Errors

How to check a pulse transformer with a multimeter on the board. How to check a pulse transformer with a multimeter

If you take pulse transformer power supply, for example a line scan isolation transformer, connect it according to Fig. 1, apply to the I winding U = 5 - 10V F = 10 - 100 kHz sinusoid through C = 0.1 - 1.0 μF, then on the II winding with the help of an oscilloscope we observe the shape of the output voltage.

Rice. 1. Connection diagram for method 1

Having “driven” the AF generator at frequencies from 10 kHz to 100 kHz, you need to get a pure sinusoid in some area (Fig. 2 on the left) without surges and “humps” (Fig. 2 in the center). The presence of diagrams in the entire range (Fig. 2. on the right) indicates turn-to-turn closures in the windings, etc. etc.

This technique, with a certain degree of probability, makes it possible to reject power transformers, various isolation transformers, partly line transformers. It is only important to choose the frequency range.

Rice. 2. Forms of the observed signals

Method 2

Necessary equipment:

LF generator,
Oscilloscope

Principle of operation:

The principle of operation is based on the phenomenon of resonance. An increase (from 2 times or more) in the amplitude of oscillations from the LF generator indicates that the frequency of the external generator corresponds to the frequency of the internal oscillations of the LC circuit.

To check, short-circuit winding II of the transformer. The oscillation in the LC circuit will disappear. It follows from this that short-circuited loops break the resonance phenomena in the LC circuit, which is what we sought.

The presence of short-circuited turns in the coil will also lead to the impossibility of observing resonance phenomena in the LC circuit.

We add that to test the pulse transformers of power supplies, the capacitor C had a nominal value of 0.01 mkF-1 mkF. The generation frequency is selected empirically.

Method 3

Necessary equipment: LF generator, Oscilloscope.

Principle of operation:

The principle of operation is the same as in the second case, only a variant of a sequential oscillatory circuit is used.

Rice. 4. Connection diagram for method 3

The absence (breakdown) of oscillations (rather sharp) when the frequency of the LF generator changes indicates the resonance of the LC circuit. Everything else, as in the second method, does not lead to a sharp breakdown of oscillations on the control device (oscilloscope, AC millivoltmeter).

To test the performance of a pulse transformer, you can use both an analog multimeter and a digital one. The use of the second is preferable because of its ease of use. The essence of preparing a digital tester comes down to checking the battery and test leads. At the same time, an arrow-type device is additionally additionally adjusted.

The analog device is configured by switching the operating mode to the measurement area of the minimum possible resistance. After that, two wires are inserted into the tester's sockets and short-circuited. With a special trimming handle, the position of the arrow is set opposite to zero. If the arrow cannot be set to zero, then this indicates discharged batteries that will need to be replaced.

How to test a pulse transformer with a multimeter

To check the pulse transformer, you can use both an analog instrument and a digital multimeter. The use of the second is preferable because of its ease of use. The essence of preparing a digital tester comes down to checking the battery and test leads. At the same time, an arrow-type device is additionally additionally adjusted.

Test procedure with an analog (pointer) measuring device

The analog device is configured by switching the operating mode to the measurement area of the minimum possible resistance.
After that, two wires are inserted into the tester's sockets and short-circuited.
With a special trimming handle, the position of the arrow is set opposite to zero. If the arrow cannot be set to zero, then this indicates discharged batteries that will need to be replaced.

Defect detection procedure

An important step in checking the transformer with a multimeter is to determine the windings. Moreover, their direction does not play a significant role. This can be done by the markings on the device. Usually a certain code is indicated on the transformer.

In some cases, a diagram of the arrangement of the windings can be applied to the IT, or even their conclusions can be signed. If the transformer is installed in the device, then the principle will help in finding the pinout. electrical circuit or specification. Also, often the designations of the windings, namely the voltage and the common terminal, are signed on the PCB itself near the connectors to which the device is connected.

After the conclusions are determined, you can proceed directly to checking the transformer. The list of malfunctions that may occur in the device is limited to four points:

core damage;
burnt-out contact;
breakdown of insulation, leading to turn-to-turn or frame short circuit;
wire break.

