LG LMV1925SB Page 32 Service Manual Download

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7-21

PROBLEM - A:

“PLEASE SET TIME OF DAY” does not appear in display window when power supply cord is

plugged into wall outlet.

PROBLEM - B:

Display does not show correct numbers and/or

correct indications when programmed.

Check: 1. POWER SUPPLY

2. FUSE (See “CHECKOUT PROCEDURES FOR FUSE BLOWING: on page 7-18)

3. OVEN CAVITY THERMOSTAT

C. TROUBLE SHOOTING

Before following this troubleshooting read “TRIAL

OPERATION” on page 6-1.

• “DISPLAY” Problems, “A” thru “C”

• “HELP UP” Problems, “D” thru “E”

• “BUZZER Problems, “F”

Measure voltage between pin 1

and pin 3 of connector CN1.

Measure resistance of touch

key board after removing

connector S1.

(See page 7-4 and 7-17)

120

120V

Replace

circuit board

Normal

circuit board

Normal

resistance

Voltage

incorrect

Normal

resistance

Resistance

incorrect

Replace touch

key board.

Normal touch

key board

Poor

contact

Correct

seating

Contact

Replace

circuit board

Normal

circuit board

Normal

contact

Check contact

of connector S1

Correct

connections

120

Runs

Summary of Contents for LMV1925SB

Page 1: ...MICROWAVE OVEN SERVICE MANUAL MODEL LMV1925SW BEFORE SERVICING THE UNIT READ THE SAFETY PRECAUTIONS IN THIS MANUAL LMV1925SB LMV1925SBQ CAUTION Website http us lgservice com ...

Page 2: ... proper alignment integrity and connections d Any defective or misadjusted components in the interlock monitor door seal and microwave generation and transmission systems shall be repaired replaced or adjusted by procedures described in this manual before the oven is released to the owner e A Microwave leakage check to verify compliance with the CSA Standard should be performed on each oven prior ...

Page 3: ...AM 5 1 MATRIX CIRCUIT FOR TOUCH KEY BOARD 5 2 GENERAL INFORMATION FOR SERVICE 6 1 GENERAL PRECAUTIONS IN USE 6 1 TRIAL OPERATION 6 1 FEATURES AND SPECIFICATIONS FEATURES 6 1 SERVICE INFORMATION 7 1 PRECAUTIONS AND REPAIR SERVICE TIPS 7 1 MICROWAVE LEAKAGE TEST 7 2 POWER OUTPUT MEASUREMENT 7 3 DISASSEMBLY INSTRUCTIONS 7 4 INTERLOCK SYSTEM 7 12 INTERLOCK CONTINUITY TEST 7 14 TEST AND CHECKOUT PROCED...

Page 4: ...ty Thermostat Open at 110 C 5 C Fuse 20A Primary Interlock Switch Secondary Interlock Switch Interlock Monitor Magnetron 2M248 High Voltage Capacitor Capacitor 1 0µF 2 1 KV AC High Voltage Diode Diode 350mA 9 0 KV Cook top Lamp 125 V 30 W Cavity Lamp 125 V 30 W Timer Digital up to 99 mim 99 sec in each cooking stage Tray Tempered Safety Glass Overall Dimensions 2915 16 W x167 16 D x155 8 H Oven Ca...

Page 5: ...area Proper 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 Unlike other appliances the microwave oven is high voltage and high current equipment Though it is free from ...

Page 6: ...d at all times In the event of an electrical short circuit grounding reduces the risk of electrical shock The plug must be plugged into an outlet that is properly installed and grounded BEFORE YOU BEGIN READ THE FOLLOWING INSTRUCTIONS COMPLETELY AND CAREFULLY WARNING Improper use of the grounding plug can result in a risk of electric shock Do not under any circumstances cut or remove the third gro...

Page 7: ...CONTROL PANEL 4 1 OPERATING INSTRUCTIONS 25 21 24 28 26 23 4 7 9 12 10 20 22 27 2 5 3 6 11 8 13 18 17 14 15 16 19 1 ...

