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MICROWAVE OVEN

SERVICE MANUAL

MODEL: MB-3949G

CAUTION

BEFORE SERVICING THE UNIT, READ THE SAFETY PRECAUTIONS IN THIS MANUAL.

Website: http://biz.lgservice.com

P/NO : MFL30190712

March, 2010

Printed in Korea

삼

흥

정

판

Internal Use Only

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Summary of Contents for MB3949G

Page 1: ...VEN SERVICE MANUAL MODEL MB 3949G CAUTION BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL Website http biz lgservice com P NO MFL30190712 March 2010 Printed in Korea 삼 흥 정 판 Internal Use Only ...

Page 2: ... 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 ...

Page 3: ...ON 4 4 SERVICE INFORMATION 5 1 TOOLS AND MEASURING INSTRUMENTS 5 1 MICROWAVE LEAKAGE TEST 5 1 MEASUREMENT OF MICROWAVE POWER OUTPUT 5 3 DISASSEMBLY AND ADJUSTMENT 5 3 INTERLOCK CONTINUITY TEST 5 7 COMPONENT TEST PROCEDURE 5 8 TROUBLE SHOOTING 5 12 EXPLODED VIEW 6 1 REPLACEMENT PARTS LIST 7 1 CONTENTS LGE Internal Use Only Copyright 2007 LG Electronics Inc All right reserved Only for training and s...

Page 4: ... Power level Max Full power throughout the cooking time Med High approx 80 of Full power Medium approx 60 of Full power Defrost approx 40 of Full power Low Warm approx 20 of Full power Owner s manual Glass tray Roller Rest Grill rack 1 1 ITEM MODEL Power Requirement Power Output Microwave Frequency Magnetron Timer Outside Dimensions Cavity Dimensions Net Weight Shipping weight Control Complement R...

Page 5: ...ron 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 from danger in ordinary use extreme care should be taken dur...

Page 6: ...ring or after cooking of the Grill and Combination mode This glass is very hot during heater operating 9 Do not operate the oven at microwave and combination mode with Grill rack placed in the cavity when the oven is empty EARTHING INSTRUCTIONS This microwave oven is designed to be used in a fully earthed condition It is imperative therefore to make sure it is properly earthed before servicing WAR...

Page 7: ...OK Used to select the auto cook 5 AUTO DEFROST Used to select the auto weight defrost 6 CLOCK Used to set the time of day 7 COOK TIME Used to cook food for a desired time 8 STOP CLEAR Used to stop oven and clear all entries except time of day 9 COMBI Used to select the combination cooking 10 QUICK DEFROST Used to select the quick defrost 11 MORE LESS Used to change the cooking time desired weight ...

Page 8: ... COOKING 5 GRILL COOKING 6 COMBINATION COOKING 7 AUTO WEIGHT DEFROST 8 CHILD LOCK This oven has a CHILD LOCK feature TO SET CHILD LOCK TO CANCEL CHILD LOCK 9 AUTO COOK 10 MULTI STAGE MICROWAVE COOKING 1ST STAGE 2ND STAGE 11 QUICK WEIGHT DEFROST 12 MORE AND LESS Stop Clear Clock Clock Time minutes Clock Time hour Stop Clear Power Start Time Stop Clear Grill Start Time Stop Clear Combi Start Time St...

Page 9: ...SCHEMATIC DIAGRAM 4 3 LGE Internal Use Only Copyright 2007 LG Electronics Inc All right reserved Only for training and service purposes ...

Page 10: ...n WHEN THE OVEN IS SET AT ANY LEVEL EXCEPT MAXIMUM The micom controller controls the ON OFF time of relay 2 by the applied signal to vary the average output power of microwave oven as POWER LEVEL refer to page 1 1 WHEN THE DOOR IS OPENED DURING COOKING Both the primary switch and relay 2 are cut off primary winding voltage of the high voltage transformer ON OFF of relay 2 is coupled electrically w...

Page 11: ...nter 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 5cm 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 s...

Page 12: ...erwise 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 is moved horizontally along the oven surface this may possibly cause probe damage RECORD KEEPING AND NOTIFICATI...

Page 13: ...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 thd 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 t...

Page 14: ... 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 ...

Page 15: ...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 cuttin...