The inspection sequence is reduced to an initial external inspection of the transformer. It is carefully checked for blackening, chips, and odor. If no obvious damage is found, then proceed to measuring with a multimeter.

How to check a pulse transformer for turn-to-turn circuit and open circuit

To check the integrity of the windings, it is best to use a digital tester, but you can also examine them using a dial gauge.

In the first case, the diode continuity mode is used, indicated on the multimeter by the diode symbol in the diagram.

To determine the breakage, test leads are connected to the digital device.
One plugs into the connectors labeled V / Ω, and the other plugs into COM.
The gallet switch is transferred to the continuity area.
Measuring probes consistently touch each winding, red - to one of its terminals, and black - to the other. If it is intact, the multimeter will beep.

With an analog tester, the test is performed in the resistance measurement mode. For this, the smallest resistance measurement range is selected on the tester. This can be done via buttons or a switch. The probes of the device, as in the case of a digital multimeter, touch the beginning and end of the winding. If it is damaged, the arrow will remain in place and will not deviate.

In the same way, there is a check for turn-to-turn and short circuit.

A short circuit can occur due to insulation breakdown. As a result, the resistance of the winding will decrease, which will lead to a redistribution of the magnetic flux in the device.

The meter switches to resistance test mode for testing.

Touching the probes to the windings, they look at the result on the digital display or on the scale (arrow deviation).

This result should not be less than 10 ohms.

To make sure that there is no short circuit to the magnetic circuit, one probe touches the "gland" of the transformer, and the second - sequentially to each winding. There should be no deviation of the arrow or the appearance of a sound signal. It is worth noting that the tester can only ring the turn-to-turn circuit in an approximate form, since the error of the device is quite high.

Video: How to check a pulse transformer?

How to check a pulse transformer with a multimeter

The main element of the power supply for digital devices is a current and voltage conversion device. Therefore, when equipment breaks down, it is often the suspicion that falls on him. The easiest way to check the pulse transformer is with a multimeter. There are several measurement methods. Which one to choose depends on the situation and the expected damage. At the same time, it is not difficult to independently check any of them.

Converter design

Before proceeding directly to checking a pulse transformer (IT), it is advisable to know how it works, to understand the principle of operation and to distinguish between existing types. Such an impulse device is used not only as part of the power supply unit, it is used in the construction of short-circuit protection in idle mode and as a stabilizing element.

A pulse transformer is used to convert the magnitude of current and voltage without changing their shape. That is, it can change the amplitude and polarity of various kinds of impulses, coordinate various electronic cascades with each other, and create reliable and stable feedback. Therefore, the main requirement for it is the preservation of the pulse shape.

The magnetic circuit in the transformer is made of electrical steel plates, except for the toroidal shape, in which it is made of rolled or ferromagnetic material. Coil frames are placed on insulators, and only copper wires are used. The thickness of the plates is selected depending on the frequency.

The arrangement of the windings can be made in a spiral, conical and cylindrical form. A feature of the first type is the use of not wire, but a wide thin foil tape. Second, they are made with different insulation thicknesses, which affect the voltage between the primary and secondary windings. The third type is a structure with a wire wound on a rod in a spiral.

How the device works

The principle of operation of IT is based on the occurrence of electromagnetic induction. So, if voltage is applied to the primary winding, then alternating current will begin to flow through it. Its appearance will lead to the emergence of a non-constant magnetic flux. Thus, this coil is a kind of magnetic field source. This flux is transmitted through the short-circuited core to the secondary winding, inducing an electromotive force (EMF) on it.

The value of the output voltage depends on the ratio of the number of turns between the primary winding and the secondary, and the maximum current strength depends on the cross-section of the wire used. When a powerful load is connected to the output, current consumption increases, which, with a small wire cross-section, leads the transformer to overheating, insulation damage and burnout.

The operation of IT also depends on the frequency of the signal that is fed to the primary winding. The higher this frequency is, the less losses will occur during energy transformation. Therefore, at a high speed of the supplied pulses, the dimensions of the device can be smaller. This is achieved by operating the magnetic circuit in saturation mode, and a small air gap is used to reduce the residual induction. This principle is used in the construction of an IT, to which a signal with a duration of only a few microseconds is applied.

