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Model
MB-4342A
Pages
44
Size
1.42 MB
Type
PDF
Document
Service Manual
Brand
Device
Microwave Oven
File
mb-4342a.zip
Date

LG MB-4342A Service Manual ▷ View online

K. PCB ASSEMBLY REMOVAL
1) Remove the control panel assembly from the
cavity. (Refer to control panel assembly removal
on previous page.)
2) Remove screws which hold the PCB SUB ASS’Y to
the control panel.
3) Disconnect the flat cable from the PCB SUB
ASS’Y and take off the PCB SUB ASS’Y.
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
Key Membrane
Control Panel PCB Sub ASS'Y
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
A. PRIMARY INTERLOCK SWITCH TEST
When the door release button is depressed slowly
with the door closed, an audible click should be
heard at the same time or successively at
intervals. When the button is released slowly, the
latches should activate the switches with an
audible click.
If the latches do not activate the switches when
the door is closed, the switches should be a
adjusted in accordance with the adjustment
procedure. Disconnect the wire lead from the
primary switch. Connect the ohmmeter leads to
the common (COM) and normally open (NO)
terminal of the switch. The meter should indicate
an open  circuit in the door open condition.
When the door is closed, the meter should
indicate a closed circuit.
When the primary switch operation is abnormal,
make the necessary adjustment or replace the
switch only with the same type of switch.
B. SECONDARY INTERLOCK SWITCH TEST
Disconnect the wire lead from the secondary
switch.
Connect the ohmmeter leads to the common
(COM) and normally open (NO) terminals of the
switch. The meter should indicate a open circuit in
the door open condition. When the door is closed,
meter should indicate an closed circuit. When the
secondary switch operation is abnormal, make the
necessary adjustment or replace the switch only
with the same type of switch.
C. MONITOR SWITCH TEST
Disconnect the wire lead from the monitor switch.
Connect the ohmmeter leads to the common
(COM) and normally closed (NC) terminals of the
switch. The meter should indicate closed circuit in
the door open condition. When the door is closed,
meter should indicate an open circuit. When the
monitor switch operation is abnormal, replace with
the same type of switch.
NOTE: After repairing the door or the interlock
system, it is necessary to do this continuity
test before operating the oven.
5-7
WARNING : FOR CONTINUED PROTECTION AGAINST EXCESSIVE RADIATION 
EMISSION, REPLACE ONLY WITH IDENTICAL REPLACEMENT PARTS.
TYPE NO. SZM-V 16-FA-63 OR VP-533A-OF FOR PRIMARY SWITCH 
TYPE NO. SZM-V 16-FA-62 OR VP-532A-OF FOR MONITOR SWITCH 
TYPE NO. SZM-V 16-FA-63 OR VP-533A-OF FOR SECONDARY SWITCH
COMPONENTS
TEST PROCEDURE
RESULTS
SWITCHES
Check for continuity of the 
Door
Door
(Wire leads removed)
switch with an Ohm-meter
open
closed
Primary
Switch
Monitor
Switch
NOTE : After checking for the continuity of switches, make sure that are
connected correctly.
NO
COM
NC
COM
NO
COM
INTERLOCK CONTINUITY TEST
Secondary
Switch
5-8
CAUTIONS
1. DISCONNECT THE POWER SUPPLY CORD FROM THE OUTLET WHENEVER REMOVING THE
OUTER CASE FROM THE UNIT. PROCEED WITH THE TEST ONLY AFTER DISCHARGING THE HIGH
VOLTAGE CAPACITOR AND REMOVING THE WIRE LEADS FROM THE PRIMARY WINDING OF THE
HIGH VOLTAGE TRANSFORMER. (SEE PAGE 2-1)
2. ALL OPERATIONAL CHECKS WITH MICROWAVE ENERGY MUST BE DONE WITH A LOAD (1 LITER
OF WATER IN CONTAINER) IN THE OVEN.
COMPONENTS
TEST PROCEDURE
RESULTS
HIGH VOLTAGE
TRANSFORMER
(Wire leads removed)
MAGNETRON
(Wire leads removed)
1. Measure the resistance.
(Ohm-meter scale: Rx1 and Rx100)
• Primary winding
• Secondary winding
• Filament winding
2. Measure the resistance.
(Ohm-meter scale: Rx1000)
• Primary winding to ground
• Filament winding to ground
1. Measure the resistance.
(Ohm-meter scale: Rx1)
• Filament terminal
2. Measure the resistance.
(Ohm-meter scale: Rx1000)
• Filament to chassis
Approx.: 2.5 ohm
Approx.: 110 ohm
Less than: 0.4 ohm
Normal: Infinite
Normal: Infinite
Normal: Less than 1 ohm
Normal: Infinite
PRIMARY  
TERMINAL
SECONDARY 
TERMINAL
FILAMENT 
WINDING
TERMINAL
COMPONENT TEST PROCEDURE
5-9
COMPONENTS
TEST PROCEDURE
RESULTS
HIGH VOLTAGE
CAPACITOR
HIGH VOLTAGE
DIODE
NOTE :
Some inexpensive meters
may indicate infinite
resistance in both direction.
Measure the resistance.
(Ohm-meter scale: Rx1000)
• Terminal to terminal.
Measure the resistance.
(Ohm-meter scale: Rx1000)
• Terminal to case.
Measure the continuity (Forward).
(Ohm-meter scale: Rx10000)
Measure the continuity (Reverse).
(Ohm-meter scale: Rx10000)
Normal: Momentarily indicates
several ohms, and then
gradually returns to 
infinite.
Normal: Infinite.
Normal: Continuity.
Abnormal: Infinite.
Normal: Infinite.
Abnormal: Continuity.
NOTE: When testing the magnetron, be sure to install the magnetron gasket
in the correct position and be sure that the gasket is in good condition.
Antenna
Gasket
Chassis
Filament
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