Lg Jes735bf Service Manual
MICROW AVE OVEN
SER VICE MANUAL
MODEL: MS-74ML
CAUTION
BEFORE SERVICING THE UNIT, READ THE
SAFETY PRECAUTIONS IN THIS MANUAL.
Jan, 2000
Printed in Korea
P/NO:3828W5S1403
website: http://biz.lgservice.com
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 should be performed on each oven prior to release to the owner.
CAUTION
MICROWAVE RADIATION
DO NOT BECOME EXPOSED TO RADIATION FROM THE MICROWAVE GENERATOR
OR OTHER PARTS CONDUCTING MICROWAVE ENERGY.
SAFETY PRECAUTIONS
(Page)
SAFETY PRECAUTIONS
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Inside front cover
SPECIFICATIONS
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1-1
CAUTIONS
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2-1
INSTALLATIONS
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3-1
OPERATING INSTRUCTIONS
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4-1
FEATURES
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4-1
CONTROL PANEL
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4-1
OPERATING SEQUENCE
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4-2
SCHEMATIC DIAGRAM
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4-3
CIRCUIT DESCRIPTION
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4-4
SERVICE INFORMATION
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5-1
TOOLS AND MEASURING INSTRUMENTS
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5-1
MICROWAVE LEAKAGE TEST
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5-1
MEASUREMENT OF MICROWAVE POWER OUTPUT
-----------------------------------------------------------
5-3
DISASSEMBLY AND ADJUSTMENT
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5-3
INTERLOCK CONTINUITY TEST
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5-7
COMPONENT TEST PROCEDURE
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5-8
TROUBLE SHOOTING
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5-12
EXPLODED VIEW
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6-1
REPLACEMENT PARTS LIST
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7-1
SCHEMATIC DIAGRAM OF P.C.B.
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8-1
PRINTED CIRCUIT BOARD
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8-2
P.C.B. PARTS LIST
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9-1
CONTENTS
1-1
This microwave oven is designed for household use only.
It is not recommended for commercial purposes.
ITEM
MODEL
Power Requirement
Power Output
Microwave Frequency
Magnetron
Timer
Outside Dimensions
Cavity Dimensions
Net Weight
Shipping weight
Control Complement
Nameplate Location
Accessories
DESCRIPTION
MS-74ML
120 V 60 Hz
1,050 Watts
Single phase, 3 wire grounded
700 Watts full microwave power (IEC705)
2,450 MHz
2M214 - 39F, 2M218J, 2M254J
0 ~ 99 min. 90 sec.
483 (W) x 285 (H) x 360 (D) mm
312 (W) x 198 (H) x 316 (D) mm
12.5 kg (approx.)
14 kg (approx.)
Microwave Power for Variable Cooking
Power level
HIGH
-------------------------------
Full power throughout the cooking time
9 (Saute)
------
approx. 90% of Full power, 8 (Reheat)
--------
approx. 80%
7 (Med.-High)
--------------
approx. 70%, 6 (Medium)
--------
approx. 60%
5 (Med.-Low)
---------------
approx. 50%, 4 (Defrost)
---------
approx. 40%
3 (Low)
--------------------
approx. 30%, 2 (Simmer)
--------
approx. 20%
1 (Warm)
------------------
approx. 10%
Owner's manual & cooking guide
Glass turntable
Rotating Ring
Back Side
SPECIFICATIONS
• 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.
• DO NOT touch any parts of the control panel circuit. A
resulting static electric discharge may damage this
P.C.B.
• 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.
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
WARNINGTHIS 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 E or 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
N or colored black.
The wire which is colored brown must be connected
to the terminal in the plug which is marked with the
letter L or colored red.
BEFORE YOU BEGIN, READ THE FOLLOWING INSTRUCTIONS COMPLETELY AND CAREFULLY.
The wires in this mains lead are colored in
accordance with the following code:
Green-and-yellow: Earth
Blue: Neutral
Brown: Live
10cm
FEATURES
CONTROL PANEL
1. INDICATORS
2. SET CLOCK: Used to set the time of day.
3. AUTO COOK: Used to cook the foods listed by one
touch.
4. AUTO DEFROST: Used to select the desired auto
weight defrost programmed with weight pad.
5. POWER: Used to select the desired power level
for cooking.
6. COOK TIME: Used to cook food for a desired time.
7. START: One tap allows oven to begin functioning.
8. STOP/CLEAR: Used to stop oven and clear all entries
except time of day.
9. DISPLAY WINDOW
10. KITCHEN TIMER
4-1
OPERATING INSTRUCTIONS
Oven Frot Plate
Window Door Screen
Door Seal
Display Window
Control Panel
Safety Door Lock System
Turntable
Rotating Ring
Reloj Tiempo
Cocción Automática
10 min 1 min 10 seg
0.1kg1kg
Papas
Vegetales
Frescos
Vegetalesegetales
CongeladosCongelados
Descong
Automático
1.Car1.Carnene
2.Pollo2.Pollo
..............
3.Pescado3.Pescado
........
4.Pan4.Pan
....
