Circuit Description - LG LMC1575BD Service Manual

CIRCUIT DESCRIPTION

GENERAL DETAILS
• The SMPS 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 BUTTON
• The coil of the relay is energized by the micom controller.
• Power input is supplied to the Inverter PCB through the fuse to the primary
switch and relay 2 .
• Turntable rotates.
• The fan motor rotates and cools the magnetron by blowing the air (coming from
the intake on the Back-plate).
FUSE
L
N
• The air is also directed into the oven to exhaust the vapor in the oven through
the Left side plate.
• Cooking time starts counting down.
• 3.3 volts AC is generated from the filament winding of the inverter PCB. This 3.3
volts is applied to the magnetron to heat the magnetron filament through two
noise-preventing choke coils.
• The inverter PCB generates high voltage of approximately 4,000V negative DC.
The voltage is applied to the filament of the magnetron.
PRIMARY
SWITCH
inverter
MONITOR
SWITCH
SECONDARY
RELAY 2
SWITCH
MICOM CONTROLLER
WHEN THE OVEN IS SET AT POWER LEVEL
• The inverter control micro wave out-put power from 100 % to 30 % by controlling
power consumption.
20% and 10% Power are controlled by relay on/off working.
• One complete cycle of relay 32 seconds.
WHEN THE DOOR IS OPENED DURING COOKING
• Both the primary switch and relay cut off input voltage of inverter PCB.
• ON-OFF of relay 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.
PRIMARY
FUSE
SWITCH
L
MONITOR
SWITCH
N
SECONDARY
RELAY 2
SWITCH
MICOM CONTROLLER
PRIMARY
FUSE SWITCH
L
MONITOR
SWITCH
N
SECONDARY
4-5
SWITCH
RELAY 2
MICOM CONTROLLER
PRIMARY
FUSE
SWITCH
L
N
RELAY 2
MICOM CONTROLLER
Door open
PRIMARY
FUSE SWITCH
L
inverter
N
RELAY 2
MICOM CONTROLLER
inverter
MONITOR
inverter
SWITCH
SECONDARY
SWITCH
MONITOR
inverter
SWITCH
SECONDARY
SWITCH