Page 8: ...at poultry fish Touch this pad to select food type and defrost food by weight 11 TIME DEFROST Touch this pad to defrost most other frozen foods 12 Q DEFROST This pad provides you with the RAPID defrosting method for 1 0 pounds frozen foods 13 NUMBER Touch number pads to enter cooking time power level quantities or weights 14 KITCHEN TIMER Touch this pad to set the kitchen timer 15 CLOCK Touch this...

Page 9: ...5 1 SCHEMATIC DIAGRAM OVERALL CIRCUIT DIAGRAM ...

Page 10: ...5 2 MATRIX CIRCUIT FOR TOUCH KEY BOARD CUSTOM SET CUSTOM COOK Q DEFROST Ez On ...

Page 11: ...y light comes on The unit will begin cooking and the display window will show the time counting down by seconds D After about 5 minutes make sure the primary interlock switch the secondary interlock switch and the interlock monitor switch operate properly by opening and closing the door several times Touch the START key each time the door is closed E Continue operating the unit Four long beep soun...

Page 12: ...All service adjustments should be made for minimum microwave energy leakage readings 3 Do not operate the unit until it is completely repaired if any of the following conditions exist The unit must not be operated a The door does not close firmly b The hinge is broken c The door seal is damaged d The door is bent or warped or there is any other visible damage on the unit that may cause microwave e...

Page 13: ...k 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 EQUIPMENT TESTER VOLTS DC AC Ohmmeter Microwave survey meter Holaday HI 1500 HI 1501 Narda 8100 8200 600 cc non conductive material beake...

Page 14: ... leakage not be more than 2 mW cm2 after determining that all parts are in good condition functioning properly and genuine replacement parts which are listed in this manual have been used 3 At least once a year have the electromagnetic energy leakage monitor checked for calibration by its manufacturer 1 Microwave power output measurement is made with the microwave oven supplied at its rated voltag...

Page 15: ...SPECIALLY SWITCHES AND HIGH VOLTAGE CIRCUIT A REMOVING POWER AND CONTROL CIRCUIT BOARD Figures 1 2 and 3 1 Remove a screw securing the control panel assembly to the oven cavity 2 Remove the control panel with pushing it upward 3 Remove the connector CN1 and wire leads Relay6 from the circuit board 4 Remove 3 screws securing the circuit board 5 Remove the FPC connector from the terminal socket foll...

Page 16: ... F P C connector into the terminal socket securely with the fingers 2 Hold the plastic fastener with thumb and forefinger of the other hand and push it slowly into the terminal socket Figure 6 NOTE When reconnecting the F P C connector make sure that the holes on the F P C connector are properly engaged with the hooks on the plastic fastener 3 Lock the level of the plastic fastener into the hook o...

Page 17: ...ng the screws 1 or 2 screws securing it to the out case 4 Remove two screws on the left central edge and one screws on the right central edge of Base plate Remove the Mount All from the out case by removing one screw securing it to the out case 5 Remove the outcase with disconnecting power cord connector Vent Grille Controller Door Mounting Plate 1 or 2 screws Out Case Mount All Figure 8 7 6 ...

Page 18: ... WH from cooktop lamp Secondary Interlock Switch Monitor Interlock Switch Primary Interlock Switch PK from P C B BL from P C B WH from H V Transformer RD from H V Transformer 7 7 C REMOVING THE DOOR INTERLOCK SWITCHES Figures 9 10 1 Disconnect the wire leads from the interlock switches 2 Remove two screws securing the Latch Board 3 Make necessary replacements and check microwave energy leakage acc...

Page 19: ...ULLY NOTES When removing the magnetron make sure that its dome does not hit any adjacent parts or it may be damaged When replacing the magnetron be sure to install the magnetron gasket in the correct position and be sure that the gasket is in good condition After replacing the magnetron check for microwave energy leakage with a survey meter Check microwave energy leakage must be below the limit of...

Page 20: ...k that the primary interlock switch the secondary interlock switch and the interlock monitor switch is in good operating normally After replacing the door check for microwave energy leakage with a survey meter Microwave energy leakage must be below the limit of 5mW cm2 With a 275 ml water load G DISASSEMBLING DOOR Figure 17 1 Remove the dielectric choke by using knife blade or small screw driver e...

