LG MS-192H User manual

MICROWAVE OVEN
SERVICE MANUAL
MODEL: MS-192H/ MS-197H
CAUTION
BEFORE SERVICING THE UNIT, READ THE SAFETY PRECAUTIONS IN THIS MANUAL.

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(31/2 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

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
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.
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.
5-2
WARNING : AVOID CONTACTING ANY
HIGH VOLTAGE PARTS
(Magnetron, H.V. Transformer,
H.V. Capacitor, H.V. Cable Ass’y,
H.V. Fuse)

• Microwave power output measurement is made with
the microwave oven supplied at its rated voltage and
operated at its maximum microwave power setting with
a load of (1000±5) g of potable water.
• The water is contained in a cylindrical borosilicate glass
vessel having a maximum material thickness of 3 mm
and an outside diameter of approximately 190mm.
• The oven and the empty vessel are at ambient
temperature prior to the start of the test.
• The initial temperature (T1) of the water is (10±2)°C It
is measured immediately before the water is added to
the vessel. After addition of the water to the vessel,
the load is immediately placed on the center of the
turntable which is in the lowest position and the
microwave power switched on.
• The time T for the temperature of the water to rise by a
value ∆T of (10±2)°K is measured, where T is the time
in seconds and ∆T is the temperature rise. The initial
and final water temperatures are selected so that the
maximum difference between the final water
temperature and the ambient temperature is 5°K.
• The microwave power output P in watts is calculated
from the following formula :
4187 x (∆T)
T
is measured while the microwave generator is
operating at full power. Magnetron filament heat-up
time is not included. (about 3 sec)
• The water is stirred to equalize temperature throughout
the vessel, prior to measuring the final water
temperature.
• Stirring devices and measuring instruments are
selected in order to minimize addition or removal of
heat.
A. OUTER CASE REMOVAL
1) Disconnect the power supply cord from the outlet.
2) Remove the screws from the rear and along side
edges of the case.
The outer case must be moved backward to be lifted
off.
B. POWER SUPPLY CORD
1) Remove the outer case.
2) Disconnect two terminals, and remove one screw of
the earth terminal.
CAUTION: DISCHARGE THE HIGH VOLTAGE
CAPACITOR BEFORE SERVICING
(refer to page 2-1)
C. CONTROL PANEL ASSEMBLY
1) Disconnect the leadwire from the Timer motor
2) Remove the screws for securing the control panel.
3) Lift control panel ASS’Y from the oven by the tab
unhooked.
5-3
WATER LOAD
TURNTABLE
MEASUREMENT OF MICROWAVE POWER OUTPUT
P =
DISASSEMBLY AND ADJUSTMENT

D. DOOR GROSS ASSEMBLY REMOVAL
1) Open the door.
2) Remove the choke cover cap very carefully with a
flat-blade screwdriver.
CAUTION : Be careful not to damage door seal plate
by screwdriver.
3) Lift up and push the door.
NOTE:
1. After replacing the door, be sure to check that the
primary switch, monitor switch, and secondary switch
operate normally.
2. After replacing the door, check for microwave energy
leakage with a survey meter. Microwave energy must
be below the limit of 5 mW/cm. (with a 275 ml water
load)
3. When mounting the door assembly to the oven
assembly, be sure to adjust the door assembly parallel
to the chassis. Also adjust so the door has no play
between the inner door surface and oven frame
assembly. If the door assembly is not mounted
properly, microwaves may leak from the clearance
between the door and the oven.
E. HIGH VOLTAGE TRANSFORMER
REMOVAL
1) Discharge the high voltage capacitor.
2) Disconnect the leadwire from magnetron, high voltage
transformer, and capacitor.
3) Remove the screw holding the high voltage
transformer to the baseplate.
F. FAN MOTOR ASSEMBLY REMOVAL
1) Discharge the high voltage capacitor.
2) Disconnect the leadwire from fan motor, noise filter
and high voltage capacitor.
3) Remove the two screws holding the the suction guide
ASS’Y to the oven cavity and remove the high voltage
diode earth screw.
4) Remove the screw of the capacitor bracket.
5) Remove the two screws holding the fan motor ASS’Y
to the suction guide ASS’Y.
G. HIGH VOLTAGE CAPACITOR AND
DIODE REMOVAL
1) Discharge the high voltage capacitor.
2) Disconnect the leadwire from fan motor, noise filter
and high voltage capacitor.
3) Remove the screw holding the suction guide ASS’Y to
the oven cavity and remove the high voltage diode
earth screw.
4) Remove the screw holding the high voltage capacitor
bracket.
5-4
Remove choke cover cap
Remove door
H.V.
Transformer
Suction
Guide
H.V.
Diode
H.V.
Fuse
H.V.
Capacitor
Fan Motor
ASS’Y

