LG MB-4042G Service Manual ▷ View online
4-2
OPERATING SEQUENCE
The following is a description of component functions
during oven operation.
during oven operation.
1. SETTING THE CLOCK
NOTE: You can set 12 hour clock or 24 hour clock
optionally.
2. CANCEL FUNCTION
Touch the pad whenever you need to
cancel an entry or a function currently in use.
The display will either return to the last item entered
or to the clock.
cancel an entry or a function currently in use.
The display will either return to the last item entered
or to the clock.
3. QUICK START
4. MICROWAVE COOKING
5. GRILL COOKING
6. COMBINATION COOKING
7. AUTO WEIGHT DEFROST
8. CHILD LOCK
This oven has a CHILD LOCK feature.
• TO SET CHILD LOCK
•TO CANCEL CHILD LOCK
9. AUTO COOK
Stop/Clear
Set
clock
Set the
correct time
Stop/Clear
Start
Stop/Clear
Desired
auto cook
category
Desired
cooking
cooking
weight
Stop/Clear
Stop/Clear
(Touch and
Hold)
Stop/Clear
Stop/Clear
(Touch and
Hold)
STOP/CLEAR
Set
clock
Stop/Clear
Desired
defrost
category
Desired
cooking
cooking
weight
Start
Stop/Clear
Grill
Desired
cooking time
Start
Stop/Clear
Desired
combi
category
Desired
cooking time
Start
Start
Stop/Clear
Desired
power level
Desired
cooking time
Start
SCHEMATIC DIAGRAM
4-3
CIRCUIT DESCRIPTION
GENERAL DETAILS
• The low voltage transformer supplies the necessary
voltage to the micom controller when power cord is
plugged in.
plugged in.
• When the door is closed, the primary switch is ON, the
secondary switch is ON, and the monitor switch opens
(contact COM and NO).
(contact COM and NO).
WHEN SELECTING COOKING POWER
LEVEL AND TIME
• The micom controller memorizes the function you set.
• The time you set appears in the display window.
• Each indicator light turns on to indicate that the stage
• The time you set appears in the display window.
• Each indicator light turns on to indicate that the stage
has been set.
WHEN TOUCHING THE START PAD
• The coil of the relay is energized by the micom
controller.
• Power input is supplied to the high voltage transformer
through the fuse to the primary switch and relay 2.
• Turntable rotates.
• The fan motor rotates and cools the magnetron by
blowing the air (coming from the intake on the
baseplate).
baseplate).
• The air is also directed into the oven to exhaust the
vapor in the oven through the upper plate.
• Cooking time starts counting down.
• 3.2 volts AC is generated from the filament winding of
• 3.2 volts AC is generated from the filament winding of
the high voltage transformer. This 3.2 volts is applied to
the magnetron to heat the magnetron filament through
two noise-preventing choke coils.
the magnetron to heat the magnetron filament through
two noise-preventing choke coils.
• A high voltage of approximately 2100 volts AC is
generated in the secondary of the high voltage
transformer which is increased by the action of the high
voltage diode and charging of the high voltage
capacitor.
transformer which is increased by the action of the high
voltage diode and charging of the high voltage
capacitor.
• The negative 4,000 Volts DC is applied to the filament
of the magnetron.
WHEN THE OVEN IS SET AT ANY LEVEL
EXCEPT MAXIMUM.
• The micom controller controls the ON-OFF time of
relay 2 by the applied signal to vary the average output
power of microwave oven as POWER LEVEL.
(refer to page 1-1)
• One complete cycle of relay 2 is 22 seconds.
WHEN THE DOOR IS OPENED DURING
COOKING
• Both the primary switch and relay 2 are cut off primary
winding voltage of the high voltage transformer.
• ON-OFF of relay 2 is coupled electrically with opening
and closing of the secondary switch.
• When the door is opened, the secondary switch is
opened and when the door is closed, the secondary
switch is closed.
switch is closed.
• The cooking time stops counting down.
• Relay stops functioning.
• As the door is opened, if the contact of primary switch
• Relay stops functioning.
• As the door is opened, if the contact of primary switch
fails to open, the fuse opens due to the large current
surge caused by the monitor switch activation, which in
turn stops magnetron oscillation.
surge caused by the monitor switch activation, which in
turn stops magnetron oscillation.
WHEN TOUCHING THE START KEY
WITH THE GRILL COOKING FUNCTION
SELECTED
• The contacts of the primary switch and the secondary
switch close the circuit.
• A.C. voltage is applied to the grill heater through grill
thermostat as shown by the solid line.
