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LG LMVM1945SB, Service Manual, Page: 15 / 46

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LG LMVM1945SB Service Manual Download Page 15

IMPORTANT NOTES:

UNIT MUST BE DISCONNECTED FROM ELEC-
TRICAL OUTLET WHEN MAKING REPAIRS, RE-
PLACEMENTS,  ADJUSTMENTS  AND  CONTIN-
UITY CHECKS.
WHEN RECONNECTING THE WIRE LEADS TO
ANY PART, MAKE SURE THE WIRING CONNE-
CTIONS AND LEAD COLORS ARE CORRECTLY
MATCHED ACCORDING TO THE OVERALL CIR-
CUIT DIAGRAM. (ESPECIALLY SWITCHES AND
HIGH VOLTAGE CIRCUIT.)

A.  REMOVING POWER AND CONTROL

CIRCUIT BOARD (Figures 1, 2 and 3)

(1) Remove a screw securing the control panel

assembly to the oven cavity.

(2) Remove the control panel with pushing it upward.
(3) Remove the connector (CN1) and wire leads

(Relay2) from the circuit board.

(4) Remove 3 screws securing the circuit board. 

(5)  Remove the circuit board from the control bracket 

carefully.

7-4

Figure 2

Control Bracket

Figure 3

 Circuit Board

DISASSEMBLY INSTRUCTIONS

Figure 1

 Control Panel

Screw

(CN2)

(CN4)

(CN5)

(RY2)

(CN1)

(CN6)

(CN7)

Power 
Transformer

Summary of Contents for LMVM1945SB

Page 1: ...MICROWAVE OVEN SERVICE MANUAL MODEL LMVM1945SW BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL LMVM1945SB LMVM1945SBQ LMVM1945T CAUTION website http www lgservice com ...

Page 2: ...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 ove...

Page 3: ...M 5 1 MATRIX CIRCUIT FOR TOUCH KEY BOARD 5 2 GENERAL INFORMATION FOR SERVICE 6 1 GENERAL PRECAUTIONS IN USE 6 1 TRIAL OPERATION 6 1 FEATURES AND SPECIFICATIONS FEATURES 6 1 SERVICE INFORMATION 7 1 PRECAUTIONS AND REPAIR SERVICE TIPS 7 1 MICROWAVE LEAKAGE TEST 7 2 POWER OUTPUT MEASUREMENT 7 3 DISASSEMBLY INSTRUCTIONS 7 4 INTERLOCK SYSTEM 7 11 INTERLOCK CONTINUITY TEST 7 13 TEST AND CHECKOUT PROCEDU...

Page 4: ... at 110 C 5 C Close at 0 C 5 C Fuse 20A Primary Interlock Switch Secondary Interlock Switch Interlock Monitor Switch Inverter 120 V Magnetron 2M261 Cook top Lamp 125 V 20 W 2EA Halogen Cavity Lamp 125 V 20 W Halogen Timer Digital up to 99 mim 99 sec in each cooking stage Tray Tempered Safety Glass Overall Dimensions 2915 16 W x167 16 H x155 8 D Oven Cavity Size 231 2 W x103 16 H x141 2 D Effective...

Page 5: ... 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 fro...

Page 6: ...d at all times In the event of an electrical short circuit grounding reduces the risk of electrical shock The plug must be plugged into an outlet that is properly installed and grounded BEFORE YOU BEGIN READ THE FOLLOWING INSTRUCTIONS COMPLETELY AND CAREFULLY 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 gro...

Page 7: ...CONTROL PANEL 4 1 OPERATING INSTRUCTIONS 17 19 21 25 26 18 20 22 27 23 24 2 3 4 8 10 11 13 5 7 6 9 12 14 16 15 1 28 ...

Page 8: ...OST This pad provides you with the RAPID defrosting method for 1 0 pound ground beef 15 HOLD WARM Touch this pad to keep hot cooked foods warm in your microwave oven for up to 99 minutes 99 seconds 16 CUSTOM SET Touch this pad to change the oven s default settings for clock set sound display speed and defrost weight 17 TIMER Touch this pad to set the kitchen timer 18 LIGHT TIMER Touch this pad to ...

Page 9: ...5 1 SCHEMATIC DIAGRAM OVERALL CIRCUIT DIAGRAM ...

Page 10: ...5 2 MATRIX CIRCUIT FOR TOUCH KEY BOARD ...

Page 11: ... 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 Touch the START key each time the door is closed E Continue operating the unit Two short and a long beep sound signal is heard when the time is up The unit will shut off automatically F Confirm the wat...

Page 12: ...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 e...

Page 13: ... of the microwave radiation leakage emitted by the microwave oven should not exceed 1mW cm sq And always start measuring of an unknown field to assure safety for operating personnel from radiation leakage NOTE The standard is 5mW cm sq while in the customer s home 1mW cm sq stated here is manufacturer s own voluntary standard for units in customer s home EQUIPMENT TESTER VOLTS DC AC Ohmmeter Micro...

Page 14: ...l have been used 3 At least once a year have the electromagnetic energy leakage monitor checked for calibration by its manufacturer 1 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 2 The water is contained in a cylindrical borosilicate glass vessel having a...

