LG MC-785BC Service Manual ▷ View online
MICROWAVE/GRILL/
CONVECTION OVEN
CONVECTION OVEN
SERVICE MANUAL
MODEL : MC-784DC/MC-785DC/MC-785BC
CAUTION
BEFORE SERVICING THE UNIT, READ THE SAFETY PRECAUTIONS
IN THIS MANUAL.
IN THIS MANUAL.
●
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)
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.
turns on while the oven is in operation.
WHEN COOKING POWER LEVEL AND
COOKING TIME ARE SET
COOKING TIME ARE SET
●
The contacts of the primary switch and the secondary
switch close the circuit.
switch close the circuit.
●
230V A.C. is applied to the high voltage transformer
through power control switch as shown by the solid
line.
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.
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.
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.
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
COOKING
●
Both primary switch and secondary switch open to cut
off the primary winding voltage to the high voltage
transformer to stop microwave oscillation.
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
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.
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.
WITH THE CONVECTION/GRILL
COOKING FUNCTION SELECTED.
●
The contacts of the primary switch and the secondary
switch close the circuit.
switch close the circuit.
●
230V A.C. is applied to the grill heater through grill
thermostat as shown by the solid line.
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.
vapor in the oven through the base plate and back
plate.
Circuit Description
10
FUSE
10A
PRIMARY
SWITCH
N
L
RELAY 1
H.V.T
MONITOR
SWITCH
FUSE
10A
PRIMARY
SWITCH
N
L
RELAY 1
H.V.T
MONITOR
SWITCH
FUSE
CONVECTION
HEATER
RELAY 2
L
N
E
N
L
G-Y
RELAY 5
GRILL
HEATER
OVEN THERMOSTAT
FUSE
L
N
E
N
L
G-Y
RELAY 5
GRILL
HEATER
OVEN THERMOSTAT
This device is to be serviced only by properly qualified service personnel.
Consult the Service Manual for proper service procedures to assure continued safety operation and for precautions to
be taken to avoid possible exposure to excessive microwave energy.
Consult the Service Manual for proper service procedures to assure continued safety operation and for precautions to
be taken to avoid possible exposure to excessive microwave energy.
SAFETY PRECAUTIONS
PRECAUTIONS TO BE OBSERVED
BEFORE AND DURING SERVICING TO
AVOID POSSIBLE EXPOSURE TO
EXCESSIVE MICROWAVE ENERGY
A) Do not operate or allow the oven to be operated with the door open.
B) Make the following safety checks on all ovens to be serviced before activating the magnetron or other
microwave source, and make repairs as necessary; (1) Interlock operation, (2) proper door closing,
(3) seal and sealing surfaces (arcing, wear, and other damage), (4) damage to or loosening of hinges
and latches, (5) evidence of dropping or abuse.
(3) seal and sealing surfaces (arcing, wear, and other damage), (4) damage to or loosening of hinges
and latches, (5) evidence of dropping or abuse.
C) Before turning on microwave power for any service test or inspection within the microwave generating
compartments, check the magnetron, wave guide or transmission line, and cavity for proper alignment,
integrity, and connections.
integrity, and connections.
D) Any defective or misadjusted components in the interlock, monitor, door seal, and microwave generation and
transmission systems shall be repaired, replaced, or adjusted by procedures described in this manual before
the oven is released to the owner.
the oven is released to the owner.
E) A microwave leakage check should be performed on each oven prior to release to the owner.
CAUTION
MICROWAVE RADIATION
DO NOT BECOME EXPOSED TO RADIATION FROM THE MICROWAVE
GENERATOR OR OTHER PARTS CONDUCTING MICROWAVE ENERGY.
TABLE OF CONTENTS
3
(Page)
SAFETY PRECAUTIONS ................................................................................................. Inside front cover
SPECIFICATIONS ........................................................................................................................................ 4
CAUTIONS .................................................................................................................................................... 5
INSTALLATIONS .......................................................................................................................................... 6
OPERATING INSTRUCTIONS ..................................................................................................................... 7
FEATURES .............................................................................................................................................. 7
CONTROL PANEL ................................................................................................................................... 7
OPERATING SEQUENCE ....................................................................................................................... 8
SCHEMATIC DIAGRAM ............................................................................................................................... 9
CIRCUIT DESCRIPTION ....................................................................................................................... 10
SERVICE INFORMATION .......................................................................................................................... 11
TOOLS AND MEASURING INSTRUMENTS ......................................................................................... 11
MICROWAVE LEAKAGE TEST ............................................................................................................. 11
MEASUREMENT OF MICROWAVE POWER OUTPUT ........................................................................ 13
DISASSEMBLY AND ADJUSTMENT.......................................................................................................13
INTERLOCK CONTINUITY TEST .......................................................................................................... 17
COMPONENT TEST PROCEDURE ...................................................................................................... 18
TROUBLE SHOOTING GUIDE .............................................................................................................. 23
EXPLODED VIEW ...................................................................................................................................... 29
REPLACEMENT PART LIST ...................................................................................................................... 36
MICOM CONTROLLER SCHEMATIC DIAGRAM ...................................................................................... 39
MICOM CONTROLLER P.C.B LAYOUT ..................................................................................................... 40
TACT SWITCH BUTTON POSITION........................................................................................................... 41
MICOM CONTROLLER P.C.B PARTS LIST .............................................................................................. 42
PACKING AND ACCESSORIES ............................................................................................................... 45