Lg Gms-1120tw Service Manual

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MICROWAVE OVEN

SERVICE MANUAL

MODEL : GMS-1120TW

CAUTION

BEFORE SERVICING THE UNIT, READ THE SAFETY PRECAUTIONS IN THIS MANUAL.

P/NO : 3828W5S2299

Printed in Korea

SAFETY PRECAUTIONS

This device is to be serviced only by properly qualified service personnel.

Consult the service manual for proper service procedures to assure continued safety operation and for precautions to be taken to avoid possible exposure to excessive microwave energy.

PRECAUTIONS TO BE OBSERVED BEFORE AND DURING SERVICING TO AVOID POSSIBLE EXPOSURE 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 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 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 Federal Performance Standard should be performed on each oven prior to release to the owner.

CONTENTS

(Page)

SAFETY PRECAUTIONS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Inside front cover SPECIFICATIONS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 1-1 CAUTIONS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2-1 INSTALLATIONS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3-1 OPERATING INSTRUCTIONS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4-1

FEATURES- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4-1 CONTROL PANEL - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4-1 OPERATING SEQUENCE- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4-2 SCHEMATIC DIAGRAM - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4-3 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 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 5-11

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

SPECIFICATIONS

ITEM		DESCRIPTION
MODEL	GMS-1120TW
Power Requirement	120 Volts AC 60 Hz
	1,500 Watts (13 A)
	Single phase, 3 wire grounded
Power Output	1,100 Watts full microwave power (IEC60705)
Microwave Frequency	2,450 MHz
Magnetron	2M246
Timer	0 ~ 99 min. 99 sec.
Outside Dimensions	201/8” (W) x 12” (H) x 155/16” (D)
Cavity Dimensions	137/8” (W) x95/16” (H) x 143/16” (D)
Net Weight	33 lbs (approx.)
Shipping weight	35 lbs (approx.)
Control Complement	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. 60%
	5 (Med.-Low) --------------------	approx. 50%,	4 (Defrost) ---------	approx. 40%
	3 (Low) ---------------------------	approx. 30%,	2 (Simmer)---------	approx. 20%
	1 (Warm)--------------------------	approx. 10%
Accessories	Owner's manual & cooking guide
	Glass turntable
	Rotating ring

It is not recommended for commercial purposes.

1-1

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 during repair.

•DO NOT operate on a 2-wire extension cord during repair and use.

•NEVER TOUCH any oven components or wiring during operation.

•BEFORE TOUCHING any parts of the oven, always remove the power plug from the outlet.

•For about 30 seconds after the oven stops, an electric charge remains in the high voltage capacitor. When replacing or checking, you must discharge the high voltage capacitor by shorting across the two terminals with an insulated screwdriver.

•Remove your watches whenever working close to or replacing the Magnetron.

•DO NOT touch any parts of the control panel circuit. A resulting static electric discharge may damage this P.C.B.

•NEVER operate the oven with no load.

•NEVER injure the door seal and front plate of the oven cavity.

•NEVER put iron tools on the magnetron.

•NEVER put anything into the latch hole and the interlock switches area.

MICROWAVE RADIATION

Personnel should not be exposed to the microwave energy which may radiate from the magnetron or other microwave generating device if it is improperly used or connection. All input and output microwave connections, waveguide, flange, and gasket must be secure never operate the device without a microwave energy absorbing load attached.

Never look into an open waveguide or antenna while the device is energized.

•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.

ANTENNA

Gasket

COOLING FIN

FILAMENT

TERMINALS

MAGNETRON

CHASSIS GROUND

MAGNETRON

THE OVEN IS TO BE SERVICED ONLY BY PROPERLY QUALIFIED SERVICE PERSONNEL.

2-1

INSTALLATIONS

BEFORE YOU BEGIN, READ THE FOLLOWING INSTRUCTIONS COMPLETELY AND CAREFULLY.

INSTALLING

1.Empty the microwave oven and clean inside it with a soft, damp cloth. Check for damage such as misaligned door, damage around the door or dents inside the cavity or on the exterior.

2.Put the oven on a counter, table, or shelf that is strong enough to hold the oven and the food and utensils you put in it. (The control panel side of the oven is the heavy side. Use care when handling.)

3.Do not block the vent and the air intake openings. Blocking vent or air intake openings can cause damage to the oven and poor cooking results. Make sure the microwave oven legs are in place to ensure proper air flow.

4.The oven should not be installed in any area where heat and steam are generated, because they may damage the electronic or mechanical parts of the unit.

Do not install the oven next to a conventional surface unit or above a conventional wall oven.

5.Use microwave oven in an ambient temperature less than 104°F (40°C).

6.Place the microwave oven on a sturdy and flat 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.

10cm

GROUNDING INSTRUCTIONS

For personal safety, this appliance must be fully grounded 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.

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 ground prong from the power cord plug.

PREFERRED METHOD

ENSURE PROPER GROUND

EXISTS BEFORE USE

TEMPORARY METHOD (ADAPTER PLUGS NOT PERMITTED IN CANADA)

ALIGN LARGE

PRONGS/SLOTS

ENSURE PROPER GROUND

AND FIRM CONNECTION

BEFORE USE

3-1

OPERATING INSTRUCTIONS

FEATURES

Window Door Screen Oven Front Plate

Door Seal

Display Window

Control Panel

Safety Door Lock System

Turntable

Rotating Ring

CONTROL PANEL

1. DISPLAY. The display includes a clock and

indicators that tell you time of day, cooking time

settings, and cooking functions selected.