Page 15: ...LTAGE CIRCUIT A REMOVING POWER AND CONTROL CIRCUIT BOARD Figures 1 2 and 3 1 Remove a screw securing the control panel assembly to the oven cavity 2 Remove the control panel with pushing it upward 3 Remove the connector CN1 and wire leads Relay2 from the circuit board 4 Remove 3 screws securing the circuit board 5 Remove the circuit board from the control bracket carefully 7 4 Figure 2 Control Bra...

Page 16: ...ng the screws 1 or 2 screws securing it to the out case 4 Remove two screws on the left central edge and two screws on the right central edge of Base plate Remove the Mount All from the out case by removing one screw securing it to the out case 5 Remove the outcase with disconnecting power cord connector Vent Grille Controller Door Mounting Plate 1 or 2 screws Out Case Mount All Figure 4 7 5 ...

Page 17: ...7 11 Latch Board Secondary Interlock Switch Interlock Monitor Switch Interlock Switch Primary Latch Board WH from Inverter YL from Turntable Motor PK from Cooktop lamp BL from Oven Thermostat Secondary Interlock Switch Monitor Interlock Switch Primary Interlock Switch PK from P C B BL from P C B WH from Inverter RD from Inverter Figure 5 Figure 6 WIRE COLOR SYMBOL COLOR WH BK BR RD BL PK GY N P WH...

Page 18: ...rvice adjustments should be made for minimum microwave energy leakage readings E REMOVING THE INVERTER MODULE Figures 9 Through 11 1 Remove the vent grille by loosening two screws Figure 7 2 Remove the outcase See page 7 5 3 Remove the base plate by loosening four screws Figure 9 4 Disconnect two leadwires of the fan motor assembly 5 Disconnect the leadwire of the inverter PCB and the H V cable of...

Page 19: ...er replacing the door be sure to check that the primary interlock switch the secondary interlock switch and the interlock monitor switch is in good operating normally After replacing the door check for microwave energy leakage with a survey meter Microwave energy leakage must be below the limit of 5mW cm2 With a 275 ml water load H DISASSEMBLING DOOR Figure 15 1 Remove the dielectric choke by usin...

Page 20: ...e mounting plate by loosening mounting plate screws 1 or 2 screws securing it to the back plate See Figure 16 2 Remove MOUNT ALL loosening one screw loosening one screw securing the ventilation Motor and back plate See Figure 17 a 3 Carefully pull the ventilation motor ASS Y out of the microwave oven See Figure 17 b K REPLACING THE HUMIDITY SENSOR 1 Remove the sensor by removing two screws securin...

Page 21: ...rews securing it to the oven cavity Figure 20 4 Disconnect the leadwire from the turntable motor terminals 5 Remove the 1 screw securing the turntable motor to the oven cavity ASS Y Figure 21 NOTES Remove the leadwire from the turntable motor VERY CAREFULLY Be sure to grasp the connector not the wires when removing Wire Leads Turntable Motor 7 10 Figure 19 Figure 20 Figure 21 ...

Page 22: ...djustment of the latch board may not be necessary Go to Steps 5 and 6 to check the sequence of the switches NOTE To correct sequence of the Secondary Interlock Switch Primary Interlock Switch and the Interlock Monitor Switch is very important If any gap is larger than 1 64 0 5 mm you will need to adjust the latch board Go to step 3 and follow all steps in order ADJUST THE LATCH AND SWITCH CLOSING ...

Page 23: ...o to the body of the switches in the following sequence Interlock Monitor Switch Primary Interlock Switch Secondary Interlock Switch NOTE The Interlock Monitor Switch is an added safety check on the Primary and Secondary Interlock Switches If the Primary and Secondary Interlock Switches allow the oven to operate with the door open the Monitor Switch will blow the fuse 7 When you achieve the proper...

Page 24: ... 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 a closed circuit in the door open condition When the door is closed the meter sho...

Page 25: ...removed MAGNETRON Lead wires removed Note Do not try to repair the inverter board nor try to make any adjustments to the board Check wiring to the inverter 1 Unplug the oven s main power supply 2 Visually inspect 4 connectors on the inverter board CN701 CN702 CN703 E701 to see whether there are any signs of failure due to loose wires bad crimping sign of overheating etc 1 Measure the resistance Oh...

Page 26: ...The oven will not generate microwave energy for the first 28 seconds of the sensor cooking cycle 1 Disconnect sensor connector from micom computer board 2 Measure resistance terminal to terminal Select the ohm scale on the meter NOTE MAKE SURE THE LEAD WIRES ARE IN THE CORRECT POSITION WHEN REMOVING THE LEAD WIRES FROM THE PARTS BE SURE TO GRASP THE CONNECTOR NOT THE WIRES NOTE When testing the ma...

Page 27: ...0 150 ohms Abnormal Infinite or several ohms A B 76 ohms B C 22 ohms A C 96 ohms Normal Approx 2 4K ohms Abnormal Infinite or several ohms A RD B BK C WH Relay 2 Normal Approx 125 to 135 ohms Abnormal Infinite or several ohms Normal ON 0 ohm OFF Infinite ohms Abnormal Infinite or several ohms Measure the resistance Ohm meter scale Rx100 RELAY2 Check for continuity of relay 2 with an ohm meter Remo...

