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After plugging your oven into a standard household socket, press start button or turn the timer. And then switches
(primary, secondary, timer) close the circuit.
Eventually the input power will be applied to turntable motor, timer motor, fan motor, oven lamp and high voltage transformer.
A high voltage of 2,100 volts AC is generated in the second winging of H.V.Transformer. And the voltage is doubled by
H.V.Capacitor & H.V.Diode. The 4Kv DC voltage is applied to filament of magnetron, then magnetron start to produce microwave.
This microwave is injected to cavity.

4-2. How does the microwave oven operate?

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Summary of Contents for MS-194A

Page 1: ...MICROWAVE OVEN SERVICE MANUAL MODEL MS 194A 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: ... 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 SCHEMATIC DIAGRAM OF P C B 8 1 PRINTED CIRCUIT BOARD 8 2 P C B PARTS LIST 9 1 CONTENTS ...

Page 4: ...lts AC 60 Hz 1 200 Watts Single phase 3 wire grounded 800 Watts full microwave power IEC705 2 450 MHz 2M214 39F 2M218J 2M254J 0 99 min 90 sec 483 W x 285 H x 360 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 Full power throughout the cooking time Med High approx 80 of Full power Medium approx 60 of Full power Defrost approx 40 of Ful...

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: ...P CLEAR Used to stop oven and clear all entries except time of day 6 DISPLAY WINDOW 7 KITCHEN TIMER 8 POWER Used to select the desired power level for cooking 9 COOK TIME Used to cook food for a desired time 10 START One tap allows oven to begin functioning 4 1 OPERATING INSTRUCTIONS Oven Frot Plate Window Door Screen Door Seal Display Window Control Panel Safety Door Lock System Turntable Rotatin...

Page 8: ...CROWAVE COOKING 5 MULTI STAGE MICROWAVE COOKING 6 AUTO WEIGHT DEFROST COOKING 7 CHILD LOCK This oven has a CHILD LOCK feature TO SET CHILD LOCK Touch the pad Touch STOP pad L appear in the display TO CANCEL CHILD LOCK Touch the pad touch STOP pad L disappears 8 AUTO COOK 4 2 Stop Set clock Set the correct time Stop Start Stop Desired auto cook category STOP STAGE 1 Set clock Stop Stop Desired defr...

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

Page 10: ...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 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: ...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 cause...

Page 13: ...nal 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 Stirring d...

Page 14: ...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 ASS Y...

Page 15: ... 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 L 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 turntable ba...

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

Page 17: ... 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 op...

Page 18: ...ONENTS 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 ...

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: ... meter scale R x 1000 POWER LEVEL 20 6 sec 16 sec 40 10 sec 12 sec 60 14 sec 8 sec 80 18 sec 4 sec 100 22 sec 0 sec Normal Abnormal or several Ω Normal Approx 100 200 Abnormal or several 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...

Page 21: ...static charge built up in your body Micom model only CONDITION Microwave oven does not work Inserting many plug into one plug 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 occur Inconsistent intensity o...

Page 22: ...ing cooking cycle 11 Display time of day does not reappear when cooking is finished 12 Beep sound is not heard when correct key is touched 5 12 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 tigh...

Page 23: ...f 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 Defective thermostat Replace thermost...

Page 24: ...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 25: ... unit Check high vol tage transformer Abnormal Defective circuit protector Replace circuit protector Normal Check circuit protector 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 magnetr...

Page 26: ...unit NOTE Make sure the wire leads correct position When Removing the wire leads from the parts be sure to grasp the connector not the wires When removing the magnetron be sure to install the magnetron gasket in the correct position and in good condition CONDITION CHECK RESULT CAUSE REMEDY TROUBLE 5 No microwave oscillation even though oven lamp and fan motor run Display operates properly ...

Page 27: ...DOOR PARTS LATCH BOARD PARTS CONTROL PANEL PARTS INTERIOR PARTS BASE PLATE PARTS OVEN CAVITY PARTS 6 1 EXPLODED VIEW INTRODUCTION ...

Page 28: ...6 2 13581A 14970A 14026A 13552A 13536A 15006A 13213A 13720D 13352A DOOR PARTS ...

Page 29: ...6 3 WTP018 26638A 23572A 23550D 24930D 24781M 268711 CONTROL PANEL PARTS ...

Page 30: ...6 4 33052M 340511 33112U WTT021 34960A 34036W 36549S WTP013 33390G 35889A OVEN CAVITY PARTS ...

Page 31: ...6 5 43501A 43500A 466001 WSZ085 466003 466002 44510A LATCH BOARD PARTS ...

Page 32: ...6 6 56201B WSZ002 WSZ002 WTT028 WSZ002 WTT028 WSZ062 50FZZA WSZ002 WTT037 50CZZH 56324A 55262A 54810C 56851C 56851D 55900A 56549F 56411A 56201A 56930V 568771 54974S 56912B INTERIOR PARTS ...

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

Page 34: ...n interesting property they are absorbed by water fats and sugars When they are absorbed they are converted directly into atomic motion heat Microwaves in this frequency range have another interesting property they are not absorbed by most plastics glass or ceramics Metal reflects microwaves which is why metal pans do not work well in a microwave oven 2 Type of Microwave Oven 1 MICROWAVE COOKING s...

