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LG MS-1902H, Service Manual

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LG MS-1902H Service Manual Download Page 21

COMPONENTS

TEST PROCEDURE

RESULTS

5-11

TIMER MOTOR
(Wire leads removed)

Measure the resistance.
(Ohm-meter scale: R x 100)

Measure the resistance.
(Ohm-meter scale: R x 1000)

Note: A is ON,OFF switch B is
power supply terminal of the
timer motor C is defrost switch 

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.

C
(2-3)

B
(2-M)

A
(1-2)

A

B

C

A

Turn on

Approx. 25 K

Ω

Turn Off

B

FAN MOTOR
(Wire leads removed)

TURNTABLE
MOTOR
(Wire leads removed)

Normal: 

Abnormal: 

∞

or several 

Ω

Normal: Approx. 100~200 

Ω

Abnormal: 

∞

or several 

Ω

A ~ B

A ~ C

30 ~ 50

Ω

300~500

Ω

Summary of Contents for MS-1902H

Page 1: ...MICROWAVE OVEN SERVICE MANUAL MODEL MS 1902H CAUTION BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL ...

Page 2: ...nd 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 transmission line and cavity for proper alignment integrity and connections D Any defective or misadjusted components in t...

Page 3: ...TING SEQUENCE 4 2 SCHEMATIC DIAGRAM 4 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 7 COMPONENT TEST PROCEDURE 5 8 TROUBLE SHOOTING 5 12 EXPLODED VIEW 6 1 REPLACEMENT PARTS LIST 7 1 CONTENTS ...

Page 4: ...ight Control Complement Nameplate Location Accessories DESCRIPTION MS 1902H 230 Volts AC 50 Hz 1 000 Watts 4 5 A Single phase 3 wire grounded 700 Watts full microwave power IEC705 2 450 MHz 2M213 09 0 60 min 483 W x 285 H x 355 D mm 312 W x 198 H x 316 D mm 12 5 kg approx 14 kg approx Microwave Power for Variable Cooking Power level Max 500W 350W Defrost 70W Owner s manual cooking guide Glass turn...

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: ...lat 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 EARTHING INSTRUCTIONS This microwave oven is designed to be used in a fully earthed condition It is imperative therefore to make sure it is properly earthed before servicing WARNING THIS APPLIANCE MUST BE EARTHED IMPORTANT As the colors of the wire...

Page 7: ...Power Knob Door Open Button Safety Door Lock System Turntable Rotating Ring Timer Knob 2 1 Watt Min 70 Defrost 350 500 max 0 1Kg 0 2 0 3 0 4 0 5 1 2 3 4 5 6 7 8 9 10 20 30 40 50 60 0 1 POWER CONTROL KNOB Used in selected the desired power level for cooking 2 TIMER KNOB Used to set the cooking time ...

Page 8: ...king starts At the end of cooking time you will a single ring sound and the lamp is turn off NOTE Each number represents minutes To ensure accurate timing it is advisable to turn the timer knob slightly passed the desired cooking time and then back to the proposed setting Press the door opener to check the cooking condition during oven operation Opening the door during oven operation automatically...

Page 9: ...SCHEMATIC DIAGRAM 4 3 ...

Page 10: ...en through the upper plate Timer starts rotating 3 2 volts AC is generated from the filament winding of the high voltage transformer This 3 2 volts is applied to the magnetron to heat the magnetron filament through two noise preventing choke coils A high voltage of approximately 2100 volts AC is generated in the secondary of the high voltage transformer which is increased by the action of the diod...

Page 11: ...ity of the microwave radiation leakage emitted by the microwave oven should not exceed 5 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 12: ...aster 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 the oven surface this may possibly...

Page 13: ...n the final water temperature and the ambient temperature is 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 St...

Page 14: ...AL 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 noise filter and high voltage capacitor 3 Remove the two screws holding the the suction guide AS...

Page 15: ...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 J REMOVING THE TURNTABLE MOTOR 1 Remove the turntable 2 Remove the turntable shaft VERY CAREFULLY 3 Lay the unit down on its back 4 Remove the turntable motor cover The turn...

Page 16: ...N 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 button Door movement should be less than 0 5 mm 1 64 inch Don t push the door release button while making adjustment Make sure that the latch moves...

Page 17: ...osed 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 18: ...TS TEST PROCEDURE RESULTS HIGH VOLTAGE TRANSFORMER Wire leads removed MAGNETRON Wire leads removed 1 Measure the resistance Ohm meter scale Rx1 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 Between Filament terminal 2 Measure the resistance Ohm mete...

Page 19: ...le Rx1000 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 Normal Continuity Abnormal Normal Abnormal Continuity NOTE When testing the magnetron be sure to install the magnetron gasket in the correct position and be sure that the gask...

Page 20: ...NOTE If the fuse is blown check the primary the secondary and 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 operate normally Normal Abnormal ...

Page 21: ...OTE 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 C 2 3 B 2 M A 1 2 A B C A Turn on Approx 25 KΩ Turn Off B FAN MOTOR Wire leads removed TURNTABLE MOTOR Wire leads removed Normal Abnormal or several Ω Normal Appro...

Page 22: ...oading 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 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 powde...

Page 23: ...former Malfunction of the monitor switch Replace fuse primary monitor and secondary switches 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 TROUBLE 1 Oven lamp does not turn on when the timer knob is pushed with doo...

Page 24: ...No continuity No continuity replace Malfunction of the timer switch Faulty thermostat replace Check the continuity of the timer switch contacts Check the continuity of the thermostat 1 Oven does not operate No continuity No continuity Adjust or replace Malfunction of the primary switch Malfunction of the secondary switch Adjust or replace Check the continuity of the primary switch with door closed...

Page 25: ...oking state Check the monitor resistor Abnormal Defective AC relay Replace Normal Check the AC relay Abnormal Open the secondary winding of the high voltage transformer of faulty insulation of filament winding Replace Check H V transformer Abnormal Shorted H V diode Replace Check H V diode Abnormal Faulty capacitor Replace Check H V capacitor Abnormal Faulty magnetron Replace Magnetron TROUBLE 4 O...

Page 26: ...DOOR PARTS LATCH BOARD PARTS CONTROL PANEL PARTS INTERIOR PARTS BASE PLATE PARTS OVEN CAVITY PARTS 6 1 EXPLODED VIEW INTRODUCTION ...

Page 27: ...6 2 13552A 13213A 13581A 13720D 14970A 14026A 13536A 13352A DOOR PARTS ...

Page 28: ...6 3 24781T 23572A 24510L 250201 24970A 249401 WTP015 26549T CONTROL PANEL PARTS ...

Page 29: ...6 4 33052M 340511 33112U WTT021 34960A 36549S WTP013 33390G 35889A OVEN CAVITY PARTS ...

Page 30: ...6 5 43501A 43500A 466002 WSZ085 WTT028 466001 466003 56912B 55262A 969201 WTT028 LATCH BOARD PARTS ...

Page 31: ...6 6 56201B WSZ002 WSZ002 WTT028 WSZ062 50FZZA WSZ002 50CZZH 56324A 56411A 56201A 56930V 568771 WTT021 30RMZZ 54974S 56549F WTT037 55900A INTERIOR PARTS ...

Page 32: ...6 7 56170D WTT021 WSZ002 65006B 65006B 50CZZH WSZ002 54810C 56851D 56901A 63302A 63303A BASE PLATE PARTS ...

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