LG LMV1762SB User manual

MICROWAVE OVEN
SERVICE MANUAL
MODEL: LMV1762SB
LMV1762SW
LMV1762ST
LMV1763ST
CAUTION
BEFORE SERVICING THE UNIT, READ THE SAFETY PRECAUTIONS IN THIS MANUAL.
P/NO : MFL06272540
March, 2016
Printed in Korea
Internal Use Only

-2-
CAUTION
WARNING TO SERVICE TECHNICIANS
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.
• Proper operation of the microwave oven requires that the magnetron be assembled to the wave guide 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.
• Routine service safety procedures should be exercised at all times.
• Untrained personnel should not attempt service without a thorough review of the test procedures and safety
information contained in this manual.

FOREWORD
Read this manual carefully. Failure to adhere to or observe the information in this manual may result in exposing
yourself to the microwave energy normally contained within the oven cavity.
CONTENTS
(Page)
Safety Precautions .............................................................................................................................................. 2
1. Specifications .................................................................................................................................................. 4
2. Cautions ........................................................................................................................................................... 5
3. Installation ....................................................................................................................................................... 6
4. Operation ......................................................................................................................................................... 7
4-1. Control Panel Features .............................................................................................................................. 7
4-2. Explanation of Control Panel...................................................................................................................... 8
5. Wiring Diagram / Key Matrix........................................................................................................................... 9
5-1. Wiring Diagram .......................................................................................................................................... 9
5-2. Key Matrix ............................................................................................................................................... 10
6. Troubleshooting ............................................................................................................................................ 11
6-1. General Information for Service ............................................................................................................... 11
6-2. Safety Caution.......................................................................................................................................... 12
6-3. Basic Check Summary............................................................................................................................. 13
6-4. Troubleshooting........................................................................................................................................ 14
7. Microwave Leakage Test .............................................................................................................................. 24
8. Power Output Measurement......................................................................................................................... 26
9. Interlock System............................................................................................................................................ 27
9-1. Interlock Mechanism ................................................................................................................................ 27
9-2. Interlock Continuity Test ........................................................................................................................... 29
10. Component Testing Information ................................................................................................................ 30
11. Disassembly Instructions ........................................................................................................................... 34
12. Exploded View ............................................................................................................................................. 41
-3-

-4-
1. SPECIFICATIONS
Rated Power Consumption ................................ 1600W maximum (Microwave oven+Cook top lamps+Ventilation fan)
Microwave Output............................................... 1000W (IEC60705)
Frequency .......................................................... 2450 MHz ±50 MHz
Power Supply .................................................... 120 VAC, 60 Hz
Rated Current .................................................... 14 Amp. (Microwave oven+Cook top lamps+Ventilation fan)
Magnetron Cooling ............................................ Forced Air Cooling
Rectification ....................................................... Rectification Voltage Double Half-Wave
Door Sealing ...................................................... Choke System
Safety Devices ................................................... OVEN TCO 110/0
............................................................................ MGT TCO 150/0
............................................................................ Bottom TCO : 150/0
............................................................................ Fuse (20A)
............................................................................ Primary Interlock Switch
............................................................................ Secondary Interlock Switch
............................................................................ Interlock Monitor Switch
Magnetron ......................................................... 2M214 - 161GP
Cook Top Lamp ................................................. 125 V, 30 W or 40 W
Cavity Lamp ....................................................... 125 V, 30 W or 40 W
Timer ................................................................. Digital, up to 99 min. 99 sec. (in each cooking stage)
Tray ................................................................... Tempered Safety Glass
Overall Dimensions ........................................... 2915/16” (W) x 167/16” (H) x 1615/16” (D)
Oven Cavity Size ............................................... 219/16” (W) x 141/8” (H) x 8 7/8” (D)
Effective Capacity of Oven Cavity ..................... 1.7cu.ft.
Accessories ....................................................... Ownerʼs Manual & Cooking Guide, Installation Manual,
............................................................................ Exhaust Adapter, Exhaust Damper, Mounting Kit and Filter,
............................................................................ Glass Tray, Metal Rack, Rotating Ring Assembly.
SWITCH CHART
SWITCH MODE
CONDITIONS
OPEN OPEN CLOSE
CLOSE CLOSE OPENDOOR CLOSED
PRIMARY
INTERLOCK
SWITCH
SECONDARY
INTERLOCK
SWITCH
INTERLOCK
MONITOR
SWITCH
COM
NO
COM
NO
COM
NC
NOTE: Use the above switch chart with circuit diagram on page 5-1.
DOOR OPEN

