LG MB-4022W User manual

MICROWAVE OVEN
SERVICE MANUAL
MODEL : MB-4022W/MH-6022W
CAUTION
BEFORE SERVICING THE UNIT, READ THE
SAFETY PRECAUTIONS IN THIS MANUAL.

This device is to be serviced only by properly qualified service personnel.
Consult the service manual for proper service procedures to assure continued safety operation and for precautions to be
taken to avoid possible exposure to excessive microwave energy.
PRECAUTIONS TO BE OBSERVED BEFORE AND
DURING SERVICING TO AVOID POSSIBLE
EXPOSURE TO EXCESSIVE MICROWAVE ENERGY
A) Do not operate or allow the oven to be operated with the door open.
B) Make the following safety checks on all ovens to be serviced before activating the magnetron or other
microwave source, and make repairs as necessary; (1) interlock operation, (2) proper door closing, (3)
seal and sealing surfaces (arcing, wear, and other damage), (4) damage to or loosening of hinges and
latches, (5) evidence of dropping or abuse.
C) Before turning on microwave power for any service test or inspection within the microwave generating
compartments, check the magnetron, wave guide or transmission line, and cavity for proper alignment,
integrity, and connections.
D) Any defective or misadjusted components in the interlock, monitor, door seal, and microwave generation
and transmission systems shall be repaired, replaced, or adjusted by procedures described in this manual
before the oven is released to the owner.
E) A microwave leakage check to verify compliance with the Federal Performance Standard should be
performed on each oven prior to release to the owner.
SAFETY PRECAUTIONS
CAUTION
MICROWAVE RADIATION
DO NOT BECOME EXPOSED TO RADIATION FROM THE MICROWAVE GENERATOR
OR OTHER PARTS CONDUCTING MICROWAVE ENERGY.

(Page)
SAFETY PRECAUTIONS --------------------------------------------------------------------- Inside front cover
SPECIFICATIONS
----------------------------------------------------------------------------------------------------- 1-1
CAUTIONS
-------------------------------------------------------------------------------------------------------------- 2-1
INSTALLATIONS
------------------------------------------------------------------------------------------------------ 3-1
OPERATING INSTRUCTIONS
------------------------------------------------------------------------------------ 4-1
FEATURES ------------------------------------------------------------------------------------------------------------------------ 4-1
CONTROL PANEL -------------------------------------------------------------------------------------------------------------- 4-1
OPERATING SEQUENCE
---------------------------------------------------------------------------------------------------- 4-2
SCHEMATIC DIAGRAM
------------------------------------------------------------------------------------------------------ 4-3
CIRCUIT DESCRIPTION ----------------------------------------------------------------------------------------------------- 4-4
SERVICE INFORMATION ------------------------------------------------------------------------------------------ 5-1
TOOLS AND MEASURING INSTRUMENTS --------------------------------------------------------------------------- 5-1
MICROWAVE LEAKAGE TEST
-------------------------------------------------------------------------------------------- 5-1
MEASUREMENT OF MICROWAVE POWER OUTPUT
----------------------------------------------------------- 5-3
DISASSEMBLY AND ADJUSTMENT ------------------------------------------------------------------------------------- 5-3
INTERLOCK CONTINUITY TEST
------------------------------------------------------------------------------------------ 5-7
COMPONENT TEST PROCEDURE
-------------------------------------------------------------------------------------- 5-8
TROUBLE SHOOTING ------------------------------------------------------------------------------------------------------ 5-12
EXPLODED VIEW ------------------------------------------------------------------------------------------------ 6-1
REPLACEMENT PARTS LIST
------------------------------------------------------------------------------------ 7-1
CONTENTS

This microwave oven is designed for household use only.
It is not recommended for commercial purposes.
DESCRIPTION
MB-4022W, MH-6022W
230 Volts AC 50 Hz
Single phase, 3 wire grounded
Microwave 1,200W
Grill 1,100W
Combi 2,250W
800 Watts full microwave power (IEC 60705)
2,450 MHz
2M214 - 39F, 2M218J, 2M254J
60 Min.
485 (W) x 280 (H) x 350 (D) mm
312 (W) x 198 (H) x 316 (D) mm
13.5 kg (approx.)
15.0 kg (approx.)
Microwave Power for Variable Cooking
Power level
Max
600W
360W
Defrost
90W
Grill
Combi - 1, 2, 3
Owner's manual
Glass tray
Rotating ring
Grill rack
1-1
ITEM
MODEL
Power Requirement
Power Output
Microwave Frequency
Magnetron
Timer
Outside Dimensions
Cavity Dimensions
Net Weight
Shipping weight
Control Complement
Name Plate Location
Accessories
SPECIFICATIONS
Back side