Page 21: ...te by loosening mounting plate screws 1 or 2 screws securing it to the back plate See Figure 18 2 Remove MOUNT ALL loosening one screw loosening one screw securing the ventilation Motor and back plate See Figure 19 a 3 Carefully pull the ventilation motor ASS Y out of the microwave oven See Figure 19 b J REPLACING THE HUMIDITY SENSOR For sensor model only 1 Remove the sensor by removing two screws...

Page 22: ...ews securing it to the oven cavity Figure 21 4 Disconnect the leadwire from the turntable motor terminals 5 Remove the 2 screws securing the turntable motor to the oven cavity ASS Y Figure 22 NOTES Remove the leadwire from the turntable motor VERY CAREFULLY Be sure to grasp the connector not the wires when removing Wire Leads Turntable Motor 7 11 Figure 20 Figure 21 Figure 22 ...

Page 23: ...justment of the latch board may not be necessary Go to Steps 5 and 6 to check the sequence of the switches NOTE To correct sequence of the Primary Interlock Switch Secondary Interlock Switch and the Interlock Monitor Switch is very important If any gap is larger than 1 64 0 5 mm you will need to adjust the latch board Go to step 3 and follow all steps in order ADJUST THE LATCH AND SWITCH CLOSING 3...

Page 24: ...ro to the body of the switches in the following sequence Interlock Monitor Switch Primary Interlock Switch Secondary Interlock Switch NOTE The Interlock Monitor Switch is an added safety check on the Primary and Secondary Interlock Switches If the Primary and Secondary Interlock Switches allow the oven to operate with the door open the Monitor Switch will blow the fuse 7 When you achieve the prope...

Page 25: ... 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 a closed circuit in the door open condition When the door is closed the meter sho...

Page 26: ... each filament terminal of the magnetron and the chassis ground with an ohm mater on high test scale 1 Measure the resistance With an ohm meter on Rx1 scale a Primary winding b Filament winding c Secondary winding 2 Measure the resistance With an ohm meter on highest scale a Primary winding to ground b Filament winding to ground Normal reading Less than 1 ohm Normal reading Infinite ohms NOTE Repl...

Page 27: ...tinuity 1 Forward Ohm meter Figure 26 a 1 Reverse Ohm meter Figure 26 b Normal reading Momentarily indicates several ohms and then gradually returns to infinite ohms Abnormal reading Indicates continuity or infinite ohms from the beginning Normal readings Infinite Abnormal reading Indicates continuity Normal readings continuity Abnormal reading Infinite Normal readings Infinite Abnormal reading co...

Page 28: ... hooks on the plastic fastener MATRIX CIRCUIT FOR TOUCH KEY BOARD CONNECTOR KEY CON 7 17 COMPONENTS TEST PROCEDURES RESULTS TOUCH KEY BOARD SENSOR For sensor model only Resistance value When When not touched touched Less than More than 400 ohms 1 mega ohm 1 2 3 4 5 6 7 8 9 10 11 12 13 FPC CONNECTOR Top Normal Approximately BK RD 4 5 6 2 Kohm RD WH 2 0 3 5 Kohm BK WH 2 0 3 5 Kohm Abnormal Infinite ...

Page 29: ... switches and or the interlock monitor switch Malfunction of the high voltage transformer the high voltage capacitor including the diode the magnetron the blower motor or the circuit board PROBLEMS CAUSES POWER LEVEL 1 2 3 4 5 6 7 8 9 10 4 sec 6 sec 8 sec 10 sec 12 sec 14 sec 16 sec 18 sec 20 sec 22 sec 18 sec 16 sec 14 sec 12 sec 10 sec 8 sec 6 sec 4 sec 2 sec 0 NOTES If the fuse is blown by an i...

Page 30: ...ll operate GOOD Replace the circuit board Replace RELAY1 PROBLEM B FAN motor and oven lamp turn on When the door is closed and START key is touched Measure the voltage at pin NO 35 of U01 Voltage reading 0 Vdc 10 of U03 Voltage reading about 15V Replace the circuit board Defective RELAY1 or poor connection of RELAY1 Defective RELAY1 Replace RELAY1 or correct the connection NO NO YES YES NO NO YES ...