-5-
2. 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.
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 connected.
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.
• 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.
• 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 the
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.
THE OVEN IS TO BE SERVICED ONLY
BY PROPERLY QUALIFIED SERVICE
PERSONNEL.
Gasket
ANTENNA
COOLING FIN
MAGNETRON
CHASSIS GROUND FILAMENT
TERMINALS
MAGNETRON

-6-
3. INSTALLATION
BEFORE YOU BEGIN, READ THE FOLLOWING INSTRUCTIONS COMPLETELY AND CAREFULLY.
PRECAUTIONS ON INSTALLATION
A. Plug the power supply cord into a 120V AC, 60Hz,
single-phase power source with a capacity of at
least 20 amperes.
B. Avoid placing the unit in a location where there is
direct heat or splashing water.
C. Install the unit on the mounting plate firmly.
D. Place the unit as far away as possible from TV,
radio, 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 electric shock.
The plug must be plugged into an outlet that is
properly installed and grounded.
CAUTION
This unit is equipped with a 3-prong plug for your
safety. If the wall outlet is a grounded 3-hole type,
the unit will be grounded automatically.
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.

-7-
4. OPERATION
4-1. Control Panel
12
14
15
17
23
20
16
21
22
19
13
2
3
1
6
7
9
11
8
10
4
5
18

-8-
4-2. Explanation of Control Panel
1. DISPLAY. The Display includes a clock and
indicators to tell you time of day, cooking time
settings and cooking functions selected.
2. Popcorn. Touch this pad when popping popcorn
in your microwave oven.
3. Potato. Touch this pad to cook up to 4 potatoes
without entering a cook time or power.
4. Frozen Entree. uch this pad to cook a 10 to 20
ounce (284 to 567 g) frozen entree without
entering a cook time or power.
5. Auto Cook. Tuch this pad to cook microwavable
foods without entering a cook time or power.
6. Soften. Touch this pad to soften butter, icecream,
cream cheese,frozen juice.
7. Melt. Touch this pad to melt butter or
margarine, chocolate,cheese,marshmallow.
8. Time. Touch this pad followed by number pads to
set a cooking time.
9. NUMBER- Touch number pads to enter cooking
time, power level, quantities or weights.
10. Less. Touch this pad to subtract ten seconds of
cooking time each time you press it.
11. Light On/Off. Touch this pad to turn the cooktop/
countertop light on or off.
12. Pizza. Touch this pad to reheat one or several
slices of pizza without entering a cook time or
power.
13. Auto Reheat. Touch this pad to reheat
microwavable foods without entering a cook time
or power.
14. Time Defrost. Touch this pad to set a defrost
time.
15. Auto Defrost. Touch this pad followed by
number pads to thaw frozen meat by weight.
16. Power Level. Touch this pad to select a cooking
power level.
17. Clock. Touch this pad to enter the time of day.
18. START Enter. Touch this pad to start a function.
If you open the door after oven begins to cook,
retouch START Enter.
19. STOP Clear. Touch this pad to stop the oven or
clear all entries.
20. Energy Saving. Touch this pad to save energy.
21. More. Touch this pad to add ten seconds of
cooking time each time you press it.
22. Add 30 Sec. Touch this pad to add 30 seconds
of cooking time each time you press it.
23. Vent Hi/Low/Off. Touch this pad to turn the Vent
on or off.
NOTE: If you try to enter incorrect instructions,
you will not hear any tones. Touch STOP Clear and
re-enter the instructions.

-9-
5. WIRING DIAGRAM / KEY MATRIX
5-1. Wiring Diagram
BR
PK
YL
BK
BK
BK
RY8
C/T Lamp
RY9
Vent Slow
RY3
Vent High
RY4
Vent Low
FUSE
SR5
SMPS
1
3
4
5
6
7
8
9
SECONDARY
SWITCH
1
2
BOTTOM
BR
BL
RD
YL
DIODE
BL
H.V.FUSE
H.V.CAPACITOR
H.V.TRANSFORMER
MONITOR SWITCH
WH
RY2
POWER
RY1
Oven Lamp
RV
U
MGT
GN
9
BK BL WH PK BR GY

-10-
5-2. Key Matrix
KEY MATRIX
Turntable On/Off
Power LevelTime CookHold WarmC/T Lamp On/OffStart
13
MoreSensor Cook
time & weight
Defrost
N.AN.A
N.A
N.A
Sensor Popcorn
12
LessSensor ReheatTimer
0
987
11
Melt
654
321
10
SoftenQuick DefrostAdd 30 Sec.Energy SavingClockVent Hi/Low/OffClear
9
8
76543212st
KEY MATRIX

