LG MS-0747C Service Manual
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Website http://biz.lgservice.com
MICROWAVE OVEN
SERVICE MANUAL
MODEL: MS-0747C
CAUTION
BEFORE SERVICING THE UNIT, READ THE SAFETY PRECAUTIONS IN THIS MANUAL.
P/NO : MFL34456302
May, 2007
Printed in Korea
SAFETY PRECAUTIONS
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.
CAUTION
MICROWAVE RADIATION
DO NOT BECOME EXPOSED TO RADIATION FROM THE MICROWAVE GENERATOR
OR OTHER PARTS CONDUCTING MICROWAVE ENERGY.
CONTENTS
(Page)
SAFETY PRECAUTIONS
SPECIFICATIONS
CAUTIONS
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INSTALLATIONS
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OPERATING INSTRUCTIONS
FEATURES
CONTROL PANEL
OPERATING SEQUENCE
SCHEMATIC DIAGRAM
CIRCUIT DESCRIPTION
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SERVICE INFORMATION
TOOLS AND MEASURING INSTRUMENTS
MICROWAVE LEAKAGE TEST
MEASUREMENT OF MICROWAVE POWER OUTPUT
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Inside front cover
1-1
2-1
3-1
4-1
4-1
4-1
4-2
4-3
4-4
5-1
5-1
5-1
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5-3
DISASSEMBLY AND ADJUSTMENT
INTERLOCK CONTINUITY TEST
COMPONENT TEST PROCEDURE
TROUBLE SHOOTING
EXPLODED VIEW
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REPLACEMENT PARTS LIST
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SCHEMATIC DIAGRAM OF P.C.B.
PRINTED CIRCUIT BOARD
P.C.B. PARTS LIST
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5-3
5-7
5-8
5-12
6-1
7-1
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8-1
8-2
9-1
SPECIFICATIONS
ITEM
MODEL
Power Requirement
Power Output
Microwave Frequency
Magnetron
Timer
Outside Dimensions
Cavity Dimensions
Net Weight
Shipping weight
Control Complement
DESCRIPTION
MS-0747C
120 Volts AC 60 Hz
1000 Watts
Single phase, 3 wire grounded
700 Watts full microwave power (IEC60705)
2450 MHz
2M213 - 240GP
10 sec.~ 99 min. 50 sec
455 (W)x 284 (H)x 320 (D)mm
327 (W)x 202 (H)x 286 (D)mm
9.5 kg (approx.)
11 kg (approx.)
Microwave Power for Variable Cooking
Power level
MAX .................................................. Full power throughout the cooking time
MED.-HIGH......................................... approx. 80% of Full power
MEDIUM ............................................. approx. 60% of Full power
DEFROST........................................... approx. 40% of Full power
LOW/WARM........................................ approx. 20% of Full power
Rating Label Location
Owner's manual
Accessories
Glass turntable
Rotating ring
This microwave oven is designed for household use only.
It is not recommended for commercial purposes.
Back Side
1-1
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.
• 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.
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.
• 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.
ANTENNA
Gasket
•
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.
COOLING FIN
FILAMENT
TERMINALS
MAGNETRON
CHASSIS GROUND
MAGNETRON
THE OVEN IS TO BE SERVICED ONLY
BY PROPERLY QUALIFIED SERVICE
PERSONNEL.
2-1
INSTALLATIONS
BEFORE YOU BEGIN, READ THE FOLLOWING INSTRUCTIONS COMPLETELY AND CAREFULLY.
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.
GROUNDING INSTRUCTIONS
For personal safety, this appliance must be fully
grounded at all times.
In the event of an electrical short circuit, grounding
reduces the risk of electrical shock.
The plug must be plugged into an outlet that is
properly installed and grounded.
WARNING
Improper use of the grounding plug can result in a
risk of electric shock.
Do not, under any circumstances, cut or remove the
third ground prong from the power cord plug.
PREFERRED METHOD
ENSURE PROPER GROUND
EXISTS BEFORE USE
TEMPORARY METHOD
(ADAPTER PLUGS NOT
PERMITTED IN CANADA)
ALIGN LARGE
PRONGS/SLOTS
10cm
ENSURE PROPER GROUND
AND FIRM CONNECTION
BEFORE USE
3-1
OPERATING INSTRUCTIONS
Oven Front Plate
Window Door Screen
Door Seal
Safety Door Lock System
Glass Turntable
Rotating Ring
Control Panel
FEATURES
CONTROL PANEL
1. INDICATORS
2. ONE TOUCH CONTROL: Used to cook the foods
listed by one touch.
1
2
34
5
6
7
3. Q-DEFROST
4. CLOCK: Used to set the time of day.
5. NUMBER: Used to set for time of day, cooking time,
power level or defrost weight.
6. TIME: Used to cook food for a desired time.
7. POWER: Used to select the desired power level for
cooking.
