LG MC-924JL, Service Manual

Page: 10 / 39

• As the door is closed, the contact of MONITOR
SWITCH opens. This switch creates the short circuit to
blow 10 A fuse during operation under abnormal
condition.(ie, should the contacts of primary fail to open
the circuit)
• The latches are secured by latch board. The oven light
turns on while the oven is in operation.
WHEN COOKING POWER LEVEL AND
COOKING TIME ARE SET
• The contacts of the primary switch and the secondary
switch close the circuit.
• 230V A.C. is applied to the high voltage transformer
through power control switch as shown by the solid
line.
• Turntable and circulation motor rotate.
• The fan motor rotates and cools the magnetron by
blowing the air (coming from the intake on the
backplate) over the magnetron.
• The air is also directed into the oven to exhaust the
vapor in the oven through the base plate and back
plate.
• 3.5V A.C. is generated from the filament winding of the
high voltage transformer. This 3.5V is applied to the
magnetron to heat the magnetron filament through two
noise preventing choke coils. A high voltage of
approximately 2100V A.C. is generated in the
secondary of the high voltage transformer which is
increased by the action of the diode and charging of
the high voltage capacitor. The negative D.C. voltage is
then applied to the filament of the magnetron.
WHEN THE DOOR IS OPEN DURING
COOKING
• Both primary switch and secondary switch open to cut
off the primary winding voltage to the high voltage
transformer to stop microwave oscillation.
• Turntable and fan motor stop.
• As the door is opened, if the contact of primary switch
and relay 2 and/or secondary switch fail to open, the
10A 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.
• 230V A.C. is applied to the grill heater through grill
thermostat as shown by the solid line.
• Turntable rotate.
• The fan motor and circulation motor rotate.
• The air is also directed into the oven to exhaust the
vapor in the oven through the base plate and back
plate.
Circuit Description
4-4
FUSE
10A
PRIMARY
SWITCH
N
L
RELAY 2
H.V.T
MONITOR
SWITCH
FUSE
10A
PRIMARY
SWITCH
N
L
RELAY 2
H.V.T
MONITOR
SWITCH
CONVECTION
HEATER
RELAY 4
L
N
E
N
L
G-Y
RELAY 3
GRILL
HEATER
OVEN THERMOSTAT
L
N
E
N
L
G-Y
RELAY 3
GRILL
HEATER
OVEN THERMOSTAT