A microwave transformer is an important link in the microwave generating circuit. This is a voltage converter to the value supplied to the magnetron input. A 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 a malfunction. Since we are talking about high voltages, self-intervention is possible only if all safety measures are followed.
Where to get high voltage?
Food in microwave ovens is heated due to the operation of microwave waves. A special emitter - a magnetron - generates microwaves. To work in the given characteristics, it needs a high voltage - 2,000 V. This is almost an order of magnitude higher than what a household electrical network (220 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 cause electric shock (U up to 5,000 V).
Types of high voltage converters
Elements of the converter installed in the microwave oven:
- magnetic circuit;
- frame;
- primary winding;
- two secondary windings.
U = 220 V enters the primary winding. The filament is fed from the secondary. The first of two secondary windings is made of a large cross-section wire. U at the output - approximately 3 V. At the output of the second winding - variable high U = 4 kV.
In microwave ovens of different brands, converting devices of various production 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;
- way of fixing.
The secondary coil, like one of the terminals of the emitter, is shorted to the housing.
Circuit diagram
In the circuit diagram of a microwave oven, in addition to the converter, there are:
- diode;
- high voltage capacitor;
- magnetron;
- fuse;
- electric motor - one or two (for rotation of the pallet, if it is provided for by the design, and for the fan);
- Control block.
In expensive microwave ovens, instead of the converter, a pulse block 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. It is possible to suspect a malfunction of this particular element by the following symptoms:
- the microwave is unusually loud;
- food placed in the cell is not heated or warmed slightly;
- when working, it smells of burnt insulation, the technique smokes.
If at least one of the listed symptoms appears, it is better not to turn on the device until the problem is resolved. Turning on a faulty stove can aggravate the breakdown.
One of the most common causes of failure of electrical equipment is power surges. If there is a suspicion that the device is malfunctioning due to changes in the network, urgent repair is required. However, it is possible that during the repair work a factory marriage will be discovered.
Causes of malfunctions
The converter fails most often due to:
- Wire breakage. The wire of one of the windings may break.
- Short circuit in the windings. This can happen in one coil or in both.
- An open or short 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 determined by eye, but they do not happen often. The vast majority of problems are nevertheless 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 outlet;
- unscrew the screws and remove the casing;
- discharge the capacitor;
- remove the terminals from the transformer;
- check the coil with a tester - if there are no deviations, put back;
- if damage is detected - the wire is broken or a circuit has occurred, change the device;
- assemble the oven and check its functioning.
If the device still does not work after the measures taken, continue troubleshooting or check that the device is energized.
A transformer with traces of melted insulation and a burning odor does not need further verification: it is broken and cannot be repaired.
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 his contacts with each other - this can be done, for example, with pliers.
Diagnostic Options
Consider common options for finding the cause of a breakdown.
Secure check
The safest test is carried out by the tester and consists in examining the coils for damage. Procedure:
- The multimeter is adjusted to the required limits and determined with its help the resistance of all windings - primary and two secondary. The study is done on a removed transformer.
- If the unit displays on the tester, then an open has occurred.
- When the circuit is closed, a value in the range of 2–4.5 Ω appears on the primary coil (the tester is set to 200 Ω). On the filament - 3.5–8 Ohms, on the high-voltage secondary (2,000 Ohms) - 140–350 Ohms.
If the resistance value is outside the specified ranges, an inter-turn short circuit has probably occurred.
When measuring, you must take into account your own multimeter error. It can be determined by short-circuiting the probes in the set limit. The resulting value is the error.
You can perform a safe check yourself or invite a specialist from the service. To ring the windings, the user just needs to know the basics of electrical engineering and have the skills to work with the tester.
Live test
If measurements are taken, the measurements obtained are normal, 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:
- 220V is supplied to the microwave.
- A tester measures U at the outputs of both secondary windings. High voltage - 2 kV, glow - 3 V.
This method requires equipment that can measure an alternating voltage of more than 2 kV.
Reverse check
This option is less problematic. 220 V is brought to the secondary winding, about 24 V. is removed from the primary winding. The coefficient is 9.1. If you apply 12 V to the primary winding, it will be about 109 V. on the secondary.
If the transformer heats up during idle, an inter-turn short circuit has probably occurred. If the device heats up under load, and when it turns off, it stops warming up, you should continue to search for a problem.
How to choose a verification method
It is important to choose a converter research option based on your qualifications, knowledge and skills. The safest thing is to simply ring the chains for integrity. If 220 V is connected during measurements, special precautions must be taken.
If you are not confident in 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 Samsung, LG, Daewoo brands.
Given the big names of the 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, because the statistics of breakdowns is higher. But when calculating the number of breakdowns by the number of units sold, it becomes obvious that they break down no more often than other well-known brands.
Precautions
When conducting live measurements, an electric shock can occur, including 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 take measurements, it is necessary to put probes - “crocodiles” on the clamps of the tester - with them and connect to sections of the circuit.
- If you need to touch the 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. Thanks to this precaution, you protect yourself from the discharge of a capacitor. The microwave circuit has a resistor to discharge the capacitor, but it does not exclude the danger by 100%. A resistor may burn out or be completely forgotten to install, and such a mistake can cost a lover an independent repair.
Repair of any electrical equipment is associated with the danger of electric shock. When checking the transformer in the microwave, you need to be especially careful because of the high voltage and capacitor. Use safe measurement methods and follow safety guidelines.