8. STOP/CLEAR: Used to stop oven and clear all
entries except time of day.
9. START: One tap allows over to begin functioning.
8
9
4-1
OPERATING SEQUENCE
The following is a description of component functions
during oven operation.
1. SETTING THE CLOCK
PARAR/BORRAR
ex.) To set 4:30, touch number key [4],[3], and [0].
NOTE: 1) This is a 12 hour clock.
2) Clock will operate as long as power is
applied to the oven.
RELOJ NUMBER RELOJ
2. CANCEL FUNCTION
Touch the
cancel an entry or a function currently in use.
The display will either return to the last item entered
or to the clock.
PARAR/BORRAR
pad whenever you need to
3. ONE TOUCH COOKING
PARAR/BORRAR
POPCORN
4. MICROWAVE COOKING
PARAR/BORRAR
TIEMPO NUMBER
NUMBER
INICIO
POTENCIA
5. TIME COOKING
6. MULTI-STAGE MICROWAVE COOKING
1ST STAGE
PARAR/BORRAR
2ND STAGE
1ST STAGE
TIEMPO NUMBER
NUMBER
TIEMPO NUMBER
NUMBER
INICIO
POTENCIA
POTENCIA
7. AUTO DEFROST COOKING
PARAR/
BORRAR
DESCONGELADO
AUTOMÁTICO
NUMBER OF
WEIGHT
INICIO
8. CHILD LOCK
This oven has a CHILD LOCK feature
TO SET CHILD LOCK
• Touch the 0 pad
• Touch and hold 0 pad L appear on
the display.
TO CANCEL CHILD LOCK
• Touch the 0 pad
• touch and hold 0 pad L disappears.
PARAR/BORRAR
TIEMPO NUMBER
NUMBER
INICIO
POTENCIA
4-2
SCHEMATIC DIAGRAM
4-3
CIRCUIT DESCRIPTION
L
FUSE
H.V.
TRANS-
FORMER
RELAY 2
MICOM CONTROLLER
SECONDARY
SWITCH
PRIMARY
SWITCH
N
MONITOR
SWITCH
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.
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)
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.
FUSE
PRIMARY
SWITCH
• 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.
generated in the secondary of the high voltage
• A high voltage of approximately 2100 volts AC is
transformer which is increased by the action of the high
voltage diode and charging of the high voltage
capacitor.
• The negative 4000 Volts DC is applied to the filament
of the magnetron.
L
N
RELAY 2
MICOM CONTROLLER
MONITOR
SWITCH
TRANS-
FORMER
SECONDARY
SWITCH
H.V.
4-4
SERVICE INFORMATION
TOOLS AND MEASURING INSTRUMENTS
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
MICROWAVE LEAKAGE TEST
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/cm
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.
2
and should repair any
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
• 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)
1
/2 in.)
MEASURING MICROWAVE ENERGY
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.
• Set the energy leakage monitor to 2450 MHz and
use it following the manufacturer's recommended
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
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
MEASUREMENT WITH OUTER CASE
REMOVED
• When you replace the magnetron, measure for
microwave energy leakage before the outer case is
installed and after all necessary components are
replaced or adjusted.
Special care should be taken in measuring the
following parts. (Circled area of below Fig.)
- Around the magnetron
- The waveguide
WARNING :AVOID CONTACTING ANY
HIGH VOLTAGE PARTS
NOTES WHEN MEASURING
• Do not exceed meter full scale deflection.
• The test probe must be removed no faster than
1 inch/sec (2.5 cm/sec) along the shaded area,
otherwise a false reading may result.
• The test probe must be held with the grip portion of the
handle.
A false reading may result if the operator's hand is
between the handle and the probe.
• When testing near a corner of the door, keep the probe
perpendicular to the surface making sure the probe
horizontally along the oven surface, this may possibly
cause probe damage.
RECORD KEEPING AND NOTIFICATION
AFTER MEASUREMENT
• After adjustment and repair of any microwave energy
interruption or microwave energy blocking device,
record the measured values for future reference. Also
enter the information on the service invoice.
• The microwave energy leakage should not be more
than 4 mW/cm.sq. after determining that all parts are in
good condition, functioning properly and genuine
replacement parts which are listed in this manual have
been used.
• At least once a year, have the electromagnetic energy
leakage monitor checked for calibration by its
manufacturer.
MEASUREMENT WITH A FULLY
ASSEMBLED OVEN
• After all components, including the outer case, are fully
assembled, measure for microwave energy leakage
around the door viewing window, the exhaust opening,
and air inlet openings.
• Microwave energy leakage must not exceed the values
prescribed below.
NOTE: Leakage with the outer case removedless than
5 mW/cm.sq. Leakage for a fully assembled
oven (Before the latch switch (primary) is
interrupted) with the door in a slightly opened
position-less than 2 mW/cm.sq.
5-2
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