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3-2. Conventional heating vs. dielectric heating

1. Conventional heating

* The heat energy from the sources of the heating power shall be transmitted

from the warm surface to the cold inside.

* Heating with the strong fire: The surface of the food shall be well done, but be

burnt to have a black side, and the center of the food shall not be well-done.

* Heating with the weak fire: The surface of the food shall be burnt and have a

little black side, but it shall be taken lots of time for the center to be well-done.

* The thermal conductivity in the water or in the food is low.

2. Dielectric heating

1) The heating is uniform.
2) The temperature rise is fast (high).
3) If you break the electric power: The microwave oven stops

heating at 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

HEAT

FOOD

TRANSMITTED

BY CONDUCTION

It shall be heated by the sources of the electric heater, the gas, and the briquet.

WELL-DONE

HALF-DONE

UNDER

DONE

WAVE

MOLECULES

FOOD

• If you give microwave to food with the microwave oven, the food and

molecules of the water included in the food is turned, or moved and generates
heat with the friction among the the molecules.

Summary of Contents for MA-2005ST

Page 1: ...MICROWAVE OVEN SERVICE MANUAL MODEL MA 2005ST CAUTION BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL http www LGEservice com E mail Techsupport LGEservice com ...

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: ...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 4: ...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 5: ...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 6: ...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 7: ...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 8: ...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 9: ... 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 10: ...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 11: ...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 12: ...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 13: ...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 14: ... 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 15: ... 20 What is Multi Wave The multi Wave system heats food more evenly than convectional microwave ovens 5 1 Multiwave system ...

Page 16: ...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 17: ...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 18: ...e grounded 1 150 Watts full microwave power IEC705 2 450 MHz 2M246 2M248J 0 99 min 99 sec 237 8 W x 139 16 H x 1813 16 D 171 16 W x1013 16 H x 185 16 D 42 lbs approx 46 lbs 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 19: ...0 seconds of cooking time 7 STOP CLEAR It used to stop oven and clear all entries except time of day 8 CUSTOM SET You can select sound on off clock on off scroll speed lbs kg choice language choice demo on off mode 9 TIME You can set the desired cook time 10 POWER You can select the desired power level for cooking 11 TIMER You can use the timer function of your oven for purpose other than cooking ...

Page 20: ...splay TO CANCEL CHILD LOCK Touch and hold 0 pad LOCKED disappears 9 MORE LESS The cook time is adjustable by MORE pad or LESS pad 10 CUSTOM COOK You can program the cook time and power level by using CUSTOM COOK pad ex To set cook time 10 mine 30seconds touch number key 1 0 3 and 0 11 CUSTOM SET You can select Sound On Off Clock On Off Scroll Speed Lbs Kg Choice Demo On Off modes To turn ON OFF so...

Page 21: ...MP MONITOR SWITCH TURN TABLE MOTOR FAN MO TOR 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 CRITICAL COMPONENTS IN THE SHADED AREAS OF THE SCHEMATIC DIAGRAM NOTICE SINCE THIS IS BA...

Page 22: ...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 23: ...ion leakage MEASURING MICROWAVE ENERGY LEAKAGE Pour 275 15cc of 20 5 C 68 9 F water in a beaker which 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 Ope...

Page 24: ...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 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 probe damage RECORD KEEPING AND NOTIFICA...

Page 25: ...erature is 5 K The microwave power output P in watts is calculated from the following formula 4187 x ÆT 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 sele...

Page 26: ...g 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 the do...

Page 27: ...5 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 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 pinchi...

Page 28: ...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 Mount the...

Page 29: ...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 30: ...EDURE 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 Rx...

Page 31: ... 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 32: ...ec 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 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 NOTE A MICROWAVE LEAKAGE TEST MUST ALWAYS BE PERFORMED WHEN THE UNIT IS SERVICED FOR ANY REASON MAKE SURE THE WIRE LEADS ...

Page 33: ...s 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 occur Inc...

Page 34: ... does not turn on after setting cooking cycle 11 Display time of day does not reappear when cooking is finished 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 tightly Check the conn ection b...

Page 35: ...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 36: ...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 37: ... relay 2 and check continuity relay 2 Operate the unit 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...

Page 38: ...DOOR PARTS LATCH BOARD PARTS CONTROL PANEL PARTS INTERIOR PARTS BASE PLATE PARTS OVEN CAVITY PARTS 6 1 EXPLODED VIEW INTRODUCTION ...

Page 39: ...6 2 13552A 13213A 13581A 13720D 14970A 14026A 13536A 13352A DOOR PARTS ...

Page 40: ...6 3 26638A 23572A 23550D 268711 24781M WTP018 WTT028 24510L 250201 24970A CONTROLLER PARTS ...

Page 41: ...6 4 948503 340511 33052M 36549S 34036W 33390G 35889A WTP013 WTT020 WSZ185 33112U OVEN CAVITY PARTS ...

Page 42: ...6 5 43501A 43500A 466001 WSZ085 466001 466003 LATCH BOARD PARTS ...

Page 43: ...6 6 568771 56930V 56411A 54974S 55006F 50FZZA WSZ002 WTT028 WSZ085 WSZ002 56549F WTT037 WSZ002 WTT028 WSZ002 55900A 56851D 54810C 55262A 56912B 50CZZH 56324A WSZ002 WSZ002 34930W 948502 INTERIOR PARTS ...

Page 44: ...6 7 63302L 63303L 63303R 948501 63302R 56170D WSZ002 WTT021 WTT021 65006B 65006B BASE PLATE PARTS ...

Page 45: ...8 1 SCHEMATIC DIAGRAM OF P C B ...

Page 46: ...8 2 PRINTED CIRCUIT BOARD ...

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