LG MH-706CL User manual

MICROWAVE/GRILL OVEN
SERVICE MANUAL
MODEL: MH-706CL
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
SCHEMATIC DIAGRAM OF P.C.B.
------------------------------------------------------------------------------ 8-1
PRINTED CIRCUIT BOARD ------------------------------------------------------------------------------------------------- 8-2
P.C.B. PARTS LIST --------------------------------------------------------------------------------------------------- 9-1
CONTENTS

This microwave oven is designed for household use only.
It is not recommended for commercial purposes.
DESCRIPTION
MH-706CL
240 Volts AC 50 Hz
Single phase, 3 wire grounded
Microwave 1,400W
Grill 1,300W
Combination 2,600W
900 Watts full microwave power (IEC705)
2,450 MHz
2M214 - 39F
99 min. 50 sec.
530 (W) x 322 (H) x 404 (D) mm
348 (W) x 232 (H) x 373 (D) mm
18 kg (approx.)
20 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
Grill, COMBI
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
Nameplate 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
Display Window
Safety Door Lock System
Grill Rack Glass Tray
Rotating Ring
Control panel
Oven front face
Window door screen
Door seal
7
8
9
10
11
12
6
2
1
3
4
5
1. 2.
3. 4.
1.
2. 3.
4.
1. POWER: Used to select the desired power level
for cooking.
2. COMBI: Used to select the combination cooking.
3. AUTO COOK: Used to cook the foods listed by one
touch.
4. AUTO DEFROST: Used to select the auto weight
defrost.
5. COOK TIME: Used to cook food for a desired time.
6. INDICATORS
7. KITCHEN TIMER
8. SET CLOCK: Used to set the time of day.
9. GRILL: Used to select the grill cooking.
10. LESS/MORE: Used to change cooking time.
WEIGHT: Used to select the desired weight.
11. STOP/CLEAR: Used to stop oven and clear all
entries except time of day.
- CHILD LOCK
12. START: One tap allows oven to begin functioning.

4-2
OPERATING SEQUENCE
The following is a description of component functions
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.
3. QUICK START
4. MICROWAVE COOKING
5. MULTI-STAGE MICROWAVE
COOKING
6. GRILL COOKING
7. COMBINATION COOKING
8. AUTO WEIGHT DEFROST
9. 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.
10. AUTO COOK
Stop Set
clock Set the correct time
Stop Start
Stop Desired auto cook
category
Desired
cooking
weight
STOP
STAGE 1
Set
clock
Stop
Stop
Desired
defrost
category
Desired
cooking
weight Start
Start
Stop Grill Desired
cooking time Start
Stop Desired combi
category Desired
cooking time 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
Grill
or Combi Desired
cooking time

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.
• 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.
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
vapor in the oven through the base plate and upper
plate.
4-4
L
FUSE
H.V.
TRANS-
FORMER
RELAY 2
MICOM CONTROLLER
SECONDARY
SWITCH
PRIMARY
SWITCH
N
MONITOR
SWITCH
MONITOR
SWITCH
L
FUSE
H.V.
TRANS-
FORMER
RELAY 2
MICOM CONTROLLER
SECONDARY
SWITCH
PRIMARY
SWITCH
N
RELAY 3
L
N
GRILL
THERMOSTAT
GRILL
HEATER
L
G -Y
N
E

DOOR PARTS
LATCH BOARD PARTS
CONTROL PANEL PARTS
INTERIOR PARTS
BASE PLATE PARTS
OVEN CAVITY PARTS
6-1
EXPLODED VIEW
INTRODUCTION

6-2
13720D
13350F
13581A
14970A
14026A
13552A
15006A
13213A
14890A
DOOR PARTS

6-3
WTP004
268711
268712
23790D
23572A
24781S
250203
250201
250202
24970A
24510L
23550F
CONTROL PANEL PARTS

6-4
33112U
35300A
348101
35264A
35301A
WTT021 WTT021
WTT010
348102
33550H
WMT002
33390G
35889A
34960A
33052M
36549S
WTP013
34370T
35026G
WSZ092
OVEN CAVITY PARTS

6-5
WSZ085
466003
466001
43501A
43500A
466001
LATCH BOARD PARTS

6-6
WSZ002
WTT028
WSZ002
WTT028
WSZ062
50FZZA
WSZ002
WTT037
WSZ002
50CZZH
56324A
55262A
54810C
56851C
56851D
55900A
56549F
56411A
56201A
56930V 56930G
568771
54974S
56912B
56930M
WTP004
56201B
INTERIOR PARTS

6-7
56170D
63302A
63303A
WTT021
WSZ002
WSZ062
WTT030
647781
BASE PLATE PARTS

8-1
SCHEMATIC DIAGRAM OF P.C.B

8-2
PRINTED CIRCUIT BOARD