Electrolux In General

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Summary

Microwave Technology Fundamentals

Microwave Technology Advantages

Discusses benefits like time-saving cooking, healthy cooking, and energy saving.

Frequency and Radiation Spectrum

Explains microwave frequencies and their placement in the non-ionizing radiation spectrum.

Microwave Behavior and Material Interaction

Explains reflection, interpenetration, and absorption of microwaves by different materials.

Suitable Ovenware

Details which types of cookware are suitable or unsuitable for microwave use.

Electromagnetic Energy Conversion and Penetration

Explains how microwave energy heats food and its penetration depth.

Oven Operation and Control

Wave Guiding and Distribution

Explains the wave duct and wave agitator (stirrer) for distributing microwaves.

Microwave Capacity Control

Details how magnetron power is controlled using on/off cycles to achieve different power levels.

Input and Control Panels

Describes mechanical and electronic timer controls and their functions.

Metal in the Oven: Usage and Safety

Discusses the use and risks of metal objects within the microwave oven.

Safety Systems

Wiring Diagram

Presents the electrical wiring diagram for a timer-controlled microwave oven.

Mechanical Safety System

Details the wave trap and door sealing to suppress microwave leakage.

Electromagnetic and Interlock Safety Systems

Explains the 'interlock'-microswitch system for safety interlocks and door monitoring.

Interlock System Operation

Illustrates the door interlock system's function when the door is opened or closed.

High Voltage Circuitry

Primary and Secondary Circuits

Describes the main power input, control elements, and high-voltage secondary circuit.

High Voltage Transformer

Explains the function and windings of the high-voltage transformer.

Voltage Doubling Circuit

Details how the voltage doubler circuit converts AC to high DC voltage for the magnetron.

AK Diode (Protector)

Explains the role of the AK diode in protecting the transformer during normal and fault conditions.

Magnetron Operation

Describes the magnetron as the heart of the oven, generating microwave energy.

Testing, Measurement, and Troubleshooting

Measurements and Repairs - Safety Notes

Provides important safety notes and general procedures for measurements and repairs.

Capacity Measurement Methods

Details simple methods for measuring microwave output power using water.

Leaky Rays Rules and Measurement

States legal limits for microwave leakage and provides a procedure for measurement.

Interlock System Electrical Checks

Explains how to electrically check the primary, secondary, and monitor interlock switches.

Component Testing: Fuse Diode, HV Diode

Guides on how to test the fuse diode (AK-Diode) and the high-voltage diode.

Component Testing: Magnetron, HV Capacitor, HV Transformer

Details resistance checks for magnetron, capacitor, and transformer windings.

Fault Finding Tree - Operation and Power Issues

Presents diagnostic flowcharts for troubleshooting oven operation and power issues.

Fault Finding Tree - Operation Stops and Low Power

Presents diagnostic flowcharts for oven stopping or low power issues.

Fault Finding Tree - No Microwave Capacity

Presents diagnostic flowcharts for troubleshooting ovens with no microwave capacity.

Fault Finding Tree - No Function; No Entry

Presents diagnostic flowcharts for troubleshooting ovens with no function or entry reaction.

Consumer Guidance

Consumer Cooking and Defrosting Advice

Offers tips on cooking, defrosting, and using instant meals in the microwave.

Setting Microwave Capacity Levels

Provides guidance on selecting appropriate power levels for different cooking processes.

This document serves as a service manual for Electrolux microwave ovens, focusing on general principles, fundamentals, measuring techniques, and fault-finding. It is designed for technicians and provides comprehensive information for the maintenance and repair of these appliances.

Function Description

Microwave ovens utilize electromagnetic waves, specifically microwaves at a fixed frequency of 2,450 MHz, to heat food. This process involves the absorption of microwave energy by water molecules within the food, converting it into heat. The heating is rapid and efficient, offering advantages such as time-saving cooking, preservation of natural flavors and vitamins, energy efficiency, quick defrosting, and ease of cleaning.

The core component is the magnetron, which generates the microwaves. These waves are guided into the oven cavity through a metallic wave channel and distributed by a wave agitator (stirrer) or turntable to ensure even heating. Capacity control is achieved by pulsing the magnetron's switch-on duration, as the magnetron itself operates at 100% power when active. This allows for various power levels, from 80W for defrosting cheese to 900W for heating liquids.

Safety is paramount in microwave oven design. A mechanical safety system, including a wave trap and magnetic door seal, prevents microwave leakage. An electromagnetic safety system, known as the "Interlock"-microswitch system, ensures that the power supply is interrupted when the door is opened. This system comprises primary, secondary, and monitor microswitches that work in conjunction to prevent microwave generation if the door is not securely closed.

