MB-4322AH — LG Microwave Oven Service Manual (repair manual)

Model
MB-4322AH
Pages
40
Size
944.9 KB
Type
PDF
Document
Service Manual
Brand
Device
Microwave Oven
File
mb-4322ah.zip
Date

View LG MB-4322AH Service Manual online

MICROWAVE OVEN
SERVICE MANUAL
MODEL : MB-4322AH
CAUTION
BEFORE SERVICING THE UNIT, READ THE
SAFETY PRECAUTIONS IN THIS MANUAL.
4-4
CIRCUIT DESCRIPTION
•  As the door is closed, the contact of MONITOR
SWITCH opens. This switch creates the short circuit to
blow fuse during operation under abnormal condition.
(ie, should the contacts of primary and secondary
switch fail to open the circuit)
•  The latches are secured by latch board. The oven light
turns on while the oven is in operation.
WHEN MICROWAVE POWER LEVEL
AND COOKING TIME SET
•  The contacts of the timer switch changes to ON
position when the timer knob is rotated.
(While power control knob is set at “Full Power”)
•  The contacts of primary and secondary switch close
the circuit.
•  Input Volts AC. is applied to the high voltage
transformer through power control switch as shown by
the solid line.
•  Turntable rotates.
•  The fan motor rotates and cools the magnetron by
blowing the air (coming from the intake holes on the
baseplate) over the magnetron.
•  The air is also directed into the oven to exhaust the
vapor in the oven through the upper plate.
•  Timer starts rotating.
•  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.
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
diode and charging of the high voltage capacitor.
The negative DC voltage is then applied to the filament
of the magnetron.
WHEN THE DOOR IS OPENED 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.
•  Timer, turntable and fan motor stop.
•  As the door is opened, if the contact of primary 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.
WHEN THE GRILL COOKING FUNCTION
SELECTED
•  The contacts of the timer switch change to ON
position.
•  The contacts of the grill select switch close the circuit.
•  Input volts AC is applied to the grill heater through
thermostat-grill as shown by the solid line.
•  The fan motor and turntable rotates.
FUSE
PRIMARY
SWITCH
SECONDARY
SWITCH
MONITOR
SWITCH
L
N
H.V.T
TIMER
SWITCH
POWER
CONTROL
SWITCH
FUSE
PRIMARY
SWITCH
SECONDARY
SWITCH
L
N
H.V.T
TIMER
SWITCH
POWER
CONTROL
SWITCH
MONITOR
SWITCH
PRIMARY
SWITCH
TIMER
SWITCH
GRILL
SELECT
SWITCH
L
N
THERMOSTAT
GRILL
GRILL 
HEATER
L
G -Y
N
E
CAUTIONS
• Be sure to check microwave leakage prior to
servicing the oven if the oven is operative prior to
servicing.
• The service personnel should inform the
manufacture importer, or assembler of any
certified oven unit found to have a microwave
emission level in excess of 5 mW/cm
2
and should
repair any unit found to have excessive emission levels
at no cost to the owner and should ascertain the cause
of the excessive leakage. The service personnel
should instruct the owner not to use the unit until the
oven has been brought into compliance.
• If the oven operates with the door open, the service
personnel should:
- Tell the user not to operate the oven.
- Contact the manufacturer. 
• The service personnel should check all surface and
vent openings for microwave leakage.
• Check for microwave leakage after every servicing.
The power density of the microwave radiation leakage
emitted by the microwave oven should not exceed 
4 mW/cm
2
. Always start measuring of an unknown field
to assure safety for operating personnel from radiation
leakage.
MEASURING MICROWAVE ENERGY
LEAKAGE
• Pour 275±15cc of 20±5°C(68±9°F) water in a beaker
which is graduated to 600 cc, and place the beaker
on the center of the turntable.
• Set the energy leakage monitor to 2,450 MHz and
use it following the manufacturer's recommended
test procedure to assure correct result.
• When measuring the leakage, always use the 2-
