LG MH-1355M Page 22 Service Manual Download | Manualshive

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NECESSARY TOOLS AND
MEASURING INSTRUMENTS

NECESSARY TOOLS

Tools normally used for TV servicing are sufficient.
Standard tools are listed below.
• Diagonal pliers
• Long nose pliers
• Cross head screwdriver
• Socket wrench (size 5 mm)
• Nutdriver (size 5 mm)
• Adjustable wrench
• Soldering iron
• Solder
• Vinyl insulation tape
• Polishing cloth

NECESSARY MEASURING INSTRUMENTS

• Tester (Volt DC, AC-ohmmeter)
• Inch scale
• Electromagnetic radiation monitor
• 600 cc glass beaker or equivalent
• Glass thermometer 100°C
• Two 1 liter beakers or equivalent

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Summary of Contents for MH-1355M

Page 1: ...AVE OVEN SERVICE MANUAL MODEL MH 1355M MH 1356M MH 1357M CAUTION BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL Website http biz lgservice com P NO 3828W5S6174 July 1998 Printed in Korea ...

Page 2: ...OSURE TO EXCESSIVE MICROWAVE ENERGY A Do not operate or allow the oven to be operated with the door open B Make the following safety checks on all ovens to be serviced before activating the magnetron or other microwave source and make repairs as necessary 1 interlock operation 2 proper door closing 3 seal and sealing surfaces arcing wear and other damage 4 damage to or loosening of hinges and latc...

Page 3: ...ON AND ADJUSTMENT OF THE INTERLOCK SYSTEM 23 INTERLOCK CONTINUITY TEST 25 DISASSEMBLY AND PARTS REPLACEMENT PROCEDURE 26 TROUBLESHOOTING 30 COMPONENT TEST PROCEDURE 36 PROCEDURE FOR MEASURING MICROWAVE ENERGY LEAKAGE 42 EXPLODED VIEW AND PARTS LIST 44 INTRODUCTION 44 1 DOOR PARTS 45 2 CONTROL PANEL PARTS 46 3 OVEN CAVITY PARTS 47 4 OVEN INTERIOR PARTS 1 48 5 OVEN INTERIOR PARTS 2 49 6 LATCH PARTS ...

Page 4: ... Lamp 125V 25W Timer 99 mim 99 sec Microwave Convection and Combination Power Control MICOM Outer Dimension 15 x 221 4 x 1913 16 H x W x D Cavity Dimension 103 16 x 149 16 x 1411 16 H x W x D Safety Device Primary Interlock Switch Secondary Interlock Switch Monitor Switch Fuse 15 Amp Magnetron Thermostat Open at 145 C 6 C Close at 60 C 15 C Oven Thermostat Open at 130 C 6 C Close at 60 C 15 C IEC6...

Page 5: ...gnetron 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 CAUTIONS Unlike other appliances the microwave oven is high voltage and high current equipment Though it is free from danger in ordinary use extreme care should be taken dur...

Page 6: ...ce 8 This oven must be plugged into a 15A outlet 9 Do not touch the front glass during or after cooking of the Grill and Combination mode This glass is very hot during heater operating 10 Do not operate the oven at microwave and combination mode with Grill rack placed in the cavity when the oven is empty EARTHING INSTRUCTIONS This microwave oven is designed to be used in a fully earthed condition ...

Page 7: ...ial Turntable 1 Each Rotating Ring Asm 1 Each Convection Rack 1 Each Cookbook 1 Each Owner s Manual 1 Each Do not use this Microwave Convection Oven for commercial purposes This Microwave Convection Oven is made for household use only SAFETY INTERLOCK SYSTEM CONVECTION RACK TURNTABLE ROTATING RING ASM SEE THROUGH DOOR AIR VENTS CONTROL PANEL Fig 3 ...

Page 8: ...r time after cooking end HOLD WARM Used to keep the food warm NUMBERS Used to enter the Time of day Cooking times Cooking powers Cooking temperatures Weight for Auto Combination cooking START Starts the oven NOTE A beep tone sounds when a pad on the control panel is touched to indicate a setting has been entered CONVECTION Used in setting convection cooking or pre heat REHEAT Used to reheat foods ...

