LG LSC27990TT Service Manual

CAUTION

PLEASE READ CAREFULLY THE SAFETY PRECAUTIONS OF THIS MANUAL BEFORE CHECKING OR OPERATING THE REFRIGERATOR.

REFRIGERATOR

SERVICE MANUAL

MODEL : LSC27990TT COLOR : TITANIUM

http://aic.lgservice.com

CONTENTS

WARNINGS AND PRECAUTIONS FOR SAFETY ................................................................................................................ 3

SPECIFICATIONS................................................................................................................................................................... 4

PARTS IDENTIFICATION ........................................................................................................................................................5

HOW TO INSTALL THE REFRIGERATOR ............................................................................................................................ 6

HOW TO ADJUST DOOR HEIGHT...................................................................................................................................... 6

FILTER ................................................................................................................................................................................. 7

HOW TO CONTROL THE ICEMAKER WATER SUPPLY.................................................................................................... 8

MICOM FUNCTION ................................................................................................................................................................ 9

EXPLANATION OF MICOM CIRCUIT...................................................................................................................................22

EXPLANATION OF PWB CIRCUIT .....................................................................................................................................22

PWB PARTS DIAGRAM AND LIST .....................................................................................................................................37

PWB CIRCUIT DIAGRAM ...................................................................................................................................................43

ICEMAKER AND DISPENSER WORKING PRINCIPLES AND REPAIR ............................................................................45

WORKING PRINCIPLES.................................................................................................................................................... 45

FUNCTION OF ICEMAKER ............................................................................................................................................... 46

CIRCUIT................................................................................................................................................................................ 48

TROUBLE DIAGNOSIS........................................................................................................................................................ 49

TROUBLESHOOTING ....................................................................................................................................................... 49

FAULTS .............................................................................................................................................................................. 59

COOLING CYCLE HEAVY REPAIR ................................................................................................................................... 76

HOW TO DEAL WITH CLAIMS.......................................................................................................................................... 83

TV-RADIO ............................................................................................................................................................................. 88

SAFETY PRECAUTIONS................................................................................................................................................... 88

FEATURE........................................................................................................................................................................... 88

CONTROLS........................................................................................................................................................................ 89

REMOTE CONTROL KEY FUNCTIONS ........................................................................................................................... 90

TROUBLESHOOTING ....................................................................................................................................................... 91

BLOCK DIAGRAM.............................................................................................................................................................. 92

TV PART DISASSEMBLE .................................................................................................................................................. 93

HOW TO DISASSEMBLE AND ASSEMBLE....................................................................................................................... 94

DOOR................................................................................................................................................................................. 94

HANDLE ............................................................................................................................................................................. 95

FAN SHROUD GRILLE ...................................................................................................................................................... 95

WATER VALVE DISASSEMBLY METHOD .........................................................................................................................96

FAN and FAN MOTOR DISASSEMBLY METHOD..............................................................................................................96

DISPENSER....................................................................................................................................................................... 97

EXPLODED VIEW ................................................................................................................................................................ 99

REPLACE PARTS LIST.......................................................................................................................................................106

- 2 -

WARNINGS AND PRECAUTIONS FOR SAFETY

Please observe the following safety precautions to use the refrigerator safely and correctly and to prevent accident or injury when servicing.

1. Be careful of an electric shock. Disconnect the power cord from wall outlet and wait for more than three minutes before replacing PWB parts. Shut off the power whenever replacing and repairing electric components.

2. When connecting the power cord, please wait for more than five minutes after the power cord was disconnected from the wall outlet.

3. Check if the power cord is pinched between the refrigerator and the wall. If the plug or cord is damaged, it could cause a fire or an electric shock

4. If the wall outlet is overloaded, it may cause a fire. Use a dedicated circuit for the refrigerator.

5. Make sure the outlet is properly grounded. Particularly in a wet or damp area.

6. Use standard electrical components.

7.Remove dust and foreign materials from the housing and

connecting parts.

8. Do not fray, damage, run over, kink, bend, pull out, or twist the power cord.

9. Check for evidence of moisture intrusion in the electrical components. Replace the parts or mask with insulation tape if moisture intrusion was confirmed.

