LG LTM9020B Service Manual Download Page 26 | Manualshive

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NOTE: A MICROWAVE ENERGY LEAKAGE TEST MUST ALWAYS BE PERFORMED WHEN THE UNIT IS

SERVICED FOR ANY REASON.

(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) The buzzer does not sound or continues to sound.

(4) 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 flicker.
(8) Some of the indicators do no light up.
(9) The clock does not keep time properly.

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Summary of Contents for LTM9020B

Page 1: ...MICROWAVE OVEN SERVICE MANUAL MODEL LTM9020W LTM9020B CAUTION BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL http www lgservice com ...

Page 2: ... 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 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 pr...

Page 3: ...ions in Use 5 4 Trial Operation 5 5 Features and Specifications 6 7 6 Overall Circuit Diagram 8 9 7 Operating Procedures 10 11 8 Procedure for Measuring Microwave Energy Leakage 12 13 9 Disassembly Instructions 14 17 10 Interlock Continuity Test 18 11 Test and Checkout Procedures and Troubleshooting A Test Procedures 19 22 B Checkout Procedures 23 25 C Troubleshooting 26 31 12 Exploded View 32 38 ...

Page 4: ...Go to step 3 and follow all steps in order ADJUST THE LATCH AND SWITCH CLOSING 3 Loosen the two screws holding the plastic latch board as shown 4 With the oven door closed tightly move the latch board upward toward the top of the oven and or away from the door latch until the gaps are less than 1 64 0 5 mm Hold the latch board tightly in this position until you check the sequence of the switches i...

Page 5: ... 4 LATCH LATCH BOARD 0 1 64 0 1 64 Latch Board Secondary Interlock Switch A Interlock Monitor Switch Primary Interlock Switch Figure 1 a Figure 1 b ...

Page 6: ...rs in the display window D Touch the START key Make sure the cavity light comes on The unit will begin cooking and the display window will show the time counting down by seconds E After about 5 minutes make sure the primary interlock switch the secondary interlock switch and the interlock monitor and oven lamp switch operate properly by opening and closing the door several times Touch the START ke...

Page 7: ...al readout And MWO mode and Toaster mode can be displayed to avoid confusion D Three different cooking stages can be set The oven remembers three cooking stages and changes from one cooking stage to another This is made possible with the memory function of the microprocessor Toaster A The safety systems incorporated in this toaster are 1 Toaster door switch 2 Toaster thermostat Note This thermosta...

Page 8: ...Thermostat Open at 145 C 5 C Close at 60 C 5 C Magnetron 2M214 High Voltage Capacitor Capacitor 0 95µF 2 1KV Ac High Voltage Diode 350mA 9 0KV Cavity Lamp 125V 20W Timer Digital up to 99 mm 99 sec in each cooking stage Tray Tempered Safety Glass Thermistor NTC 150 C 3 Crumb Tray Crumbs of bread lay on it Overall Dimensions 215 16 W x 123 16 H x 169 16 D Oven Cavity Size 131 2 W x 811 16 H x 143 16...

Page 9: ...CTION 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 Figure 3 ...

Page 10: ... BOARD 9 Figure 4 STOP CLEAR START CLOCK Ez ON KITCHEN TIMER AUTO DEFROST DINNER PLATE POPCORN POTATO DARKER LIGHTER 1 7 2 3 4 5 6 8 9 0 STOP CLEAR TOAST BAGEL START COOK TIME POWER Toaster Key BEVERAGE FRESH VEGETABLE FROZEN ENTREE ...

Page 11: ...u time of day cooking time settings and cooking functions selected 2 STOP CLEAR Touch this pad to stop the oven or clear entries 3 START Touch this pad to start all entries except the Auto Cook and Add Minute function which start automatically and to turn Child Lock on or off 4 AUTO COOK Touch this pad to select programming food items 5 Ez ON Touch this pad to cook at 100 cook power for 1 minute t...

