DOWNLOAD LG MC-804AR Service Manual ↓ Size: 1.4 MB | Pages: 39 in PDF or view online for FREE

4-3

• 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)

• The latches are secured by latch board. The oven light

turns on while the oven is in operation.

• The contacts of the primary switch and the secondary

switch close the circuit.

• 230V A.C. is applied to the high voltage transformer

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.

• The air is also directed into the oven to exhaust the

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.

• Both primary switch and secondary switch open to cut

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

and relay 2 and/or secondary 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.

• The contacts of the primary switch and the secondary

switch close the circuit.

• 230V A.C. is applied to the grill heater through grill

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.

4-4

FUSE

10A

PRIMARY

SWITCH

N

L

RELAY 2

H.V.T

MONITOR

SWITCH

FUSE

10A

PRIMARY

SWITCH

N

L

RELAY 2

H.V.T

MONITOR

SWITCH

CONVECTION

HEATER

RELAY 4

L

N

E

N

L

G-Y

RELAY 3

GRILL

HEATER

OVEN THERMOSTAT

L

N

E

N

L

G-Y

RELAY 3

GRILL

HEATER

OVEN THERMOSTAT

Tools normally used for TV servicing are sufficient.
Standard tools are listed below.

• Diagonal pliers
• Long nose pliers
• Cross head screwdriver
• Wrench (size 5 mm)
• Nutdriver (size 5 mm)
• Adjustable wrench
• Soldering iron
• Solder
• Vinyl insulation tape
• Polishing cloth

• Be sure to check a microwave emission prior to

servicing the oven if the oven is operative prior to
servicing.

• If the oven operates with door open, the service

personnel should;
—Tell the user not to operate the oven

• The service personnel should check all surface and

vent openings for microwave emission testing.

• Check for microwave energy leakage after every

servicing. The power density of the microwave
radiation leakage emitted by the microwave oven
should not exceed 4 mW/cm

2

.

And always start measuring of an unknown field to
assure safety for operating personnel from radiation
leakage.

: The standard is 5 mW/cm

2

while in the

customer’s home. 4 mW/cm

2

stated here is

manufacturer’s own voluntary standard for units in
customer’s home.

• Microwave Survey Meter
• 600cc glass beaker
• Glass thermometer 100°C

• TESTER (VOLTS-DC, AC, Multmeter)
• Microwave survey meter

—Holaday H1-1500, Hi-1501
—Narda 8100, 8200

• Inch scale
• 600 cc non conductive material beaker (glass or

plastic), inside diameter: approx. 8.5cm (3

1

/

2

in.)

•  Cylindrical and made of borosilicate glass vessel max.

thickness: 3mm
outside diameter: approx. 190mm
height: approx. 90mm

•  Glass thermometer: 100°C or 212°F (1 deg scale)

• Pour 275 ± 15cc of 20°C ± 5°C 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.

5-1

Move probe along shaded area.

Probe scanning speed;
Less than 2.5 cm/sec

• When you replace the magnetron, measure microwave

energy leakage before the out case is installed and
after all necessary components are replaced or
adjusted.
Special care should be taken in measuring the
following parts. (Shaded area of below Fig.)
— Around the magnetron
— The waveguide

• 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.

NOTES:
Leakage with the outer case removed - less than 
5 mW/cm

2

.

Leakage for a fully assembled oven (“Before the latch
switch (primary) is interrupted”) with the door in a slightly
opened position - less than 4 mW/cm

2

.

• 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.

• 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.

• Should the microwave energy leakage not be more

than 4 mW/cm

2

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
manufacture.

5-2