10. Do not insert fingers or tools into the icemaker. The geared motor drive could cause an injury or damage to tools or the icemaker .

11. Do not suggest that customers repair their refrigerator

themselves. This work requires special tools and knowledge. Non-professionals could cause fire, injury, or damage to the product.

12. Do not store flammable materials such as ether, benzene, alcohol, chemicals, or gas.

13. Do not put anything on top of the refrigerator, especially something containing water, like a vase.

14. Do not put glass bottles with full of water into the freezer. The contents will freeze and break the glass bottles.

15. When you scrap or discard the refrigerator, remove the doors and dispose of it where children are not likely to play in or around it.

16. This is a consumer grade product. It is not intended for precise storage of medication.

- 3 -

SPECIFICATIONS

724 mm (28

in.)

1004 mm (391/2 in.)

908 mm (39

/16 in.)

779 mm (30

in.)

829 mm (32

in.)

897 mm (35

in.)

1261 mm (49

in.)

1741.5 mm (68

in.)

1746.5 mm (68

in.)

1771 mm (69

in.)

1771 mm (69

in.)

1. Ref No. : GR-G277STSA(LSC27990TT)

ITEMS SPECIFICATIONS

DIMENSIONS 908 X 896 X 1771 mm

X D X

H (35

NET WEIGHT 145 kg (319.7 lbs.)

COOLING SYSTEM Fan Cooling

TEMPERATURE CONTROL Micom Control

DEFROSTING SYSTEM Full Automatic

INSULATION Cyclo-Pentane

COMPRESSOR PTC Starting Type

EVAPORATOR Fin Tube Type

CONDENSER Wire Condenser

REFRIGERANT R134a (185g) (6

LUBRICATING OIL FREOL @10G (320 cc)

/16X355/16X6911/16 in.)

Heater Defrost

/2 oz.)

ITEMS SPECIFICATIONS

DRIER MOLECULAR SIEVE XH-7

CAPILLARY TUBE ID Ø0.83

FIRST DEFROST 4 - 5 Hours

DEFROST CYCLE 13 - 15 Hours

DEFROSTING DEVICE Heater, Sheath

ANTI-SWEAT HEATER Dispenser Duct Door Heater

Dispenser Heater

ANTI-FREEZING HEATER Water Tank Heater

Damper Heater

FREEZER LAMP 40W (1 EA)

REFRIGERATOR LAMP 40W (4 EA)

DISPENSER LAMP 15W (1 EA)

Front View Top View

- 4 -

PARTS IDENTIFICATION

1. Ref No. : GR-G277STSA(LSC27990TT)

PWB Cover

Frame Display

Dispenser Lamp

Ice & Water

Dispenser Button

Automatic Icemaker

Freezer

Compartment

Water Tubes

Refrigerator

Compartment

Dairy Product Corner

Water Filter

Lamp Shelf

Lamp

Shelf

Drawer

Door Rack

Drawer

Door Rack

Lower Cover OptiFresh Display Humidity Switch

- 5 -

Shelf

Snack Drawer

Door Rack

Lamp

Bottle Guide

Vegetable Drawer

OptiFresh

Door Rack

HOW TO INSTALL REFRIGERATOR

Adjusting Screw

Driver

Height Difference

Height

Difference

Keeper nut

Down

Adjustment hinge pin

Tool for adjustment

1. How to Adjust Door Height of Refrigerator

■ Make the refrigerator level first. (If the refrigerator is not installed on a flat floor, the height of freezer and refrigerator door may not be the same.)

1) If the freezer door is lower than the refrigerator door:

2) If the freezer door is higher than the refrigerator door:

Insert a driver  into the groove  of the adjusting screw and turn in the direction of the arrow (clockwise) until the refrigerator is level.

3) When the refrigerator door is lower than the freezer door

Adjust the level when the refrigerator door is lower than the freezer door during

the use of the refrigerator. (1) Using the wide side of the tool for adjustment , turn the

keeper nut  ( ) clockwise to loosen the keeper nut.

