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Model
MB-4322A
Pages
40
Size
943.47 KB
Type
PDF
Document
Service Manual
Brand
Device
Microwave Oven
File
mb-4322a.zip
Date

LG MB-4322A Service Manual ▷ View online

5-3
MEASUREMENT OF MICROWAVE POWER OUTPUT
DISASSEMBLY AND ADJUSTMENT
A. OUTER CASE REMOVAL
1) Disconnect the power supply cord from the outlet.
2) Remove the screws from the rear and along side
edges of the case.
The outer case must be moved backward to be lifted
off.
B. POWER SUPPLY CORD
1) Remove the outer case.
2) Disconnect two terminals, and remove one screw of
the earth terminal.
CAUTION: DISCHARGE THE HIGH VOLTAGE 
CAPACITOR BEFORE SERVICING
(refer to page 2-1)
C. CONTROL PANEL ASSEMBLY
1) Disconnect the leadwire from the PCB SUB ASS’Y.
2) Remove the screws for the earth and securing the
control panel.
3) Lift control panel ASS’Y from the oven by the tab
unhooked.
• Microwave power output measurement is made with
the microwave oven supplied at its rated voltage and
operated at its maximum microwave power setting with
a load of (1000±5) g of potable water.
• The water is contained in a cylindrical borosilicate glass
vessel having a maximum material thickness of 3 mm
and an outside diameter of approximately 190mm.
• The oven and the empty vessel are at ambient
temperature prior to the start of the test.
• The initial temperature (T1) of the water is (10±2)°C It
is measured immediately before the water is added to
the vessel. After addition of the water to the vessel,
the load is immediately placed on the center of the
turntable which is in the lowest position and the
microwave power switched on.
• The time T for the temperature of the water to rise by a
value 
T of (10±2)°K is measured, where T is the time
in seconds and 
T is the temperature rise.   The initial
and final water temperatures are selected so that the
maximum difference between the final water
temperature and the ambient temperature is 5°K.
• The microwave power output P in watts is calculated
from the following formula :
is measured while the microwave generator is
operating at full power. Magnetron filament heat-up
time is not included. (about 3 sec)
• The  water is stirred to equalize temperature throughout
the vessel, prior to measuring the final water
temperature.
• Stirring devices and measuring instruments are
selected in order to minimize addition or removal of
heat.
WATER LOAD
TURNTABLE
P =
• T
2
: Temperature after heating
• T
0
: Temperature after bown
• M: Weight of bowl
4187 x (
T) + 0.55 X (T
- T
0
) X M
T
D. DOOR GROSS ASSEMBLY REMOVAL
1) Open the door.
2) Remove the choke cover cap very carefully with a
flat-blade screwdriver.
CAUTION : Be careful not to damage door seal plate
by screwdriver.
3) Lift up and push the door.
NOTE:
1. After replacing the door, be sure to check that the
primary switch, monitor switch, and secondary switch
operate normally.
2. After replacing the door, check for microwave energy
leakage with a survey meter. Microwave energy must
be below the limit of 5 mW/cm. (with a 275 ml water
load)
3. When mounting the door assembly to the oven
assembly, be sure to adjust the door assembly parallel
to the chassis. Also adjust so the door has no play
between the inner door surface and oven frame
assembly. If the door assembly is not mounted
properly, microwaves may leak from the clearance
between the door and the oven.
E. HIGH VOLTAGE TRANSFORMER 
REMOVAL
1) Discharge the high voltage capacitor.
2) Disconnect the leadwire from magnetron, high voltage
transformer, and capacitor.
3) Remove the screw holding the high voltage
transformer to the baseplate.
F. FAN MOTOR ASSEMBLY REMOVAL
1) Discharge the high voltage capacitor.
2) Disconnect the leadwire from fan motor, noise filter
and high voltage capacitor.
3) Remove the two screws holding the the suction guide
ASS’Y to the oven cavity and remove the high voltage
diode earth screw.
4) Remove the screw of the capacitor bracket.
5) Remove the two screws holding the fan motor ASS’Y
to the suction guide ASS’Y.