Page 9: ...10 cooking powers listed below If cooking power is not programmed the oven operates at cooking power HI 3 Digital Readout Display Numbers of Touch Pads Cooking Power Time Example 99 min and 99 sec Microwave Emission Time sec cycle ON OFF 1 2 3 4 5 10 20 30 40 50 10 20 30 40 50 4 6 8 10 12 18 16 14 12 10 Numbers of Touch Pads Cooking Power Microwave Emission Time sec cycle ON OFF 6 7 8 9 60 70 80 9...

Page 10: ...o be browned evenly without losing any of the juices Heated air is circulated in the oven by a fan to enable the heating and cooking of food Since hot air remains in the oven as it circulates cooking is very efficient The temperature inside the oven can be con trolled according to the type of food being cooked COMBINATION COOKING With microwave energy and hot air this solid state control can cook ...

Page 11: ...STAGE 3 AUTO WEIGHT DEFROST STAGE 1 STAGE 2 HOLD WARM AUTO WEIGHT DEFROST STAGE 1 STAGE 2 AUTO WEIGHT DEFROST STAGE 1 HOLD WARM AUTO WEIGHT DEFROST STAGE 1 AUTO WEIGHT DEFROST HOLD WARM AUTO WEIGHT DEFROST STAGE 1 STAGE 2 STAGE 3 HOLD WARM STAGE 1 STAGE 2 STAGE 3 STAGE 1 STAGE 2 HOLD WARM STAGE 1 STAGE 2 STAGE 1 HOLD WARM STAGE 1 HOLD WARM AUTO WEIGHT COMBINATION REHEAT POPCORN START REHEAT AUTO W...

Page 12: ...o 0 If this occurs please reset the clock If STOP CLEAR is touched or door is opened after cooking the TIME OF DAY will appear in the display window If you don t set the time of day the display counts up per minute REGULAR TIMER 1 Touch MICRO TIME 2 Touch numbers for desired time 3 Touch MICRO POWER 4 Touch 0 5 Touch START MICRO TIME COOKING 1 Touch MICRO TIME 2 Touch numbers for desired cooking t...

Page 13: ...oven does not operate When five short beeps sound during cooking please turn over foods Don t cook with plugging in the temperature probe If you touch Auto Weight Combination Cook key the cooking data input already in each stage is cancelled If you are going to reprogram a certain cooking function after programming Auto Weight Combination data STOP CLEAR must always be touched before Weight can be...

Page 14: ...the oven will operate normally but Micro Power and Heater Power will be zero and cooking can not take place At this time if you start to cook L will appear in the display window for 1 sec at first To Cancel Child Lock 1 Touch 0 more than 2 seconds NOTE When you cancel Child Lock STOP CLEAR must always be touched before selection MULTI STAGE COOKING Let s start to cook with a first stage 4 minutes ...

Page 15: ... RD RD OVEN LAMP SWITCH NC YL NO COM BL WH WH WH WH AC 120V 60Hz THERMOSTAT OVEN FUSE GN OVEN LAMP O L TURNTABLE MOTOR T T M FAN MOTOR F M C M CIRCULATION MOTOR RECTIFIRE FUSE CONVECTION HEATER REL AY2 MONITOR SWITCH REL A Y1 NOTE 1 DOOR IS CLOSED 2 COOK OFF 3 CIRCUIT BE SU B JECT TO CHANGE WITHOU T NOTICE SYMBOL COLOR WH WHI TE BK BL ACK BL BLUE RD RED YL YELLOW PK PINK BN BROWN HIGH VOLTAGE DIOD...

Page 16: ...EN LAMP SWITCH NC YL NO COM BL WH WH WH WH AC 120V 60Hz THERMOSTAT OVEN FUSE GN OVEN LAMP O L TURNTABLE MOTOR T T M FAN MOTOR F M C M CIRCULATION MOTOR RECTIFIRE FUSE CONVECTION HEATER REL AY2 MONITOR SWITCH REL A Y1 NOTE 1 DOOR IS CLOSED 2 COOK OFF 3 CIRCUIT BE SU B JECT TO CHANGE WITHOU T NOTICE SYMBOL COLOR WH WHI TE BK BL ACK BL BLUE RD RED YL YELLOW PK PINK BN BROWN HIGH VOLTAGE DIODE MAGNETR...

