LG LRM1250W Service Manual Download Page 25

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5-14

(TROUBLE 3) Display shows 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 operation but little heat is produced in oven load.

1.Setting time

does not count
down when
touching START
pad.

2. Fan motor or

oven lamp do
not turn on.

No continuity.

Continuity.

Defective
secondary switch.

Replace
secondary switch.

Check continuity
of secondary
switch (with
door closed).

Check the con-
nection between
CN1 connector
and PCB
assembly.

Continuity

No continuity

Abnormal

Normal

Defective fan motor.

Defective oven lamp.

Defective PCB
assembly.

Loose connection.

Output is low.

Lower than 90% of
rating voltage.

Normal.

Decrease in power
source voltage
with load.

Suggest customer
contact local
electric power
utility co. or
qualified
electrician.

Check the
power source
voltage.

Disconnect the
wire leads from
relay 2 and
check on and off
time with
multitester.

Measure the
output power.

Abnormal.

Normal.

Defective PCB
assembly.

Defective
magnetron.

Replace PCB
assembly.

Replace
magnetron.

Replace PCB
assembly.

Connection then
tightly.

Replace fan motor.

Defective oven lamp.

Check fan motor.

Check oven lamp.

CONDITION

CHECK

RESULT

CAUSE

REMEDY

CONDITION

CHECK

RESULT

CAUSE

REMEDY

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.

Summary of Contents for LRM1250W

Page 1: ...MICROWAVE OVEN SERVICE MANUAL MODEL LRM1250W CAUTION BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL Website http us lgservice com P NO 3828W5S5129 February 2005 Printed in Korea ...

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: ...4 1 OPERATING SEQUENCE 4 2 SCHEMATIC DIAGRAM 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: ...ox 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 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 Requireme...

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 from...

Page 6: ...ional 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 personal safety this appliance must be fully grounded at...

Page 7: ...juice 8 AUTO REHEAT Touch this pad to reheat without entering a cook time or power 9 AUTO DEFROST Touch this pad to defrost foods by entering weight 10 QUICK DEFROST Touch this pad to defrost foods quickly 11 KITCHEN TIMER Touch this pad to use your microwave oven as a kitchen timer 12 CUSTOM SET Touch this pad to select sound control time of day clock Off or On scroll speed lbs kg choice 13 MORE ...

Page 8: ...ears on the display TO CANCEL CHILD LOCK Touch and hold pad LOCKED disappears 8 MORE LESS The cook time is adjustable by MORE pad or LESS pad 9 AUTO REHEAT NOTE Then the oven will start automatically 10 QUICK DEFROST 11 KITCHEN TIMER 12 FAST BREAKFAST NOTE Then the oven will start automatically 13 CHICKEN CHOICES NOTE Then the oven will start automatically Ez On STOP CLEAR POPCORN NUMBER OF TABLE ...

Page 9: ...en will start automatically 16 AUTO COOK NOTE Then the oven will start automatically 17 CUSTOM SET NOTE Then the oven will start automatically AUTO COOK NUMBER OF TABLE STOP CLEAR CUSTOM SET NUMBER OF TABLE STOP CLEAR MELT NUMBER OF TABLE STOP CLEAR SOFTEN NUMBER OF TABLE STOP CLEAR ...

Page 10: ...SCHEMATIC DIAGRAM 4 4 ...

Page 11: ...oximately 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 12: ...ity 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 NECESSARY MEASURING INSTRUMENTS TESTER VOLTS DC AC Ohmmeter Microwave survey meter Holaday HI 1500 HI 1501 Narda 8100 8200 Inch scale 600 cc non conductive material beaker glass or plastic inside d...

Page 13: ... 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 befween 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 KEE...

Page 14: ...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 order to minimize addition or removal...

Page 15: ...eplacing the 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...

Page 16: ...ter 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 H 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 ...

Page 17: ...RLOCK 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 3 INSTALLATION AND ADJUSTMENT OF THE LATCH BOARD TO THE OVEN ASSEMBLY Mou...

Page 18: ...is closed 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 ...