Page 12: ...r food in decimal increments from 0 1 to 6 0 pounds 4 Touch START 5 At beeping turn food over by following the instructions in the manual 6 After turning food over touch START to resume defrosting 6 TIMED COOKING 1 Touch STOP CLEAR 2 Touch COOK TIME 3 Touch number for cooking time 4 Touch POWER 5 Touch number for cooking power level 6 Touch START 7 MULTI STAGE COOKING 1 Touch STOP CLEAR 2 Touch CO...

Page 13: ...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 Electromagnetic energy leakage monitor NARDA 8100B HOLADAY HI 1501 600cc glass beaker Glass thermometer 100 C B MEASURING MI...

Page 14: ...information on the service invoice 2 Should the microwave energy leakage not be more than 1mW cm sq after determining that all parts are in good condition functioning properly and genuine replacement parts which are listed in this manual have been used 3 At least once a year have the electromagnetic energy leakage monitor checked for calibration by its manufacturer G POWER OUTPUT MEASUREMENT 1 Fil...

Page 15: ...VING OUT CASE Figures 7 1 Remove four screws from the rear section 2 Remove one screw from the side section 3 Push the outer case back about 1 inch 3cm 4 Lift the case from the set B REMOVING TOASTER ASSEMBLY Figure 8 CAUTION BE CAREFUL HOT SURFACE AFTER TOASTING ENTIRE TOASTER S SURFACES ARE VERY HOT BEFORE SERVICING COOL DOWN THE TOASTER PARTS ENOUGH NOT TO GET BURNT 1 Open the door 2 Remove 2 s...

Page 16: ...mally 2 After replacing the door check for microwave energy leakage with a survey meter Microwave energy must be below the limit of 5 mW cm sq 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 no play between the inner door surface and oven frame assembly If the door assembly is no...

Page 17: ...etron To prevent microwave leakage tighten the mounting screws properly making sure there is no gap between the waveguide and the magnetron E REMOVING THE TURNTABLE MOTOR Figure 11 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 lea...

Page 18: ...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 from the 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 to the oven asse...

Page 19: ...hould indicate an closed circuit When 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 closed circuit in the door open condition Wh...

Page 20: ...oved MAGNETRON Wire leads removed 1 Measure the resistance Select the ohm scale on the meter Primary winding Secondary winding Filament winding 2 Measure the resistance Select the ohm scale on the meter Primary winding to ground Filament winding to ground 1 Measure the resistance Select the ohm scale on the meter Filament terminal 2 Measure the resistance Select the ohm scale on the meter Filament...

Page 21: ... 1 Check DC 9V battery before performing tests 2 Select the DCV scale on the meter 3 Using the meter battery and jump wire connect the items as illustrated in figures Terminal to case Normal Approximately 9V Normal Approximately 0V or a value displayed in mV Will be seen NOTE When testing the magnetron be sure to install the magnetron gasket in the correct position and be sure that the gasket is i...

Page 22: ...ems as illustrated in Figure 14 b This has the positive side of the battery connected to the cathode of the diode 3 The diode should be forward biased therefore a voltage reading of approximately 4 7 VDC to 6 4 VDC will be read depending on meter battery strength etc Note If the meter leads were reversed a negative voltage of the same amount would be seen STEP 3 Test the diode for reverse biasing ...

Page 23: ...c 3 8 sec 14 sec 4 10 sec 12 sec 5 12 sec 10 sec 6 14 sec 8 sec 7 16 sec 6 sec 8 18 sec 4 sec 9 20 sec 2 sec 10 22 sec 0 sec Normal A Approximately 95 120 ohms B Approximately 10 25 ohms Abnormal Infinite Normal Approx 2 5 3 5 Kohms Abnormal Infinite or several ohm 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 CO...

Page 24: ... 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 the defective switches and the fuse at the same time After replacing the defective switches with new ones make sure that they are correctly connected Check for microwave ene...

Page 25: ...ive RELAY or poor connection of relay Replace RELAY or correct the connection NO Microwave Oven NO YES NO NO YES YES PROBLEM A FAN motor and indicator light turn 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 GOOD Replace the circuit board PROBLEM B FAN motor and indicator light turn on When the doo...