Page 16: ... 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 c...

Page 17: ...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 indicat...

Page 18: ... 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 Filament terminal 2 Measure the resistance Ohm meter scale Rx1000 Filament to chassis Approx 1 4 ohm Approx 90 ohm Less than 1 o...

Page 19: ...r scale Rx10000 Measure the continuity Reverse Ohm meter scale Rx10000 Normal Momentarily indicates several ohms and then gradually returns to infinite Normal Infinite Normal Continuity Abnormal Infinite Normal Infinite 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 ...

Page 20: ... 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 Check for P C B connector Normal Abnormal 1 3 5 Relay 2 Relay 1 Cooking Start OFF Cooking Start OFF 0 C Approx 90 C Approx...

Page 21: ... Normal Approx 100 200 Ω Abnormal or several Ω 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 A B C A B A C 40 60Ω 300 500Ω LGE Internal Use Only Copyright 2007 LG Electronics Inc All right reserved Only for t...

Page 22: ...nd 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 occurring Inconsistent intensity of microwave by their characteristics 1 Wrap the thinner part with aluminum foil 2 Use plastic wrap or lid 3 Stir once or twice while ...

Page 23: ...n of the monitor switch Replace primary and monitor switches Check continuity of monitor switch with door closed Check continuity of primary switch with door opened No continuity Disconnect one side of the wire lead connected from transformer to the high voltage capacitor and operate the unit No continuity Continuity Shorted contact at the primary switch Replace primary and monitor switches Fuse b...

Page 24: ...Abnormal Abnormal Normal Defective fan motor Defective oven lamp Replace fan motor Replace oven lamp Loose connection Connection then tightly CONDITION CHECK RESULT CAUSE REMEDY Output is low Lower than 90 of rating voltage Normal Normal Abnormal Abnormal Measure the output power Disconnect the wire leads from relay 2 and check on and off time with multitester Defective P C B assembly Replace P C ...

Page 25: ...high voltage transformer Check H V transformer normal normal Abnormal Defective high voltage Diode Replace high voltage Diode Check H V diode Abnormal Defective high voltage capacitor Replace high voltage capacitor Check H V capacitor Abnormal Defective magnetron Replace magnetron Check Magnetron TROUBLE 4 No microwave oscillation even though oven lamp and fan motor run LGE Internal Use Only Copyr...

Page 26: ...CK RESULT CAUSE REMEDY Output is full when you set lower power level Abnormal Disconnect the wire leads from relay 2 and check continuity relay 2 Operate the unit Defective P C B assembly Replace P C B assembly LGE Internal Use Only Copyright 2007 LG Electronics Inc All right reserved Only for training and service purposes ...

Page 27: ...INTERIOR PARTS BASE PLATE PARTS LATCH BOARD PARTS CONTROL PANEL PARTS DOOR PARTS OVEN CAVITY PARTS MAY000 MFL552 OWNERS MANUAL 6 1 EXPLODED VIEW INTRODUCTION EV MODEL ...

Page 28: ... 6 2 13552A 13213A 13581A 13720D 14970A 14026A 13536A 14890A DOOR PARTS EV ...

Page 29: ... 6 3 23506A 23572A 24510L 250201 24970A 268711 WTT028 24781M CONTROL PANEL PARTS EV ...

Page 30: ... 6 4 33390G 35889A WSZ185 WTT021 33112U 34810H 34810H 44360A 35300A WNH001 WTP013 36549S 33052M WTT010 35026G 33808A Button Head Torx style 2 OVEN CAVITY PARTS EV ...

Page 31: ... 6 5 466001 466003 WSZ085 466001 43500A 948503 56912B 55262A 43501A LATCH BOARD PARTS EV ...

Page 32: ... 6 6 WTT028 WTT037 50CZZH 54810C 948501 56851D 55900A 56549F 54974S WSZ002 568771 56930V 56411A WTT028 56324A WSZ062 50FZZA 56201A WSZ002 WTT028 55238A WSZ002 WSZ002 56901A INTERIOR PARTS EV ...

Page 33: ... 6 7 56170D 63302A 63303A WTT021 WSZ002 65006B 65006B 948502 BASE PLATE PARTS EV ...

Page 34: ......

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