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A microwave transformer is an important link in a circuit that generates microwave radiation. This is a voltage converter of the mains to the value supplied to the input of the magnetron. The high-voltage converter often causes damage to the microwave oven.
Checking the transformer for operability is a mandatory item in the list of measures for technical diagnostics to find out the causes of the malfunction. Since we are talking about high voltages, self-intervention is possible only if all safety measures are observed.
Where can I get high voltage?
Food in microwave ovens is heated by the work of microwaves. Microwaves are generated by a special emitter – a magnetron. To work in the given characteristics, it needs a high voltage – 2 V. This is almost an order of magnitude higher than what the household power supply (000 V) gives.
Where do kilovolts come from? They are created at the output of the secondary winding of the high-voltage converter.
Important! A microwave oven, even disconnected from the mains, can be electrocuted (U up to 5 V).
Types of high voltage converters
Elements of the converter installed in the microwave oven:
- magnetic circuit;
- skeleton;
- primary winding;
- two secondary windings.
U = 220 V is supplied to the primary winding. The filament is fed from the secondary. The first of the two secondary windings is made of heavy gauge wire. U at the output – approximately 3 V. At the output of the second winding – variable high U u4d XNUMX kV.
In microwave ovens of different brands, converting devices of various manufactures are used. The transducers do not look the same and have different characteristics. They differ:
- power;
- output voltage of the secondary windings;
- the number of turns in the coils and the cross section of the wire;
- dimensions;
- fastening method.
The secondary coil, like one of the outputs of the emitter, is closed to the housing.
Electrical circuit diagram
In the electrical circuit of the microwave oven, in addition to the converter, there are:
- diode;
- high voltage capacitor;
- magnetron;
- fuse;
- electric motor – one or two (for rotating the pallet, if it is provided for by the design, and for the fan);
- Control block.
In expensive microwave ovens, instead of a converter, a pulse unit is used, which has a more complex device, but weighs less.
What are the faults?
You need to check the transformer in two cases: when the stove does not work well and when it does not work at all. You can suspect a malfunction of this particular element by the following signs:
- the microwave oven is unusually loud;
- food placed in the chamber is not heated or heated slightly;
- when working, it smells of burnt insulation, the equipment smokes.
If at least one of the listed symptoms appears, it is better not to turn on the device until the problem is fixed. Turning on a faulty stove can lead to an aggravation of the breakdown.
One of the most common causes of electrical equipment failure is power surges. If there is a suspicion that the device is faulty due to power outages, urgent repairs are needed. However, it is possible that during the repair work a factory defect will be found.
Causes of malfunctions
The converter fails most often due to:
- Wire break. The wire of one of the windings may break.
- Short circuit in windings. This can happen in one coil or both.
- Open or short circuit in the magnetron coil.
The magnetic circuit of the converter is assembled from steel plates. If the plates peel off, the machine will make noise. It is necessary to find out the power of the transformer and replace it. Such global breakdowns can be easily identified by eye, but they do not happen often. The vast majority of problems are still provoked by coils.
Verification Procedure
To check the health of the high-voltage converter, you need to arm yourself with a multimeter, you will also need:
- screwdrivers with different tips;
- pliers;
- ohmmeter.
Sequencing:
- turn off the device – remove the plug from the socket;
- unscrew the screws and remove the casing;
- discharge the capacitor;
- remove the terminals from the transformer;
- check with a coil tester – if there are no deviations, put back;
- if damage is detected – the wire breaks or a short circuit occurs, the device is changed;
- assemble the oven and check its operation.
If the device still does not work after the measures taken, continue troubleshooting or check the device under voltage.
The transformer, with traces of melted insulation and a burning smell, does not need further examination: it is broken and beyond repair.
Important! To check the transformer, you have to disassemble the microwave oven – this can only be done when it is disconnected from the mains.
A high-voltage capacitor easily stores a huge electric charge, so it must be discharged before measurements. How to achieve this? Just close its contacts with each other – this can be done, for example, with pliers.
Diagnostic options
Consider common options for finding the causes of a breakdown.
Secure check
The safest examination is carried out by a tester and consists in examining the coils for damage. Procedure:
- The multimeter is adjusted to the required limits and with its help the resistance of all windings is determined – the primary and two secondary. The study is done on a removed transformer.
- If the unit is displayed on the tester, then a break has occurred.
- With a closed circuit, a value in the range of 2–4,5 ohms will appear on the primary coil (the tester is set to 200 ohms). On the incandescent – 3,5-8 ohms, on the high-voltage secondary (2 ohms) – 000-140 ohms.
If the resistance value is outside the specified ranges, an interturn short circuit has probably occurred.
When measuring, it is necessary to take into account the own error of the multimeter. You can determine it by short-circuiting the probes within the specified limit. The resulting value is the error.
You can perform a secure check yourself or invite a specialist from the service. To ring the windings, the user only needs to know the basics of electrical engineering and have the skills to work with a tester.
Voltage test
If the measurements are taken, the measurements are correct, but the stove still does not work, it is necessary to investigate a number of characteristics. Measuring the output voltage on the secondary windings is a rather dangerous business. Procedure:
- 220 V is supplied to the microwave.
- The tester measures U at the outputs of both secondary windings. High-voltage – 2 kV, incandescent – 3 V.
This method requires equipment that can measure AC voltages greater than 2 kV.
Reverse Check
This option is less problematic. 220 V is supplied to the secondary winding, about 24 V is removed from the primary winding. The coefficient is 9,1. If 12 V is applied to the primary winding, the secondary will be about 109 V.
If the transformer heats up during idling, an inter-turn short circuit has probably occurred. If the device heats up under load, and when it is turned off, it stops heating, you should continue to look for a problem.
How to choose a verification method
It is important to choose the converter study option based on your qualifications, knowledge and skills. The safest thing is to just ring the chains for integrity. If 220 V is connected during measurements, special precautions must be taken.
If you are not sure of your knowledge, it is better to contact a professional.
Which microwave ovens have problems
Most often, problems with the converter occur in microwave ovens of the Samsung, LG, Daewoo brands.
Considering the famous brands, it is difficult to assume that they all neglect the quality of the components used in the electrical circuits. Most likely, this trend is associated with the popularity of these brands. They are bought more, and therefore the breakdown statistics are higher. But when calculating the number of breakdowns per number of units sold, it becomes clear that they break no more often than other well-known brands.
Safety measures
Measurements under voltage can result in electrical shock or even death. Two rules will help to avoid danger:
- It is strictly forbidden to touch the internal parts of the microwave oven during its operation. To perform measurements, it is necessary to put on the tester clamps the “crocodile” probes – with them and connect to the sections of the circuit.
- If you need to touch high-voltage parts with your hands, you should not only disconnect the stove from the mains: you can prevent electric shock by shorting the magnetron leads to the housing. With this precaution, you will protect yourself from discharging the capacitor. There is a resistor in the microwave circuit to discharge the capacitor, but it does not eliminate the danger by 100%. The resistor may burn out or they forgot to install it at all, and such a mistake can cost the life of a self-repair lover.
Repair of any electrical equipment is associated with the danger of electric shock. When testing a transformer in a microwave, you need to be especially careful due to the high voltage and capacitor. Use safe measurement methods and follow safety regulations.