LG Electronics MS3447GRS service manual Circuit Description

Page 10

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.

PRIMARY

FUSE SWITCH

L

 

 

H.V.

 

TRANS-

 

FORMER

N

MONITOR

SWITCH

 

•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 4000 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 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.

 

SECONDARY

RELAY 2

SWITCH

MICOM CONTROLLER

PRIMARY

FUSE SWITCH

L

MONITOR

H.V.

• The fan motor rotates and cools the magnetron by

SWITCH

TRANS-

blowing the air (coming from the intake on the base-

plate).

• 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.

FORMER

N

RELAY 2

SECONDARY

SWITCH

 

MICOM CONTROLLER

Copyright © 2007 LG Electronics. Inc. All right reserved.

4-4

LGE Internal Use Only

Only for training and service purposes

 

 

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Contents Microwave Oven Safety Precautions Microwave RadiationContents Approx % of Full power SpecificationsFull power throughout the cooking time Approx %Microwave Radiation AntennaInstalling InstallationEarthing Instructions More Pressing More will add 10 seconds to the cooking time Features Control PanelOperating Instructions Cooking timeOperating Sequence Schematic Diagram Circuit Description Microwave Leakage Test Service InformationTools and Measuring Instruments Necessary ToolsMeasurement with a Fully Assembled Oven Measurement with Outer Case RemovedAround the magnetron Waveguide Power Supply Cord Measurement of Microwave Power OutputDisassembly and Adjustment Control Panel AssemblyPCB Assembly Removal Door Main Assembly RemovalRemoving the Turntable Motor AIR Duct Assembly RemovalMagnetron Removal Very CarefullyHigh Voltage Capacitor and Diode Removal FAN Motor Assembly RemovalHigh Voltage Transformer Removal Interlock SystemMonitor Switch Test Primary Interlock Switch TestSecondary Interlock Switch Test SwitchesFilament Winding Primary Terminal Component Test ProcedureHigh Voltage Transformer Wire leads removed MagnetronCapacitor High VoltageMeasure the resistance Normal Momentarily indicates Measure the continuity Forward Normal ContinuityLevel PowerRelay FAN MotorTrouble Shooting Condition Cause RemedySome inputs cannot be programmed Defective PCB assemblyDefective key membrane assembly Defective PCB assembly Continuity No continuityReplace power supply cord Check continuity Continuity Monitor Switch with Door closedPower supply Fuse blowsDefective PCB Replace PCB Assembly Setting time Check continuitySecondary switch Power source Rating voltage Voltage Normal DisconnectAbnormal Defective PCB assembly Defective PCB assembly Defective high voltage transformerReplace high voltage diode Replace magnetron Exploded View IntroductionDoor Parts Control Panel Parts Oven Cavity Parts Larch Board Parts Interior Parts WTT021 WTP004 56501A 54974TBase Plate Parts

MS3447GR, MS3447GRS specifications

The LG Electronics MS3447GRS and MS3447GR are innovative microwave models designed to enhance your cooking experience with a blend of advanced technology and user-friendly features. Both models are built to accommodate various culinary needs, making them ideal for any kitchen.

One standout feature of the MS3447GRS and MS3447GR is the Smart Inverter technology. This technology provides precise cooking power control, allowing users to defrost, reheat, and cook food evenly. This results in better texture and flavor retention in various dishes, surpassing traditional microwaves that may only provide two or three levels of heating.

Another significant characteristic is the EasyClean interior. This feature ensures that maintaining a clean microwave is hassle-free. The interior surface can be wiped down easily, helping to prevent the buildup of food residues and odors, which allows for a more hygienic cooking environment over time.

The LG MS3447GRS and MS3447GR also come equipped with a range of auto-cook options. These preset cooking modes simplify meal preparation, allowing users to cook a variety of dishes such as popcorn, baked potatoes, and frozen meals with just the push of a button. This is particularly beneficial for busy individuals and families looking to streamline their cooking process.

Additionally, these models boast a sleek and modern design that seamlessly integrates into any kitchen decor. The clean lines, polished finishes, and intuitive control panel make it an attractive and functional appliance. The user interface is designed for ease of use, with clear indicators and a layout that simplifies operation.

Both microwaves feature a spacious interior, which provides ample room for a variety of cookware sizes, making it easier to heat larger dishes. The turntable ensures that food is cooked evenly, while the powerful wattage guarantees efficient cooking times.

In conclusion, the LG Electronics MS3447GRS and MS3447GR microwave models are exemplary devices that combine cutting-edge technology with practical features. Their Smart Inverter, EasyClean technology, and flexible cooking options cater to the needs of modern kitchens, affirming LG's commitment to innovation and quality in kitchen appliances. Whether you're reheating leftovers or preparing a family meal, these microwaves make cooking simpler and more efficient.
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