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LG GoldStar MAB745B, Service Manual

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LG GoldStar MAB745B Service Manual Download Page 25

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

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.

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

o

C temperature rise is normal condition.

Summary of Contents for GoldStar MAB745B

Page 1: ...MICROWAVE OVEN SERVICE MANUAL MODEL MAB745W MAB745B CAUTION BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL Website http us lgservice com P NO 3828W5S3839 May 2004 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: ...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 12 EXPLODED VIEW 6 1 REPLACEMENT PARTS LIST 7 1 ...

Page 4: ...x 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 Requiremen...

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: ...nal 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 a...

Page 7: ...select the desired auto weight defrost programmed with weight pad 4 NUMBER Used to set for time of day cooking time power level or defrost weight 5 STOP CLEAR Used to stop oven and clear all entries except time of day 6 CLOCK Used to set the time of day 7 TIME Used to cook food for a desired time 8 POWER Used to select power level for cooking 9 Ez On Allows you to cook for 30 seconds at 100 power ...

Page 8: ...tered or to the clock 3 Ez On 4 ONE TOUCH COOKING NOTE Heat only 1 package at a time 5 TIME COOKING 6 MULTI STAGE COOKING 1ST STAGE 2ND STAGE 7 AUTO DEFROST COOKING 8 CHILD LOCK This oven has a CHILD LOCK feature TO SET CHILD LOCK Touch the pad Touch and hold 0 pad L appear on the display TO CANCEL CHILD LOCK Touch the pad Touch and hold 0 pad L disappear STOP CLEAR CLOCK CLOCK NUMBER Ez On STOP C...

Page 9: ...SCHEMATIC DIAGRAM I Check the Rating Model No 4 3 ...

Page 10: ...SCHEMATIC DIAGRAM II Check the Rating Model No ADD Noise filter 4 4 ...

Page 11: ...ximately 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 a...

Page 12: ...nt openings for microwave leakage Check for microwave leakage after every servicing The power density 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 ...

Page 13: ...ed 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 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 this may possibly cause probe damage RECORD KEEPING AND NOTIFICA...

Page 14: ...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 order to minimize addition o...

Page 15: ...he clearance between the door and the oven E HIGH VOLTAGE TRANSFORMER REMOVAL 1 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 and high voltage capa...

Page 16: ...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 J REMOVING THE TURNTABLE MOTOR 1 Remove the turntable 2 Remove the turntable shaft VERY CAREFULLY with a slotted screwdriver 3 Lay the unit down on its back 4 Remove the turntable motor cover The turntable base c...

Page 17: ...ave 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 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 butt...

Page 18: ...tion When the door 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 c...

Page 19: ...VOLTAGE TRANSFORMER Wire leads removed MAGNETRON Wire leads removed Approx 0 3 0 8 ohm Approx 100 200 ohm Less than 1 ohm Normal Infinite Normal Infinite Normal Less than 1 ohm Normal Infinite PRIMARY TERMINAL SECONDARY TERMINAL FILAMENT WINDING TERMINAL COMPONENTS TEST PROCEDURE RESULTS 1 Measure the resistance Ohm meter scale Rx1 and Rx100 Primary winding Secondary winding Filament winding 2 Mea...

Page 20: ...ormal Momentarily indicates several ohms and then gradually returns to infinite Normal Infinite Normal Continuity Abnormal Infinite Normal Infinite Abnormal Continuity 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: ...T POSITION WHEN REMOVING THE WIRE LEADS FROM THE PARTS BE SURE TO GRASP THE CONNECTOR NOT THE WIRES Relay 1 Relay 2 A RD B BK C WH Measure the resistance Ohm meter scale R x 1000 Normal A B Approx 65 80 ohm B C Approx 10 30 ohm A C Approx 85 105 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 ...

Page 22: ...tallic 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 w...

Page 23: ...ce key membrane assembly Defective PCB assembly Replace PCB assembly 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 t...

Page 24: ...ntinuity No continuity Malfunction of the monitor switch Replace fuse primary monitor secondary 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 Normal Replace f...

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

Page 28: ...6 2 DOOR PARTS 13581A 14970A 14026A 13552A 13213A 13352A 13720D 13536A EV ...

Page 29: ...6 3 CONTROLLER PARTS 23506A 23572A 268711 WTT028 24781M EV ...

Page 30: ...6 4 OVEN CAVITY PARTS 33390G 35889A WSZ185 33112U WTP013 36549S 33052A WTT010 WTT020 MAB745B For model For model MAB745W EV ...

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

Page 32: ...CZZH 54810C 56851D 55900A 56549F 54974S WSZ002 WSZ002 55006F 50FZZA Check the Rating Model No Check the Rating Model No Check the Rating Model No Check the Rating Model No WSZ002 EV Model MAB745W MAB745B Check the rating label of Model and order SVC parts according to the Model No ...

Page 33: ...C 56851D 55900A 56549F 54974S WEB001 WSZ002 50FZZA 56201A WTT028 Check the Rating Model No Check the Rating Model No Check the Rating Model No Check the Rating Model No WEB001 EV Model MAB745W 01 MAB745B 01 Check the rating label of Model and order SVC parts according to the Model No ...

Page 34: ...6 8 BASE PLATE PARTS 56170D 63302A 63303A WTT021 WSZ002 65006B 65006B EV ...

Page 35: ......

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