LG MB-3071MC Service Manual Download Page 27 | Manualshive

Page: 27 / 38

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5-17

CONDITION

CHECK

RESULT

CAUSE

REMEDY

No microwave
oscillation.

No continuity.

Continuity.

Abnormal

Defective high
voltage
transformer.

Replace high
voltage
transformer.

Normal

Defective PCB
assembly.

Replace PCB
assembly.

Disconnect the
wire leads from
relay 2 and
check continuity
of relay 2.
(Operate the unit)

Check high vol-
tage transformer

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.

(Display operates properly)

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Summary of Contents for MB-3071MC

Page 1: ...MICROWAVE GRILL OVEN SERVICE MANUAL MODEL MB 3071MC CAUTION BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL ...

Page 2: ...tron or other microwave source and make repairs as necessary 1 interlock operation 2 proper door closing 3 seal and sealing surfaces arcing wear 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 transmiss...

Page 3: ... CIRCUIT DESCRIPTION 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 8 COMPONENT TEST PROCEDURE 5 9 TROUBLE SHOOTING 5 13 EXPLODED VIEW 6 1 REPLACEMENT PARTS LIST 7 1 SCHEMATIC DIAGRAM OF P C B 8 1 PRINTED CIRCUIT BOARD 8 2 P C B PARTS LIST 9 1 CONTENTS ...

Page 4: ...hase 3 wire grounded 900 Watts full microwave power IEC705 2 450 MHz 2M214 39 0 99 min 99 sec 530mm W x 315mm H x 394mm D 348mm W x 222mm H x 373mm D 14 9 Kg approx 16 7 Kg approx Touch Control 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 6...

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: ...t and steam are generated because they may damage the electronic or mechanical parts 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 possi...

Page 7: ...K To set the clock 11 HOLD WARM To keep the food warm after the cooking is done 12 STOP CLEAR To stop oven and clear all entries except time of day 13 START One tap allows oven to begin functioning 14 DISPLAY WINDOW Provides indications of the functions selected normally current time displayed 4 1 OPERATING INSTRUCTIONS Oven Front Plate Window Door Screen Door Seal Display Window Control Panel Doo...

Page 8: ...AR pad LOCK appear on the display TO CANCEL CHILD LOCK Touch the pad Touch and hold PARAR BORRAR pad LOCK disappears 9 CUSTOM SET You can select ON OFF of beeper automatic start or manual start of the one touch cook and food weight measurement unit pounds or kilograms Lbs kg of beeper To select automatic language selection To select sound ON OFF To select language speed 4 2 PARAR BORRAR RELOJ NUMB...

Page 9: ...L BLUE YL YELLOW RD RED WH WHITE PK PINK GN GREEN P NO 3854W3A314A 2 2 1 1 O L F M T T M SECONDARY SWITCH SCHEMATIC DIAGRAM CN1 RY2 IMPORTANT SAFETY NOTE THE SHADED AREAS ON THIS SCHEMATIC DIAGRAM INCORPORATE SPECIAL FEATURES IMPORTANT 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 CR...

Page 10: ...roximately 2100 volts AC 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...

Page 11: ...ich is graduated to 600 cc and place the beaker on the center 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 radi...

Page 12: ...e test probe must be removed no faster than 1 inch sec 2 5 cm sec along the shaded area otherwise 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 horizontally along t...

Page 13: ...s 5 K The microwave power output P in watts is calculated from the following formula 4187 x T T is measured while the microwave generator is operating at full power Magnetron filament heat up time is not included about 3 sec The water is stirred to equalize temperature throughout the vessel prior to measuring the final water temperature Stirring devices and measuring instruments are selected in or...

Page 14: ... door 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 cm 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 ha...

Page 15: ...imit of 5 mW cm2 With a 275 ml water load Make sure that gasket is rigidly attached to the magnetron To prevent microwave leakage tighten the mounting screws properly making sure there is no gap between the waveguide and the magnetron 5 5 Magnetron 30 Waveguide Magnetron Gasket Magnetron Dome Magnetron hanger G SUCTION GUIDE MAIN ASSEMBLY NOTE Suction Guide Main ASS Y consists of Latch Board ASS Y...

