Electrolux In General User manual

SERVICE MANUAL
© AEG Hausgeräte GmbH
Muggenhofer Straße 135
D-904 9 Nürnberg
Germany
Fax [phone]
TSE - N
Publ.-Nr.:
599 510 968
03.2001
MICROWAVE OVENS
IN GENERAL
Trainingsunterlagen
EN
Ausgabe:
Microwave
Ovens
in general
Fundamentals
Measuring technique
Fault-finding
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3 Microwave technology  advantages
Frequencies
Radiation spectru
4 How do icrowaves behave...
5 What for are the various cooking utensils suitable for
6 Electro agnetic conversion of energy
Interpenetration/Penetration
7 Guiding of waves
8 Microwave capacity
9 Input  control panels
10 Metal in the oven  so eti es even useful
11 Wiring diagra of a ti er-controlled icrowave oven
12 Mechanical safety syste
Electro echanical safety syste
13 Interlock safety syste
14 Pri ary circuit
15 High-voltage transfor er
16 Voltage doubling
17 Fuse diode
18 Magnetron
19 Measure ents in practice
20 Voltage easure ent Easy Way
Measure ent of capacity levels
21 Rules for leaky rays
Measure ent of leaky rays
22 Checking of the interlock door safety syste
Measuring the fuse diode
Checking the high-voltage diode
23 Measuring the agnetron
Measuring the high-voltage capacitor
Checking the high-voltage transfor er
24 Fault finding trees
25 Fault finding tree
26 Fault finding tree
27 Fault finding tree
28 Well-ai ed advises for the end
29 Note for setting of voltage
Page Content
Service infor ation for icrowave ovens with additional equip ent (Duo,
Co bi) and different chassis designs are included in TDS syste under the
corresponding ovens.
Here you can also find the appropriate wiring diagra s.
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Microwave Technology - A vantages
3 - 30 KHz
30 - 300 KHz
300 - 3000 KHz
3 - 30 MHz
30 - 300 MHz
300 - 3000 MHz
3 - 30 GHz
- VLF
- LF
- MF
- HF
- VHF
- UHF
- SHF
Transmitting frequencies and microwa e frequencies in the UHF range are fixed by
- Very low frequency - Telephone
- Low frequency - Ultrasonics
- Frequency modulation - Radio
- High frequency - Radio, Broadcast
- Very high frequency - TV, Broadcast
- Ultra high frequency - Radar, Microwa es
- Super high frequency - Satellite Transmissions
The frequencies are determined by the number of current oscillations resp. of the
electromagnetic wa es per second.
Classification of Frequency Bands:
2450 MHz
Ra iation Spectrum
- time-sa ing cooking speed
- the taste (natural flower)
- healthy cooking, no fat used, no loss of itamins
- energy sa ing, no pre-heating, time-sa ing speed
- quick and problem free defrosting
- less washing up, foot cooked in the ser ing dish
- easy to clean
- easy to use
Frequency
Microwa es are in the
nonionizing range.
They therefore also do not
ha e anything to do with
radioacti ity.
Radioacti ity can only
occur with essentially
higher frequencies.
The microwa e effect only
influences a heating of
water molecules which,
whate er capacity is
affecting, does not exceed
100°C.
international agreements.
To a oid any influences and interferences,
the microwa e frequency is fixed to:
ionizing  nonionizing
The different frequency
bands are di ided into
ionizing and nonionizing
frequencies
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How do microwa es beha e
The microwa es for the heating of meals beha e like the electromagnetic wa es which one
knows by e.g. broadcast and tele ision. 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 microwa es beha e in connection with substances, in this
case different dishes.
Reflection
Microwa es are reflected by metal. This is also used in the o en ca ity to spread the wa es.
Howe er, the meals wood be shielded from the microwa es when using metal pots. It may
lead to sparks or, when the wa es ha e a retrospecti e effect on the magnetron, to a
damaging of its anode.
Therefore, never use an e pty icrowave oven!!!
