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20

HEATER ELEMENT
(Wire leads removed)

FUSE, H.V. FUSE
(Wire leads removed.)

Normal

Abnormal

0¡c~Approx 150¡C

Approx 150¡C

OVEN THERMOSTAT
MAGNETRON
THERMOSTAT

Normal : 

●

Grill heater
Approx. 40.7 ½
(at 20~30¡C)

Normal : more than 0.5M ½

Measure the resistance with 500V-100M
½ insulation resistance meter.

Measure the resistance.
(Multi-meter scale : Rx1) 

Check for continuity of the switch with a
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.

NOTE : Make sure heater is fully cooled when tested.

21

GRILL HEATER
(Wire leads removed)

SOLENOID

RECTIFIRE ASM
VOLTAGE FOR
SOLENOID

CIRCULATION
(Wire leads removed)

NOTE:
*(     )=WIRE COLOR

Normal : COM-230V : Approx. 150 ½

COM-24V : Approx. 20 ½

Abnormal : Infinite or several ohm.

Normal : Approx. 200~300 ½
Abnormal : Infinite or several

ohm.

Normal : Approx. 134 ½
Abnormal : Infinite or several ohm.
DC : 24V

24V
(BN)

COM
(YL)

230V(BL)

AC 28V

DC 24V

INPUT

OUT PUT

BN

YL

Measure the resistance.
(Multi-meter scale : Rx1) 

Measure the resistance.
(Multi-meter scale : Rx1) 

22

RELAY 3,4, OF P.C.B
(Disconnect the 7 pin 
connector from P.C.B)
See Schematic Dagram on
page 9)

RELAY 1,2,3 OF P.C.B
(Wire leads removed.)
RY1 : Microwave
RY2 : Convection
RY3 : Turn Table, 

Fan Motor, Roti-Motor
(For MC-783RC only), 
Oven Lamp 

RY4 : Circulation Motor
RY5 : Grill

MEMBRANE KEY

Check continuity between
switch terminals, by pressing an
appropriate pad on key board.
The contacts assignment of the
respective pads on the key
board is as shown left figures.

Cooking Start

OFF

CN2

1

3

5

7

Relay 3

Relay 4

Relay 1

Relay 5

Relay 2

1
2
3
4
5
6
7
8
9

10
11

1
2
3
4
5
6
7
8
9
10
11

Membrane

Panel

P.C.B

Cooking Start

OFF

NOTE : A MICROWAVE ENERGY LEAKAGE TEST MUST ALWAYS BE PERFORMED WHEN THE UNIT IS

SERVICED FOR ANY REASON.
MAKE SURE THE WIRE LEADS ARE CORRECT POSITION.
WHEN REMOVING THE WIRE LEAD FROM THE PARTS, BE SURE TO GRASP THE
CONNECTOR, NOT THE WIRES.

23

1. Check grounding before checking for other trouble.

2. Be careful of the high voltage circuit.

3. When checking the continuity of the switches or transformer, disconnect one lead wire from these parts and

then check continuity without turning the power source on.

4. Do not touch any part of the circuitry on the control circuit board, since static electric discharge may damage

this control circuit.
Always touch yourself to ground while working on this circuit to discharge any static charge built up in your
body.

5. First operate the microwave oven following the correct operating.

6. If the oven become inoperative because of a fuse, check the primary, the secondary and the monitor switches

before replacing the fuse.

The fuse blows when power
cord is plugged into wall
receptacle.

Shorted lead wise assy or
wire hardness.

Defective monitor switch or
out of adjustment.

Test procedure switches.

": 0" does not appear in 
displasy window when
power cord is first plugged
into wall outlet.

Microwave oven plug is not
inserted tightly.

No power at outlet.

Check home fuse.

Replace or repair wiring.

Test procedure membrane
key.

Defective membrane key of
P.C.B.

Display does not operate
properly when CLOCK is
touched.

Open wire in power cord,
wiring harness, or wiring
between control panel
assembly units.

Insert microwave oven plug
securely.

Replace lead wire or check
and repair wire hardness.

Blown fuse.

Test procedure fuse.