Preparation and verification

It's easier with a digital multimeter. Its design uses an analyzer that monitors the condition of the battery and, if its parameters deteriorate, displays a message on the tester's screen about the need to replace it.

When checking the parameters of a transformer, two fundamentally different approaches are used. The first is to assess the health directly in the circuit, and the second is independent from it. But it is important to understand that if the IT is not removed from the circuit, or at least not disconnected from a number of pins, then the measurement error can be very large. This is due to other radioelements that bypass the input and output of the device.

Defect detection procedure

In some cases, a diagram of the arrangement of the windings can be applied to the IT, or even their conclusions can be signed. If the transformer is installed in the device, then the circuit diagram or specification will help in finding the pinout. Also, often the designations of the windings, namely the voltage and the common terminal, are signed on the PCB itself near the connectors to which the device is connected.

After the conclusions are determined, you can proceed directly to checking the transformer. The list of malfunctions that may occur in the device is limited to four points:

core damage;
burnt-out contact;
breakdown of insulation, leading to turn-to-turn or frame short circuit;
wire break.

The inspection sequence is reduced to an initial external inspection of the transformer. It is carefully checked for blackening, chips, and odor. If no obvious damage is found, then proceed to measuring with a multimeter.

To check the integrity of the windings, it is best to use a digital tester, but you can also examine them using a dial gauge. In the first case, the diode continuity mode is used, indicated on the multimeter by the symbol - |> | -))). To determine the breakage, test leads are connected to the digital device. One plugs into the connectors labeled V / Ω, and the other plugs into COM. The gallet switch is transferred to the continuity area. Measuring probes consistently touch each winding, red - to one of its terminals, and black - to the other. If it is intact, the multimeter will beep.

In the same way, there is a short circuit check. A short circuit can occur due to insulation breakdown. As a result, the resistance of the winding will decrease, which will lead to a redistribution of the magnetic flux in the device. The meter switches to resistance test mode for testing. Touching the probes to the windings, they look at the result on the digital display or on the scale (arrow deviation). This result should not be less than 10 ohms.

Voltage and current measurements

If you suspect a transformer malfunction, testing can be carried out without disconnecting it completely from the circuit. This method of verification is called direct, but it is associated with the risk of getting hit. electric shock. The essence of actions in measuring current is to perform the following steps:

one of the legs of the secondary winding is soldered from the circuit;
the black wire is inserted into the COM jack of the multimeter, and the red wire is connected to the connector marked with the letter A;
the switch of the device is moved to the position corresponding to the ACA zone.
with a probe connected to the red wire, touch the free leg, and to the black one - the place to which it was soldered.

When voltage is applied, if the transformer is operational, a current will begin to flow through it, the value of which can be seen on the tester screen. If the IT has several secondary windings, then the current strength is checked on each of them.

The measurement of the voltage is as follows. The circuit with the transformer installed is connected to the power supply and then the tester switches to the ACV (alternating signal) area. Wire plugs plug into V / Ω and COM sockets and touch the beginning and end of the winding. If the IT is OK, the result will be displayed on the screen.

Removing characteristics

To be able to check a transformer with a multimeter in this way, its current-voltage characteristic is required. This graph displays the relationship between the potential difference at the terminals of the secondary windings and the current strength, leading to their magnetization.

The essence of the method is as follows: the transformer is removed from the circuit, pulses of different magnitudes are fed to its secondary winding with the help of a generator. The power supplied to the coil must be sufficient to saturate the magnetic circuit. Each time the pulse changes, the current in the coil and the voltage at the output of the source are measured, and the magnetic circuit is demagnetized. For this, after removing the voltage, the current in the winding increases in several approaches, after which it decreases to zero.

As the I - V characteristic is taken, its real characteristic is compared with the reference one. A decrease in its steepness indicates the appearance of an interturn short circuit in the transformer. It is important to note that to plot the current-voltage characteristic, it is necessary to use a multimeter with an electrodynamic head (pointer).

Thus, using an ordinary multimeter, it is possible with a high degree of probability to determine the operability of IT, but for this it is best to perform a set of measurements. Although for a correct interpretation of the result, one should understand the principle of operation of the device and imagine what processes occur in it, but in principle, for a successful measurement, it is enough just to be able to switch the device to different modes.

