Professional advice to help identify the causes of microwave oven failure and eliminate them

The article was written with the support of specialists from the household appliance repair shop - Absolute.

This household appliance has become so familiar that if difficulties arise, panic immediately begins. But don’t worry, it’s not so difficult to deal with the main malfunctions of a non-working microwave, and also to fix the problems. You can learn how to diagnose and repair microwave ovens yourself, which will significantly save costs. Let's look at methods for solving the most popular microwave oven problems.

Microwave won't turn on

Most often, this problem is not associated with the purchase of expensive parts. But, repairs will have to be carried out. To begin with:

Make sure that the outlet to which the household appliance is connected is working properly. To do this, the plug must be connected to another power source.
Check the functionality of the cable that supplies power to the device.
If after the above steps the device still does not turn on, check the fuses located inside the microwave oven: mains fuse and temperature sensor. Replace them if necessary.
See if the latch micro switch on the door is working, otherwise it will signal that the door is open and the oven will not turn on.
Check the control board transformer.

If there is voltage at the output of the secondary winding, then take into account that some models on the block transformer additionally have a thermal fuse, which is located inside the transformer (under the thermal tape or cap). If necessary, replace the faulty element.

If there is no voltage, then the primary winding of the transformer has burned out and needs to be replaced.

If the door latch does not work, the oven may not turn on.

No response to button presses

The keypad can be constructed structurally as a solid plate or as separate buttons. The difference is in the number of contacts: wires are connected to each element separately or one to the entire panel. In modern models it looks like this: the touch panel is made in the form of a multilayer film, and touch information is read from it.

If the buttons do not work, but the display is turned on, most likely the problem is with loose contacts. The repair consists of the technician replacing the loose wires.

A common problem is a burnt-out board. In this case, the touchpad does not work completely. You have to buy a new one and change it. The same thing has to be done when repairing contacts does not bring the desired result.

The main reasons for keyboard failure:

Broken conductive paths.
Contacts sticking.
Lost contact.

The stove doesn't heat

In the microwave, the backlight works, the plate rotates, the grill also works, but the food in the device does not warm up. The reason is the failure of a high-voltage capacitor or magnetron.

In rare cases, this may be a malfunction of the high-voltage transformer. In this case, repairing it yourself will be difficult; it is better to contact microwave oven repair professionals.

To identify the cause, a diagnosis should be made:

when starting the furnace, check the presence of voltage on the primary winding (observe safety precautions),
if there is voltage, make sure that the contacts on the high-voltage transformer, high-voltage diode and magnetron are reliable,
if all contacts are normal, it is necessary to replace the magnetron or high-voltage diode.

Front Panel

On the front panel of the microwave oven there is a mechanical programmer that sets the modes. Under the round handle lies a shaft equipped (in our case) with two cam disks. The first is responsible for powering the transformer that forms the power supply for the magnetron, the second is responsible for the quartz grill lamps. The buttons of two relays are controlled by cam mechanisms:

a key transistor that blocks power supply to the magnetron;
quartz grill lamps.

If the cam is low, the button is released, the relay is in normal position. When the protrusion height is high, the relay button is pressed. It is easy to see that this way we will ensure a constant supply of voltage, but we need to regulate the power. We'll talk more below, but first let's get back to the start relay. The contraption, which initially removes the current load, is connected in parallel to the input winding of the transformer. Power contacts are connected in series. There is a capacitor and a zener diode in parallel with the relay.

When the front forms a spark, the capacitance presents zero resistance to the differential, the inductance of the transformer is separated by open contacts. Large current does not flow! The capacitance begins to charge to a voltage limited by the zener diode. A diode turned in the right direction prevents the discharge. When the threshold value is exceeded, the relay is activated and a large current flows to the transformer and power supply to the magnetron. Due to a well-thought-out design, microwave oven timers with a protective relay almost never burn out. Now the programmer!

Equipped with a gear, toothed transmission that regulates the clock. Depending on this, the periods of operation and downtime of the magnetron change. The longer the rest, the less power is released. About the magnetron, let us add: the introduction of inverter control shifts the control of cycles from the timer to the sensor circuit for measuring temperature. The sensor evaluates the emission spectrum of the food and decides how to operate the microwave oven. It is not the downtime (operation) of the cycle that changes, but the duty cycle of the pulses. More frequent packets, more power. As a result, it becomes possible to flexibly adapt to the current situation.

