LG MS-1904H User manual

MICROWAVE OVEN
SERVICE MANUAL
MODEL: MS-1904H
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 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 --------------------------------------------------------------------- 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

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-1904H
230 Volts AC 60 Hz
1,000 Watts
Single phase, 3 wire grounded
700 Watts full microwave power (IEC705)
2,450 MHz
2M218J
0 ~ 99 min. 50 sec.
483 (W) x 285 (H) x 360 (D) mm
312 (W) x 198 (H) x 316 (D) mm
11 kg (approx.)
12.5 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
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
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

FEATURES
CONTROL PANEL
1. DISPLAY WINDOW.
2. AUTO COOK: Used to cook the foods listed by one touch.
3. WEIGHT PAD/COOK TIMER
4. STOP/CLEAR: It used to stop oven and clear all entries
except time of day.
5. DEFROST: This feature provides you with the best
defrosting method for frozen foods.
6. START/EZ on: This feature turns the oven on instantly
7. POWER: Used to set power.
8. DIAL
4-1
OPERATING INSTRUCTIONS
Oven Front Plate
Window Door Screen
Door Seal
Display Window
Control Panel
Door Open Button
Safety Door Lock
System
Turntable
Rotating Ring
1
2
3
46
7
5

OPERATING SEQUENCE
The following is a description of component functions
during oven operation.
1. MICROWAVE COOKING
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. AUTO WEIGHT DEFROST COOKING
5. AUTO COOK
4-2
Stop Start
Stop
Desired
auto cook
category
STOP
Stop
Desired
defrost
category
Desired
cooking
weight
Desired
food weight
Start
Start
Stop Desired
power level
Desired
cooking time Start

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.
4-4
L
FUSE
H.V.
TRANS-
FORMER
RELAY 2
MICOM CONTROLLER
SECONDARY
SWITCH
PRIMARY
SWITCH
N
MONITOR
SWITCH
L
FUSE
H.V.
TRANS-
FORMER
RELAY 2
MICOM CONTROLLER
SECONDARY
SWITCH
PRIMARY
SWITCH
N
MONITOR
SWITCH

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

6-2
13552A
13213A
13581A
13720D
14970A
14026A
13536A
13352A
DOOR PARTS

6-3
23572A
24781M
WTP018
268711
WTT028
WTP004
24510L
250201
24970A
26638A
CONTROL PANEL PARTS
FOR MS-198H

6-4
CONTROL PANEL PARTS
FOR MS-199H
23572A
24781M
WTP018
268711
WTT028
WTP004
24510L
250201
24970A
249401
26638A

6-5
33052M
33112U
WTT021
34960A
36549S
WTP013
33390G
35889A
340511
OVEN CAVITY PARTS

6-6
466001
466003
WTT028
466001
435001
56912B
55262A
WSZ085
LATCH BOARD PARTS

6-7
56201B
568771
56930V
56411A
54974S
56201A 56549F
WTT037
WTT028
WSZ002
55900A
56324A
WSZ002
50FZZA
INTERIOR PARTS

6-8
56170D
63302A
63303A
WTT021
WSZ002
65006B
65006B
50CZZH
WSZ002
54810C
56851D
56901A
BASE PLATE PARTS

8-1
SCHEMATIC DIAGRAM OF P.C.B

8-2
PRINTED CIRCUIT BOARD