but not accurate, especially with low ohmic resistance of the windings and a small number of short circuits.)

2. Checking the winding using a special device — a short circuit analyzer.

3. Checking the transformation ratios at idle speed. The transformation factor is defined as the ratio of the voltages indicated by two voltmeters. In the presence of turn-to-turn closures, the transformation ratio will be less than normal.

4. Measurement of coil inductance.

5.Measurement of idle power consumption. In power transformers, one of the signs of a short circuit is excessive heating of the winding.

The simplest health check of semiconductor diodes

The simplest health test of semiconductor diodes is to measure their forward resistance Rnp and reverse resistance Ro6p. The higher the Ro6p / Rnp ratio, the higher the quality of the diode. For measurement, the diode is connected to a tester (ohmmeter) or to an ammeter. In this case, the output voltage of the measuring device should not exceed the maximum permissible for this semiconductor device.

A simple check of the transistors

When repairing home radio equipment, it becomes necessary to check the serviceability of semiconductor triodes (transistors) without soldering them outside the circuit. One way to do this is to measure the resistance between the emitter and collector terminals with an ohmmeter when you connect the base to the collector and when you connect the base to the emitter. In this case, the collector power source is disconnected from the circuit. With a working transistor, in the first case, the ohmmeter will show a low resistance, in the second - on the order of several hundred thousand or tens of thousands of ohms.

Checking the transistors that are not included in the circuit for a short circuit is done by measuring the resistance between their electrodes.To do this, the ohmmeter is connected in series to the base and emitter, to the base and collector, to the emitter and collector, changing the polarity of the connection of the ohmmeter. Since the transistor consists of two junctions, each of which is a semiconductor diode, you can test transistor in the same way as a diode. To check the health of the transistors, an ohmmeter is connected to the respective terminals of the transistor. In a working transistor, the forward resistances of the transitions are 30 — 50 Ohms, and the reverse ones — 0.5 — 2 MΩ. With significant deviations of these values, the transistor can be considered defective. Special devices are used for a deeper inspection of transistors.