H. AIR DUCT ASSEMBLY REMOVAL
1) Disconnect the leadwire from lamp, A.C Relay and
monitor resistor.
2) Remove the mounting screw to the magnetron.
I. MAGNETRON REMOVAL
1) Disconnect the leadwire from the high voltage
transformer and high voltage capacitor.
2) Carefully remove the mounting screws holding the
magnetron and the waveguide.
3) Remove the magnetron ASS’Y until the tube is
clear from the waveguide.
NOTE:
1. When removing the magnetron, make sure its
dome does not hit any adjacent parts, or it may be
damaged.
2. When replacing the magnetron, be sure to install
the magnetron gasket in the correct position and
be sure that the gasket is in good condition.
3. After replacing the magnetron, check for microwave
leakage with a survey meter around the
magnetron. Microwave energy must be below the
limit of 5 mW/cm2. (With a 275 ml. water load).
Make sure that gasket is rigidly attached to the
magnetron. To prevent microwave leakage,
tighten the mounting screws properly, making sure
there is no gap between the waveguide and the
magnetron.
J. REMOVING THE TURNTABLE MOTOR
1) Remove the turntable.
2) Remove the turntable shaft VERY CAREFULLY.
3) Lay the unit down on its back.
4) Remove the turntable motor cover.
The turntable base cover is easily removed by
pinching the six parts with a wire cutting.
5) Disconnect the leadwire from the turntable motor
terminals.
6) Remove the screw securing the turntable motor to
the oven cavity ASS’Y
7) After repairing the motor, rotate the removed
turntable motor cover.
8) Fit the turntable motor cover’s projecting part to the
base plate slit.
NOTE:
1. Remove the wire lead from the turntable motor
VERY CAREFULLY.
2. Be sure to grasp the connector, not the wires, when
removing.
5-5
Waveguide
Air Duct
Magnetron
Gasket
Magnetron
Dome
Waveguide
Bracket
Magnetron
Wire Leads
Turntable Motor

K. TIMER MOTOR REMOVAL
1) Remove the control panel assembly from the
cavity.
2) Remove screws which hold the timer motor to the
control panel.
3) Remove the timer motor from the control panel.
4) Remove the power control knob and the timer
knob.
L. INTERLOCK SYSTEM
1) INTERLOCK MECHANISM
The door lock mechanism is a device which has
been specially designed to eliminate completely
microwave activity when the door is opened during
cooking and thus to prevent the danger resulting
from the microwave leakage.
2) MOUNTING OF THE PRIMARY/MONITOR/
SECONDARY SWITCHES TO THE LATCH
BOARD
3) INSTALLATION AND ADJUSTMENT OF THE
LATCH BOARD TO THE OVEN ASSEMBLY
• Mount the latch board to the oven assembly.
• Adjust the latch board in the arrow direction so that
oven door will not have any play in it when the door
is closed.
• Tighten the mounting screw.
•Check for play in the door by pushing the door
release button. Door movement should be less
than 0.5 mm. (1/64 inch)
Don't push the door release button while making
adjustment. Make sure that the latch moves
smoothly after adjustment are completed and that
the screws are tight. Make sure the primary, monitor,
and secondary switches operate properly by
following the continuity test procedure.
5-6
Motor
Timer Knob
Door Open Button
Power Knob
Release
Lever
PRIMARY
SWITCH
ADJUSTMENT
DIRECTION
MONITOR
SWITCH
SECONDARY
SWITCH
CAUTION: CHECK THE CORRECT POSITION
MAGNETRON
H.V. TRANSFORMER
PRIMARY CIRCUIT PROTECTOR
H.V. CAPACITOR
H.V.
DIODE
FIG. 1

