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© AEG Hausgeräte GmbH
Muggenhofer Straße 135
D-90429 Nürnberg
Germany
Fax +49 (0)911 323 1420
TSE - N
Ausgabe:
03.2001
Publ.-Nr.:
599 510 968
Trainingsunterlagen
EN
created by TSE-N, Reiner Kurzke
SERVICE MANUAL
MICROWAVE OVENS
IN GENERAL
Fundamentals
Measuring technique
Fault-finding
Microwave
Ovens
in general
Page 1
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- Page 1 SERVICE MANUAL MICROWAVE OVENS IN GENERAL Fundamentals Measuring technique Fault-finding Microwave Ovens © AEG Hausgeräte GmbH Publ.-Nr.: in general 599 510 968 Muggenhofer Straße 135 D-90429 Nürnberg Trainingsunterlagen Germany Fax +49 (0)911 323 1420 TSE - N Ausgabe: 03.2001 Page 1 created by TSE-N, Reiner Kurzke...
- Page 2 Page Content Microwave technology – advantages Frequencies Radiation spectrum How do microwaves behave... What for are the various cooking utensils suitable for Electromagnetic conversion of energy Interpenetration/Penetration Guiding of waves Microwave capacity Input – control panels Metal in the oven – sometimes even useful Wiring diagram of a timer-controlled microwave oven Mechanical safety system Electromechanical safety system...
- Page 3 Microwave Technology - Advantages - time-saving cooking speed - the taste (natural flower) - healthy cooking, no fat used, no loss of vitamins - energy saving, no pre-heating, time-saving speed - quick and problem free defrosting - less washing up, foot cooked in the serving dish - easy to clean - easy to use Frequency...
- Page 4 Fundamentals... How do microwaves behave The microwaves for the heating of meals behave like the electromagnetic waves which one knows by e.g. broadcast and television. The frequency of 2,450 MHz means that the radiated energy is oscillating 2,450,000,000 times a second. The graphic below shows how microwaves behave in connection with substances, in this case different dishes.
- Page 5 Suitable Ovenware O suitable - non suitable 1) excluding silver, gold, platinum or metal decoration 2) does not include glaze containing metal 3) please note the maximum temperature stated by the manufacturer CLOSED CONTAINERS LIKE BOTTLES, FOOD GLASSES AND EGGS ALSO ARE NOT TO BE USED IN THE MICROWAVE OVEN !!! Page 5 created by TSE-N, Reiner Kurzke...
- Page 6 Electromagnetic conversion of energy In any food, positively/negatively charged liquid molecules are accidentally arranged in disorder. If we now put this food into an electromagnetic field, these molecules will adjust to the +/- field direction. If we now change this field +/-, also the adjustment of molecules will change.
- Page 7 Guiding of Waves Wave Duct The microwaves produced by the magnetron are guided to the oven cavity through a metallic wave channel. Wave Agitator (Stirrer) The wave agitator consists of reflecting metal and is turning. As it is continuously in another position, the reflection and distribution of waves is changing, too.
- Page 8 Microwave-Capacity A magnetron cannot be controlled continuously. When it is functioning, it always runs at 100%. In order to get a capacity control, one pulses the switch-on duration, i.e. the desired capacity achieved by switching on/ off the magnetron over a certain period of time.
- Page 9 Input Control Panels Mechanical timer ”Easy-to-use” electronic 1. capacity 2. timer display 3. door opener capacity timer 4 –8. start button and functions door opener Here, the mechanical timer is replaced by an electronic with a display. Instead of a controller it is also possible to use input fields.
- Page 10 Metal in the oven – sometimes even very useful: When cooking liquids, especially when cooking repeatedly or in slim, high containers, a so-called boiling delay may occur. In this case the liquid is in fact boiling hot, the typical air bubbles however do not arise. Shaking, e.g.
- Page 11 Wiring diagram of a timer-controlled microwave oven The various sections are explained on the following pages. Page 11 created by TSE-N, Reiner Kurzke...
- Page 12 Mechanical safety system The task of this system is to suppress leaky microwave rays between oven and closed door. -The wave trap, whose size and structure is depending on the microwave length -The door sealing of magnetic material in order to thus absorb possible remaining radiation The magnetic sealing integrated...