Interpenetration
Many materials let microwa es pass through without that they react themsel es (glass,
porcelain, pottery, plastic (suitable for microwa es!) and paper/board (dry)).
This is used during the microwa e operation. The wa es can penetrate into the food
without loss.
Absorbtion
Liquids and nearly all organic food absorb microwa es and con ert their energy into
heat (cooking): Depending on the liquid contents of the food, this heating beha iour is
different, too.
Fun amentals...
CLOSED CONTAINERS SUCH AS BOTTLES,
SCREW CAP GLASSES AND EVEN EGGS (SHELL!)
DO NOT BELONG IN THE MICROWAVE OVEN.
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CLOSED CONTAINERS LIKE BOTTLES, FOOD GLASSES AND EGGS
ALSO ARE NOT TO BE USED IN THE MICROWAVE OVEN !!!
Suitable Ovenware
O suitable - non suitable
1) excluding sil er, gold, platinum or metal
decoration
2) does not include glaze containing metal
3) please note the maximum temperature
stated by the manufacturer
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Electromagnetic conversion of energy
Penetration
The heat reaction as a result of the correlation of microwa es and water molecules is letting
up after penetration into the food. This is measured in W/cm².
Depending on the dielectric beha iour of the food, the energy is falling progressi ely with
increasing depth of penetration.
On the left, the loss of capacity of
the microwa es in the food is
shown graphically. The thermal
output has a declining effect from
the outside to the inside.
Therefore it is ad isable to reduce
the capacity e.g. with large meat
pieces, and to extend the time, that
the heat can better spread in the
food.
Liquids such as soups should be
stirred for a change for the same
reason. This helps to distribute the
heat and pre ents too high
temperatures on the surface. In
the extreme case, this could attack
the upper edge of the material
when using plastic containers.
In any food, positi ely/negati ely 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.
If this changes rather fast, the molecules as well will
mo e correspondingly fast. The molecules are
rubbing with each other and produce heat.
In case of a microwa e frequency of 2,450 MHz, this
results in 4,900,000,000 changes per second.
Thereby the required cooking temperature is
produced.
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Wave Duct
The microwa es produced by the magnetron are guided to the o en ca ity through a metallic
wa e channel.
Wave Agitator (Stirrer)
The wa e agitator consists of reflecting metal and is turning. As it is continuously in another
position, the reflection and distribution of wa es is changing, too. The wa e agitator may ha e
arious forms, in most cases it is a kind of propeller.
It is run by a motor. With older o ens, also the air flow of the fan is partly used in order to operate
the wa e agitator by it.
Various ways of feeding and
distribution of microwa es.
Using turntables guarantees a
good distribution of wa es for the
food.
Gui ing of Waves
Oven with stirrer:
1 - Bottom Plate
2 - Housing
3 - Cooking Area
4 - Sheet
5 - Stirrer
6 - Microwa e Input
7 - Duct
8 - Anode
9 - Magnetron
10 - Ventilator
11 - High Voltage Transformer
Oven without stirrer.
Special MW-input and turntable
ensures MW-distribution:
2 - Housing
3 - Cooking Area
7 - Duct
8 - Anode
9 - Magnetron
10 - Ventilator
11 - High Voltage Transformer
12 - Microwa e Input + Fat Shield
12 - Grill
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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 is
achie ed by switching on/
off the magnetron o er a
certain period of time. The
same principle as e.g. in
o ens or with hot plates.
A timing cycle is normally
29/30 seconds.
<(example 29 sec).
If 48(50)% capacity is
required, that means
14(15) seconds ON and
15 seconds OFF.
The timing cycles can
differ a little bit due to the
different types
(electronic/timer), the
principle is always the
same!
Thus, 10 of these cycles
will pass within 5 min.
Following i portant note:
Never switch on a icrowave oven without
energy-absorbing food in the oven. If despite
that icrowave energy is fed to an e pty
oven, these waves work off their energy
where it is not welco e.
