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How to Repair a Microwave

repair a microwave

The microwave oven has long entered and firmly established itself in the list of traditionally used household appliances. Instant cooking appliances raise the level of comfort and save time. But microwave ovens, despite the high degree of their manufacturability, are not immune to breakdowns. Therefore, such moments when the microwave oven does not work, does not heat, does not turn on, is not controlled, etc., are frequent breakdowns that should be considered. Moreover, many of the breakdowns of microwave ovens are quite affordable to fix with your own hands.

Before considering appliance repair, it would be correct to touch upon the principle of operation of the device. Food inside a microwave oven is heated by electromagnetic radiation. Moreover, only substances structurally containing moisture are heated.

A typical household microwave oven operates at 2450 MHz (microwave range).

High-frequency radiation inside the working chamber of the device creates a magnetron, one of the main parts of the electrical circuit.

A magnetron requires a high voltage of several thousand volts to generate microwaves. Such a voltage is obtained at the expense of other circuit components:

  • high voltage transformer;
  • powerful rectifier diode;
  • high voltage capacitor;
  • control and switching circuits.

Let’s take a closer look at microwave troubleshooting.

microwave 2

What to do if the microwave does not turn off?

The microwave oven continues to operate in the oven door open mode is usually associated with a defective interlock switch. To fix this, you need microwave repair.

Functionally, the door switch provides power to the microwave oven circuitry. If the door is open, power is not supplied by default. The design of the microwave oven door has a stem that activates/deactivates a switch located on the chassis. To check if it works:

  • Detach the microwave from the chassis cover.
  • Find a microswitch on the chassis.
  • Check for contact on its terminals.

The connection at the terminals is usually labeled C (common) and NO (normally open). A multimeter is used to measure the state of the switch contacts in the positions of the closed and open chamber doors. The circuit is closed when the door is closed. The circuit is open when the door is open.

If the closure remains in both positions, the switch is faulty (burnt). A similar situation, but does not allow turning on the microwave, is given by a microswitch damaged with a complete break in the contact group.

When the microwave does not turn off with the stop button but turns off when the door is opened, a similar cause is usually associated with the control electronics. The electronic board controls the microwave through a micro relay. Sometimes the failure of the board’s electronic components leads to the sticking of the relay. The fault can be determined by testing the relay for voltage on the power contacts. But such an appliance repair requires the skills of an electronics engineer and an electrician.

If the microwave does not heat

There are several relatively simple reasons why the microwave turns on but doesn’t heat up.

  • The first reason is a broken high-voltage diode in the magnetron power circuit (as a rule, the fuse blows out simultaneously). This electronic part, located inside the microwave, is easy to check:
  1. Remove power from the microwave.
  2. Discharge the high voltage capacitor (see above).
  3. Check the integrity of the fuse.
  4. Check the resistance of the diode with a multimeter.

For a good diode, the test should show low resistance in one direction and high resistance in another. If the resistance is low in both directions or the diode does not ring, it must be replaced for appliance repair.

  • A working diode indicates a problem with the high voltage circuit. However, it is already necessary to turn to specialists if there is no appropriate qualification here.

There is a high risk of testing high voltage circuits.

  • The second reason for the lack of heating of the microwave oven is a burned-out magnetron. This malfunction usually has an accompanying reason, which is determined visually. You should open the door of the microwave oven and carefully examine the sidewall, where the microwave window is located, closed with a gasket.

Traces of partially burnt or completely burnt gaskets indirectly indicate a burnt-out magnetron. As a rule, the end part of the waveguide also burns out on the dismantled magnetron.

  • The third relatively simple reason for the lack of heating is the failure of thermal sensors. Almost every microwave oven model is equipped with similar devices, protective devices against overheating. The sensors are usually located on the walls of the camera body, from the side of the chassis. The design of the sensors is simple. It is a miniature two-terminal device tested in the same way as a standard fuse.
fix a microwave

What to do if the microwave is noisy?

If the appliance is operating but makes an unusual noise, there may be a malfunction in the electric motor of the traveling platform. The round pan is connected to the motor shaft via an adapter. Long-term operation of the equipment often leads to wear of the adapter and then to microwave repair. Wear, in turn, will cause the shaft to skew and ultimately damage the motor. Any damaged part must be replaced.

To access the engine:

  • Unplug the microwave.
  • Remove the protective cover of the equipment.
  • Open the bottom panel of the casing.

If the microwave oven emits similar to buzzing, this symptom may indicate that the magnetron is not working properly. Before checking the magnetron:

  • Disconnect the supply voltage.
  • Remove the protective cover.
  • Discharge the high voltage capacitor.
  • Check the tightness of the fastening screws.
  • Check the high voltage diode is working properly.

The capacitor should be discharged by short-circuiting the terminals, but always through resistance with a power of at least 2 watts, with a nominal value of several tens of ohms.

If there is a residual discharge on the capacitor and the high-voltage diode is intact, there remains a high probability of a malfunction of the magnetron. Only replacement will help here. The microwave oven tray often generates unusual noise during movement. Here, a malfunction of the support rollers can cause noise. You just need to remove the tray from the microwave oven and check the crossings with rollers for damage or wear. You need to replace the support rollers if it is necessary for appliance repair.

The cooling fan is often the source of the noise

The cooling fan is often the source of the noise generated by microwave ovens. This device cools the magnetron heatsink during the operation of the microwave oven. The fan is located inside the case.

For diagnostics and repair:

  • Unplug the microwave ove.
  • Open the microwave oven chassis cover.
  • Remove the fan assembly cover.
  • Make sure that the impeller is intact and does not touch nearby objects.
  • Check shaft play and bearing integrity.

How to fix a microwave membrane switch?

The touch panel buttons do not work. Each individual touchpad button on some models is a Mylar foil switch. Such a switch contains two plates covered with a conductive material on the sides facing one another. Meanwhile, sensory-type constructions are also encountered.

When the user presses a key on the touch panel, the plates contact, completing the electrical circuit. This sends a signal to the electronic control board.

The conductive coating of the membrane switch plates wears out over time, leading to a button malfunction. In this case, the defective button (and in the case of sensors, the panel) must be replaced for microwave repair:

  • Unplug the microwave.
  • Remove the microwave oven casing.
  • Find the membrane switch. The membrane switch system is a modular part of the control board and is connected with a flat ribbon cable. First of all, you should check the integrity of the connecting cable.
  • To test the touch buttons directly, you will need the basic schedule service of the microwave oven, where the matrix arrangement of the membrane switches is indicated.
  •  Check the integrity of the contacts of the touch buttons using a multimeter. The transition resistance between the functional buttons’ contacts should be several ohms.

For your technique to serve as long as possible, be sure to read the instructions before use. But if, nevertheless, appliance repair is required, then contact a professional. If you absolutely do not understand anything about the repair, then our specialists will help you.

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