• DO NOT operate on a 2-wire extension cord during
repair and use.
• NEVER TOUCH any oven components or wiring during
operation.
• BEFORE TOUCHING any parts of the oven, always
remove the power plug from the outlet.
• For about 30 seconds after the oven stops, an electric
charge remains in the high voltage capacitor. When
replacing or checking, you must discharge the high
voltage capacitor by shorting across the two terminals
with an insulated screwdriver.
• Remove your watches whenever working close to or
replacing the Magnetron.
• NEVER operate the oven with no load.
• NEVER injure the door seal and front plate of the oven
cavity.
• NEVER put iron tools on the magnetron.
• NEVER put anything into the latch hole and the
interlock switches area.
• Proper operation of the microwave oven requires that
the magnetron be assembled to the waveguide and
cavity. Never operate the magnetron unless it is
properly installed.
• Be sure that the magnetron gasket is properly
installed around the dome of the tube whenever
installing the magnetron.
2-1
CAUTIONS
Unlike other appliances, the microwave oven is
high-voltage and high-current equipment.
Though it is free from danger in ordinary use,
extreme care should be taken during repair.
THE OVEN IS TO BE SERVICED ONLY
BY PROPERLY QUALIFIED SERVICE
PERSONNEL.
MICROWAVE RADIATION
Personnel should not be exposed to the
microwave energy which may radiate from the
magnetron or other microwave generating
device if it is improperly used or connection.
All input and output microwave connections,
waveguide, flange and gasket must be secure
never operate the device without a microwave
energy absorbing load attached.
Never look into an open waveguide or antenna
while the device is energized.
Gasket
ANTENNA
COOLING FIN
MAGNETRON
CHASSIS GROUND
FILAMENT
TERMINALS
MAGNETRON

INSTALLATIONS
3-1
INSTALLING
1. Empty the microwave oven and clean inside it with
a soft, damp cloth. Check for damage such as
misaligned door, damage around the door or dents
inside the cavity or on the exterior.
2. Put the oven on a counter, table, or shelf that is
strong enough to hold the oven and the food and
utensils you put in it. (The control panel side of the
oven is the heavy side. Use care when handling.)
3. Do not block the vent and the air intake openings.
Blocking vent or air intake openings can cause
damage to the oven and poor cooking results.
Make sure the microwave oven legs are in place to
ensure proper air flow.
4. The oven should not be installed in any area where
heat and steam are generated, because they may
damage the electronic or mechanical parts of the
unit.
Do not install the oven next to a conventional
surface unit or above a conventional wall oven.
5. Use microwave oven in an ambient temperature
less than 104°F(40°C).
6. Place the microwave oven on a sturdy and flat
surface at least 10 cm(4 inches) from the wall.
7. Place the microwave oven as far away as possible
from TV, RADIO, COMPUTER, etc., to prevent
interference.
8. Do not touch the front glass during or after cooking
of the Grill and Combination mode.
This glass is very hot during heater operating.
9. Do not operate the oven at microwave and
combination mode with Grill rack placed in the
cavity when the oven is empty.
EARTHING INSTRUCTIONS
This microwave oven is designed to be used in a fully
earthed condition.
It is imperative, therefore, to make sure it is properly
earthed before servicing
WARNING-
THIS APPLIANCE
MUST BE EARTHED
IMPORTANT
As the colors of the wires in the mains lead of this
appliance may not correspond with the colored
markings identifying the terminals in your plug,
proceed as follows.
The wire which is colored green-and-yellow must be
connected to the terminal in the plug which is marked
with the letter Eor by the earth symbol ( ) or
colored green or green-and-yellow.
The wire which is colored blue must be connected to
the terminal in the plug which is marked with the letter
Nor colored black.
The wire which is colored brown must be connected
to the terminal in the plug which is marked with the
letter Lor colored red.
BEFORE YOU BEGIN, READ THE FOLLOWING INSTRUCTIONS COMPLETELY AND CAREFULLY.
10cm
The wires in this mains lead are colored in
accordance with the following code:
Green-and-yellow: Earth
Blue: Neutral
Brown: Live

4-1
OPERATING INSTRUCTIONS
FEATURES
CONTROL PANEL
Grill Rack
Oven Front Plate
Window Door Screen
Door Seal
Control Panel
Safety Door Lock System
Turntable
Rotating Ring
01
2
3
4
5
6
7
8
9
10
20
30
40
50
60
90
360
600
0.5
0.1
0.2
0.4
0.3
1
1. POWER CONTROL KNOB: Used in selected the desired power level for cooking.
2. TIMER KNOB: Used to set the cooking time.