(2) Using the narrow side of the tool for adjustment, turn the

adjustment hinge pin  ( ) clockwise or ( ) counterclockwise to level the refrigerator and freezer door.

(3) After setting the level of the door, turn the keeper nut ( )

counterclockwise to tighten.

Caution : Do not force too hard to level the height. The hinge

pin can be pulled out (Adjustable range of height: Maximum of 2/10

- 6 -

Insert a driver  into the groove  if the adjusting screw and turn in the direction of the arrow (clockwise) until the refrigerator is level.

HOW TO INSTALL REFRIGERATOR

2. Filter

Replace the filter when the indicator light comes on or the performance of the icemker or water dispenser decreases noticeably.

After changing the water filter cartridge, reset the water filter status display and indicator light by pressing and holding the FILTER Button for 3 seconds. (page 13)

1) Remove the old cartridge.

Twist the knob of the cartridge counterclockwise.

2) Replace with a new cartridge.

Take the new cartridge out of its packaging and remove protective cover from the o-rings.

With cartridge knob in the vertical position, push the new filter cartridge into the cover until it stops.

If you can’t turn the filter from side to side, it isn’t fully inserted. Push it in firmly and twist it into place. You will hear the snap when it clicks into place.

Using the handle, twist the cartridge clockwise about 1/4 turn.

When the cartridge is removed, you will feel it click .

Pull out the cartridge.

NOTE: There will be some water (25cc) in the filter

cartridge. Some spilling may occur. Catch it in a bowl or towel.

3) Flush the Water System After Replacing Filter

Dispense water through the water dispenser for 3 minutes to purge the system. There may be a little air in the line, causing noise or hissing. Run the water at the dispenser until the hissing stops to purge the air from the system.

NOTE: - To purchase replacement water filter cartridges,

visit your local appliance dealer or part distributor.

- You can also visit our website : www.lgappliances.com or call 1-877-714-7481.

LG MDL PART NO MAKER

GR-G277STSA

(LSC27990TT)

5231JA2006A CUNO

- 7 -

HOW TO INSTALL REFRIGERATOR

Water Amount Indicator Light

Power Switch

Water Amount Selection Button

Feeler Arm

Check water level

3. How to Control the Amount of Water Supplied to Icemaker.

3-1. Confirm the amount of water supplied to the icemaker.

1) Confirm the amount of water supplied to the icemaker

(1) Press the button (Figure 1) to selsct the level of water (Optimum level

2) Icemaker Operation Test (Test mode)

(1) Press the button (Figure 1) for more than 3 seconds and It will start the Test mode.

(2) Test the operation of the operating part of the icemaker.

(3) If there is no problem with the operation, water is supplied through the water tube (up to the

selected lebel of water).

(4) The test mode is completed after the water is supplied.

Note : When using the test mode more than twice consecutively, water can overflow.

When the water overflows, wipe the ice storage bin.

Large Small.)

* It is acceptable if the adjusted level of water is a bit smaller than optimum level.

Figure 1.

- 8 -

MICOM FUNCTION

Temperature Adjust Button

MENU Selection Button Dispenser Selection Button Lock Button Door Alarm Button

Dispenser Light Button

Calendar & Anniversary Reminder

1. Monitor Panel

1-1. GR-G277STSA(LSC27990TT)

- 9 -

MICOM FUNCTION

Door Alarm Buzzer Mute Mode

Communication Data Check Mode

LCD Check Mode

Demo Mode

1-2. Display Second Function

1. Door Alarm Buzzer Mute Mode

Press button to the buzzer on or off.

2. Demo Mode

Demo mode is available for displaying the refrigerator in a sales setting or similar condition. It allows the display, dispenser, lights, and fan to operate without running the compressor.

To enter the DEMO mode, press and hold the TEMPERATURE and button simultaneously for 5 seconds until the Ding~ sounds in the lock status.

To exit the DEMO mode and return to normal operation, press and hold the TEMPERATURE and button simultaneously for 5 seconds until the Ding~ sounds again in the lock status. The refrigerator will default to the NORMAL mode (DEMO mode OFF) if the power fails.