Page 16: ... Guide Main ASS Y consists of Latch Board ASS Y and Suction Guide ASS Y To repair any of them the Suction Guide Main ASS Y should be removed first 1 Disconnect the leadwire from fan motor 2 Remove the fan 3 Remove the two screws holding the fan motor assembly to the suction guide ass y Fan Motor ASS Y Suction Guide J HIGH VOLTAGE TRANSFORMER REMOVAL 1 Discharge the high voltage capacitor 2 Disconn...

Page 17: ...Leads Turntable Motor M INTERLOCK SYSTEM 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 from the microwave leakage 2 MOUNTING OF THE PRIMARY MONITOR SECONDARY SWITCHES TO THE LATCH BOARD PRIMARY SWITCH ADJUSTMENT DIRECTION MONITOR S...

Page 18: ...losed meter should 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...

Page 19: ...E 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 resistance Ohm meter scale Rx1000...

Page 20: ...0 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: ...h an Multi meter Normal Gill heater Approx 55 Ω at 20 30 C Normal more than 0 5M Ω NOTE Make sure heater is fully cooled when tested NOTE If the fuse is blown check primary the secondary 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 ope...

Page 22: ...EL 1 4 sec 18 sec 2 6 sec 16 sec 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 Approx 200 300 ohm Abnormal Infinite or several ohm Normal Approx 10 20K ohm 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...

Page 23: ...n 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 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 occu...

Page 24: ... does not turn on after setting cooking cycle 11 Display time of day does not reappear when cooking is finished 5 14 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 b...

Page 25: ...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 2 Fuse does not blow No continuity Continuity ...

Page 26: ...ws all figures set but oven does not start cooking while desired program times are set and START pad is touched TROUBLE 4 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 Lower than 90 ...

Page 27: ...y 2 and check continuity of relay 2 Operate the unit Check high vol tage transformer 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 thou...

Page 28: ...nnect the wire leads from relay 2 and check continuity relay 2 Operate the unit Abnormal Malfunction the heater Replace Normal Heater Abnormal Defective PCB assembly Replace PCB assembly Disconnect the wire leads from relay 3 and check continuity relay 3 Operate the unit TROUBLE 6 Grill NOTE Make sure the wire leads correct position When Removing the wire leads from the parts be sure to grasp the ...

Page 29: ...DOOR PARTS SUCTION GUIDE MAIN PARTS CONTROL PANEL PARTS INTERIOR PARTS OVEN CAVITY PARTS BASE PLATE PARTS 6 1 EXPLODED VIEW INTRODUCTION ...

Page 30: ...6 2 13213A 13552A 15006A 13536A 13581A 14026A 14970A 13720D 13352A DOOR PARTS ...

Page 31: ...6 3 26638A 23572A 268711 24781M WTP015 WTT028 24510L 250201 24970A CONTROL PANEL PARTS ...

Page 32: ...6 4 33112U WTT021 948502 33052M 948501 WTP013 368771 WTT011 35889A 33390G 36549S 340511 35026G 348102 33550H 35300A 348101 35264A WSZ002 MWT002 OVEN CAVITY PARTS ...

Page 33: ...6 5 55900A WTT037 56549F WSZ084 54974S 568771 56912B WTT028 466001 466002 466003 43500A 50FZZA SUCTION GUIDE PARTS 56930V ...

Page 34: ...6 6 WSZ002 56411A 56324A WSZ002 56930G 54826A WTT028 INTERIOR PARTS ...

Page 35: ...WSZ002 WTT028 647781 647781 63302L 56170D 63302R 50CZZH 56851D 54810C WSZ002 WTT021 63303L 63303R 6 7 BASE PLATE PARTS ...

Page 36: ...8 1 SCHEMATIC DIAGRAM OF P C B ...

Page 37: ...8 2 PRINTED CIRCUIT BOARD ...

Page 38: ...July 1997 Printed in Korea P NO 3828W5S0450 July 1997 P NO 3828W5S0450 Printed in Korea ...

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