inch (5cm) spacer supplied with the probe.
• Operate the oven at its maximum output.
• Measure the microwave radiation using and
electromagnetic radiation monitor by holding the
probe perpendicular to the surface being measured
Move probe along shaded area
Probe scanning speed
Less than 2.5 cm/sec
( 1in/sec)
5-1
SERVICE INFORMATION
TOOLS AND MEASURING INSTRUMENTS
MICROWAVE LEAKAGE TEST
NECESSARY TOOLS
Tools normally used for TV servicing are sufficient.
Standard tools are listed below.
• Diagonal pliers
• Long nose pliers
• Phillips screwdriver
• Flat blade screwdriver
• Wrench (size 5mm)
• Nutdriver (size 5mm)
• Adjustable wrench
• Soldering iron
• Solder
• Vinyl insulation tape
• Polishing cloth
NECESSARY MEASURING INSTRUMENTS
• TESTER(VOLTS-DC, AC., Ohmmeter)
• Microwave survey meter
- Holaday HI-1500
HI-1501
- Narda     8100
8200
• Inch scale
• 600 cc non conductive material beaker (glass or plastic),
inside diameter: approx. 8.5 cm(3
1
/2
in.)
• Cylindrical and made of borosilicate glass vessel.
max. thickness: 3 mm
outside diameter: approx. 190mm
height: approx. 90mm
• Glass thermometer: 100°C or 212°F (1 deg scale)
5-2
MEASUREMENT WITH OUTER CASE
REMOVED
• When you replace the magnetron, measure for
microwave energy leakage before the outer case is
installed and after all necessary components are
replaced or adjusted.
Special care should be taken in measuring the
following parts. (Circled area of below Fig.)
- Around the magnetron
- The waveguide
MEASUREMENT WITH A FULLY
ASSEMBLED OVEN
• After all components, including the outer case, are fully
assembled, measure for microwave energy leakage
around the door viewing window, the exhaust opening,
and air inlet openings.
• Microwave energy leakage must not exceed the values
prescribed below.
NOTE: Leakage with the outer case removedless than
5 mW/cm.sq. Leakage for a fully assembled
oven (Before the latch switch (primary) is
interrupted) with the door in a slightly opened
position-less than 2 mW/cm.sq.
NOTES WHEN MEASURING
• Do not  exceed meter full scale deflection.
• The test probe must be removed no faster than  
1 inch/sec (2.5 cm/sec) along the shaded area,
otherwise a false reading may result.
• The test probe must be held with the grip portion of the
handle.
A false reading may result if the operator's hand is
between the handle and the probe.
• When testing near a corner of the door, keep the probe
perpendicular to the surface making sure the probe
horizontally along the oven surface, this may possibly
cause probe damage.
RECORD KEEPING AND NOTIFICATION
AFTER MEASUREMENT
• After adjustment and repair of any microwave energy
interruption or microwave energy blocking device,
record the measured values for future reference. Also
enter the information on the service invoice.
• The microwave energy leakage should not be more
than 4 mW/cm.sq. after determining that all parts are in
good condition, functioning properly and genuine
replacement parts which are listed in this manual have
been used.
• At least once a year, have the electromagnetic energy
leakage monitor checked for calibration by its
manufacturer.
WARNING : AVOID CONTACTING ANY
HIGH VOLTAGE PARTS
(Magnetron, H.V. Transformer,
H.V. Capacitor, H.V. Cable Ass’y,
H.V. Circuit Protector)
Page of 40
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Here you can view online or download LG MB-4322AH Service Manual in pdf. This Service Manual can help you recover, restore, fix, disassemble and repair LG MB-4322AH Microwave Oven. Information contained in LG MB-4322AH service manual (repair manual) typically includes:

  • Disassembly, troubleshooting, programming, maintenance, remote, adjustment, installation and setup instructions.
  • Schematics, wiring and block diagrams.
  • Printed wiring boards (PWB) and printed circuit boards (PCB).
  • Parts list (bill of materials).