LG LMAB1240ST Service Manual Download

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MICROWAVE OVEN

SERVICE MANUAL

MODEL: LMAB1240ST

CAUTION

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

P/NO : 3828W5S5057

December, 2004

Printed in Korea

Website: http://us.lgservice.com

Summary of Contents for LMAB1240ST

Page 1: ...MICROWAVE OVEN SERVICE MANUAL MODEL LMAB1240ST CAUTION BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL P NO 3828W5S5057 December 2004 Printed in Korea Website http us lgservice com ...

Page 2: ...r 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...

Page 3: ...SEQUENCE 4 2 SCHEMATIC DIAGRAM I 4 3 SCHEMATIC DIAGRAM II 4 4 CIRCUIT DESCRIPTION 4 5 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 11 EXPLODED VIEW 6 1 REPLACEMENT PARTS LIST 7 1 ...

Page 4: ...rol System Clock 1 00 12 59 Microwave Power for Variable Cooking Power level HIGH Full power throughout the cooking time 9 Saute approx 90 of Full power 8 Reheat approx 80 7 Med High approx 70 6 Medium approx 60 5 Med Low approx 50 4 Defrost approx 40 3 Low approx 30 2 Simmer approx 20 1 Warm approx 10 Owner s manual cooking guide Glass turntable Roller Rest ITEM MODEL Power Requiremen Power Outpu...

Page 5: ...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 Unlike other appliances the microwave oven is high voltage and high current equipment Though it is free from ...

Page 6: ...rts of the unit Do not install the oven next to a conventional surface unit or above a conventional wall oven 5 Use microwave oven in an ambient temperature less than 104 F 40 C 6 Place the microwave oven on a sturdy and flat surface at least 10 cm 4 inches from the wall 7 Place the microwave oven as far away as possible from TV RADIO COMPUTER etc to prevent interference GROUNDING INSTRUCTIONS For...

Page 7: ... pads to enter cook time power level quantities or weights 6 TIME Touch this pad to set a cook time 7 POWER Touch this pad to set a cook power 8 STOP CLEAR It used to stop oven and clear all entries except time day 9 Ez ON You can extend cooking time in multiples of 30 seconds by repeatedly touching this pad during cooking 10 START This feature allows oven to begin functioning 11 CLOCK Touch this ...

Page 8: ...GE 2ND STAGE 7 AUTO DEFROST COOKING 8 CHILD LOCK This oven has a CHILD LOCK feature TO SET CHILD LOCK Touch the STOP CLEAR pad Touch and hold 0 pad LOCK appear on the display TO CANCEL CHILD LOCK Touch and hold 0 pad LOCK disappears STOP CLEAR ex To set 4 30 touch number key 4 3 and 0 NOTE 1 This is a 12 hour clock 2 Clock will operate as long as power is applied to the oven CLOCK CLOCK NUMBER STO...

Page 9: ...PROTECTION FROM MICROWAVE RADIATION FIRE ELECTRICAL SHOCK AND HAZARDS WHEN SERVICING IT IS ESSENTIAL THAT ONLY MANUFACTURER S SPECIFIED PARTS BE USED FOR THE CRITICAL COMPONENTS IN THE SHADED AREAS OF THE SCHEMATIC DIAGRAM NOTICE SINCE THIS IS BASIC SCHEMATIC DIAGRAM THE VALUES OF COMPONENTS AND SOME PARTIAL CONNECTIONS ARE SUBJECT TO CHANGE FOR IMPROVEMENT ...

Page 10: ...TANT FOR PROTECTION FROM MICROWAVE RADIATION FIRE ELECTRICAL SHOCK AND HAZARDS WHEN SERVICING IT IS ESSENTIAL THAT ONLY MANUFACTURER S SPECIFIED PARTS BE USED FOR THE CRITICAL COMPONENTS IN THE SHADED AREAS OF THE SCHEMATIC DIAGRAM NOTICE SINCE THIS IS BASIC SCHEMATIC DIAGRAM THE VALUES OF COMPONENTS AND SOME PARTIAL CONNECTIONS ARE SUBJECT TO CHANGE FOR IMPROVEMENT ...

Page 11: ...C is generated in the secondary of the high voltage transformer which is increased by the action of the high voltage diode and charging of the high voltage capacitor The negative 4 000 Volts DC is applied to the filament of the magnetron 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 o...

Page 12: ...ompliance If the oven operates with the door open the service personnel should Tell the user not to operate the oven Contact the manufacturer and CDRH Center for Devices and Radiological Health immediately NOTE Address on CDRH Office of Compliance HFZ 312 Center for Devices and Radiological Health 1390 Piccard Drive Rockville MD 20850 The service personnel should check all surface and vent opening...

Page 13: ... a false reading may result The test probe must be held by 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 horizontally along the oven surface Hold vertically when testing the top and bottom and horizontally along RECORD KEEPI...

Page 14: ...ssel are at ambient temperature prior to the start 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 the lowest position and the microwave power switched on The time T for the temperature of the water to r...

