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LG LMVM1935SB, Service Manual

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LG LMVM1935SB Service Manual Download Page 32

(3) CHECKOUT PROCEDURES FOR CIRCUIT

BOARD

The following symptoms indicate a defective circuit
board.

1) The start function fails to operate but the high

voltage Systems, the 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 the indicators do no flicker light up.
9) The clock does not keep time properly.

7-20

NOTE:

A MICROWAVE ENERGY LEAKAGE TEST MUST ALWAYS BE PERFORMED WHEN THE UNIT IS
SERVICED FOR ANY REASON.

Summary of Contents for LMVM1935SB

Page 1: ...OVEN SERVICE MANUAL MODEL LMVM1935SB LMVM1935SW LMVM1935SBQ LMVM1935T CAUTION BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL P NO 3828W5S4601 June 2005 Printed in Korea website http us 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: ... 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 12 INTERLOCK CONTINUITY TEST 7 14 TEST AND CHECKOUT PROCEDURES AND TROUBLE SHOOTING 7 15 A TEST PROCEDURES 7 15 B CHECKOUT PROCEDURES 7 18 C TROUBLE SHOOTING 7 21 EXPLODED VIEW 8 1 REPLACEMENT PARTS LIST...

Page 4: ...y Thermostat Open at 110 C 5 C Fuse 20A Primary Interlock Switch Secondary Interlock Switch Interlock Monitor Magnetron 2M248 High Voltage Capacitor Capacitor 1 0µF 2 1 KV AC High Voltage Diode Diode 350mA 9 0 KV Cook top Lamp 125 V 30 W Cavity Lamp 125 V 30 W Timer Digital up to 99 mim 99 sec in each cooking stage Tray Tempered Safety Glass Overall Dimensions 2915 16 W x167 16 D x155 8 H Oven Cav...

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: ...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 3 1 INSTALLATIONS BEFORE YOU BEGIN READ THE FOLLOWING INSTRUCTIONS COMPLETELY AND CAREFULLY 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 aut...

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

Page 8: ...ble OFF will appear in the display See page 11 for more information 14 Q DEFROST This pad provides you with the RAPID defrosting method for 1 0 pound ground beef 15 CUSTOM SET Touch this pad to change the oven s default settings for clock set sound display speed and defrost weight 16 COOK TIME Touch this pad followed by Number pads to set a cooking time 17 MORE Touch this pad to add ten seconds of...

Page 9: ...5 1 OVERALL CIRCUIT DIAGRAM SCHEMATIC DIAGRAM I Check the Model No ...

Page 10: ...5 2 SCHEMATIC DIAGRAM II Check the Model No ADD Noise filter ...

Page 11: ...5 3 MATRIX CIRCUIT FOR TOUCH KEY BOARD ...

Page 12: ...ght 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 Touch the START key each time the door is closed E Continue operating the unit Four long beep sound si...

Page 13: ...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 14: ... microwave leakage after every servicing The power density of the microwave radiation leakage emitted by the microwave oven should not exceed 4 mW cm2 Always start measuring of an unknown field to assure safety for operating personnel from radiation leakage EQUIPMENT TESTER VOLTS DC AC Ohmmeter Microwave survey meter Holaday HI 1500 HI 1501 Narda 8100 8200 600 cc non conductive material beaker gla...

Page 15: ...ve 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 max...

Page 16: ...O 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 Relay6 from the circuit board 4 Remove 3 screws securing the circuit board 5 Remove the FPC connect...

Page 17: ... F P C connector into the terminal socket securely with the fingers 2 Hold the plastic fastener with thumb and forefinger of the other hand and push it slowly into the terminal socket Figure 6 NOTE When reconnecting the F P C connector make sure that the holes on the F P C connector are properly engaged with the hooks on the plastic fastener 3 Lock the level of the plastic fastener into the hook o...

Page 18: ...ng the screws 1 or 2 screws securing it to the out case 4 Remove two screws on the left central edge and one 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 7 6 Vent Grille Controller Door Mounting Plate 1 or 2 screws Out Case Mount All Figure 8 ...