2. LCD Check Mode Press TEMPERATURE and button simultaneously for 1 second in the lock status.

4. Communication Data Check Mode

Press MENU and button simultaneously for 6 seconds in the lock status.

- 10 -

MICOM FUNCTION

2. Description of Function

2-1-1. Function of Temperature Selection

Division Power Initially On 1st Press 2st Press 3th Press 4th Press

Setting Temperature

Temperature Control

Freezer Control

Refrigeration Control

* The temperature can vary ±5°F (±3°C) depending on the load condition.

❉ Whenever pressing button, setting is repeated in the order of COLD ➝ COLDER ➝ COLDEST ➝ COOL ➝ COLDER.

• The actual inner temperature varies depending on the food status, as the indicated setting temperature is a target temperature, not actual temperature within refrigerator.

• Refrigeration function is weak in the initial time. Please adjust temperature as above after using refrigerator for minimum 2~3 days.

• Freezer Notch is fixed COLDER unconcerned with display Notch during Icemaking Control Mode and Icemaker Stop switch is selected with ON.

2-1-2. Outside temperature display function

1. The ambient temperature sensor is located under the upper right hinge cover. This sensor reads the

2. The ambient temperature is displayed between 16 °F and 120 °F. Outside of that range, the display will

3. Since the ambient temperature sensor is located at the hinge, its reading may differ from other

COLD COLDER COLDEST COOL COOLER

-2 °F -5 °F -8 °F7 °F1 °F

37 °F 34 °F 32 °F 46 °F 41 °F

temperature of the room and displays it in the upper right corner of the display.

show Er.

thermometers in the room.

- 11 -

MICOM FUNCTION

2-1-3. Lock function

1. If desiring to lock the dislay the dispenser and control panel, push on button more than 3 seconds. Lock icon is appeared at the right of display with lock status.

2. The buzzer sound and control panel and dispenser function is not performed even if pressing display button other than lock key in the lock status.

3. If desiring to release the lock status and pressing the lock button more than 3 seconds. Lock icon is disappeared at the right of display with the lock release status.

LED

2-1-4. Filter condition display function

1. There is a replacement indicator light for the water filter cartridge on the dispenser.

2. Water filter needs replacement once six months.

3. You will see a reminder pop-up window in the LCD screen 2 weeks before / 1 week before / due date to replace the filter to notify you that the filter needs to be replaced.

4. If you want to reset the filter,use the Menu → Refrigerator → Filter Reset menu.

- 12 -

MICOM FUNCTION

Pressing

Switch

2-2. Dispenser use selection

You can select water or ice.

❉ Select WATER, CRUSHED ICE, or CUBED ICE by pressing the DISPENSER button as you desire.

❉ Use your cup to press lightly on the actuator.

• Each graphic is indicated for the selected function.

• You’ll hear a CLICK when the ice door closes 5 seconds after ice is dispensed.

REFERENCE : Hold your cup in the dispenser for a few seconds after dispensing

ice or water to catch the last few drops or pieces of ice.

2-3. ICE PLUS Freezing

Select this function to expedite freezing.

• Turn on/off the IcePlus function using the IcePlus button within the Temperature function.

• The "IcePlus" icon remains at the ON status after animation when selecting Special Refrigeration IcePlus FRZ

• ICE PLUS freezer function automatically turns off after a set time.

2-4. Dispenser Light

• The dispenser light function is repeated following below whenever pressing button.

- 13 -

MICOM FUNCTION

2-5. ICE PLUS freezing

1. ICE PLUS freezing is a function to increase the cooling speed of the freezer compartment by running both the compressor and the fan simultaneously.

2. ICE PLUS is cancelled and the refrigerator returns to its default setting in the event of a power interruption.

3. Selecting ICE PLUS changes only the speed of the cooling without affecting the set temperature.

4. The temperature can be adjusted even when ICE PLUS has been selected and is in progress.

5. The freezer operates at whatever temperature was set at the time ICE PLUS was selected.

6. If you select ICE PLUS, the compressor and fan will run until it is deselected or the cycle time has elapsed. (3 hours : compressor and fan run / 3 ~ 24 hours : COLDEST operation)

7. If a defrost cycle occurs while an ICE PLUS is already running, ICE PLUS runs for its remaining cycle time after the defrost cycle is completed. If the defrost cycle takes longer than 30 minutes, ICE PLUS will run for only 2 hours at the end of the defrost cycle.

