LG MC-3182NBR, Service Manual

Page: 10 / 37

4-4
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 BUTTON
• 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.
• 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.
• 3.2 volts AC is generated from the filament winding of the
high voltage transformer. This 3.2 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 relay 2 is 32 seconds.
WHEN THE DOOR IS OPENED DURING
COOKING
• Both the primary switch and relay 2 are cut off 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 fails to open, the fuse opens due to the large
current surge caused by the monitor switch activation,
which in turn stops magnetron oscillation.
WHEN TOUCHING THE START KEY
WITH THE CONVECTION/GRILL
COOKING FUNCTION SELECTED
• The contacts of the primary switch and the secondary
switch close the circuit.
• A.C. voltage is applied to the grill heater through the
oven thermal cut-out as shown by the solid line.
• Turntable rotates.
• The fan motor rotates.
• The air is also directed into the oven to exhaust the vapor
in the oven through the base plate and upper plate.