Page 28: ...is touched Improper operation of the primary interlock secondary interlock switches and or the interlock monitor switch Malfunction of the high voltage transformer the high voltage capacitor including the diode the magnetron the blower motor or the circuit board PROBLEMS CAUSES NOTES If the fuse is blown by an improper switch operation replace all switches and the fuse at the same time After repla...

Page 29: ...eplace the circuit board Defective FAN motor Defective Wire Assembly Replace FAN motor NO NO YES YES NO NO YES YES GOOD PROBLEM A Oven lamp turns on without touching START key when the door is closed Remove the mate connector of I O CON from the circuit board Does the unit still operate GOOD Replace the circuit board Replace Wire Assembly PROBLEM B Oven lamp turns on When the door is closed and ST...

Page 30: ...he interlock switches the door sensing and the relay check good 2 The unit with a normal relay continuously operates 3 Proper temperature measurement is not obtained 4 The buzzer does not sound or continues to sound 5 Some segments of one or more digits do not light up or they continue to light up or segments light when they should not 6 Wrong figures appear 7 The figures of all digits 8 Some of t...

Page 31: ...control panel Always touch yourself to ground while working on this panel to discharge any static charge built up in your body Micom model only CONDITION Microwave oven does not work Inserting many plugs into one outlet and using them at the same time blown fuse or breaker Microwave oven plug is not inserted tightly Using metallic ware and allowing it to touch the oven wall Sparks occur Inconsiste...

Page 32: ... after setting cooking cycle 11 Display time of day does not reappear when cooking is finished TROUBLE 1 The following visual conditions indicate a probable defective control circuit CONDITION CHECK RESULT CAUSE REMEDY 1 No input can be programmed Continuity No continuity Defective door PCB assembly Loose connection Replace door PCB assembly Connect them tightly Check the conn ection between membr...

Page 33: ... fuse primary monitor switches and P C B Assembly Check continuity of monitor switch with door closed Check continuity of primary switch with door opened Disconnect one side of the lead wires connected from Inverter Replace fuse 2 Fuse does not blow No continuity Continuity No continuity Defective power supply cord Replace power supply cord Defective thermostat Replace thermostat Check continuity ...

Page 34: ...een CN1 connector and control PCB assembly TROUBLE 3 Display shows all figures set but oven does not start cooking while desired program times are set and START pad is touched 3 The display shows F 9 No continuity Continuity Loose connection Connect them tightly Check the connection between magnetron door control PCB and inverter module Abnormal Normal Defective Relay2 Replace control PCB assembly...

Page 35: ...Normal Defective Magnetron Replace Magnetron Decrease in power source voltage with load Suggest customer contact local electric power utility co or qualified electrician Check the power source voltage CONDITION CHECK RESULT CAUSE REMEDY 4 The display shows F 4 Abnormal Normal Loose connection Connect them tightly Check the connection between sensor wire and control PCB Abnormal Normal Defective se...

Page 36: ...8 1 EXPLODED VIEW DOOR PARTS 13552A 13536A 13213A 13581A 14890A 13720D WTT029 WTT027 13806D 14760A 14970A 14026A 13651A WTP004 ...

Page 37: ...8 2 CONTROLLER PARTS I 23506A 268711 ...

Page 38: ...8 3 CONTROLLER PARTS II 268712 WTT028 250201 23572A 24810P 24781M ...

Page 39: ...8 4 OVEN CAVITY PARTS 34960A 33550P WTT021 33530A 34810Q 33112U 34930R 35026G 330342 349311 33390A WTP005 63302A 330341 WTT025 36912C 35230A 535501 WTT022 WTT029 WTT027 WTT029 WTT027 WTT029 WTT027 ...

Page 40: ...8 5 LATCH BOARD PARTS 43500A WSZ085 43501A 466001 466003 466001 44510A ...

Page 41: ...1A 552381 568711 54974S 559002 56549F 56324A 552382 50CZZH 35012A 568772 56851H 53550F 54930F 36549S WTP013 340511 53300B 35889A 34351A 559001 54980A WTT028 WTT028 WTT028 WTT028 WSZ002 WTT028 WTT028 WTT028 WTT028 WTP015 WTT034 WSZ002 ...

Page 42: ...8 7 INTERIOR PARTS II 56501A 36549V 50FZZA 56549B 55262A 568771 56411A 568776 568775 WTT024 WTP005 WTP005 568773 WTT028 568774 56201A 535502 55231C 56804A 56912B WTT024 ...

Page 43: ...8 8 INSTALLATION PARTS 44360A WSZ133 WWZ068 WSZ204 WSZ203 WSZ136 WSZ098 WWZ068 63300M 65862D 65862B 63861A ...

Page 44: ...8 17 SCHEMATIC DIAGRAM OF P C B ...

Page 45: ...8 18 PRINTED CIRCUIT BOARD ...

Page 46: ...P NO 3828W5S3133 June 2003 Printed in Korea ...

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