-11-
6. TROUBLESHOOTING
6-1. General Information for Service
GENERAL PRECAUTIONS IN USE
A. Never operate the unit when it is empty.
Operating the oven with no load may shorten the
life of the magnetron. Whenever cooking dry foods
(dried fish, bread, etc.)or a small amount of food,
be sure to put a glass of water into the cooking
compartment. The glass turntable may become
hot after operating, be careful when touching it.
B. Aluminum foil should be avoided because it will
disrupt cooking and may cause arcing. However,
small pieces may be used to cover some parts of
food to slow the cooking. Any aluminum foil used
should never be closer than 1 in. (2.5 cm) to any
side wall of the oven.
TRIAL OPERATION
After installation, the following sequences and
results should be checked carefully.
A. Put a container filled with water (about 1 liter) into
the oven, and close the door tightly.
B. Set cooking time for 10 minutes by touching 1 and
then 0 three times. 1, 0, 0, 0 appears in the display
window.
C. Press the START button
Make sure the cavity light comes on. The unit will
begin cooking and the display window will show
the time counting down by seconds.
D. After about 5 minutes, make sure the primary
interlock switch, the secondary interlock switch
and the interlock monitor switch operate properly
by opening and closing the door several times.
Press the START button each time the door is
closed.
E. Continue operating the unit. Two short beeps and
one long beep will sound when the time is up. The
unit will shut off automatically.
F. Confirm the water is hot.
G. Finally, measure the output power according to
the POWER OUTPUT MEASUREMENT on
page 8.
FEATURES AND SPECIFICATIONS
FEATURES
A. The safety systems incorporated in this model
are:
(1) Primary interlock switch
(2) Secondary interlock switch
(3) Interlock monitor switch
(4) Choke system
(5) Oven cavity thermostat
(Note This thermostat located on the oven
cavity will open and stop the unit from
operation only if a high temperature is reached,
such as, a fire created by overcooking food.)
B. Any one of 10 power output levels ranging 0 W to
1,000 W can be selected by the touch control and
electronic computer system.
C. Cooking time can be displayed on the digital
readout.
D. Three different cooking stages (including defrost)
can proceed from one cooking stage to another.
This is made possible with the memory function of
the microprocessor.

-12-
A. SINCE NEARLY 4,000 VOLTS EXISTS IN SOME
CIRCUITS OF THIS UNIT REPAIRS SHOULD BE
CARRIED OUT WITH GREAT CARE.
The filament leads of the magnetron carry High
Voltage with respect to the ground. Extreme
caution must be exercised. Never plug the unit
into a power source to determine which
component is defective in the high voltage section.
B. TO AVOID POSSIBLE EXPOSURE TO
MICROWAVE ENERGY LEAKAGE, THE
FOLLOWING PRECAUTIONS MUST BE TAKEN
BEFORE SERVICING.
(1) Before the power is applied:
(a) Make sure the primary interlock switch, the
secondary interlock switch and the interlock
monitor switch operate properly by opening
and closing the door several times.
(b) Make sure the perforated screen and the
dielectric choke of the door are correctly and
firmly mounted.
(2) After power is applied:
(a) Make sure the interlock switch mechanism
is operating properly by opening and closing
the door.
(b)
Check microwave energy leakage must be
below
the limit of 5 mW/cm2.
(All service adjustments should be made for
minimum microwave energy leakage
readings).
(3) Do not operate the unit until it is completely
repaired. If any of the following conditions exist,
the unit must not be operated.
(a) The door does not close firmly.
(b) The hinge is broken.
(c) The door seal is damaged.
(d) The door is bent or warped, or there is any
other visible damage on the unit that may
cause microwave energy leakage.
NOTE: Always keep the seal clean.
(e) Make sure that there are no defective parts
in the interlock mechanism.
(f) Make sure that there are no detective parts
in the microwave generating and transmission
assembly (especially waveguide).
(4) The following items should be checked after the
unit is repaired:
(a) The interlock monitor switch is connected
correctly and firmly.
(b) The magnetron gasket is properly positioned
and mounted.
(c) The waveguide and the oven cavity are
intact. (no microwave energy leakage)
(d) The door can be properly closed and the
safety switches work properly.
(e) The unit must stop when the door is opened
or the time is up.
The unit must not be operated with any of the above
components removed or bypassed.
1. Press “Defrost weight/time” for 2 seconds , unit will
display “TEST” and Beep once;
2. The unit will check if the PCB humidity sensor and
PCB thermistor are short or open.
3. If it has an error, it will beep and display an error
code.
4. If the unit is normal , it will beep and display
"PASS".
5.Press “ Clear” to return to Standby mode.
6-2. Safety Caution
6-3 Self diagnosis (humidity Sensor and PCB thermistor check) &
Error code
Error code
F-1
F-2
F-4
Symptom
PCB thermistor short
PCB thermistor open
Humidity sensor open or short