• Turntable rotates.
• The fan motor rotates.
• The air is also directed into the oven to exhaust the
• The fan motor rotates.
• The air is also directed into the oven to exhaust the
vapor in the oven through the base plate and upper
plate.
plate.
4-4
L
FUSE
H.V.
TRANS-
FORMER
RELAY 2
MICOM CONTROLLER
SECONDARY
SWITCH
SWITCH
PRIMARY
SWITCH
N
MONITOR
SWITCH
L
FUSE
H.V.
TRANS-
FORMER
RELAY 2
MICOM CONTROLLER
SECONDARY
SWITCH
SWITCH
PRIMARY
SWITCH
N
MONITOR
SWITCH
RELAY 3
L
N
GRILL
HEATER
GRILL
THERMOSTAT
L
G -Y
N
E
CAUTIONS
• Be sure to check microwave leakage prior to
servicing the oven if the oven is operative prior to
servicing.
servicing.
• The service personnel should inform the
manufacture importer, or assembler of any
certified oven unit found to have a microwave
emission level in excess of 5 mW/cm
certified oven unit found to have a microwave
emission level in excess of 5 mW/cm
2
and should
repair any unit found to have excessive emission levels
at no cost to the owner and should ascertain the cause
of the excessive leakage. The service personnel
should instruct the owner not to use the unit until the
oven has been brought into compliance.
at no cost to the owner and should ascertain the cause
of the excessive leakage. The service personnel
should instruct the owner not to use the unit until the
oven has been brought into compliance.
• If the oven operates with the door open, the service
personnel should:
- Tell the user not to operate the oven.
- Contact the manufacturer.
- Contact the manufacturer.
• The service personnel should check all surface and
vent openings for microwave leakage.
• Check for microwave leakage after every servicing.
The power density of the microwave radiation leakage
emitted by the microwave oven should not exceed
4 mW/cm
emitted by the microwave oven should not exceed
4 mW/cm
2
. Always start measuring of an unknown field
to assure safety for operating personnel from radiation
leakage.
leakage.
MEASURING MICROWAVE ENERGY
LEAKAGE
LEAKAGE
• Pour 275±15cc of 20±5°C(68±9°F) water in a beaker
which is graduated to 600 cc, and place the beaker
on the center of the turntable.
on the center of the turntable.
• Set the energy leakage monitor to 2,450 MHz and
use it following the manufacturer's recommended
test procedure to assure correct result.
test procedure to assure correct result.
• When measuring the leakage, always use the 2-
inch (5cm) spacer supplied with the probe.
• Operate the oven at its maximum output.
• Measure the microwave radiation using and
• Measure the microwave radiation using and
electromagnetic radiation monitor by holding the
probe perpendicular to the surface being measured
probe perpendicular to the surface being measured
Move probe along shaded area
Probe scanning speed
Less than 2.5 cm/sec
( 1in/sec)
Less than 2.5 cm/sec
( 1in/sec)
5-1
SERVICE INFORMATION
TOOLS AND MEASURING INSTRUMENTS
MICROWAVE LEAKAGE TEST
NECESSARY TOOLS
Tools normally used for TV servicing are sufficient.
Standard tools are listed below.
Standard tools are listed below.
• Diagonal pliers
• Long nose pliers
• Phillips screwdriver
• Flat blade screwdriver
• Wrench (size 5mm)
• Nutdriver (size 5mm)
• Adjustable wrench
• Soldering iron
• Solder
• Vinyl insulation tape
• Polishing cloth
• Long nose pliers
• Phillips screwdriver
• Flat blade screwdriver
• Wrench (size 5mm)
• Nutdriver (size 5mm)
• Adjustable wrench
• Soldering iron
• Solder
• Vinyl insulation tape
• Polishing cloth
NECESSARY MEASURING INSTRUMENTS
• TESTER(VOLTS-DC, AC., Ohmmeter)
• Microwave survey meter
• Microwave survey meter
- Holaday HI-1500
HI-1501
- Narda 8100
8200
• Inch scale
• 600 cc non conductive material beaker (glass or plastic),
• 600 cc non conductive material beaker (glass or plastic),
inside diameter: approx. 8.5 cm(3
1
/2
in.)
• Cylindrical and made of borosilicate glass vessel.
max. thickness: 3 mm
outside diameter: approx. 190mm
height: approx. 90mm
outside diameter: approx. 190mm
height: approx. 90mm
• Glass thermometer: 100°C or 212°F (1 deg scale)
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