8. If you press ICE PLUS during a defrost cycle, the ICE PLUS indicator will illuminate but the compressor will not operate until the defrost cycle is complete.

9. If you press ICE PLUS within 7 minutes of compressor cut-off, the compressor will not operate until the 7-minute delay has passed.

10. The freezer fan motor runs at high speed during the ICE PLUS cycle.

2-6. OptiFresh Function

1. The OptiFresh bin is positioned at the bottom of the refrigerator compartment and has a separate temperature control to allow perfect storage of fruits and vegetables.

2. OptiFresh comprises of OptiFresh sensor at the rear of OptiFresh and a damper between OptiFresh and Freezer compartment and a temperature adjusting display at the top of it.

3. When powered on, the initial NOTCH of OptiFresh display will be on OptiFresh Crisper. If only the refrigerator door is opened, the OptiFresh LED will be ON.

4. The OptiFresh sensor opens and closes the damper based on the temperature.

5. The OptiFresh damper will cycle every hour to prevent icing up.

• Press the button to toggle between ON and OFF.

- 14 -

MICOM FUNCTION

Doors of freezer, refrigerator, or home bar.

BUZZER

Closing

Opening

Less than

one minute

One minute

seconds30seconds30seconds

Opening

Closing Closing

3 Times 3 Times 3 Times 3 Times

2-7. Control of variable type freezing fan

1. To increase cooling speed and response to load, the MICOM will vary the speed of the freezer fan between low and high.

2. The MICOM runs the fan at high speed only at power-up and for ICE PLUS cycles, and runs at low speed for all other settings.

3. If you open the freezer door, the refrigerator door, or the home bar door, and the freezer fan was running at high speed, it will reduce to low speed. If it was running at low speed when a door was opened, it will turn off.

4. If the MICOM determines the BLDC fan motor is locked up, (no signal for 115 seconds) it will show a failure code on the display and cut power to the fan. To power the fan again, unplug the refrigerator for a few seconds and plug it in again.

2-8. Control of cooling fan motor

1. The cooling fan motor performs ON/OFF control by linking with the COMPRESSOR.

2. It controls at the single RPM without varying RPM.

3. Failure sensing method is same as in fan motor of freezing fan motor (refer to failure diagnosis function table for failure display).

2-9. Door opening alarm

1. The buzzer sounds when any door is held open for more than one minute.

2. After any door has been open for one minute, the buzzer sounds three times for times for

3. When all open doors have been closed, the buzzer stops.

second each every thirty seconds until the door is closed.

second each, then it sounds three

2-10. Ringing of button selection buzzer

1. If pressing the front display button, Ding ~ sound rings.

- 15 -

MICOM FUNCTION

2-11. Ringing of manual operation, manual frost defrost buzzer

1. The buzzer sounds briefly when the test button on the main PCB is pressed.

2. If you select manual operation, the buzzer sounds three times for second each every thirty seconds until the door is closed.

3. If you select manual defrost, the buzzer sounds three times for each every thirty seconds until the door is closed.

2-12. Defrost function

1. Defrost is cycled whenever the compressor’s runtime reaches 7 ~ 7 hours.

2. In providing initial power (or returning power failure), defrost starts whenever total operation time of compressor becomes 4 ~ 4

3. Defrost is completed if temperature of a frost removal sensor becomes more than 5°C after starting frost removal. Poor frost removal is not displaced if it does not arrive at 5°C even if two hours have passed after starting frost removal.

4. No defrost cycle is run if the defrost sensor fails.

hour.

2-13. Refrigerator room lamp automatic off

• Refrigerator room lamp turn on and off by refrigerator door switch.

• If refrigerator room lamp continuously turns on more than 7 minutes, the refrigerator room lamp turns off automatically.