A. PRIMARY INTERLOCK SWITCH TEST
When the door release button is depressed slowly
with the door closed, an audible click should be
heard at the same time or successively at
intervals. When the button is released slowly, the
latches should activate the switches with an
audible click.
If the latches do not activate the switches when
the door is closed, the switches should be a
adjusted in accordance with the adjustment
procedure. Disconnect the wire lead from the
primary switch. Connect the ohmmeter leads to
the common (COM) and normally open (NO)
terminal of the switch. The meter should indicate
an open circuit in the door open condition.
When the door is closed, the meter should
indicate a closed circuit.
When the primary switch operation is abnormal,
make the necessary adjustment or replace the
switch only with the same type of switch.
B. SECONDARY INTERLOCK SWITCH TEST
Disconnect the wire lead from the secondary
switch.
Connect the ohmmeter leads to the common
(COM) and normally open (NO) terminals of the
switch. The meter should indicate a open circuit in
the door open condition. When the door is closed,
meter should indicate an closed circuit. When the
secondary switch operation is abnormal, make the
necessary adjustment or replace the switch only
with the same type of switch.
C. MONITOR SWITCH TEST
Disconnect the wire lead from the monitor switch.
Connect the ohmmeter leads to the common
(COM) and normally closed (NC) terminals of the
switch. The meter should indicate closed circuit in
the door open condition. When the door is closed,
meter should indicate an open circuit. When the
monitor switch operation is abnormal, replace with
the same type of switch.
NOTE: After repairing the door or the interlock
system, it is necessary to do this continuity
test before operating the oven.
5-7
WARNING : FOR CONTINUED PROTECTION AGAINST EXCESSIVE RADIATION
EMISSION, REPLACE ONLY WITH IDENTICAL REPLACEMENT PARTS.
TYPE NO. SZM-V 16-FA-63 OR VP-533A-OF FOR PRIMARY SWITCH
TYPE NO. SZM-V 16-FA-61 OR VP-531A-OF FOR MONITOR SWITCH
TYPE NO. SZM-V 16-FA-63 OR VP-533A-OF FOR SECONDARY SWITCH
COMPONENTS TEST PROCEDURE RESULTS
SWITCHES Check for continuity of the Door Door
(Wire leads removed) switch with an Ohm-meter open closed
Primary
Switch
Monitor
Switch
NOTE : After checking for the continuity of switches, make sure that are
connected correctly.
NO
COM
NC
COM
NC
COM
NO
COM
INTERLOCK CONTINUITY TEST
Secondary
Switch

5-8
CAUTIONS
1. DISCONNECT THE POWER SUPPLY CORD FROM THE OUTLET WHENEVER REMOVING THE
OUTER CASE FROM THE UNIT. PROCEED WITH THE TEST ONLY AFTER DISCHARGING THE HIGH
VOLTAGE CAPACITOR AND REMOVING THE WIRE LEADS FROM THE PRIMARY WINDING OF THE
HIGH VOLTAGE TRANSFORMER. (SEE PAGE 2-1)
2. ALL OPERATIONAL CHECKS WITH MICROWAVE ENERGY MUST BE DONE WITH A LOAD (1 LITER
OF WATER IN CONTAINER) IN THE OVEN.
COMPONENTS TEST PROCEDURE RESULTS
HIGH VOLTAGE
TRANSFORMER
(Wire leads removed)
MAGNETRON
(Wire leads removed)
1. Measure the resistance.
(Ohm-meter scale: Rx1)
• Primary winding
• Secondary winding
• Filament winding
2. Measure the resistance.
(Ohm-meter scale: Rx1000)
• Primary winding to ground
• Filament winding to ground
1. Measure the resistance.
(Ohm-meter scale: Rx1)
• Between Filament terminal
2. Measure the resistance.
(Ohm-meter scale: Rx1000)
• Filament to chassis
Approx.: 1.4 Ω
Approx.: 90 Ω
Less than: 0.1 Ω
Normal: ∞
Normal: ∞
Normal: Less than 1 Ω
Normal: ∞
PRIMARY
TERMINAL
SECONDARY
TERMINAL
FILAMENT
WINDING
TERMINAL
COMPONENT TEST PROCEDURE