Page 15: ...oor be sure to check that the primary switch monitor switch and secondary switch operate normally 2 After replacing the door check for microwave energy leakage with a survey meter Microwave energy must be below the limit of 4 mW cm2 with a 275 ml water load 3 When mounting the door assembly to the oven assembly be sure to adjust the door assembly parallel to the chassis Also adjust so the door has...

Page 16: ... the magnetron To prevent microwave leakage tighten the mounting screws properly making sure there is no gap between the waveguide and the magnetron G REMOVING THE TURNTABLE MOTOR 1 Remove the turntable and rotating ring 2 Lay the unit down on its back 3 Remove the turntable motor cover The turntable base cover is easily removed by pinching the eight parts with a wire cutting 4 Disconnect the lead...

Page 17: ...M 1 INTERLOCK MECHANISM The door lock mechanism is a device which has been specially designed to eliminate completely microwave activity when the door is opened during cooking and thus to prevent the danger resulting microwave leakage 2 MOUNTING OF THE PRIMARY MONITOR SECONDARY SWITCHES TO THE LATCH BOARD 3 INSTALLATION AND ADJUSTMENT OF THE LATCH BOARD TO THE OVEN ASSEMBLY Mount the latch board t...

Page 18: ... operation is abnormal make the necessary adjustment or replace the switch 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 the meter should indicate an open circuit...

Page 19: ... THE OVEN COMPONENTS TEST PROCEDURE RESULTS HIGH VOLTAGE TRANSFORMER Wire leads removed MAGNETRON Wire leads removed 1 Measure the resistance Ohm meter scale Rx1 and Rx100 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...

Page 20: ... Terminal to case Measure the continuity Forward Ohm meter 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 ...

Page 21: ...R x 1 Check for continuity of relay 2 with an ohm meter Remove wire leads from relay 2 and operate the unit Measure the resistance Ohm meter scale R x 1 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 Normal A ...

Page 22: ...ug 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 occur Inconsistent intensity of microwave by their characteristics 1 Use plastic wrap or lid 2 Stir once or twice while cooking soup cocoa or milk etc Uneven cooking Ceramic ware trimmed in gold or silver powder is used Avoid using ot...

Page 23: ...light does not turn on after setting cooking cycle 11 Display time of day does not reappear when cooking is finished PROBLEM 1 The following visual conditions indicate a probable defective control circuit CONDITION CHECK RESULT CAUSE REMEDY Everything works as specified Continuity No continuity Still have trouble Defective key membrane assembly Defective PCB assembly Loose connection Defective PCB...

Page 24: ...of primary switch with door opened Disconnect one side of the wire lead connected from transformer to the high voltage capacitor and operate the unit Replace fuse Continuity Malfunction of secondary switch Replace fuse primary monitor secondary switches and RELAY RY2 of P C B Assembly No continuity Check continuity of secondary switch with door opened TROUBLE 2 Oven does not operate at all Display...

Page 25: ...ch with door closed Check fan motor Check oven lamp Abnormal Abnormal Normal Defective fan motor Defective oven lamp Replace fan motor Replace oven lamp Loose connection Connect them 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 ...

Page 26: ... capacitor Replace high voltage capacitor Check high vol tage capacitor Abnormal Defective magnetron Replace magnetron Check magnetron TROUBLE 5 No microwave oscillation even though oven lamp and fan motor run Display operates properly Output is full power 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 as...

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

Page 28: ...DOOR PARTS 6 2 13552A 13213A 13352A 13581A 14970A 14026A 15006A 13536A 13551A EV ...

Page 29: ...CONTROL PANEL PARTS 6 3 24781M 23551A 23550D 24510L 24970A 23551B 268711 WTP018 24930D EV ...

Page 30: ...OVEN CAVITY PARTS 6 4 36549S 33052A WTP013 33390G WTT010 WSZ185 33112U 35889A EV ...

Page 31: ...LARCH BOARD PARTS 6 5 WSZ085 466001 466003 466001 43500A EV ...

Page 32: ...WTT037 55900A 56324A 54810C WTT028 50CZZH 56851D 50FZZA 56912B 55262A 34930W 948501 54980A WSZ002 35012A 55006F Check the Rating Model No Check the Rating Model No Check the Rating Model No Check the Rating Model No EV Model LMAB1240ST Check the rating label of Model and order SVC parts according to the Model No ...

Page 33: ... WTT037 55900A 56324A 54810C WTT028 50CZZH 56851D 50FZZA 56912B 55262A 34930W 948501 54980A WSZ002 35012A 56201A Check the Rating Model No Check the Rating Model No Check the Rating Model No Check the Rating Model No Model LMAB1240ST 01 Check the rating label of Model and order SVC parts according to the Model No ...

Page 34: ...BASE PLATE PARTS 6 8 56170D 63302A 63303A WTT021 WSZ002 WTT028 647781 948502 EV ...

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