Page 17: ...RD RD RD OVEN LAMP SWITCH NC YL NO COM BL WH WH WH WH AC 120V 60Hz THERMOSTAT OVEN FUSE GN OVEN LAMP O L TURNTABLE MOTOR T T M FAN MOTOR F M C M CIRCULATION MOTOR RECTIFIRE FUSE CONVECTION HEATER REL AY2 MONITOR SWITCH REL A Y1 NOTE 1 DOOR IS CLOSED 2 COOK OFF 3 CIRCUIT BE SU B JECT TO CHANGE WITHOU T NOTICE SYMBOL COLOR WH WHI TE BK BL ACK BL BLUE RD RED YL YELLOW PK PINK BN BROWN HIGH VOLTAGE DI...

Page 18: ...ltant is then applied to the magnetron via the filament The disturbance wave generated by the magnetron is suppressed by the choke coils filter capacitors and the magnetron shielded case so that TV and RADIO programs are not impaired by noise WHEN TOUCHING THE START PAD WITH THE CONVECTION COOKING FUNCTION SELECTED Relay 2 is closed to provide a current path to the Convection Heater The microwave ...

Page 19: ...trons travel an orbital path between the cathode and anode see Fig 10 As the electrons approach 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 cur rent to oscillate in the resonant cavities at the very high frequency or 2 450 megahertz This RF energy is then transferred to the antenna TESTING MAGN...

Page 20: ...magnetron thermostat opens when abnormal high temperatures within the magne tron approach a critical level 145 C causing oven to shut down DOOR OPENING MECHANISM The door can be opened by pushing button and lifting the latch as a result of action by the latch spring latch and latch board jaw The latch is released from the latch board and the door can be opened PRIMARY AND SECONDARY INTERLOCK SWITC...

Page 21: ... perature is reached and alternates on and off accord ing to temperature after the setting temperature is reached The on off of the convection heater is controlled by thermistor CHAMBER ASSEMBLY FIG 12 The air heated by the heating element is circulated through the convection passage provided on the back side of the oven by means of the convection fan which is driven by the convection motor It the...

Page 22: ...rs Long nose pliers Cross head screwdriver Socket wrench size 5 mm Nutdriver size 5 mm Adjustable wrench Soldering iron Solder Vinyl insulation tape Polishing cloth NECESSARY MEASURING INSTRUMENTS Tester Volt DC AC ohmmeter Inch scale Electromagnetic radiation monitor 600 cc glass beaker or equivalent Glass thermometer 100 C Two 1 liter beakers or equivalent ...

Page 23: ...screws firmly 4 Loosen the two screws 3 holding the latch board L to the oven cavity front flange 5 With the door closed adjust the latch board by moving it back and forth or up and down 6 In and out play of the door allowed by the latch board U and L should be less than 0 5 mm 7 Secure the screws firmly CAUTION FOR CONTINUED PROTECTION AGAINST RADIATION EMISSION REPLACE ONLY WITH THESE TYPES OF S...

Page 24: ...he latch board U position pushing and pulling the upper portion of door toward the oven face Then check the lower portion of door toward the oven face Both results should be less than 0 5mm 2 Make sure the door latch closes the monitor switch and oven lamp switch after the primary switch is open This COM NO test should be performed with the door being opened very slowly 3 Re install the outer case...

Page 25: ...r open condition When door is closed the meter should indicate an open circuit When the secondary switch operation is abnormal make the necessary adjustment or replace the switch only with the same type of switch MONITOR SWITCH TEST Isolate the monitor switch by disconnecting it from leadwire Connect the ohmmeter leads to the common COM and normally closed NC terminals of the switch The meter shou...

Page 26: ... pad earth bend to the front plate 3 Remove two screws securing the control panel to the front plate 4 Lift the control panel slightly and remove from the front plate 5 Remove the F P C connector the terminal socket 6 Remove three screws securing the P C B assembly to the control panel NOTE Remove the wire leads and connector VERY CAREFULLY Be sure to grasp the connector and not the wires C REMOVI...

Page 27: ...OOLING FAN MOTOR FIG 17 1 Remove the power supply cord from the oven and disconnect lead wire from the Fuse Holder 2 Disconnect each two lead wires from the Fan Motor 3 Remove three screws securing the Fan Guide Asm to the back cover and lift up the Fan Guide Asm 4 Remove two screws securing the Fan Motor to the Fan Guide after pulling out the fan from the Fan Motor F REMOVING HIGH VOLTAGE DIODE A...