Page 19: ...7 12 WIRE COLOR SYMBOL COLOR WH BK BR RD BL PK GY N P WHITE BLACK BROWN RED BLUE PINK GREY Not Provided Latch Board Secondary Interlock Switch Interlock Monitor Switch Primary Interlock Switch Latch Board WH from H V Transformer YL from Fan Motor WH from Power Cord WH from cooktop lamp Secondary Interlock Switch Monitor Interlock Switch Primary Interlock Switch PK from P C B BL from P C B WH from ...

Page 20: ...djacent parts or it may be damaged 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 After replacing the magnetron check for microwave energy leakage with a survey meter Check microwave energy leakage must be below the limit of 5 mW cm2 All service adjustments should be made for minimum microwave energy lea...

Page 21: ...k 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 G DISASSEMBLING DOOR Figure 17 1 Remove the dielectric choke by using knife blade or small screw driver e...

Page 22: ...mounting plate by loosening mounting plate screws 1 or 2 screws securing it to the back plate See Figure 18 2 Remove MOUNT ALL loosening one screw loosening one screw securing the ventilation Motor and back plate See Figure 19 a 3 Carefully pull the ventilation motor ASS Y out of the microwave oven See Figure 19 b J REPLACING THE HUMIDITY SENSOR For sensor model only 1 Remove the sensor by removin...

Page 23: ...ews securing it to the oven cavity Figure 21 4 Disconnect the leadwire from the turntable motor terminals 5 Remove the 2 screws securing the turntable motor to the oven cavity ASS Y Figure 22 NOTES Remove the leadwire from the turntable motor VERY CAREFULLY Be sure to grasp the connector not the wires when removing 7 11 Wire Leads Turntable Motor Figure 20 Figure 21 Figure 22 ...

Page 24: ...ent 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 Primary Interlock Switch Secondary 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 3 Loos...

Page 25: ... 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 seq...

Page 26: ...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 should i...

Page 27: ...leads are removed 1 Measure the resistance Across the filament terminals of the magnetron with an ohm meter on Rx1 scale 2 Measure the resistance Between each filament terminal of the magnetron and the chassis ground with an ohm meter on high test scale 1 Measure the resistance With an ohm meter on Rx1 scale a Primary winding b Filament winding c Secondary winding 2 Measure the resistance With an ...

Page 28: ...omentarily indicates several ohms and then gradually returns to infinite ohms Abnormal reading Indicates continuity or infinite ohms from the beginning Normal readings Infinite Abnormal reading Indicates continuity Normal readings continuity Abnormal reading Infinite Normal readings Infinite Abnormal reading continuity Ohm meter Figure 25 a Ohm meter Figure 25 b Ohm meter Figure 26 a Ohm meter Fig...

Page 29: ...ately BK RD 4 5 6 2 Kohm RD WH 2 0 3 5 Kohm BK WH 2 0 3 5 Kohm Abnormal Infinite or several FPC CONNECTOR Top Resistance value When touched Less than 400 ohms When not touched More than 1 mega ohm REHEAT DEFROST ENTREE FROZEN Q 7 MORE 3 Ez Oz RICE TIMER POTATO POPCORN VEGETABLE CUSTOM BAKERY HOLD 2 SET WARM 1 6 DEFROST CHOICES CHICKEN POWER LEVEL AUTO LESS N C 4 8 9 STOP 5 0 START CLEAR N C N C N ...

Page 30: ...rlock secondary interlock switches and or the interlock monitor switches are adjusted or replaced 7 18 COMPONENTS TEST PROCEDURES RESULTS RELAY2 Check for continuity of relay 2 with an ohm meter Remove wire leads from relay 2 and operate the unit CAUTION The relay connector 2 must be correctly connected Relay 2 POWER LEVEL 1 2 3 4 5 6 7 8 9 10 4 sec 6 sec 8 sec 10 sec 12 sec 14 sec 16 sec 18 sec 2...