It results in sparks and scorch spots.
In the worst case, there will be a reaction on
the anode resp. antenna of the agnetron,
which ay even be destroyed!
Microwave-Capacity
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Mechanical timer
1. capacity
2. timer
3. door opener
Easy-to-use electronic
1 display
2 capacity
3 timer
4 8. start button and
functions
9 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.
Here is a typical portray
of the control panel
from an instruction
manual.
ust with appliances
controlled by electro-
nics, you can find the
most different equip-
ment features and pro-
grammes.
The basic function of
the microwave oven is,
on the whole, always
the same
Input Control Panels
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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 howe er do not arise.
Shaking, e.g. when taking out the container, may lead to an abruptly
o er-boiling due to a chemical reaction, so that the user may scald
himself.
In order to a oid this it is recommended to put e.g. a coffee spoon into
the container during boiling. The boiling delay is thus excluded  the
liquid is boiling normally.
Meals with skin, such as sausages or tomatoes, tend to burst during the
heating due to an internal formation of steam.
In order to a oid this unpleasant effect, the food should be pricked a little
before with a fork. Thus the steam can go out and there will be no
tensions and the skin keeps normally to be undamaged.
When using too high capacity le els, that means a too fast heating, the
bursting often can also not be a oided by pricking.
Instant meals in aluminium plates can also be heated in the microwa e
o en.
In this connection one has to obser e that the microwa e energy only
affects the food from abo e and that the required cooking duration will
thereby be extended.
Furthermore, a distance of 2 cm to the o en wall must be kept to in order
to a oid a sparko er.
Aluminium foil wrapped around thinner parts, such as ends of poultry
legs, shields the microwa e energy and thus pre ents a too strong
drying up.
Browning dishes, such as crunch plates, are coated with a specially
absorbing metal. Due to this absorption the dishes heat up and it works
in addition like a frying pan. In connection with the grilling function, one
gets, e.g. with pizza or a egetable cake, a browning from abo e and
below.
As a rule, the browning dishes are heated 2 to 3 minutes at full capacity
before the food is put in.
CLOSED CONTAINERS
SUCH AS BOTTLES OR
SCREWTAP GLASSES AS
WELL AS EGGS (SHELL!)
DO NOT BELONG IN THE
OVEN!!!
PUT ON POSSIBLE COVERS
TO AVOID THE
EVAPORATION ONLY
LOOSE!
During hea ing please pay a en ion ha he inner par of he food will achieve a
leas a empera ure of 70°C.
However, never use liquid hermome ers in he oven!!!
Metal in the oven  sometimes even very useful:
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Wiring iagram of a timer-controlle microwave oven
The various sections are explained on the following pages.
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The task of this system is to suppress leaky microwa e
rays between o en and closed door.
-The wa e trap, whose size and structure is depending
on the microwa e length
-The door sealing of magnetic material in order to thus
absorb possible remaining radiation
The agnetic
sealing integrated
in the door
When opening the door, all 3 microswitches are actuated ia at least two mechanical
systems. In doing so, primary and secondary switches interrupt the power supply.
If, for whate er reason, one of these switches does not open, the monitoring switch short-
circuits the entry circuit resp. high- oltage transformer. The triggering off of the fuse is
hereby accepted. Safety first!!!
Mechanical safety system
-pri ary
-secondary
- onitor
Interlock- icroswitch syste 
Electromagnetic safety system
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At first sight the interlock safety system can ha e a different iew from one model to the
other when looking first at the wiring diagram.
The basic functions are always the sa e!
Interlock-Safety System
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-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. safety
system<.
-More elements such as the
o erheat thermostat for the
magnetron can be installed
depending on the model
(thermostat of o en, grilling
or air duct).
-The suppressor filter is
blocking high frequencies
and demanded by law.
The function of the secondary and/
or high- oltage circuit is explained
on the following pages.