Page 35: ...of the oven This method allows food to be browned evenly without losing any of the juices Air heated by the heater is circulated in the oven by a fan This enables the efficient heating and cooking of food The temperature inside the oven can be controlled according to the type and weight of food being cooked 4 COMBINATION COOKING Using a combination of microwaves hot air and radiant heat this solid...

Page 36: ...properly unplug it from the electrical socket and then plug it back in 4 Open your oven door by pressing the DOOR HANDLE Place the ROLLER REST inside the oven and place the GLASS TRAY on top 5 Fill a microwave safe container with 300 ml 1 2 pint of water Place on the GLASS TRAY and close the oven door 6 Press the START button six times to set 3 minutes of cooking time You will hear a BEEP each tim...

Page 37: ...use of metal in your oven please read the introduction section in the cookbook If the use of aluminum foil skewers or utensils containing metal in the oven is specified in the recipe allow at least 2 5cm clearance between the metal object and the interior oven wall If arcing sparks occurs remove immediately Note Consult your cookbook individual recipes and charts for correct use of cooking contain...

Page 38: ...acuum tube called magnetron M G T it injects the electric wave of 2450MHz The vibrations of two billion four hundred and fifty million per second are given to the oven This electric wave is called the microwave The wireless electric wave having not more than 1 m of the wave length is using for the radio telephone and broad casting of T V and radar a radio locator It is similar to an electric wave ...

Page 39: ...TV or the radio and is used for the wireless communication the radar and the UHF medical instruments using 2450 MHz like that of the microwave oven etc 4 Definition of electric wave An electric wave is the electron wave of the frequency from 10 KHz to 3 000 000 MHz Wave length of 2450 MHZ 3 1 What s the microwave 2 2 λ Wave Length Where c The Velocity of Light f Frequency c f λ 300000 Km 245000 KH...

Page 40: ... once so you can t heat something with the heat of their surroundings 4 Since it heats inside the surface isn t damaged The water the oil and the foods shall absorb the electric wave well It generates heat all around the apparatus and the foods are well done with short time If you heat something for long time all of it will be burnt and can t be eaten FIRE FIRE FIRE FIRE FIRE FIRE FIRE FIRE FIRE F...

Page 41: ...OL PANEL PARTS INTERIOR PARTS BASE PLATE PARTS OVEN CAVITY PARTS Magnetron Inject microwave to oven Cavity Cabinet locking in microwave and holding food Door Gate coming in and out food It has window and seal structure Controller Control and supervise operating state of oven ...

Page 42: ...lied to turntable motor timer motor fan motor oven lamp and high voltage transformer A high voltage of 2 100 volts AC is generated in the second winging of H V Transformer And the voltage is doubled by H V Capacitor H V Diode The 4Kv DC voltage is applied to filament of magnetron then magnetron start to produce microwave This microwave is injected to cavity 4 2 How does the microwave oven operate ...

Page 43: ...s to the transformer for a complete circuit This half cycle of AC charges the capacitor to approximately 2000 Volts During the second half cycle of operation the current flows in the opposite direction again supplies 2000 Volts to the circuit This permits the capacitor to discharge its 2000 Volts on top of the 2000 Volts generated by the secondary winding creating an approximate total voltage of n...

Page 44: ...the tube The anode positive element of the tube consists of a thick walled copper cylinder with vertical vanes extending inward which surround but do not touch the cathode To complete the magnetron and make it operate distinctly different from other vacuum tubes two permanent magnets are mounted over each end of the tube CATHODE ANTENNA ELECTRONS ANODE ANTENNA OUTPUT MAGNET MAGNETIC CIRCUIT VANE F...

Page 45: ... the anode their orbital path takes them past small resonant cavities that are part of the anode The passing notion of the electrons induces electron current to oscillate in the resonant cavities at the very high frequency or 2 450 MHz This RF Radio frequency energy is then transferred to the antenna TESTING MAGNETRON TUBE Disconnect power remove the wrapper and discharge the capacitor Remove the ...

Page 46: ... 20 What is Multi Wave The multi Wave system heats food more evenly than convectional microwave ovens 5 1 Multiwave system ...

Page 47: ...er than you expected LG microwave oven reduce cooking time Our revolutionary Infrared sensor makes it 3 times faster than the ordinary microwave Infrared eye tracks the exact temperature of food and regulates the power of the microwave so that the temperature reaches you actually set We prepared the temperature LED bar and dial for your precise control and convenience Infrared sensor means fast an...

Page 48: ...eater goes down The angle of heater varies as to each menu You don t have to worry about safety The heater moves back to it s position automatically after grilling Your food is more evenly grilled and delicious when Auto Moving Heater 5 3 Auto moving heater Conventional Heater LG s Auto Moving Heater Sheath Heater Quartz Heater One touch Grilling Oven Cookie Heater 45 Pizza Frozen pizza Chicken pi...

Page 49: ...8 1 SCHEMATIC DIAGRAM OF P C B ...

Page 50: ...8 2 PRINTED CIRCUIT BOARD ...

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