The transformer tester is an indispensable device for repairing TVs, monitors and other similar devices. With great accuracy, he can indicate short-circuits in turns. Has been working for me since 2003, there are no complaints about the work. The device starts immediately and does not require adjustment. I connected it, pressed the button, looked - if there is a short circuit in the turns, it will show. I have never failed, such a tester is much better than a generator and an oscilloscope, the presence of a short compute. I assembled it according to the original scheme, only I slightly altered the Masterkit signet, squeezed it and placed the batteries on it. Further, the electrical diagram and a description from the author, published in the journal "Repair of electronic equipment":

This simple device allows you to diagnose defects from the circuit without removing the transformer from the circuit and significantly reduce the repair time. It is known that a common cause of TV and monitor failures is the failure of the power elements of power supplies and line scan. This is easily explained, because they operate in very difficult conditions, at high currents and voltages. Often, the failure of one element, for example a line transformer, provokes the failure of other related elements, such as an output transistor or damper diodes. Sometimes it is difficult to immediately detect all damaged elements and determine the cause of their failure, and if the reason is incorrectly determined, the replaced elements can fail again after a short time, increasing repair costs and, even worse, damaging the reputation of the master in the eyes of customers.

The most difficult to diagnose are power supply pulse transformers, line transformers, and CRT deflecting coils. The most common type of their failure is the appearance of short-circuited loops, and it is not diagnosed in any way using a tester. Checking by replacing it with a known good element is also not always possible, because such transformers are usually made for a specific TV model and are very expensive elements.

The offered pulse transformer tester helps to significantly facilitate the diagnosis of any transformers and chokes on ferrite cores. The idea of the device's operation is based on the fact that all such transformers operate on the principle of energy storage and therefore must have a high Q-factor, and the presence of short-circuited turns sharply reduces it. The challenge is how to evaluate it by simple means.

You can excite shock oscillations in the circuit and count the number of periods during which the amplitude will fall to a certain level. It is known that this number is proportional to the quality factor of the circuit. The device is built on this principle.

The tester consists of three parts: a shock excitation pulse generator, a “ringing” pulse comparator and a pulse counter. The pulse generator is assembled on a comparator DA1.2 (LM393), transistors VT1, VT2 and diode VD2. It generates short impulses of shock excitation with a duration of about 2 ms and a frequency of about 10 Hz. The VD2 diode sets the amplitude of the excitation pulses to about 0.7 V, which allows you to check the transformers without soldering them from the circuit, since at this voltage the p-n junctions in the circuit turn out to be closed and do not affect the measurement result.

The transformer under test is connected to terminals 3 and 4 of the tester and, together with the capacitor C3, creates an oscillatory circuit. On the decay of the excitation pulse, the transistor VT2 opens and free damped oscillations begin in the formed oscillatory circuit. These oscillations are fed through the transition capacitor C4 to the input of the pulse comparator, collected on DA1.1. The same input receives the trigger threshold voltage, which is formed by the divider R11, R12 and the reference source VD3. The threshold is selected at 10% of the excitation voltage.

A diode of the same type as in the shock excitation source is used as a reference source of the threshold, which guarantees the stability of the tester's parameters in a fairly wide range of temperatures and supply voltages. From the output of the comparator, the pulses are fed to the input of the pulse counter, assembled on the DA2 microcircuit. This microcircuit consists of two four-bit shift registers with serial inputs.

In the tester circuit, these registers are connected in series into one eight-bit register, and the information input of the first register is connected to the log. "1". The clock inputs of the microcircuit (pins 1, 9) are supplied with pulses from the comparator. LEDs are connected to all register outputs through current-limiting resistors R15 ... R22. During the formation of the excitation pulse, the registers are cleared by the Reset inputs (pins 6 and 14) and all LEDs go out. On the decay of the excitation pulse, an oscillatory process begins in the circuit of the connected transformer. The resulting oscillations are converted by the comparator into logical pulses, which are then fed to the shift register.

In the shift register, each pulse carries a log. “1” for the next discharge, lighting consecutively the LEDs HL1 ... HL8. For ease of use, the first three LEDs are red (the transformer is faulty), the next two are yellow (the situation is uncertain) and the last three are green (the transformer is operational). After the end of the oscillatory process, the number of luminous LEDs is equal to the number of oscillation periods. If the number of pulses is more than 8, then all LEDs light up.