Page 31: ...ll operate Replace the circuit board Replace RELAY1 NO NO YES YES GOOD Defective RELAY1 PROBLEM B FAN motor and oven lamp turn on When the door is closed and START key is touched Measure the voltage at pin NO 35 of U01 Voltage reading 0 Vdc 10 of U03 Voltage reading about 15V Replace the circuit board Defective RELAY1 or poor connection of RELAY1 Replace RELAY1 or correct the connection YES NO NO ...

Page 32: ...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 the indicators do no flicker light up 9 The clock does not keep time properly 7 20 NOTE A MICROWAVE ENERGY LE...

Page 33: ... 2 FUSE See CHECKOUT PROCEDURES FOR FUSE BLOWING on page 7 18 3 OVEN CAVITY THERMOSTAT 1 1 WH RD Measure voltage between pin 1 and pin 3 of connector CN1 Runs Runs 0 120 0 120 120V Replace circuit board Normal circuit board Normal resistance Voltage incorrect Correct connections Runs Runs Runs Measure resistance of touch key board after removing connector S1 See page 7 4 and 7 17 Normal resistance...

Page 34: ...seating Normal circuit board Normal contact Poor contact Normal Primary switch No continuity Adjust or replace door sensing switch Runs Runs Runs Check operation of fan motor when START key is touched Measure resistance of H V capacitor see page 7 16 Resistance incorrect Normal resistance Measure resistance of fan motor Terminal A C 140 to 150 ohm Terminal A B 25 to 40 ohm Resistance incorrect Rep...

Page 35: ...mal circuit board Contact OK Normal contact Correct seating Check contact of connector S1 Check the contact of relay 2 see page 7 18 Resistance incorrect Check the continuity of H V C see page 7 16 Normal H V T Resistance incorrect Normal H V C Abnormal Replace H V D Normal Magnetron Replace Magnetron Normal Normal H V D Check the continuity of H V D see page 7 16 Replace H V C Normal resistance R...

Page 36: ...7 24 Normal circuit board Check normal operation circuit board Replace circuit board Runs PROBLEM F No buzzing when touching the key between stages or at end of cooking 1 ...

Page 37: ... magnetron thermal fuse and oven thermostat Poor contact Replace circuit board Normal circuit board Contact OK Normal contact Correct seating Check contact of connector S1 see page 7 4 Runs Replace ventilation NO runs Normal ventilation Check the contact of magnetron thermal fuse and oven thermostat Check 1 POWER SUPPLY 2 FUSE ...

Page 38: ... 8 1 EXPLODED VIEW DOOR PARTS 1004 W136 1000 1005 1008 1002 1003 W138 W142 1015 1011 1007 1006 1012 EV ...

Page 39: ... 8 2 CONTROLLER PARTS I 2000 2041 2042 2006 EV ...

Page 40: ... 8 3 CONTROLLER PARTS II 2009 W109 2007 2002 2008 2004 EV ...

Page 41: ...3024 3010 3031 W108 W138 W109 W138 3001 W121 3029 3036 3032 5036 3026 W121 6000 5038 3014 6001 3028 W121 3033 3018 W142 W142 8 4 OVEN CAVITY PARTS EV ...

Page 42: ... 8 5 4002 4001 4000 4003 4002 4004 W111 LATCH BOARD PARTS EV ...

Page 43: ... 8 6 INTERIOR PARTS I 5058 5043 5024 3002 3012 3008 3034 5044 3004 W108 W101 5035 W101 5008 W101 5018 5000 W108 5002 5049 W101 5009 3009 5019 W105 EV ...

Page 44: ...ting Model No 5041 W109 5011 5016 5037 5014 W109 5012 5006 W146 3027 5015 W136 W101 W138 5045 5010 5007 5038 5022 5001 5032 5133 5132 MFL1 MFL3 INTERIOR PARTS II II EV Check the rating label of Model and order SVC parts according to the Model No ...

Page 45: ... 8 9 INSTALLATION PARTS 6011 6008 6010 VINYL BAG 6009 EV ...

Page 46: ......

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