Important Technical Specifications

Microwave Frequency: 2,450 MHz (fixed by international agreements to avoid interference).
Magnetron Operation: Operates at 100% power when active; capacity control is achieved by pulsing the switch-on duration over a typical 29/30 second cycle.
High Voltage Circuit: Involves a high-voltage transformer, capacitor, and diode to convert 230V AC mains voltage into over 4,000V DC for the magnetron.
Filament Voltage (Magnetron): 3.1V AC.
High Voltage (Magnetron): 2,750V AC, converted to approximately 4,000V DC.
Primary Coil Resistance (HV Transformer): < 1.7 Ω.
Heating Coil Resistance (Magnetron): 0.3 - 1 Ω.
Secondary Coil Resistance (HV Transformer): 50 - 100 Ω.
Microwave Leakage Limit: Max. 5 mW/cm² at a distance of 5 cm (legal limit in most countries). Modern ovens typically achieve less than 1 mW/cm².

Usage Features

Ovenware Compatibility: Ovenproof glass and ceramic dishes (without metal parts), glass ceramic, vitro-ceramic, ovenproof earthenware, heat-resistant plastic (up to 200°C), paper, cardboard, clingfilm, and microwave ding film are suitable. Metal reflects microwaves and should generally be avoided, except for specific applications like browning dishes or shielding thin parts of food with aluminum foil. Closed containers, screw-cap glasses, and eggs in shells are not to be used.
Capacity Settings: The manual provides a guide for various power levels:
- 900 W and over: Heating liquids, parboiling, initial frying.
- 750 W: Cooking vegetables, general food.
- 600 W: Defrosting, heating frozen foods, one-pot courses.
- 500 W: Finish cooking hot pots, cooking egg dishes.
- 450 W / 350 W: Continued cooking, sensitive food, heating baby food.
- 250 W: Swelling rice, melting gelatine.
- 150 W: Defrosting meat, fish, bread.
- 80 W: Defrosting cheese, cream, butter, raising yeast dough, preheating cold meals/beverages.
Food Preparation:
- Stir liquids and turn defrosting food for even heating.
- Prick foods with skin (e.g., sausages, tomatoes) to prevent bursting.
- Cover meals loosely to prevent drying and facilitate heat distribution.
- Add water to harder vegetables.
- Defrost frozen meat in glass or porcelain containers, preferably on a drain plate.
- Avoid defrosting food completely with microwave energy to prevent dry rims.
- Do not use liquid thermometers in the oven.
- Ensure food reaches at least 70°C internally during heating.
Control Panels: Available in mechanical timer-controlled or "easy-to-use" electronic versions with a display and input fields for setting capacity, time, and programs.

Maintenance Features

Safety First: Always pull the mains plug before any measurements or repairs. Discharge the high-voltage capacitor using suitable isolated lines.
Technician Training: Microwave ovens must only be repaired by trained and informed technicians with the necessary tools, measuring instruments, and technical documents.
Regular Safety Tests: After any repair (including opening the oven), perform a high-frequency leakage check (measurement of leaky rays) and VDE 0701 checks.
Door Integrity: Inspect the door's locking behavior, seals, surfaces, hinges, and lock bolts for any mechanical interventions. Never operate the oven with an open door.
Fault Finding Trees: The manual includes detailed fault-finding trees to diagnose common issues based on symptoms like "cavity lamp does not light," "oven does not operate but cavity lamp lights," "no microwave capacity," and "no function." These trees guide technicians through checks of components like interlock switches, fuses, thermostats, HV transformer windings, HV diode, HV capacitor, and magnetron.
Component Measurement: Instructions are provided for measuring the continuity and resistance of various components:
- Interlock Door Safety System: Check primary, secondary, and monitor switches for continuity in open and closed door states.
- Fuse Diode (AK-Diode): Check for passage in both directions; an intact diode should block in both directions.
- High-Voltage Diode: Disconnect and measure in both directions; it should block in one direction and show a three-digit kOhm value in the other (requires a supply voltage over 9V).
- Magnetron: Disconnect and measure cathode (heating) resistance (approx. 0.5 Ohm) and resistance between connections and casing mass (must be infinite).
- High-Voltage Capacitor: Check for small resistance increasing fast (ok), small resistance remaining (short-circuit), or very high resistance remaining (interruption). Always use the original capacitor for replacement.
- High-Voltage Transformer: Check continuity and resistance of primary, secondary, and filament windings.
Leakage Measurement: Use a measuring device to check for leaky rays by moving a test probe around the door and all openings/edges of the casing at a distance of 5 cm.