2. ONE TOUCH POPCORN. Touch this pad

to pop a bag of microwave popcorn without entering a

cook power or time.

3. ONE TOUCH POTATO. Touch this pad to cook up to 4

potatoes without entering a cook power or time.

4. ONE TOUCH BEVERAGE. Touch this pad to heat up to

2 cups of beverage without entering a cook power or

time.

5. ONE TOUCH FOOD PLATE. Touch this pad to heat a

plate of food without entering a cook power or time.

6. FRESH VEGETABLE. Touch this pad to cook fresh

vegetables without entering a cook power or time.

7. FROZEN ENTREE. Touch this pad to cook a 10 oz.

frozen entrée without entering a cook power or time.

8. ONE TOUCH PIZZA: Touch this pad to heat up to 3

slices of regrigerated pizza without entering a cook

power or time.

9. AUTO DEFROST. Touch this pad to meat, poultry, or

steaks/chops by entering a weight.

10. CLOCK. Touch this pad to enter the time of day.

11. NUMBER PADS. Touch number pads to enter cooking

time, power level, quantities, or weights.

12. TIME. Touch this pad to set a cooking time.

13. POWER. Touch this pad to set a cooking power.

14. STOP/CLEAR. Touch this pad to stop the oven or clear

entries.

15. EZ ON. Touch this pad to cook at 100% cook power for

30 seconds to 99 minutes, 59 seconds.

16. START. Touch this pad to start all entries (except the

ONE TOUCH and EZ ON functions, which start

automatically).

4-1

OPERATING SEQUENCE

The following is a description of component functions during oven operation.

1. SETTING THE CLOCK

STOP/CLEAR CLOCK NUMBER CLOCK

ex.) To set 4:30, touch number key [4],[3], and [0]. NOTE: 1) This is a 12 hour clock.

2)Clock will operate as long as power is applied to the oven.

2.CANCEL FUNCTION

Touch the STOP/CLEAR pad whenever you need to cancel an entry or a function currently in use.

The display will either return to the last item entered or to the clock.

3. EZ ON

STOP/CLEAR EZ on

4. ONE TOUCH COOKING

STOP/CLEAR POPCORN

NOTE: Heat only 1 package at a time

5. TIME COOKING

STOP/CLEAR TIME NUMBER POWER

NUMBER START

6. MULTI-STAGE COOKING

1ST STAGE

STOP/CLEAR TIME NUMBER POWER

NUMBER

2ND STAGE

TIME NUMBER POWER

NUMBER START

7. AUTO DEFROST COOKING

START/PAUSE			AUTO			NUMBER			START
			DEFROST			OF WEIGHT

8. CHILD LOCK

This oven has a CHILD LOCK feature

TO SET CHILD LOCK

• Touch the STOP/CLEAR pad

•Touch and hold “0” pad LOCK appear on the display.

	TO CANCEL CHILD LOCK
	• Touch the	STOP/CLEAR				pad
	• Touch and hold			pad				LOCK
			“0”
	disappears on the display.

4-2

DIAGRAM SCHEMATIC

3-4

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 BASIC SCHEMATIC DIAGRAM, THE VALUES OF COMPONENTS AND

SOME PARTIAL CONNECTIONS ARE SUBJECT TO CHANGE FOR IMPROVEMENT.

CIRCUIT DESCRIPTION

GENERAL DETAILS

•The low voltage transformer supplies the necessary voltage to the micom controller when power cord is plugged in.

•When the door is closed, the primary switch is ON, the secondary switch is ON, and the monitor switch opens (contact COM and NO).

WHEN SELECTING COOKING POWER LEVEL AND TIME

•The micom controller memorizes the function you set.

•The time you set appears in the display window.

•Each indicator light turns on to indicate that the stage has been set.

WHEN TOUCHING THE START PAD

•The coil of the relay is energized by the micom controller.

•Power input is supplied to the high voltage transformer through the fuse to the primary switch and relay 2.

•Turntable rotates.

	N
			H.V.
		MONITOR	TRANS-
			FORMER
	L	SWITCH

FUSE

	PRIMARY		SECONDARY
	SWITCH	RELAY 2
			SWITCH

MICOM CONTROLLER

•The fan motor rotates and cools the magnetron by blowing the air (coming from the intake on the baseplate).

•The air is also directed into the oven to exhaust the vapor in the oven through the upper plate.

•Cooking time starts counting down.

•3.3 volts AC is generated from the filament winding of the high voltage transformer. This 3.3 volts is applied to the magnetron to heat the magnetron filament through two noise-preventing choke coils.

•A high voltage of approximately 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 average output power of microwave oven as POWER LEVEL.

(refer to page 1-1)

•One complete cycle of the relay 2 is 22 seconds.

WHEN THE DOOR IS OPENED DURING COOKING

•Both the primary switch and relay 2 cut off the primary winding voltage of the high voltage transformer.

•ON-OFF of relay 2 is coupled electrically with opening and closing of the secondary switch.

•When the door is opened, the secondary switch is opened and when the door is closed, the secondary switch is closed.

•The cooking time stops counting down.

•Relay stops functioning.

•As the door is opened, if the contact of primary switch and relay 2 and/or secondary switch fail to open, the fuse opens due to the large current surge caused by the monitor switch activation, which, in turn, stops magnetron oscillation.

	N
			H.V.
		MONITOR	TRANS-
			FORMER
	L	SWITCH

FUSE

	PRIMARY		SECONDARY
	SWITCH	RELAY 2
			SWITCH
		MICOM CONTROLLER

4-4