Page 26: ...e high voltage Systems the interlock switches the door sensing and the relay check good 2 The unit with a normal relay continuously operates 3 The buzzer does not sound or continues to sound 4 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 flicker 8 Some of the indicators do ...

Page 27: ...working on this panel to discharge any static charge built up in your body Micom model only CONDITION Toaster and Microwave oven does not work Inserting many plugs into one outlet and using them at the same time blown fuse or breaker 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 Spark...

Page 28: ...ight does not turn on 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 PCB assembly Loose connection Replace PCB assembly Connect them tightly Check the conn ection be...

Page 29: ...y monitor switches and RELAY RY2 of 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 wire lead connected from transformer to the high voltage capacitor and operate the unit Replace fuse 2 Fuse does not blow No continuity Continuity No continuity Defective power supply cord Replace power supply cord Def...

Page 30: ...ures set but microwave oven does not start cooking while desired program times are set and START pad is touched TROUBLE 4 Microwave oven seems to be operating but little heat is produced in oven load NOTE Simple test of power output conducted by heating one liter water for one min if available Minimum 8 5 C temperature rise is normal condition CONDITION CHECK RESULT CAUSE REMEDY Output is low Lowe...

Page 31: ...relay 2 and check continuity relay 2 Operate the unit Abnormal Defective high voltage capacitor Replace high voltage capacitor Normal Check high vol tage capacitor Abnormal Defective high voltage diode Replace high voltage diode Normal Check high vol tage diode Abnormal Defective magnetron Replace magnetron Check magnetron TROUBLE 5 No microwave oscillation even though oven lamp and fan motor run ...

Page 32: ...k the continuity of heater Check the connection between CN3 connector and PCB assembly 2 F 2 code Attached Seperated 2 wire leads are shorted contact Apart 2 wire leads as far as possible Check the CN3 connector whether 2 wire leads are attached Defective PCB assembly Replace PCB assembly 3 HOT code Internal temperature is over 220 deg c Allow the toaster to cool down Automatically fan will blow f...

Page 33: ... 32 INTERIOR PARTS OVEN CAVITY PARTS BASE PLATE PARTS LATCH BOARD PARTS DOOR PARTS TOASTER PARTS EXPLODED VIEW INTRODUCTION ...

Page 34: ... 33 13536A 13552A 13213A 13581A 14890A 14970A 14026A 15006A 268712 13581S WTP004 23506A 13720D DOOR PARTS ...

Page 35: ... 34 WTP013 35889A 34370T 36549S 33390G WTT010 WTT020 WSZ185 33052A 33112U OVEN CAVITY PARTS ...

Page 36: ... 35 WSZ085 56912B 55262A 44510A 43500A 466001 466003 466001 43501A LATCH BOARD PARTS ...

Page 37: ... 36 56851D 54810C WTT024 56930V 56324A 50CZZH WSZ002 WTT028 268711 WTT037 568771 WSZ002 56411A 50FZZA WTT028 54974S WSZ002 55900A 55006F 56549F WSZ002 OVEN INTERIOR PARTS ...

Page 38: ... 37 56170D 63303A WSZ002 WTT021 WTT028 647781 65006A 63302A WTT021 BASE PLATE PARTS ...

Page 39: ...T028 768771 WTT021 75264A 73808A 75026G 74830A 74510L 466001 73550D 73720D 74830A 73300A 749701 73390M 73550H 75026C 74970A 74970A 749321 749322 75993M 73213A 73552A 73572A 73550L 73740A 768711 739302 739301 753002 753003 753001 749702 TOASTER PARTS ...

Page 40: ... 43 SCHEMATIC DIAGRAM OF P C B ...

Page 41: ...PRINTED CIRCUIT BOARD 44 ...

Page 42: ... 45 ...

Page 43: ...P NO 3828W5S3279 Apr 2003 Printed in Korea ...

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