Page 28: ...d by pinching the six parts with a wire cutter Fig 20 4 Disconnect the lead wires from the turntable motor terminals 5 Remove two screws securing the turntable motor to the oven cavity assembly 6 Lift the turntable motor 7 After repairing the motor rotate the removed turntable motor cover Fig 20 8 Fit the turntable motor cover s projecting part to the base plate s slit Fig 21 NOTE 1 Remove the lea...

Page 29: ...ed by both sides from the C Heater hanger THERMISTOR 1 Follow section I step 1 3 2 Pull up the thermistor K REMOVING PRIMARY INTERLOCK SWITCH FIG 23 1 After removing the complete control pane assembly disconnect the wire leads from the switches 2 Remove two screws holding the latch board U to the front plate flange 3 Remove the latch board U from the flange by moving it upward and push outward 4 R...

Page 30: ...erform fuse test procedure See page 39 Open wire in power cord wiring harness or wiring between control panel assembly units Replace or repair wiring CAUTION 1 Check grounding before checking for other trouble 2 Be careful of the high voltage circuit 3 When checking the continuity of the switches or transformer disconnect one lead wire from these parts and then check continuity without turning the...

Page 31: ...s but turntable motor does not operate Defective primary switch or out of adjustment Defective turntable motor Test procedure primary switch See page 25 Test procedure turntable motor See page 38 Turntable drags or makes noise Excessive weight on tray or improperly balanced Distribute food evenly cook smaller portions and or use lighter weight cookware Open wiring of turntable motor Check connecto...

Page 32: ...ut Defective membrane key of P C B Loose connection Test procedure membrane key of P C B See page 41 Connect them tightly Setting time does not count down when touch Start Defective secondary switch or out of adjustment Defective membrane key of P C B Test procedure secondary switch See page 25 Test procedure membrane key of P C B See page 41 Loose connection Test membrane key of P C B CONDITION C...

Page 33: ... page 41 Open or loose wiring to above components Check and repair wiring Output is too high when you set lower power level Defective relay 1 of P C B Test procedure relay 1 of P C B See page 40 High AC input voltage Use the microwave oven at adequate line voltage MICROWAVE Sparks occuring Using metallic ware and allowing it to touch the oven wall Do not use metallic ware for cooking except where ...

Page 34: ...Test procedure high voltage capacitor See page 37 Defective high voltage diode Test procedure high voltage diode See page 36 Defective magnetron Test procedure magnetron See page 36 Low AC input voltage Use the microwave oven at adequate line voltage Open or loose wiring to above components Check and repair wiring Oven operates properly on P HI but does not cook properly using another cooking powe...

Page 35: ...er or higher than preset Defective convection heater element Test procedure relay 4 and 2 of P C B See page 40 Defective relay 4 or 2 of P C B Defective thermistor Test procedure convection heater See page 39 Defective circulation motor Test procedure thermistor See page 40 Defective drive mechanism of circulation fan Test procedure circulation motor See page 38 Defective Solenoid Check and repair...

Page 36: ...NSFORMER Wire leads removed MAGNETRON Wire leads removed See Fig 24 1 Measure the resistance Ohm meter scale R x 1 Primary winding Secondary winding Filament winding 2 Measure the resistance Ohm meter scale R x 1000 Primary winding to ground Filament winding to ground See Fig 25 1 Measure the resistance Ohm meter scale R x 1 Filament terminal 2 Measure the resistance Ohm meter scale R x 1000 Filam...

Page 37: ...ter scale Rx1000 Terminal to case Measure the continuity Forward Ohm meter scale Rx1000 Measure the continuity Reverse Ohm meter scale Rx1000 Normal Momentary 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 posi...

Page 38: ...Ohm meter scale Rx1000 Measure the resistance Ohm meter scale Rx1 Normal Approx 51 ohm Abnormal Infinite or Several ohms Normal Approx 2800 ohm Abnormal Infinite or Several ohms Normal Approx 26 ohm Abnormal Infinite or Several ohms NOTE After checking for the continuity of switches make sure that they are correctly connected Check for continuity of the switch with an Ohm meter Door Door open clos...