Primary Circuit
Secon ary Circuit
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The high- oltage capacitor
consists of three windings:
-a primary winding
-a secondary high- oltage
winding
-a secondary low oltage
winding
Thus the high- oltage
transformer is placed in the
appliance.
The sticked-on rubber parts are
indispensable for the pre ention
of ibrations to the casing.
If the primary winding is supplied
with a mains oltage of 230 V,
following oltages are induced
into secondary windings:
-3.1 V as low oltage, directly
connected with the heating
winding of the magnetron for
heating the cathodes
-2,750 V as high oltage,
connected with the oltage
doubling
High Voltage Transformator
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The oltage doubler consists of a diode
and a capacitor.
The following indications of oltage ser e
the explanation and should ne er be
measured again.
Measuremen s, especially in he high-
vol age par , mus only be carried ou
as resis ance measuremen s in an oven
which is disconnec ed from he
mains!!!
The o er 2,000 Volt AC oltage of the
secondary winding of the high- oltage
transformer are con erted into o er 4,000
Volt DC oltage.
That operates the magnetron.
After the o en has been switched on, the
first positi e wa e charges the capacitor
with more than 2,000 Volt.
After the polarity has been changed, the
diode a oids that the capacitor is
discharging.
The oltage of the positi e half wa e is
added to the charge of the capacitor.
The desired DC oltage of approx. 4,000
Volt arises.
Voltage oubling
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AK Dio e
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The magnetron is the heart of the microwa e
o en.
With the help of transformer, rectifier and
magnetic field, it con erts the 230 Volt-50 Hz
into microwa e energy with the frequency of
2,450 MHz.
The magnetron consists of following parts:
Main body with anode (positi e) and cathode
(negati e), cooling ribs, permanent magnet,
connections for heating and high oltage as
well as antenna, in order to radiate the
microwa e energy.
The inner cylinder is heating element and
cathode at the same time.
The outer cylinder is the anode block with
the resonant chambers.
Due to the big difference in potential between
anode and cathode, the electrodes are
mo ing from the inner to the outer cylinder.
The magnetron requires a high DC oltage (4,000 Volt), a low AC
oltage for the heating of cathodes and a magnetic field to be able
to work.
The cathode is heated in order to cause the electrons emitting, so
that they will flow to the anode.
In order to achie e the oscillation, one needs a permanent
magnet. Because of its magnetic field, the electrons are mo ing
in an orbit round the cathode, instead of flowing in a straight line
from the cathode to the anode.
In this connection, the electrons are passing the resonant
chambers and produce oscillations.
These resonant chambers are specially formed. Within the high-
oltage frequency range they ha e a capaciti e and e en inducti e
effect. They also determine the produced microwa e frequency.
These oscillations are then guided ia the antenna into the o en.
Magnetron
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Measurements an 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.
ocking behaviour of the door  sealings and surfaces 
hinges and lock bolts  mechanical (foreign) interventions
from the outside.
In case of measurements or repairs:
PULL THE MAINS PLUG!!!
By all means discharge the high-voltage capacitor before.
This must be made by suitable lines with isolated peaks.
With every microwave oven it is necessary to carry out a
high frequency leakage check (measurement of leaky rays)
and the checking according to VDE 0701 after a repair (the
mere opening of the oven is also a repair).
Microwave ovens must only be repaired by technicians who
are correspondingly trained and informed and who have the
required tools, measuring instruments and technical
documents.
Measurements in practice
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The most reasonable method is the time control
of power absorption by a metra tester (left) or a
current probe (right).
If the current increases abruptly, the high-
oltage part begins operating and microwa e
energy is emitted.
The proportion of on/off switching times are to be taken from the technical documents:
Simplest rule:
50% on 50% off
50% capacity
30% on 70% off
30% capacity
Useful clock cycle:
30 seconds
1 liter water (17 -24°)
62 seconds full capacity
Measurement of capacity  simple version
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
- An exact thermometer, if
possible a digital one
- Stir the water before the
measurement
Measurement of capacity levels
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