5-9
COMPONENTS TEST PROCEDURE RESULTS
HIGH VOLTAGE
CAPACITOR
HIGH VOLTAGE
DIODE
NOTE :
Some inexpensive meters
may indicate infinite
resistance in both direction.
Measure the resistance.
(Ohm-meter scale: Rx1000)
• Terminal to terminal.
Measure the resistance.
(Ohm-meter scale: Rx1000)
• Terminal to case.
Measure the continuity (Forward).
(Ohm-meter scale: Rx10000)
Measure the continuity (Reverse).
(Ohm-meter scale: Rx10000)
Normal: Momentarily indicates
several ohms, and
then gradually returns
to infinite.
Normal: ∞
Normal: Continuity.
Abnormal: ∞
Normal: ∞
Abnormal: Continuity.
NOTE: When testing the magnetron, be sure to install the magnetron gasket
in the correct position and be sure that the gasket is in good condition.
Antenna
Gasket
Chassis
Filament
Terminals

5-10
COMPONENTS TEST PROCEDURE RESULTS
MAIN FUSE Check for continuity of the fuse with an
multi-meter.
NOTE: If the fuse is blown, check the primary, the secondary, and the monitor
switches, H.V.D. and H.V.C. before replacing the fuse.
If the fuse is blown by improper switch operation replace the defective switch
and the fuse at the same time. Replace just the fuse if the switches operate
normally.
Normal Abnormal

COMPONENTS TEST PROCEDURE RESULTS
5-11
TIMER MOTOR
(Wire leads removed)
Measure the resistance.
(Ohm-meter scale: R x 100)
Measure the resistance.
(Ohm-meter scale: R x 1000)
Note: A is ON,OFF switch B is
power supply terminal of the
timer motor C is defrost switch
NOTE : • A MICROWAVE LEAKAGE TEST MUST ALWAYS BE PERFORMED WHEN THE UNIT IS
SERVICED FOR ANY REASON.
• MAKE SURE THE WIRE LEADS ARE IN THE CORRECT POSITION.
• WHEN REMOVING THE WIRE LEADS FROM THE PARTS, BE SURE TO GRASP THE
CONNECTOR, NOT THE WIRES.
C
(2-3)
B
(2-M)
A
(1-2)
A
B
C
A
Turn on
Approx. 25 K§
Turn Off
B
FAN MOTOR
(Wire leads removed)
TURNTABLE
MOTOR
(Wire leads removed)
Normal:
Abnormal: ∞or several Ω
Normal: Approx. 100~200 Ω
Abnormal: ∞or several Ω
A ~ B A ~ C
30 ~ 50Ω300~500Ω

5-12
TROUBLE SHOOTING
WHEN YOU GET A COMPLAINT FROM YOUR CUSTOMER, EVALUATE THE COMPLAINT CAREFULLY. IF
THE FOLLOWING SYMPTOMS APPLY, PLEASE INSTRUCT THE CUSTOMER IN THE PROPER USE OF THE
MICROWAVE OVEN. THIS CAN ELIMINATE AN UNNECESSARY SERVICE CALL.
CAUTIONS
1. Check grounding before checking for trouble.
2. Be careful of the high voltage circuit.
3. Discharge the high voltage capacitor. (See page 2-1)
4. When checking the continuity of the switches or of the high voltage transformer, disconnect one lead wire
from these parts and then check continuity with the AC plug removed. To do otherwise may result in a
false reading or damage to your meter.
CONDITION
Microwave oven
does not work. Inserting many plug into one
plug outlet and using
them at the same time
(causes overloading).
Microwave oven plug is not
inserted tightly.
Output power is too low. Low AC input voltage.
Food temperature is too low.
Using metallic ware and
allowing it to touch the oven
wall.
Sparks occur.
Inconsistent intensity of
microwave by their
characteristics.
1. Use plastic wrap or lid.
2. Stir once or twice while
cooking soup, cocoa or
milk, etc.
Uneven cooking.
Ceramic ware trimmed in
gold or silver powder is used.
Avoid using other electrical
appliances when you use the
microwave oven.
Insert microwave oven plug
securely.
Use the microwave oven at
adequate line voltage.
This may not be a defect.
It is possible that the food
should be cooked for a
longer time period.
Do not use metallic ware for
cooking except where noted
in the cooking guide.
Do not use any type of
cookware with metallic
trimming.
CAUSE REMEDY
Excessive weight on tray or
improperly balanced. Distribute food evenly. Cook
smaller portions and,or use
lighter weight cookware.
Turntable drags or makes
noise.