Page 39: ...al Infinite or Several ohms NOTE If the fuse is blown check the primary the secondary and the monitor switches before replacing the fuse Refer to Test Procedure Switches on page 25 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 Check for continuity of the fuse with an Ohm meter Norm...

Page 40: ...nnector from P C B Relay 4 of P C B Disconnect the 5 pin connector from P C B Relay 3 of P C B Wire leads removed Relay 4 of P C B Wire leads removed Micro Power Cooking Start Convection Cooking Start OFF OFF OFF OFF Micro Power Cooking Start Convection Cooking Start Fig 37 Fig 38 Fig 39 Fig 40 ...

Page 41: ... 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 Membrane key CONNECTOR KEY MATRIX Check continuity between switch terminals by pressing an appropriate pad on the key board The contacts assignment of the respective pads on the key board is as shown left figures Fig 41 NOTE A MICROWAVE ENERGY LEAKAGE TEST MUST ALWAYS BE PERFORMED WHEN THE UNIT IS SERVICED FOR ANY REASON MAKE SURE THE WIRE LEADS ARE CORRECT POS...

Page 42: ...m2 sq And always start measuring of an unknown field to assure safety for operating personnel from radiation leakage NOTE The standard is 4 mW cm2 sq while in the customer s home 2 mW cm2 sq stated here is manufacturer s own voluntary standard for units in customer s home EQUIPMENT Electromagnetic energy leakage monitor NARDA 8100B HOLADAY HI 1501 600 cc glass beaker Glass thermometer 100 C or 212...

Page 43: ... in this manual have been used At least once a year have the electromagnetic energy leakage monitor checked for calibration by its manufacturer DETERMINATION OF MEASUREMENT OF MICROWAVE POWER OUTPUT Microwave power output measurement is made with the microwave oven supplied at its rated voltage and operated at its maximum microwave power setting with a load of 1000 5 cc potable water The water is ...

Page 44: ... 44 DOOR PARTS SWITHES PARTS CONTROL PANEL PARTS BASE PLATE PARTS OVEN CAVITY PARTS OUT CASE PARTS OVEN INTERIOR PARTS INTRODUCTION EXPLODED VIEW AND PARTS LIST EV ...

Page 45: ... 45 13581A 14890A 13213A 15244H 13552A 15244U 15244T 14026U 14510A 15244L 14026L 14970A 13720D WPZ017 WPZ017 1 DOOR PARTS EV ...

Page 46: ... 46 23506A 250201 23790D 23572A 268711 24781M WTP018 24970A 24510L 2 CONTROL PANEL PARTS EV ...

Page 47: ... 47 3 OVEN CAVITY PARTS 35889A 53300C 36549S WTP013 35026C 33052M 34774U 33112U WTT010 WSZ137 WTT021 WTT011 34370T WTT028 34890C EV ...

Page 48: ... OVEN INTERIOR PARTS 1 54370D 54810U 56420A WTP004 WTT021 56324A 368771 54932A 55262A 54974S 56549F 56930M WTP002 53551S WTT011 WTT021 WTP015 WSZ002 50FZZA 56201A 55900A WMT001 56411A WSZ137 WSZ137 34930W EV ...

Page 49: ...P004 WTT021 54810S 36549C WTT043 WTT021 WNH002 53504A WMT002 WTT010 56912B WTT010 56930G 53550L 34810Q 35301A WWP008 WTT022 WWS005 WNH003 33741A 35012T 35264A 56208A 54975G 55900N 35012R 568773 55900C 343501 34990A WTT021 WTT010 EV ...

Page 50: ... 50 6 SWITCHES PARTS 43501U 43500U 466004 466001 WTP007 466002 WTP010 WSZ085 WSZ085 466003 WTP007 44510A 43500L 44360A 43501L EV ...

Page 51: ... 51 7 BASE PLATE PARTS 56170D 50CZZH 56851D 54810C 34774L 63302A 63303A WSZ137 647781 WTT028 13806F 647781 WTT021 WSZ153 WSZ002 56851C EV ...

Page 52: ... 52 8 WIRING HARNESS PARTS 568772 568771 EV ...

Page 53: ... 53 9 CIRCUIT BOARD ...

Page 54: ... 54 10 CIRCUIT BOARD SCHEMATIC DIAGRAM ...

Page 55: ......

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