/10second each, then it sounds three times for 2/

second

- 16 -

MICOM FUNCTION

POWER

COMP

F-FAN

C-FAN

R-STEP MOTOR

DAMPER

OPTICHILL

STEP

DAMPER

MOTOR

FROST

REMOVAL

HEATER

OFF

FROST

REMOVAL

HEATER

DAMPER

DUCT DOOR

OPTICHILL

HEATER ON

DAMPER

DUCT DOOR

OPTICHILL

HEATER OFF

0.3

sec.

6.0

sec.

0.3

sec.

0.3

sec.

0.3

sec.

0.3

sec.

PIPE

DISP'

HEATER

OFF

0.3

sec.

COMP

0.3

sec.

F-FAN

C-FAN

0.3

sec.

R-STEP MOTOR

DAMPER

0.3

sec.

OPTICHILL

STEP

DAMPER

MOTOR

PIPE

DISP'

HEATER

TEST

SWITCH

(PRESS

Once)

OTHER

LOAD

OFF

COMP

F-FAN

C-FAN

R-STEP MOTOR

DAMPER

OPTICHILL

STEP

DAMPER

MOTOR

TEST

SWITCH

(PRESS

2 Times)

COMP

OFF

F-FAN

C-FAN

OFF

FROST

REMOVAL

HEATER

R-STEP

MOTOR

DAMPER

0.3

sec.

0.3

sec.

0.3

sec.

0.3

sec.

0.3

sec.

0.3

sec.

0.3

sec.

0.3

sec.

0.3

sec.

0.3

sec.

0.3

sec.

POWER

2-14. Sequential operation of components

Component products such as compressor, frost removal heater, freezing room fan, cooling fan, and step motor damper are

sequentially operated as follows for preventing noise and part damage occurred due to simultaneous operation of many

parts in applying initial power and completing test.

Function Load Operation Sequence Remark

When temperature of a frost removal

sensor becomes more than 45°C

If error occurs during operation, initial operation is not done.

(At purchase,

shipping)

In applying Initial power TEST MODE

When temperature of a

frost removal sensor becomes less than 45°C (In power failure,

■

Sequence of load operation when closing FREEZER and REFRIGERATOR.

service)

Test mode 1 (Manual function)

If you press the switch in the again test mode 2 or temperature of a frost removal sensor is more

Test mode 2 (Manual frost

removal)

than 5°C, it immediately returns to the test mode for initial operation (COMPRESSOR operates after 7 minutes).

- 17 -

MICOM FUNCTION

2-15. Failure Diagnosis Function

1. Failure diagnosis facilitates service when a failure code shows during product operation.

2. When a failure is detected, the buttons are deactivated.

3. If a failure code is released, the MICOM resets and normal operation continues.

4. The failure code is displayed on the display screen. All display graphics that are not part of the failure code are turned off

(1) GR-G277STSA(LSC27990TT)

- 18 -

MICOM FUNCTION

✻ LCD check function: If simultaneously pressing TEMPERATURE and button for a second in the lock status, a

back light is turned on and all display LCD graphics on. If releasing the button, the LCD graphic displays the previous status.

- 19 -

MICOM FUNCTION

2-16. Test Function

1. The test function assists in diagnosing the PWB and determining the exact mode of failure.

2. The test button is on the main PCB. When test mode is engaged, it will complete its test cycle and default to normal operation within 2 hours.

3. The buttons are disabled while the test mode is in effect.

4. When you have finished running test mode, unplug the refrigerator to reset it to normal operation.

5. If a failure is detected during test mode, release the test mode to display the failure code.

6. If a failure code is displayed, the test mode cannot be started.

Mode Operation Contents Remarks

Test 1

Test 2

Normal

Status

Press test button once (strong cold mode)

Press test button once at the test mode 1 status (forced defrost mode)

Press test button once at the test mode 2 status

1. Continuous operation of compressor

2. Continuous operation of freezing BLDC motor (high-speed RPM) and cooling BLDC motor

3. Defrost heater turns off

4. Stepping motor damper is completely opened (baffle is closed)

5. OptiFresh stepping motor damper is completely closed.

6. All display LCD graphics turn on.

1. Compressor OFF

2. Freezing BLDC motor and cooling BLDC motor turn off

3. Defrost heater turns on

4. Stepping motor damper is completely closed (baffle is closed)

5. OptiFresh stepping motor damper is completely closed.

Return to the initial status.