Working with the device during repairs. First, without soldering any components, you need to connect the device with the GND terminal to the TV chassis, and with the NOT terminal to the collector of the horizontal output transistor. If, when you press the "Test" button, more than four LEDs light up, this indicates the serviceability of the line scan output circuits. If less than two LEDs are lit, then this indicates the presence of short circuits at the output of the circuits - it is necessary to evaporate the output transistor and repeat the measurement.

If after that more than four LEDs are lit, then the output transistor needs to be replaced, otherwise the damping diode must be removed and the measurement repeated. The glow of more than four LEDs indicates the need to replace this diode. The same operations must be repeated with the flyback capacitor and the deflection coils of the CRT. If the result is negative, then it is necessary to remove the line transformer and test it outside the circuit. The glow of less than two LEDs when checking a soldered-out transformer indicates the presence of short-circuited turns in the transformer and the need to replace it.

The procedure for checking switching power supplies and deflecting coils of a CRT is similar. It should only be noted that when checking, it may be necessary to temporarily disconnect the shunt circuits that are installed in parallel with the windings.

An analogue of the 4015 microcircuit is K561IR2, it is not at all in short supply, it will be possible to buy it in stores without any problems. however, for more powerful windings (auto generator, electric motors) it is not suitable, any short circuit will show on ferrite cores, but not on transformer steel. The transistor was installed 2N5401, and in place of the field one - 2N7000, you do not need to select anything. The device starts immediately. Scheme author V. Chulkov, assembly nickolay78.

Discuss the article DEVICE FOR TESTING TRANSFORMERS

In connection with the widespread use of switching power supplies, in various equipment, in the event of a breakdown, it is required to be able to independently repair them. All this, from low-power chargers for smartphones, with voltage stabilization, power supplies for digital set-top boxes, LCD and LED TVs and monitors, to the same powerful computer power supplies, ATX format, the simplest repair cases of which, we have already considered earlier, are all will be.

Photo - switching power supply

It was also said earlier that for most measurements, an ordinary digital multimeter is enough for us. But there is one important nuance here: when checking, for example by measuring resistance, or in the mode of sound continuity, we can only conditionally determine a non-working part, by low resistance, between its legs. Usually it is somewhere from zero, to 40-50 Ohm, or an open circuit, but then for this you need to know what resistance should be between the legs of the working part, which is not always possible to check. But in the case of checking the PWM controller's performance, this is usually not enough. You need either an oscilloscope, or a determination of its performance, by indirect indications.

Cheap multimeter DT

The resistance between the legs may be higher than these limits, but the microcircuit, in fact, may be inoperative. But recently I ran into such a case: the power cable connector going from the power supply to the scaler, from above had access for measurement only to the upper one, from two rows of contacts on the connector, the lower one was hidden by the case, and access to it was available only from the back side of the board, which makes repairs very difficult. Even a simple measurement of the voltage at the connectors, in such a situation, is difficult. A second person is required who agrees to hold the board, on the connector of which you will measure the voltage at the terminals, on the back of the board, and some of the parts there are under mains voltage, and the board itself is suspended. This is not always possible, often people whom you ask to hold the board are simply afraid to pick it up, especially if these are power boards, on the one hand, they are doing the right thing, precautions with untrained personnel should always be stricter.

PWM controller - microcircuit

So what can be done? How can you quickly and without problems, conditionally check the operation of the PWM controller, and to be more precise, the power circuits, and at the same time the pulse transformer, the step-up transformer that feeds the backlight lamps? And it's very simple ... Recently I found one interesting way on U-tube, for masters, the author explained everything in a very accessible way. I'll start from afar.

