GE LMAB1240ST User Manual
Website: http://us.lgservice.com
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MICROWAVE OVEN
SERVICE MANUAL
MODEL: LMAB1240ST
CAUTION
BEFORE SERVICING THE UNIT, READ THE SAFETY PRECAUTIONS IN THIS MANUAL.
P/NO : 3828W5S5057
December, 2004
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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INSTALLATION
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OPERATING INSTRUCTIONS
FEATURES
CONTROL PANEL
OPERATING SEQUENCE
SCHEMATIC DIAGRAM (I)
SCHEMATIC DIAGRAM (II)
CIRCUIT DESCRIPTION
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SERVICE INFORMATION
TOOLS AND MEASURING INSTRUMENTS
MICROWAVE LEAKAGE TEST
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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
4-5
5-1
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5-1
5-1
MEASUREMENT OF MICROWAVE POWER OUTPUT
DISASSEMBLY AND ADJUSTMENT
INTERLOCK CONTINUITY TEST
COMPONENT TEST PROCEDURE
TROUBLE SHOOTING
EXPLODED VIEW
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REPLACEMENT PARTS LIST
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5-3
5-3
5-7
5-8
5-11
6-1
7-1
SPECIFICATIONS
Back Side
ITEM
MODEL
Power Requiremen
Power Output
Microwave Frequency
Magnetron
Timer
Outside Dimensions
Cavity Dimensions
Net Weight
Shipping weight
Control Complement
DESCRIPTION
LMAB1240ST
120 Volts AC 60 Hz (13.3A)
1500 Watts
Single phase, 3 wire grounded
1200 Watts full microwave power (IEC60705)
2450 MHz
2M246-050GF
0 ~ 99 min. 99 sec.
203/19" x 1117/20" x 1621/46"
1413/75" x 910/27" x 15"
34.9 lbs
38.6 lbs
Touch Control System
Clock : 1:00 - 12:59
Microwave Power for Variable Cooking
Power level
HIGH .................................... Full power throughout the cooking time
9 (Saute)
7 (Med.-High)
5 (Med.-Low)
3 (Low)
1 (Warm)
...............................
.......................
........................
.................................
..............................
approx. 90% of Full power, 8 (Reheat)
approx. 70%, 6 (Medium)
approx. 50%, 4 (Defrost)
approx. 30%, 2 (Simmer)
approx. 10%
..........
..........
approx. 80%
.........
approx. 60%
approx. 40%
.........
approx. 20%
Rating Label Location
Accessories
This microwave oven is designed for household use only.
It is not recommended for commercial purposes.
Owner's manual & cooking guide
Glass turntable
Roller Rest
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 watch 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.
COOLING FIN
FILAMENT
TERMINALS
MAGNETRON
CHASSIS GROUND
MAGNETRON
THE OVEN IS TO BE SERVICED ONLY
BY PROPERLY QUALIFIED SERVICE
PERSONNEL.
2-1
INSTALLATION
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.
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.
PROPERL Y POLARIZED
AND GROUNDED OUTLET
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.
10cm
Three-Pronged (Grounding) plug
3-1
OPERATING INSTRUCTIONS
Oven Front Plate
Window Door Screen
Door Seal
Display Window
Control Panel
Safety Door Lock System
Turntable
Roller Rest
FEATURES
CONTROL PANEL
1
2
3
5
6
8
11
9
4
7
10
12
1. DISPLAY: The display includes a clock and indicators
that tell you the time of day, cook time settings, and
cooking functions selected.
2. AUTO TOUCH: Touch this pad to cook without
entering a cook time or power.
3. AUTO DEFROST: Touch this pad to defrost foods by
entering weight.
4. QUICK DEFROST: Touch this pad to defrost foods
quickly.
5. NUMBER PADS : Touch number pads to enter cook
time, power level, quantities, or weights.
6. TIME : Touch this pad to set a cook time.
7. POWER : Touch this pad to set a cook power.
8. STOP/CLEAR : It used to stop oven and clear all entries
except time day.
9. Ez-ON : You can extend cooking time in multiples of 30
seconds by repeatedly touching this pad during cooking.
10. START : This feature allows oven to begin functioning.
11. CLOCK : Touch this pad to set time of day.
12. TIMER : Touch this pad to set timer.
4-1
OPERATING SEQUENCE
The following is a description of component functions
during oven operation.
1. SETTING THE CLOCK
STOP/CLEAR
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.
CLOCK CLOCKNUMBER
2. CANCEL FUNCTION
Touch the STOP/CLEAR 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. EZ ON
STOP/CLEAR
EZ ON
7. AUTO DEFROST COOKING
STOP/CLEAR
AUTO
DEFROST
NUMBER OF
WEIGHT
8. CHILD LOCK
This oven has a CHILD LOCK feature
TO SET CHILD LOCK
• Touch the STOP/CLEAR pad
• Touch and hold 0 pad LOCK appear on the
display.
TO CANCEL CHILD LOCK
• Touch and hold 0 pad LOCK disappears.
START
4. AUTO TOUCH
STOP/CLEAR
NOTE: Heat only 1 package at a time.
5. TIME COOKING
STOP/CLEAR
6. MULTI-STAGE COOKING
1ST STAGE
STOP/CLEAR
2ND STAGE
POPCORN
COOK
TIME
NUMBER
COOK
TIME
NUMBER
START
POWERNUMBER
POWERNUMBER
COOK
TIME
NUMBER
POWERNUMBER
START
4-2
SCHEMATIC DIAGRAM (I)
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.
*Check the Rating Model No.
4-3
SCHEMATIC DIAGRAM (II)
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.
*Check the Rating Model No. (ADD Noise filter)
4-4
CIRCUIT DESCRIPTION
L
FUSE
H.V.
TRANS-
FORMER
RELAY 2
MICOM CONTROLLER
SECONDARY
SWITCH
PRIMARY
SWITCH
MONITOR
SWITCH
N
L
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.
• 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 cut off the 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 fail to open, the
fuse opens due to the large current surge caused by
the monitor switch activation, which in turn stops
magnetron oscillation.
• 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.
• 3.3 volts AC is generated from the filament winding of
the high voltage transformer. This 3.3 volts is applied to
the magnetron to heat the magnetron filament through
two noise-preventing choke coils.
4-5
FUSE
N
L
L
PRIMARY
SWITCH
RELAY 2
MICOM CONTROLLER
MONITOR
SWITCH
H.V.
TRANS-
FORMER
SECONDARY
SWITCH
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