Freezer fan turns off when door is opened.

Return to the normal mode when the defrost sensor is above +5°C (+41°F)

Compressor will operate after delay for 7 minutes

- 20 -

MICOM FUNCTION

2-17. Dispenser Function

1. The dispenser allows serving ice and water without opening the door.

2. Pressing the dispenser switch dispenses crushed or cubed ice or water. If ice is selected, the switch operates the door solenoid also. The door will close 5 seconds after the ice is dispensed.

3. If the freezer door is opened, the dispenser is deactivated.

4. If there is no OFF signal 3 minutes after the ice dispenser is activated, the auger and door solenoid are turned off. The auger will stop immediately, but the door will not close for another 5 seconds.

5. The dispenser lamp turns on automatically if the crushed/cubed/water button is pressed or if the dispenser button is pressed. It will turn off automatically shortly thereafter.

6. Selection function of water/crushed/cube ice

1) Select crushed/cubed/water. The display will show your selection.

2) If you select cubed ice, the auger is rotated to dispense cubes.

3) If you select crushed ice, the auger is rotated in the opposite direction to direct the cubes through the crusher.

7. Water dispenser function

1) If you select water, the display will indicate water.

2) The water dispenser uses a solenoid connected directly to the water pipe. Pressing the dispenser switch operates the solenoid, which is at the right side of the back plate.

- 21 -

EXPLANATION FOR MICOM CIRCUIT

1. Explanation for PWB circuit

1-1. Power circuit

The power circuit includes a Switched Mode Power Supply (SMPS). It consists of a rectifier (BD1 and CE1) converting AC to DC, a switch (IC2) switching the DC voltage, a transformer, and a feedback circuit (IC3 and IC4).

Caution : Since high voltage (160 Vdc) is maintained at the power terminal, wait at least 3 minutes after unplugging the

appliance to check the voltages to allow the current to dissipate.

Voltage of every part is as follows:

Part VA1 CE1 CE2 CE3 CE4 CE5

Voltage 120 Vac 160 Vdc 14 Vdc 12 Vdc 15.5 Vdc 5 Vdc

(1) GR-G277STSA(LSC27990TT)

- 22 -

EXPLANATION FOR MICOM CIRCUIT

1-2. Oscillation circuit

The oscillation circuit generates a basic clock signal for synchronization and time calculation related to the transmission of data and calculations made by the MICOM (IC1). The oscillator (OSC1) must always be replaced with an exact replacement part. If this specification is changed, the change will affect the time calculations of the MICOM and it might not work at all.

(1) GR-G277STSA(LSC27990TT)

1-3. Reset circuit

The RESET circuit allows various parts of the MICOM, such as RAM, defrosting, etc., to be restarted from the initial state when power is interrupted or restored. A LOW signal applied to the reset terminal for 10 ms causes the MICOM to reset itself. During normal operation, the voltage at the reset terminal is 5 Vdc. If the reset fails, the MICOM will not operate.

(1) GR-G277STSA(LSC27990TT)

- 23 -

EXPLANATION FOR MICOM CIRCUIT

1-4. Load/dispenser operation, door opening circuit

1. LOAD DRIVING CIRCUIT

✽ The fan operates at the regular speed even if the door of the refrigerator or freezer is opened. When the doors are closed,

the fan reverts to its original speed.

✽ (A), (B), (C), and (D) of door switch for the freezer or refrigerator are connected to the door open sensing circuit in parallel

toward both ends of switch to determine door open at MICOM.

✽ In the TEST mode, the fan will stop if any door is opened. It will resume operation when the door is closed.