- Page 13 Interlock-Safety System At first sight the interlock safety system can have a different view from one model to the other when looking first at the wiring diagram. The basic functions are always the same! Page 13 created by TSE-N, Reiner Kurzke...
- Page 14 Primary Circuit -The clocked power control is normally integrated in the timer or is controlled by an electronic component. -Timer, fan and turntable motor are only running after switching on. -How primary, secondary and monitoring switches are cooperating with each other, see under >Electr.
- Page 15 High Voltage Transformator The high-voltage capacitor consists of three windings: -a primary winding -a secondary high-voltage winding -a secondary low voltage winding If the primary winding is supplied with a mains voltage of 230 V, following voltages are induced into secondary windings: -3.1 V as low voltage, directly connected with the heating winding of the magnetron for...
- Page 16 Voltage doubling The voltage doubler consists of a diode and a capacitor. The following indications of voltage serve the explanation and should never be measured again. Measurements, especially in the high- voltage part, must only be carried out as resistance measurements in an oven which is disconnected from the mains!!! The over 2,000 Volt AC voltage of the...
- Page 17 AK Diode Page 17 created by TSE-N, Reiner Kurzke...
- Page 18 Magnetron The magnetron is the heart of the microwave oven. With the help of transformer, rectifier and magnetic field, it converts the 230 Volt-50 Hz into microwave energy with the frequency of 2,450 MHz. The magnetron consists of following parts: Main body with anode (positive) and cathode (negative), cooling ribs, permanent magnet, connections for heating and high voltage as...
- Page 19 Measurements in practice Measurements and repairs – Important notes!!! Precautionary measures have to be made before and during a repair to prevent that the after-sales technician is possibly exposed to microwave energy. *Never put the oven into operation with an open door! *Before putting an oven to be repaired into operation, carry out the previous safety tests.
- Page 20 Measurement of capacity – simple version 1 liter water (17 -24°) 62 seconds full capacity Important - Use a container with thin material. Thick container walls extract parts from the water of the rising heat and falsify the measuring result. - If possible, initial temperature 20°C - Exact time measurement...
- Page 21 Rules for leaky rays In most countries the limit for leaky rays, which is determined by law, is fixed to: max. 5 mW/cm² in a distance of 5 cm The door of a modern microwave oven is normally designed for a HF leakiness of much less than 1 mW/cm².
- Page 22 Electric checking of the interlock door safety system PRIMARY/SECONDARY SWITCH The measuring of these switches is made with disconnected connecting leads and when the door is opened/closed. MONITORING SWITCH: It is recommended to measure the passage after the primary switch. Its connecting lead must be disconnected.
- Page 23 Measuring the magnetron disconnect the mains plug ensure that the capacitor has been discharged! separate the magnetron measure the resistance between the connections The resistance of the cathode (heating) should be approx. 0.5 Ohm. The resistance of the connections to the mass of the casing must be infinite.
- Page 24 Fault finding tree of timer-controlled microwave ovens Mains voltage existing – timer in function – door closed Fault finding tree of timer-controlled microwave ovens Mains voltage existing – timer in function – door closed Page 24 created by TSE-N, Reiner Kurzke...
- Page 25 Fault finding tree of timer-controlled microwave ovens Mains voltage existing – timer in function – door closed Page 25 created by TSE-N, Reiner Kurzke...
- Page 26 Fault finding tree for microwave ovens No microwave capacity – fan is running Page 26 created by TSE-N, Reiner Kurzke...
- Page 27 Fault finding tree for microwave ovens No function – no reaction to any entry Page 27 created by TSE-N, Reiner Kurzke...
- Page 28 For the end, some well-aimed advises for the consumer -Give enough time to the meals to get hot. There are some parts which need more time. -The meals should not be served directly from the microwave oven. When you leave them covered for some minutes, the heat can better balance itself.
- Page 29 Notes for setting the capacity Following survey shows the capacity settings with the processes, for which they are provided. 900 W - heating of liquids and over - parboiling and initial frying at the beginning of a cooking process 750 W - cooking of vegetables (rather less) - cooking of food (rather less) 600 W...