The furnace sparks

This cause occurs in microwave ovens that have a mica plate covering the magnetron. Why does a microwave oven spark and crackle? Before you carry out repairs yourself, you need to know the reasons:

Overheating of the mica plate, which is caused by drops of fat falling on it. We should not turn a blind eye to this problem. It can lead to burnout of an expensive magnetron.
Damage to the enamel in the chamber. Occurs due to irregular cleaning of the walls, fat or food particles accumulate. These contaminants cause sparks to occur.
Check if there are any metal products inside the stove. A coated plate or spoon and fork may cause sparks.

To eliminate the first malfunction, you need to replace the old plate with a new one. You can order the necessary material in the online store, on one of the sites you trust. The dimensions of the mica will not coincide with the inside of the microwave oven, they will be slightly larger.

Further actions:

remove the failed plate using a tool, as it is secured with plastic latches or self-tapping screws,
place an old piece of mica on the purchased material, cut the part strictly to size,
install a new plate,
Check the oven for functionality by placing a glass of water in it.

Important! It is recommended to turn on the microwave oven only with food inside. Otherwise, the device may break down over time.

You cannot turn on an empty microwave oven, as this will lead to its rapid failure.

Microwaves, not encountering any obstacles in their path, move on, being reflected on the walls of the chamber. The device will not turn off until the timer goes off, and the concentrated energy will negatively affect the microwave parts.

To cut the plate correctly you need to:

Use a sharp knife and a metal ruler.
Make holes for fasteners using a drill or a special punch.
Sand the sharp ends of the plate with sandpaper (fine-grained).
Eliminate all contaminated areas that were discovered when removing the old mica plate.
Install the new part into place.

To eliminate the second problem - damage to the enamel, you should purchase a special product and apply it to the internal walls of the microwave oven (organosilicon paint). It will not release harmful substances into food and is resistant to temperature changes. It is prohibited to use non-specialized substances that not only lead to damage to the device itself, but also harm human health.

If the sparks were caused by the presence of metal products inside the stove, then they simply need to be removed to eliminate the problem.

Common microwave oven malfunctions and their causes

We have long been accustomed to heating and defrosting food in the microwave. The microwave oven has long and firmly entered our everyday life and won its place there. And when suddenly this useful device fails, it greatly upsets us. If you have some knowledge in the field of electromechanics and radio engineering, then in the event of a minor breakdown, you can try to repair the microwave oven yourself. But if a significant malfunction occurs or your knowledge is insufficient, it is better to use the services of a professional technician.

Checking the locking system

Regardless of the microwave oven model, there is a magnetron inside, which is a radio-emitting device. If precautions are not taken, radiation can cause enormous harm to human health. The door with transparent glass and metal mesh prevents radiation from penetrating outside. It is tightly connected to the body; it is in this place that the electromagnetic wave has zero value.

It is very important to regularly diagnose the locking system:

First, inspect the door to determine the tightness of the seal and the security of the lock. You can use a sheet of paper for this.
Place it between the doors and the body, press it, and try to remove it from the chamber.
If effort is made to remove the paper, then everything is in order. If the sheet comes out freely, it indicates that the door needs to be adjusted.
Settings are made in two places: the hinge area and the lock area. The main goal is to tightly fit the door to the base so that the radiation does not spread beyond the boundaries of the household appliance.
Particular attention should be paid to the microswitch, both in the open and closed states. Test them using a tester and if problems are found, replace both, since they have the same service life.

To reduce the gap you need to:

loosen the screws securing the door hinges,
press the upper part of the sash so that the seal fits tightly to the oven chamber,
tighten the door hinge screws.

Attention! The microwave will not turn on unless a signal is sent to the electronic control module that the door is closed. In this case, the contacts are open, which means the limit switch is broken. It should be replaced.

Common microwave oven malfunctions and their causes

When to ring a transformer

The transformer converts the network voltage that is necessary for the magnetron to operate. It needs to be given enough attention, as it often causes the microwave to break down.

Transformer failure is one of the most common causes of failure.

The high-voltage transformer is ringed, provided that the load is turned off, as well as the primary winding. The procedure should be carried out this way:

Using pliers, remove the terminals.
Check the resistance of the primary winding, the standard value of which is 1.5 Ohms. The indicator of the secondary filament winding and high-voltage winding are the corresponding values - 0.1 Ohm and 110 - 120 Ohm.
If during the test it was not possible to ring at least one winding, this is a sign of failure of the transformer. Replacement is required; there is a special connector in the magnetron design to connect it.

You can find out the resistance value between the case and the terminals if you disconnect the terminals. If the process is successful, you need to look for damage in the filter at the feed-through capacitors. To fix the problem you should:

install a new capacitor or buy an assembled filter of a suitable rating,
remove the magnetron to make sure the condition of the antenna cap,
Having detected signs of combustion, damage to the housing, and also having determined the life of the magnetron insulator, replace the necessary elements, the main thing is that the parts match the size.