Transformer

What is, to put it simply, an ordinary transformer? These are two or more windings on one core. But there is one nuance here, which we will use, the core, like the windings themselves, in theory can be separate, and just be close to each other. In this case, the parameters will deteriorate greatly, but for our purposes, this will be more than enough. So, around each transformer, or choke, with a significant number of turns, after turning on the power of the circuit, there is a magnetic field, and it is the greater, the more turns the winding of the transformer or choke has. What will happen if we bring another choke, for example, with an inductance of 470 μH, to the winding of a transformer or choke connected to the network of the device, and we need just one loaded with an LED for our probe? For example, such as in the photo below:

In other words, the magnetic field of the choke or transformer will permeate us, the turns of our choke, and a voltage will appear at its terminals, which can be used, in our case, to indicate the operability of the power supply circuit. Of course, bring the probe as close as possible to the part to be checked, and with the throttle down. What do the parts on the board look like to which you need to bring our probe?

On the board, the pulse transformer is circled in red, and the backlight transformer in green. If the circuit is working properly, when the probe is brought up to them, the LED should light up. This means that power is supplied to our, figuratively speaking, the tested inductance. Let's analyze it in practice. If the output transistor is broken, the pulse transformer will not work.

In the diagram, it is highlighted in red again. If the Schottky diode is broken, there will be no indication on the filter choke at the output, after the transformer. But there is one nuance here, if the choke on the board has a small number of turns, the glow will either be barely noticeable, or will be absent altogether. Likewise, if pierced, for example, transistor switches, or diode assemblies, through which power comes to the step-up transformer, for backlight lamps, LCD monitors or TVs, there will be no indication when checking on this transformer.

The cost of this choke in a radio store is only 30 rubles, sometimes they are also found in blocks ATX power supply, a conventional LED, in a glass bulb 5 rubles. As a result, we have a simple, cheap, and very useful device for repairs, which allows us to carry out preliminary diagnostics of a switching power supply unit within literally one minute. Relatively speaking, with this probe you can check the presence of voltage on all the parts shown in the next photo.

I have been using this probe for only 3-4 days so far, but I already think that I can recommend it for use to all novice radio amateurs - repairmen who do not yet have an oscilloscope in their home workshop. Also, this probe can be useful for those who are on the road. Successful repairs to everyone - AKV.

It is often necessary to familiarize yourself in advance with the question of how to check a transformer. Indeed, if it fails or is unstable, it will be difficult to look for the cause of the equipment failure. This simple electrical device can be diagnosed with an ordinary multimeter. Let's see how to do this.

What is the equipment?

How to check a transformer if we do not know its design? Consider the principle of operation and types of simple equipment. Coils of copper wire of a certain section are applied to the magnetic core so that leads remain for the supply winding and the secondary.

The transfer of energy to the secondary winding is carried out in a non-contact way. It already becomes almost clear how to check the transformer. The usual inductance with an ohmmeter is called in the same way. The turns form a resistance that can be measured. However, this method is applicable when the target value is known. After all, resistance can change up or down as a result of heating. This is called turn-to-turn closure.

Such a device will no longer provide a reference voltage and current. The ohmmeter will only show an open circuit or a complete short circuit. For additional diagnostics, use the check for a short circuit to the case with the same ohmmeter. How to check a transformer without knowing the terminals of the windings?

This is determined by the thickness of the wires coming out. If the transformer is a step-down transformer, then the output conductors will be thicker than the lead ones. And accordingly, on the contrary: the input wires of the step-up are thicker. If two windings are output, then the thickness may be the same, this should be remembered. The surest way to look at the markings and find specifications equipment.

Views

Transformers are divided into the following groups:

Down and up.
Power ones are often used to reduce the supply voltage.
Current transformers for supplying the consumer with a constant current value and keeping it in a given range.
Single and multiphase.
Welding purpose.
Pulse.

Depending on the purpose of the equipment, the principle of approach to the question of how to check the transformer windings also changes. Only small devices can be called with a multimeter. Power machines already require a different approach to troubleshooting.

Dialing method

The ohmmeter diagnostic method will help with the question of how to check the power transformer. The resistance between the terminals of one winding begins to ring. This is how the integrity of the conductor is established. Before that, the body is inspected for the absence of carbon deposits, sagging as a result of equipment heating.

Next, they measure the current values in Ohms and compare them with the passport ones. If these are not available, then additional diagnostics under voltage will be required. It is recommended to ring each lead relative to the metal case of the device, where the ground is connected.

