LG lmhm2237bd User manual

삼흥
정판
MICROWAVE OVEN
SERVICE MANUAL
MODEL: LMHM2237ST
LMHM2237BD
CAUTION
BEFORE SERVICING THE UNIT, READ THE SAFETY PRECAUTIONS IN THIS MANUAL.
P/NO : MFL06272532
January, 2014
Printed in Korea
Website: http://biz.lgservice.com
삼흥
정판
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 180/60
............................................................................ Bottom TCO : 145/0
............................................................................ Fuse (20A)
............................................................................ Primary Interlock Switch
............................................................................ Secondary Interlock Switch
............................................................................ Interlock Monitor Switch
Magnetron .......................................................... 2M246 - 050GP
Cook Top Lamp ................................................. DC 12V, LED Lamp
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 ............................................ 2914/16” (W) x 17 13/18” (H) x 15 12/16 ” (D)
Oven Cavity Size ............................................... 22 (W) x 115/8” (H) x 14 5/8” (D)
Effective Capacity of Oven Cavity ...................... 2.2Cu.ft.
Accessories ........................................................ Owner’s 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
DOOR OPEN OPEN OPEN CLOSE
CLOSE CLOSE OPEN
DOOR 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.

-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
910 11 12 13 1487654321
21 22 23 24 2515 16 17 18 19 20

-8-
4-2. Explanation of Control Panel
1. AUTO REHEAT Press this button to reheat dinner
plate, soup/sauce, casserole, roll/muffin.
2. AUTO COOK Press this button to cook fresh
vegetables, frozen vegetables, rice, or casseroles.
3. POPCORN Press this button when popping
popcorn in your microwave oven.
4. DEFROST Touch this button to defrost frozen
food.
5. SOFTEN Press this button to soften butter, ice
cream, cream cheese, or frozen juice.
6. MELT Press this button to melt butter or
margarine, chocolate, cheese, or marshmallows.
7. CUSTOM COOK Touch this button to make oven
remember Cook time and Power level.
8. POWER LEVEL Press this button to select a
cooking power level.
9. DISPLAY The Display includes a clock and
indicators to tell you the time of day, cooking time
settings and cooking functions selected.
10. NUMBER Press this button to enter cooking
time, power level, quantities or weights.
11. +, - Touch this button to add or subtract ten
seconds of cooking time each time you touch it.
12. ADD 30 SEC Press this button to control the add
30sec. cook time.
13. START/ENTER Press this button to start a
function. If you open the door after oven begins
to cook, press START/ENTER again.
14. LIGHT HIGH/LOW/OFF touch this button to turn
the cooktop/coutertop light on high/low or off.
15. KIDS MEAL Select type of dish to reheat HOT
DOG, MAC & CHEESE or CHICKEN
NUGGETS.
16. CLOCK Press this button to enter the time of
day.
17. TIMER
18. COOK TIME Press this button to set a cooking
time.
19. CUSTOM SET Touch this pad to change the
oven's default setting for sound, clock, disply
speed, and defrost weight.
20. TURNTABLE ON/OFF
21. ENERGY SAVING Press this button to save
energy.
22. STOP/CLEAR Press this button to stop the oven
or clear all entries.
23. VENT ON/OFF touch button to turn the vent on
slow or off.
24. VENT 4 SPEED Touch button to change vent
speed.
25. VENT AUTO TIMESET Touch this button to set
ventilation time. (1, 3, 5, 10, and 30 minutes.)

-9-
5. WIRING DIAGRAM / KEY MATRIX
5-1. Wiring Diagram
BK
C. L.
RD
BN
YL
YL
21VAC
CAPACITOR
BK
PK
WH
BN
GY
WH
RD
WH
RD
BNYL
HW
WH
HW
H.V.FUSE
180 60
356 140
WH
WH
YL
PK
(LED)
YL
WOL
HGIH
OB
RUT
VL
12345678
SLOW
WH
OG
YL
BL
YLPK
PK GY BL
RD
7
4
10
RD
BN
BL
12345678
BK
WH

-10-
5-2. Key Matrix
Turntable On/Off
Power LevelTime CookHold WarmC/T Lamp On/OffStart
13
MoreSensor Cook
time & weight
Defrost
N.A N.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 0three 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)
BK
C. L.
RD
BN
YL
YL
21VAC
CAPACITOR
BK
PK
WH
BN
GY
WH
RD
WH
RD
BNYL
HW
WH
HW
H.V.FUSE
180 60
356 140
WH
WH
YL
PK
(LED)
YL
W
OL
HGIH
OB
R
UT
VL
12345678
SLOW
WH
OG
YL
BL
YLPK
PK GY BL
RD
7
4
10
RD
BN
BL
12345678
BK
WH

-14-
6-4. Troubleshooting
No Display or Dead
Symptom: Dead
Check: Open/Short
Symptom: Dead
Check: Open/Short
Symptom: No display
Check: connection
BK
C. L.
RD
BN
YL
YL
21VAC
CAPACITOR
BK
PK
WH
BN
GY
WH
RD
WH
RD
BNYL
HW
WH
HW
H.V.FUSE
180 60
356 140
WH
WH
YL
PK
(LED)
YL
W
OL
HGIH
OB
R
UT
VL
12345678
SLOW
WH
OG
YL
BL
YLPK
PK GY BL
RD
7
4
10
RD
BN
BL
12345678
BK
WH

-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.
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.
5Is there any beeping sound
in the continuity test between
the ends of the noise filter?
Yes
No Replace the
noise filter.
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
BK
C. L.
RD
BN
YL
YL
21VAC
CAPACITOR
BK
PK
WH
BN
GY
WH
RD
WH
RD
BNYL
HW
WH
HW
H.V.FUSE
180 60
356 140
WH
WH
YL
PK
(LED)
YL
WOL
HGIH
OB
RUT
VL
12345678
SLOW
WH
OG
YL
BL
YLPK
PK GY BL
RD
7
4
10
RD
BN
BL
12345678
BK
WH

-19-
1Repeat Door Open and close
at least three times.
Does product operate?
After power on, does the
product operate?
No
No
Yes
2Is 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 D35 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.