G. HIGH VOLTAGE CAPACITOR AND
DIODE REMOVAL
1) Discharge the high voltage capacitor.
2) Disconnect the leadwire from fan motor, noise filter
and high voltage capacitor.
3) Remove the screw holding the suction guide ASS’Y to
the oven cavity and remove the high voltage diode
earth screw.
4) Remove the screw holding the high voltage capacitor
bracket.
Door seal plate
Remove choke cover cap
Remove door
H.V.
Transformer
Suction
Guide
Fan Motor ASS’Y
H.V.
Diode
H.V.
Capacitor
5-4
5-5
H. AIR DUCT ASSEMBLY REMOVAL
1) Disconnect the leadwire from lamp.
2) Remove the mounting screw to Latch Board.
I. MAGNETRON REMOVAL
1) Disconnect the leadwire from the high voltage
transformer and high voltage capacitor.
2) Carefully remove the mounting screws holding the
magnetron and the waveguide.
3) Remove the magnetron ASS’Y until the tube is
clear from the waveguide.
NOTE:
1. When removing the magnetron, make sure its
dome does not hit any adjacent parts, or it may be
damaged.
2. When replacing the magnetron, be sure to install
the magnetron gasket in the correct position and
be sure that the gasket is in good condition.
3. After replacing the magnetron, check for microwave
leakage with a survey meter around the
magnetron. Microwave energy must be below the
limit of 5 mW/cm
2
. (With a 275 ml. water load).
Make sure that gasket is rigidly attached to the
magnetron. To prevent microwave leakage,
tighten the mounting screws properly, making sure
there is no gap between the waveguide and the
magnetron.
J. REMOVING THE TURNTABLE MOTOR
1) Remove the turntable.
2) Remove the Rotating Ring.
3) Lay the unit down on its back.
4) Remove the turntable motor cover.
The turntable base cover is easily removed by
pinching the six parts with a wire cutting.
5) Disconnect the leadwire from the turntable motor
terminals.
6) Remove the screw securing the turntable motor to
the oven cavity ASS’Y
7) After repairing the motor, rotate the removed
turntable motor cover.
8) Fit the turntable motor cover’s projecting part to the
base plate slit.
NOTE:
1. Remove the wire lead from the turntable motor
VERY CAREFULLY.
2. Be sure to grasp the connector, not the wires, when
removing.
Waveguide
Magnetron
Magnetron
Gasket
Magnetron
Dome
Waveguide 
Bracket
Wire Leads
Turntable Motor
K. TIMER MOTOR REMOVAL
1) Remove the control panel assembly from the
cavity. 
2) Remove screws which hold the timer motor to the
control panel.
3) Remove the timer motor from the control panel.
4) Remove the power control knob and the timer
knob.
L. INTERLOCK SYSTEM
1) INTERLOCK MECHANISM
The door lock mechanism is a device which has
been specially designed to eliminate completely
microwave activity when the door is opened during
cooking and thus to prevent the danger resulting
from the microwave leakage.
2) MOUNTING OF THE PRIMARY/MONITOR/
SECONDARY SWITCHES TO THE LATCH BOARD
3) INSTALLATION AND ADJUSTMENT OF THE
LATCH BOARD TO THE OVEN ASSEMBLY
• Mount the latch board to the oven assembly.
• Adjust the latch board in the arrow direction so that
oven door will not have any play in it when the door
is closed.
• Tighten the mounting screw.
• Check for play in the door by pushing the door
release button. Door movement should be less
than 0.5 mm. (1/64 inch)
Don't push the door release button while making
adjustment. Make sure that the latch moves
smoothly after adjustment are completed and that
the screws are tight. Make sure the primary, monitor,
and secondary switches operate properly by
following the continuity test procedure.
5-6
Control Panel
Timer Motor
Power Control 
Knob
Timer Knob
PRIMARY
SWITCH
SECONDARY
SWITCH
ADJUSTMENT 
DIRECTION
MONITOR
SWITCH
CAUTION: CHECK THE CORRECT POSITION
MAGNETRON
H.V. TRANSFORMER
PRIMARY
CIRCUIT PROTECTOR
H.V. CAPACITOR
H.V.
DIODE
FIG. 1
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