Disconnect all ends of the transformer before taking measurements. It is also recommended to disconnect them from the circuit for your own safety. Also check for availability electronic circuit, which is often found in modern food models. It should also be evaporated before checking.

Infinite resistance speaks of a whole isolation. Values of several kilo-ohms already raise suspicions of a breakdown to the case. It can also be due to accumulated dirt, dust or moisture in the air gaps of the device.

Energized

Tests with the supplied power are carried out when the question is about how to check the transformer for If we know the value of the supply voltage of the device for which the transformer is intended, then measure the no-load value with a voltmeter. That is, the lead wires are in the air.

If the voltage value differs from the nominal, then conclusions are drawn about turn-to-turn closure in the windings. If crackling, sparking is heard during the operation of the device, then it is better to turn off such a transformer immediately. It is defective. There are permissible deviations in measurements:

For voltage, the values may vary by 20%.
For resistance, the norm is a spread of values of 50% of the passport values.

Measurement with an ammeter

Let's figure out how to check a current transformer. It is included in the chain: standard or actually made. It is important that the current value is not less than the nominal one. Measurements with an ammeter are carried out in the primary circuit and in the secondary circuit.

The primary current is compared with the secondary readings. More precisely, the first values are divided by those measured in the secondary winding. The transformation ratio should be taken from the reference book and compared with the obtained calculations. The results should be the same.

The current transformer must not be measured at idle. In this case, too much damage to the insulation can form on the secondary winding. You should also observe the polarity of the connection, which will affect the operation of the entire connected circuit.

Typical malfunctions

Before checking the microwave transformer, here are the frequent types of breakdowns that can be eliminated without a multimeter. Power devices often fail due to a short circuit. It is established by inspection circuit boards, connectors, connections. Less often, mechanical damage to the transformer housing and its core occurs.

Mechanical wear of the connections of the terminals of the transformer occurs on moving machines. Large supply windings require constant cooling. In its absence, overheating and melting of the insulation is possible.

TDKS

Let's figure out how to check a pulse transformer. Only the integrity of the windings can be established with an ohmmeter. The operability of the device is established when connected to a circuit where a capacitor, a load and a sound generator are involved.

A pulse signal is sent to the primary winding in the range from 20 to 100 kHz. On the secondary winding, the magnitude is measured with an oscilloscope. The presence of pulse distortion is established. If they are absent, they draw conclusions about a working device.

Distortions in the waveform indicate damaged windings. It is not recommended to repair such devices yourself. They are set up in the laboratory. There are other schemes for testing pulse transformers, where the presence of resonance on the windings is investigated. Its absence indicates a faulty device.

You can also compare the shape of the pulses applied to the primary winding and output from the secondary. A deviation in shape also indicates a malfunction of the transformer.

Multiple windings

For resistance measurements, the ends are freed from electrical connections. Choose any conclusion and measure all resistances relative to the rest. It is recommended that you record the values and label the tested ends.

So we can determine the type of connection of the windings: with middle terminals, without them, with a common connection point. More often found with a separate connection of the windings. Measurement can be done with only one of all the wires.

If there is a common point, then the resistance is measured between all available conductors. The two windings with the middle lead will only matter between the three wires. Several terminals are found in transformers designed to operate in several networks with a nominal value of 110 or 220 Volts.

Nuances of diagnosis

It is normal to hum when the transformer is operating if it is a specific device. Only sparks and crackling signals indicate a malfunction. Often, the heating of the windings is the normal operation of the transformer. This is most often observed in step-down devices.

Resonance can be generated when the transformer housing vibrates. Then you should simply fix it with insulating material. The operation of the windings changes significantly with loose or dirty contacts. Most of the problems are solved by stripping the metal to a shine and rewinding the leads.

When measuring the values of voltage and current, the ambient temperature, the magnitude and nature of the load should be taken into account. Monitoring of the supply voltage is also necessary. Checking the frequency connection is mandatory. Asian and American technology is rated at 60 Hz, resulting in lower output values.

Inadequate connection of the transformer can lead to malfunction of the device. In no case are they connected to the windings. constant pressure... The coils will melt quickly otherwise. Accuracy in measurements and competent connection will help not only find the cause of the breakdown, but also, possibly, eliminate it in a painless way.