4-2
OPERATING SEQUENCE
MICROWAVE COOKING
1. Open the oven door, place the food on the
turntable in the oven, and close the oven door.
2. Set the function selector to the microwave.
3. Set the microwave power selector to the desired
power level. There are five power levels from
WARM to HIGH. The power selector can be set to
any one of these positions.
NOTE:
• Each number represents minutes. To ensure
accurate timing, it is advisable to turn the timer knob
slightly passed the desired cooking time and then
back to the proposed setting.
• Press the door opener to check the cooking
condition during oven operation. Opening the door
during oven operation automatically turns off the
oven and stops the timer. If cooking is to continue,
close the door. Cooking will be resumed until the full
cooking time has elapsed.
GRILL COOKING
1. Open the oven door, place the food on the rack in
the oven, and close the oven door.
2. Set the function.
3. Set the timer to the desired cooking time. The
turntable begins to rotate, cooking starts, and the
lamp is turned on. At the end of the cooking time
you will hear a ring sound and the lamp is turned
off.
COMBI COOKING
1. Open the oven door, place the food on the rack in
the oven, and close the oven door.
2. Set the (1, 2, 3) function.
3. Set the timer to the desired cooking time. The
turntable begins to rotate, cooking starts, and the
lamp is turned on. At the end of the cooking time
you will hear a ring sound and the lamp is turned
off.
• Refer to the note under MICROWAVE COOKING
if you want to check the cooking condition.
• Don’t touch the front screen of the door during grill &
combi operation, because the temperature of the
glass may rise to up to 100°C. Prevent children from
touching the front screen!
•
When the grill & combi is operated for the first time
after purchasing the oven, slight smoke and smell
may occur. These will soon disappear.
POSITIONS
MAX
600W
360W
DEFROST
90W

4-3
SCHEMATIC DIAGRAM

4-4
CIRCUIT DESCRIPTION
• As the door is closed, the contact of MONITOR
SWITCH opens. This switch creates the short circuit to
blow fuse during operation under abnormal condition.
(ie, should the contacts of primary and secondary
switch fail to open the circuit)
• The latches are secured by latch board. The oven light
turns on while the oven is in operation.
WHEN MICROWAVE POWER LEVEL
AND COOKING TIME SET
• The contacts of the timer switch changes to ON
position when the timer knob is rotated.
(While power control knob is set at “Full Power”)
• The contacts of primary and secondary switch close
the circuit.
• Input Volts AC. is applied to the high voltage
transformer through power control switch as shown by
the solid line.
• Turntable rotates.
• The fan motor rotates and cools the magnetron by
blowing the air (coming from the intake holes on the
baseplate) over the magnetron.
• The air is also directed into the oven to exhaust the
vapor in the oven through the upper plate.
• Timer starts rotating.
• 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.
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
diode and charging of the high voltage capacitor.
The negative DC voltage is then applied to the filament
of the magnetron.
WHEN THE DOOR IS OPENED DURING
COOKING
• Both primary switch and secondary switch open to cut
off the primary winding voltage to the high voltage
transformer to stop microwave oscillation.
• Timer, turntable and fan motor stop.
• As the door is opened, if the contact of primary switch
fail to open, the fuse opens due to the large current
surge caused by the monitor switch activation which in
turn stops magnetron, oscillation.
WHEN THE GRILL COOKING FUNCTION
SELECTED
• The contacts of the timer switch change to ON
position.
• The contacts of the grill select switch close the circuit.
• Input volts AC is applied to the grill heater through
thermostat-grill as shown by the solid line.
• The fan motor and turntable rotates.
FUSE
PRIMARY
SWITCH
SECONDARY
SWITCH
MONITOR
SWITCH
L
N
H.V.T
TIMER
SWITCH
POWER
CONTROL
SWITCH
FUSE
PRIMARY
SWITCH
SECONDARY
SWITCH
L
N
H.V.T
TIMER
SWITCH
POWER
CONTROL
SWITCH
MONITOR
SWITCH
PRIMARY
SWITCH
TIMER
SWITCH
GRILL
SELECT
SWITCH
L
N
THERMOSTAT
GRILL
GRILL
HEATER
L
G -Y
N
E