5-13
CONDITION CHECK RESULT CAUSE REMEDY
1. Fuse blows. Continuity.
No continuity.
Continuity. Shorted contact at
the primary switch.
Replace fuse,
primary, monitor
and secondary
switches.
No continuity.
Normal. Defective high
voltage capacitor. Replace high voltage capacitor.
Fuse blows again Defective high volt-
age transformer. Replace high volt- age transformer.
Malfunction of the
monitor switch. Replace fuse,
primary, monitor
and secondary
switches.
Check continuity
of monitor
switch (with
door closed).
Check continuity
of primary
switch (with
door opened).
Disconnect one
side of the wire
lead connected
from transformer
to the high
voltage
capacitor and
operate the unit.
Replace fuse
(TROUBLE 1) Oven lamp does not turn on when the timer knob is pushed with door closed.
NOTE : All these switches must be replaced at the same time.
This fuse is a special type of fuse which is kept as spare part by the importer.

5-14
(TROUBLE 3) Output power is low.
CONDITION CHECK RESULT CAUSE REMEDY
Output is low Lower than 207V.
Normal
Less than 8.5oC.
Measure the
magnetron’s
output(See test
procedure).
Faulty magnetron. Replace.
Decrease in power
source voltage
with load.
Suggest customer
contact local
electric power
utility co. or
qualified
electrician.
Check the
power source
voltage
oscillating.
No continuity.
No continuity. replace.
Malfunction of the
timer switch.
Faulty thermostat.
replace.
Check the
continuity of the
timer switch
contacts.
Check the
continuity of the
thermostat.
1. Oven does not
operate. No continuity.
No continuity. Adjust or replace.
Malfunction of the
primary switch.
Malfunction of the
secondary switch.
Adjust or replace.
Check the
continuity of the
primary switch
with door
closed.
Check the
continuity of the
secondary
switch with
secondary
switch pushed.
(TROUBLE 2) Oven does not start even though the timer is set.
CONDITION CHECK RESULT CAUSE REMEDY

5-15
CONDITION CHECK RESULT CAUSE REMEDY
No microwave
oscillation. No continuity.
Continuity.
Abnormal or burn
out. Defective monitor
resistor. Replace.
Malfunction of the
power control
switch.
Replace the power
control switch.
Check the
power control
switch(cooking
state).
Check the
monitor resistor.
Abnormal Defective AC
relay. Replace.
Normal
Check the AC
relay.
Abnormal Open the
secondary winding
of the high voltage
transformer of
faulty insulation of
filament winding.
Replace .
Check H.V.
transformer.
Abnormal Shorted H.V. diode Replace .
Check H.V.
diode.
Abnormal Faulty capacitor. Replace .
Check H.V.
capacitor.
Abnormal Faulty magnetron. Replace . Magnetron
(TROUBLE 4) Oven does not cook at all even though turntable rotates.

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
24781T
23572A
24510L
250201
24970A
249401
WTP015
26549T
CONTROL PANEL PARTS

6-4
33052M
340511
33112U
WTT021
34960A
36549S
WTP013
33390G
35889A
OVEN CAVITY PARTS