Type of Load Compressor

Measuring part (IC6) IC6-16 IC6-13 IC6-12 IC6-15 IC6-14

Status

ON Within 1 V

OFF 12 V

Defrost

Heater

AC Converting

Relay

Refrigerator

LAMP

Dispenser

Heater

(1) GR-G277STSA(LSC27990TT)

- 24 -

EXPLANATION FOR MICOM CIRCUIT

1-5. Dispenser operation circuit

(1) GR-G277STSA(LSC27990TT)

1) Check load driving status

Type of Load

Measuring part IC7-15 IC7-14 IC7-13 IC7-12 IC7-11

Status

2) Lever Switch sensing circuit

Measuring part

Lever S/W

OFF 5V

ON Within 1 V

OFF 12 V

GEARED

MOTOR

SOLENOID

CUBE

5 V

0 V

WATER VALVE

WATER

IC1(Micom) (No. 16)

PILOT

VALVE

(60 Hz)

DISPENSER

- 25 -

SOLENOID

EXPLANATION FOR MICOM CIRCUIT

1-6. Door opening sensing circuit

(1) GR-G277STSA(LSC27990TT)

Measuring part

Door of Freezer and Refrigerator

Closing 5 V ( A - B , C - D . Switch at both ends are at Off status)

Opening 0 V ( A - B , C - D . Switch at both ends are at On status)

✽ Since door switches (A) and (B) are interconnected, if either fails, the other will not respond properly. ✽ If either switch fails, the light will not come on.

IC1 (MICOM) No. (44, 45) / (45, 46) / (47, 48) Pin

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EXPLANATION FOR MICOM CIRCUIT

1-7. Temperature sensing circuit

(1) GR-G277STSA(LSC27990TT)

The circuits involving the freezer and refrigerator sensors control the temperature in both the freezer and the refrigerator. The icemaker sensor detects when ice is made. The defrost sensor determines both the need for defrosting and the efficiency of the defrost operation. See the table below for voltages and checkpoints.

SENSOR CHECK POINT

Freezing sensor POINT A Voltage

Defrost sensor POINT B Voltage

Refrigerator sensor 1 POINT C Voltage 0.5 V~4.5 V 0 V 5 V

Refrigerator sensor 2 POINT D Voltage

Magic room/ Opti Fresh Sensor POINT E Voltage

NORMAL(-22 °F ~ 122 °F) IN

SHORT IN OPEN

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EXPLANATION FOR MICOM CIRCUIT

1-8. Switch entry circuit

The following circuits are sensing signal form the damper motor reed switch for testing and diagnosing the refrigerator.

(1) GR-G277STSA(LSC27990TT)

1-9. Option designation circuit (model separation function)

(1) GR-G277STSA(LSC27990TT)

The circuits shown above vary according to which features are included on your particular model.

Separation Connection Status Application Standard

OP1

uThese circuits are preset at the factory and cannot be altered.

Connection OptiFresh exist

OUT OptiFresh don’t exist

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EXPLANATION FOR MICOM CIRCUIT

INA

INB

CCW (Reverse rotation) (Positive rotation) CW

1-10. Stepping motor operation circuit

(1) GR-G277STSA(LSC27990TT)

The motor is driven by magnetism formed in the areas of the coils and the stator. Rotation begins when a HIGH signal is

applied to MICOM Pin 33 of IC10 (TA7774F). This causes an output of HIGH and LOW signals on MICOM pins 34 and 35.

Explanation) The stepping motor is driven by sending signals of 3.33 mSEC via MICOM pins 33, 34, and 35, as shown in

the chart below. These signals are output via terminals 10, 11, 14, and 15 via input terminals 3, 6, and 8 of IC10 (TA7774F), the motor drive chip. The output signals allow the coils wound on each phase of the stator to form a magnetic field, which causes rotation. Input to the terminals INA and INB of IC10 as shown in the chart below drives the motor.

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EXPLANATION FOR MICOM CIRCUIT

1-11. Fan motor driving circuit (freezer, mechanical area)

1. The circuit cuts all power to the fan drive IC, resulting in a standby mode.

2. This circuit changes the speed of the fan motor by varying the DC voltage between 7.5 Vdc and 16 Vdc.

3. This circuit stops the fan motor by cutting off power to the fan when it senses a lock-up condition.

a , d part b part e part

Motor OFF 5V 2V or less 2V or less

Motor ON 2 ~ 3V 12 ~ 14V 8 ~ 16V

(1) GR-G277STSA(LSC27990TT)

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