LG MH-705A Service Manual ▷ View online
MICROWAVE/GRILL OVEN
SERVICE MANUAL
MODEL : MH-705A
CAUTION
BEFORE SERVICING THE UNIT, READ THE
SAFETY PRECAUTIONS IN THIS MANUAL.
SAFETY PRECAUTIONS IN THIS MANUAL.
5-9
COMPONENTS
TEST PROCEDURE
RESULTS
HIGH VOLTAGE
CAPACITOR
CAPACITOR
HIGH VOLTAGE
DIODE
DIODE
NOTE :
Some inexpensive meters
may indicate infinite
resistance in both direction.
Some inexpensive meters
may indicate infinite
resistance in both direction.
Measure the resistance.
(Ohm-meter scale: Rx1000)
• Terminal to terminal.
(Ohm-meter scale: Rx1000)
• Terminal to terminal.
Measure the resistance.
(Ohm-meter scale: Rx1000)
• Terminal to case.
(Ohm-meter scale: Rx1000)
• Terminal to case.
Measure the continuity (Forward).
(Ohm-meter scale: Rx10000)
(Ohm-meter scale: Rx10000)
Measure the continuity (Reverse).
(Ohm-meter scale: Rx10000)
(Ohm-meter scale: Rx10000)
Normal: Momentarily indicates
several ohms, and then
gradually returns to
infinite.
gradually returns to
infinite.
Normal: Infinite.
Normal: Continuity.
Abnormal: Infinite.
Abnormal: Infinite.
Normal: Infinite.
Abnormal: Continuity.
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
5-10
COMPONENTS
TEST PROCEDURE
RESULTS
FUSE
HEATER ELEMENT
(Wire leads removed.)
(Wire leads removed.)
GRILL THERMOSTAT
OVEN THERMOSTAT
MAGNETRON
THERMOSTAT
MAGNETRON
THERMOSTAT
Check for continuity of the fuse with an
multi-meter.
multi-meter.
NOTE: If the fuse is blown, check the primary, the secondary, and the monitor
switches, H.V.D. and H.V.C. before replacing the fuse.
If the fuse is blown by improper switch operation replace the defective switch
and the fuse at the same time. Replace just the fuse if the switches operate
normally.
switches, H.V.D. and H.V.C. before replacing the fuse.
If the fuse is blown by improper switch operation replace the defective switch
and the fuse at the same time. Replace just the fuse if the switches operate
normally.
NOTE: Make sure heater is fully cooled when tested.
Measure the resistance.
(Multi-meter scale: Rx1)
(Multi-meter scale: Rx1)
Normal:
*Grill heater
*Grill heater
Approx. 38
Ω
(at 20 ~ 30°C)
Normal: more than 0.5 M
Ω
Normal Abnormal
Measure the resistance with 500V-100M ohm
insulation resistance meter.
insulation resistance meter.
0°C~Approx.90°C Approx.90°C
0°C~Approx.145°C Approx.145°C
5-11
COMPONENTS
TEST PROCEDURE
RESULTS
Disconnect the 8 pin
connector from P.C.B.
(Refer to schemetic diagram
on page 4-3)
connector from P.C.B.
(Refer to schemetic diagram
on page 4-3)
RELAY 2, RELAY 3
OF P.C.B.
(Wire leads removed.)
Note: Relay
Relay 1: Fan motor
OF P.C.B.
(Wire leads removed.)
Note: Relay
Relay 1: Fan motor
Turntable motor
Oven lamp
Oven lamp
Relay 2: Microwave
Relay 3: Grill
Relay 3: Grill
FAN MOTOR
(Wire leads removed)
(Wire leads removed)
TURNTABLE
MOTOR
(Wire leads removed)
MOTOR
(Wire leads removed)
Measure the resistance.
(Ohm-meter scale: R x 1)
(Ohm-meter scale: R x 1)
Measure the resistance.
(Ohm-meter scale: R x 1000)
(Ohm-meter scale: R x 1000)
Normal:
Abnormal:
∞
or several
Ω
Normal: Approx. 100~200
Ω
Abnormal:
∞
or several
Ω
NOTE : • A MICROWAVE LEAKAGE TEST MUST ALWAYS BE PERFORMED WHEN THE UNIT IS
SERVICED FOR ANY REASON.
• MAKE SURE THE WIRE LEADS ARE IN THE CORRECT POSITION.
• WHEN REMOVING THE WIRE LEADS FROM THE PARTS, BE SURE TO GRASP THE
• WHEN REMOVING THE WIRE LEADS FROM THE PARTS, BE SURE TO GRASP THE
CONNECTOR, NOT THE WIRES.
A
B
C
Cooking Start OFF
1
3
5
7
8
Relay 2
Relay 3
Cooking Start OFF
A ~ B A ~ C
30 ~ 50
Ω
300~500
Ω
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