Page 19: ... THE OVEN HIGH VOLTAGE TRANSFORMER Wire leads removed MAGNETRON Wire leads removed Approx 0 2 0 4 ohm Approx 70 100 ohm Less than 1 ohm Normal Infinite Normal Infinite Normal Less than 1 ohm Normal Infinite PRIMARY TERMINAL FILAMENT WINDING COMPONENTS TEST PROCEDURE RESULTS 1 Measure the resistance Ohm meter scale Rx1 and Rx100 Primary winding Secondary winding Filament winding 2 Measure the resis...

Page 20: ...ormal Momentarily indicates several ohms and then gradually returns to infinite Normal Infinite Normal Infinite Abnormal Continuity Normal Continuity Abnormal Infinite Measure the resistance Ohm meter scale Rx1000 Terminal to case Measure the continuity Forward Ohm meter scale Rx10000 Measure the continuity Reverse Ohm meter scale Rx10000 HIGH VOLTAGE DIODE NOTE Some inexpensive meters may indicat...

Page 21: ...E WIRE LEADS ARE IN THE CORRECT POSITION WHEN REMOVING THE WIRE LEADS FROM THE PARTS BE SURE TO GRASP THE CONNECTOR NOT THE WIRES Measure the resistance Ohm meter scale R x 1 Normal A Approx 85 100 ohm B Approx 10 25 ohm Abnormal Infinite or several ohm Normal Approx 100 150 ohm Abnormal Infinite or several ohm 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 22: ...llic ware for cooking except where noted in the cooking guide Do not use any type of cookware with metallic trimming CAUSE REMEDY TROUBLE SHOOTING CAUTIONS 1 Check grounding before checking for trouble 2 Be careful of the high voltage circuit 3 Discharge the high voltage capacitor See page 2 1 4 When checking the continuity of the switches or of the high voltage transformer disconnect one lead wir...

Page 23: ...ly TROUBLE 1 The following visual conditions indicate a probable defective control circuit 1 Incomplete segments Segment missing Partial segment missing Digit flickering NOTE Slight flickering is normal 2 Colon does not turn on or blink 3 A distinct change in the brightness of one or more numbers in display 4 One or more digits in the display are not lighting 5 Display indicates a number different...

Page 24: ...switches and RELAY RY2 of P C B Assembly Check continuity of monitor switch with door closed Continuity No continuity Shorted contact at the primary switch Replace fuse primary monitor secondary switches and RELAY RY2 of P C B Assembly Check continuity of primary switch with door opened Continuity No continuity Malfunction of secondary switch Replace fuse primary monitor secondary switches and REL...

Page 25: ... Defective PCB assembly Loose connection Output is low Lower than 90 of rating voltage Normal Decrease in power source voltage with load Suggest customer contact local electric power utility co or qualified electrician Check the power source voltage Disconnect the wire leads from relay 2 and check on and off time with multitester Measure the output power Abnormal Abnormal Normal Defective PCB asse...

Page 26: ...uity relay 2 Operate the unit Defective PCB assembly Replace PCB assembly Replace high voltage transformer Defective high voltage capacitor Replace high voltage capacitor Abnormal normal Check high vol tage transformer Abnormal normal Check high vol tage capacitor Defective high voltage diode Replace high voltage diode Abnormal normal Check high vol tage diode Defective magnetron Replace magnetron...

Page 27: ...DOOR CONTROL PANEL BASE PLATE OUTER CASE LATCH BOARD INTERIOR 6 1 EXPLODED VIEW INTRODUCTION EV ...

Page 28: ...6 2 DOOR PARTS 13552A 13213A 13581A 14970A 14026A 13536A 15006A 14890A 13720D 143501 EV ...

Page 29: ...6 3 CONTROLLER PARTS 24781M 23506A 23572A 24510L 24970A 250201 268711 WTP018 EV ...

Page 30: ...6 4 OVEN CAVITY PARTS 33390G WTT010 WSZ185 33112U 35889A 36549S WTP013 33052A 948502 EV ...

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

Page 32: ...RIOR PARTS 568771 WSZ002 WSZ002 WEB001 WSZ002 WSZ085 WTT028 56411A 56930V 56549F 54974S WTT037 55900A 54810C WTT028 50CZZH 56851D 34930W 56324A 55262A 56912B WEB001 948501 948503 WSZ002 35012A 55006F 50FZZA EV ...

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

Page 34: ......

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