LG Electronics MS3447GRS Circuit Description, General Details, When Touching The Start Pad

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

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Only for training and service purposes