Nivel de
Cocción
Comenzar
Parar
/
Borrar
1
2
3
4
10
9
5
6
7
8
OPERATING SEQUENCE
The following is a description of component functions
during oven operation.
1. SETTING THE CLOCK
ex) To set 4:35, Press 10 min four times.
Press 1 min three times.
Press 10 sec five times.
NOTE: You can set 12 hour clock.
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.
3. QUICK START
4. MICROWAVE COOKING
5. MULTI-STAGE MICROWAVE
COOKING
6. AUTO WEIGHT DEFROST COOKING
7. CHILD LOCK
This oven has a CHILD LOCK feature
• TO SET CHILD LOCK
• Touch the pad
• Touch STOP pad L appear in
the display.
•TO CANCEL CHILD LOCK
• Touch the pad
• touch STOP pad L disappears.
8. AUTO COOK
4-2
Stop
Set
clock
Set the
correct time
Stop Start
Stop
Desired
auto cook
category
STOP
STAGE 1
Set
clock
Stop
Stop
Desired
defrost
category
Desired
cooking
weight
Desired
food weight
Start
Start
Start
Stop
Desired
power level
Desired
cooking time
Start
STAGE 2
Stop
Stop
Desired
power level
Desired
cooking time
Desired
power level
Desired
cooking time
SCHEMATIC DIAGRAM
4-3
IMPORTANT SAFETY NOTE: THE SHADED AREAS ON THIS SCHEMATIC DIAGRAM INCORPORATE SPECIAL FEATURES
IMPORTANT FOR PROTECTION FROM MICROWAVE RADIATION, FIRE, ELECTRICAL SHOCK, AND
HAZARDS. WHEN SERVICING IT IS ESSENTIAL THAT ONLY MANUFACTURER'S SPECIFIED PARTS
BE USED FOR THE CRITICAL COMPONENTS IN THE SHADED AREAS OF THE SCHEMATIC DIAGRAM.
NOTICE: SINCE THIS IS BASIC SCHEMATIC DIAGRAM, THE VALUES OF COMPONENTS AND
SOME PARTIAL CONNECTIONS ARE SUBJECT TO CHANGE FOR IMPROVEMENT.
RD
BK
PRIMARY
SWITCH
WH
THERMOSTAT
WH
WH
YL
MAGNETRON
RD RD
H.V.
CAPACITOR
H.V. DIODE
FUSE
15A
AC 120V
60Hz
BL
L
N
MICOM
CONTROLLER
F.M.
TRANSFORMER
H.V.
** NOTE : DOOR IS OPENED.
BK : BLACK BL : BLUE YL : YELLOW
RD : RED WH : WHITE PK : PINK
GN : GREEN
O.L.
CN1
PT1
1
2
3
4
5
6
7
8
BK
BK RD
GN
GN
PK
BN
SECONDARY
SWITCH
OVEN
LAMP
MONITOR
SWITCH
TURN
TABLE
MOTOR
FAN
MO TOR
RY1
RY2
GN
WH
WH
BK
T.T.M.
CIRCUIT DESCRIPTION
GENERAL DETAILS
• The low voltage transformer supplies the necessary
voltage to the micom controller when power cord is
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).
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
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).
• 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
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 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.
• The cooking time stops counting down.
• Relay stops functioning.
• As the door is opened, if the contact of primary switch
and relay 2 and/or secondary 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.
4-4
FUSE
H.V.
TRANS-
FORMER
RELAY 2
MICOM CONTROLLER
SECONDARY
SWITCH
MONITOR
SWITCH
N
PRIMARY
SWITCH
L
FUSE
N
L
PRIMARY
SWITCH
MONITOR
SWITCH
RELAY 2
MICOM CONTROLLER
H.V.
TRANS-
FORMER
SECONDARY
SWITCH
NECESSARY TOOLS
Tools normally used for TV servicing are sufficient.
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
CAUTIONS
• Be sure to check microwave leakage prior to
servicing the oven if the oven is operative prior to
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/cm2and 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.
• If the oven operates with the door open, the service
personnel should:
- Tell the user not to operate the oven.
- 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
5 mW/cm2. Always start measuring of an unknown field
to assure safety for operating personnel from radiation
leakage.
NECESSARY MEASURING INSTRUMENTS
• TESTER(VOLTS-DC, AC., Ohmmeter)
• Microwave survey meter
- Holaday HI-1500
HI-1501
- Narda 8100
8200
• Inch scale
• 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
• Glass thermometer: 100°C or 212°F (1 deg scale)
MEASURING MICROWAVE ENERGY
LEAKAGE
• Pour 275±15 cc 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.
• Set the energy leakage monitor to 2,450 MHz and
use it following the manufacturer's recommended
test procedure to assure correct result.
• When measuring the leakage, always use the 2-inch
(5 cm) spacer supplied with the probe.
• Operate the oven at its maximum output.
• Measure the microwave radiation using and
electromagnetic radiation monitor by holding the
probe perpendicular to the surface being measured
Move probe along shaded area
Probe scanning speed
Less than 2.5 cm/sec
( 1in/sec)
5-1
SERVICE INFORMATION
TOOLS AND MEASURING INSTRUMENTS
MICROWAVE LEAKAGE TEST
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