Page 31: ...he interlock switches the door sensing and the relay check good 2 The unit with a normal relay continuously operates 3 Proper temperature measurement is not obtained 4 The buzzer does not sound or continues to sound 5 Some segments of one or more digits do not light up or they continue to light up or segments light when they should not 6 Wrong figures appear 7 The figures of all digits 8 Some of t...

Page 32: ...PERATION on page 6 1 DISPLAY Problems A thru C HELP UP Problems D thru E BUZZER Problems F Measure voltage between pin 1 and pin 3 of connector CN1 Measure resistance of touch key board after removing connector S1 See page 7 4 and 7 17 0 120 120V Replace circuit board Normal circuit board Normal resistance Voltage incorrect Normal resistance Resistance incorrect Replace touch key board Normal touc...

Page 33: ... connector S1 Contact OK Replace Circuit board Correct seating Normal circuit board Normal contact Poor contact Normal Primary switch No continuity Adjust or replace door sensing switch Measure resistance of H V capacitor see page 7 16 Resistance incorrect Normal resistance Measure resistance of fan motor Terminal A C 140 to 150 ohm Terminal A B 25 to 40 ohm Resistance incorrect Replace fan motor ...

Page 34: ... H V C Abnormal Replace H V D Normal Magnetron Replace Magnetron Normal Normal H V D Check the continuity of H V D see page 7 16 Replace H V C Normal resistance Replace H V T Normal resistance NO continuity Replace circuit board Normal circuit board Poor contact Replace circuit board Normal circuit board Contact OK Normal contact Correct seating Check contact of connector S1 Check the contact of r...

Page 35: ...7 24 PROBLEM F No buzzing when touching the key between stages or at end of cooking 1 Normal circuit board Check normal operation circuit board Replace circuit board Runs ...

Page 36: ...e magnetron thermal fuse and oven thermostat Poor contact Replace circuit board Normal circuit board Contact OK Normal contact Correct seating Check contact of connector S1 see page 7 4 Replace ventilation motor ASS Y NO runs Normal ventilation motor ASS Y Check the contact of magnetron thermal fuse and oven thermostat Runs Runs Runs Runs ...

Page 37: ...8 1 EXPLODED VIEW DOOR 13581A 13552A 13536A 13213A 14970A 14026A WTT028 13720D 14890A 13650A 14760A EV ...

Page 38: ...8 2 CONTROL PANEL 24781M 24810P 23572A 07 268711 WTP013 WTT029 23506A EV ...

Page 39: ...8 3 OVEN CAVITY 33530A 34960A 33550P WTT021 WTT029 WTT028 WTT029 33112U WTT022 34810Q 34930R 330342 535502 35230A WTT022 63302A 56804A 368771 63303A 36912C WTT022 330341 35026G EV ...

Page 40: ...8 4 LATCH BOARD 466001 43501A 43500A 466003 466001 44510A WSZ084 EV ...

Page 41: ...8 5 INTERIOR I 33390G 34370T 35889A 33052A 55892A 53550S 340511 54930F WTT021 56930G WSZ002 53300B WSZ002 WTP002 56170D WSZ002 56851D 50CZZH WTT021 54810C 55238A WSZ002 56324A 36549S 568772 33700A EV ...

Page 42: ...8 6 INTERIOR II WTT028 56501A 56930V 55231C 01 568771 WTT028 56549F 55262A WTT034 36549V 56912B WTP004 WSZ002 WTT029 53550L 56411A 55900A 56804A 56901A 02 04 50FZZA WTP013 56820A EV ...

Page 43: ...8 7 INSTALLATION WSZ133 44360A WSZ098 WWZ068 WWZ068 WBZZ02 56411A 65862D 63300M 63861A WBZZ01 WSZ136 65862B EV ...

Page 44: ...8 14 SCHEMATIC DIAGRAM OF P C B ...

Page 45: ...8 15 PRINTED CIRCUIT BOARD ...

Page 46: ...P NO 3828W5S2345 June 2002 Printed in Korea ...

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