LG MH-794GS Service Manual ▷ View online
MICROWAVE/
GRILL OVEN
GRILL OVEN
SERVICE MANUAL
MODEL : MH-794GS
CAUTION
BEFORE SERVICING THE UNIT, READ THE SAFETY PRECAUTIONS
IN THIS MANUAL.
IN THIS MANUAL.
August, 1999
P/NO. 3828W5S1308
Operating Sequence
10
The following is a description of component functions during oven operation.
Programme
Desired
Cooking
Stop/
Clear
Stop/
Clear
Stop/Clear
Touch and Hold
Stop/Clear
Stop/Clear
Touch and Hold
Stop/
Clear
Stop/
Clear
Child Lock
Quick Start
More and
Less
Less
Temp
To Set CHILD LOCK
• "L" appears on the display
and you can't input any key.
• "L" disappears on the display.
To Cancel CHILD LOCK
To Set MORE/LESS
SCHEMATIC DIAGRAM
11
GENERAL DETAILS
• The low voltage transformer supplies the necessary
voltage to the micom controller when power cord is
plugged in.
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).
(contact COM and NO).
WHEN SELECTING COOKING
POWER LEVEL AND TIME
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
• 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.
• The fan motor rotates and cools the magnetron by
blowing the air(coming from the intake on the
baseplate).
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
• 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.
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.
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
LEVEL EXCEPT MAXIMUM
• The micom controller controls the ON-OFF time of
relay 5 by the applied signal to vary the average
output power of microwave oven as POWER LEVEL.
(refer to page 1-1)
(refer to page 1-1)
• One complete cycle of relay 5 is 22 seconds.
WHEN THE DOOR IS OPENED
DURING COOKING
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.
switch is closed.
• The cooking time stops counting down.
• Relay stops functioning.
• As the door is opened, if the contact of primary switch
• Relay stops functioning.
• As the door is opened, if the contact of primary switch
and 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.
to the large current surge caused by the monitor
switch activation, which in turn stops magnetron
oscillation.
WHEN TOUCHING THE START KEY
WITH THE GRILL COOKING
FUNCTION SELECTED
WITH THE 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 oven
thermal cut-out as shown by the solid line.
• Turntable rotates.
• Rotisserie Motor rotates.
• The fan motor rotates.
• The air is also directed into the oven to exhaust the
• Rotisserie Motor rotates.
• The fan motor rotates.
• The air is also directed into the oven to exhaust the
vapor in the oven through the back plate and upper
plate.
plate.
Circuit Description
12
PRIMARY
SWITCH
RELAY 2
H.V.
TRANS-
FORMER
MONITOR
SWITCH
L
N
FUSE
SECONDARY
SWITCH
MICOM CONTROLLER
PRIMARY
SWITCH
MONITOR
SWITCH
L
N
FUSE
H.V.
TRANS-
FORMER
RELAY 2
SECONDARY
SWITCH
MICOM CONTROLLER
L
N
E
N
L
G-Y
GRILL
HEATER
RELAY 3
OVEN THERMAL
CUT-OUT