-13-
6-3. Basic Check Summary
Symptom: Dead
Check: Open/Short
Symptom#1(Door is closed): Not
cooking, Not operating V.M, T. T. M.
Check: Open/Short when the door
is closed. (Switch)
Symptom #2(Door is open):
Operating V.M, T. T. M.
automatically
Check: Open/Short when the door
is open. (Switch)
Symptom #1(Door is closed): No
key, Not started, Operating O.L, V.M,
T.T.M.
Check: Open/Short when the door
is closed. (Switch)
Symptom #2(Door is open): Not
turned on O.L
Check: Open/Short when the door
is open. (Switch)
BR
PK
YL
BK
BK
BK
RY8
C/T Lamp
RY9
Vent Slow
RY3
Vent High
RY4
Vent Low
FUSE
SR5
SMPS
1
3
4
5
6
7
8
9
SECONDARY
SWITCH
1
2
BOTTOM
BR
BL
RD
YL
DIODE
BL
H.V.FUSE
H.V.CAPACITOR
H.V.TRANSFORMER
MONITOR SWITCH
WH
RY2
POWER
RY1
Oven Lamp
RV
U
MGT
GN

-14-
6-4. Troubleshooting
No Display or Dead

-15-
6
3
4
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
1When you push any Key, is
there any beeping sound?
Does the display operate?
No
No
Yes
2Is the connector connected
to the PCB?
Power Off
Yes
No Reconnect or
repair the
connector.
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
Is there any beeping sound
in the continuity test between
the power cord and the
connector ?
- Code “L” to Pin1
- Code “N” to Pin3
No
Yes
Check PCB
Go to No. 6 of
this flow chart.
Go to No. 6 of
this flow chart.
Is there any beeping sound
in the continuity test between
the ends of the fuse?
Yes
No Replace the
Fuse.
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
5Is there any beeping sound
in the continuity test between
the ends of the noise filter?
Yes
No Replace the
noise filter.
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
Replace the PCB.
(EBR75341201)

-16-
Keypad Failure

-17-
5
6
1Do only the START key and
EZ-ON keys operate?
(Door should be closed.)
Do the keys operate?
No
Yes
No
2Is there a beeping sound
in the continuity test between
the ends of the latch board?
- Secondary switch
(Door should be closed.)
Power ON
Yes
No Adjust latch
board
(Refer to section
9-1,9-2)
Check PWB
Go to No. 4 of
this flow chart.
3When the door is opened,
is the voltage of the door
sensing part over 4 V?
(CN3 Pin1 and Pin2)
Yes
No
Replace the PCB
(EBR75341201)
Reconnect or
repair the
connector.
Replace the PCB.
(EBR75341201)
4Is the connector connected
to the PCB disconnected or
disassembled?
No
Yes
Replace the keypad?
No

-18-
No Heat / No Cook
BOTTOM
BR
BL
RD
RV
U
GN
DIODE
BL
FUSE
SR5
SMPS
H.V.FUSE
H.V.CAPACITOR
H.V.TRANSFORMER
MONITOR SWITCH
WH
PTC
RD
BK
BK
BK
RY2
POWER
RY5
MGT
SECONDARY
SWITCH
RY4
Vent Low
RY3
Vent High
RY9
Vent Slow
RY7
C/T Lamp
RY7
T/T Motor
RY1
Oven Lamp
YL
YL
PK

2
-19-
1Repeat Door Open and close
at least three times.
Does product operate?
After power on, does the
product operate?
No
No
Yes
Is there any beeping sound
in the continuity test between
TAB1 and TAB2?
No
Yes
PCB
no problem
Alternate
explanation
(refer to the
Note)
3While the product is
operating under EZ-ON start,
is the voltage of both ends
of the D37 over 8 V?
No
Yes
Replace the
Relay 2
4Replace the PCB.
(EBR75341201)
[Note]
If something is caught in the door or in the sealing area, the
microwave oven cannot operate safely. The latch switches
and monitor switch will prevent operation.

-20-
5Is there any beeping sound
in the continuity test between
the ends of the latch board?
(Door should be closed)
Power Off
Yes
No Adjust the latch
board
(Refer to section
9-1,9-2)
7Is the resistance of the high
voltage Transformer out of
range?
Test Point
1. Primary winding: 0.2 ~ 0.5 Ohm
2. Secondary: 50 ~ 120 Ohm
3. Filament winding: 0 Ohm
No
Yes
Replace the
High Voltage
Transformer.
6Is the connector connected
to High Voltage Transformer
assembly disconnected or
disassembled?
No
Yes
Reconnect or
repair
the connector.