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If incorrect readings are obtained, replace the thermal cut-out.

An open circuit thermal cut-out (MG) indicates that the magnetron has overheated, this may be due to resistricted ventilation, cooling fan failure.

An open circuit thermal cut-out (OVEN) indicates that the oven cavity has overheated, this may be due to no load operation.

CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.

If the fuse 20A is blown, there is a shorts or grounds in electrical parts or wire harness. Check them and replace the defective parts or repair the wire
harness.

CARRY OUT 4R CHECKS.

CAUTION: Only replace fuse with the correct value replacement.

CARRY OUT 3D CHECKS.

1. If the fuse F8A is blown, there is a shorts or grounds in electrical parts or wire harness. Check them and replace the defective parts or repair the

wire harness.

2. If the fuse F8A is blown when the door is opened, check the monitored latch switch, monitor switch, relay RY1 and relay RY3.

If he fuse F8A is blown by incorrect door switching replace the defective switch(es) and the noise filter.

3. If the fuse F8A is blown, there could be shorts in the asymmetric rectifier or there is a ground in wire harness. A short in the asymmetric rectifier

may be occurred due to short or ground in H.V. rectifier, magnetron, high voltage transformer or H.V. wire. Check them and replace the defective
parts or repair the wire harness.

CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.

Disconnect the leads from the terminals of the noise filter. Using an ohmmeter, check
between the terminals as described in the following table. 

If incorrect readings are obtained, replace the noise filter unit.

CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.

Disconnect the leads from the motor. Using an ohmmeter, check the resistance between the two terminals as described in the table below.

If incorrect readings are obtained, replace the motor.

CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.

Before carrying out the following tests make sure the heating element is cool completely. 

1. Resistance of heating element.

Disconnect the wire leads to the heating element to be tested. Using ohmmeter with low resistance range. Check the resistance across the termi-
nals of the heating element as described in the following table.

MEASURING POINT 

INDICATION OF OHMMETER

Between N and L 

Approx. 680 k

Ω

Between terminal N and WHITE 

Short circuit

Between terminal L and RED 

Short circuit

Table: Resistance of Motor

Motors

Fan motor

Turntable motor

RMOTEA405WRZZ

RMOTDA265WRZZ

RMOTDA173WRE0

RMOTDA253WRZZ

Resistance at 20

°C

Approximately  388

Ω

Approximately   14.7k

Ω

Approximately   12.2k

Ω

Approximately   14.5k

Ω

Table: Resistance of heater

Parts name

Resistance

Grill heating elements

Approximately 61

Ω 

20A

F8A

WHT

RED

R2

N

Cx

R1

Cy

L

L

L

L (min) Cx ± 20% Cy ± 20% R2 ± 20% R1 ± 5%

1.0mH

0.22uF

680k

10M

4700pF

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2. Insulation resistance.

Disconnect the wire leads to the heating element to be tested. Check the insulation resistance between the element terminal and cavity using a
500V - 100M

Ω insulation tester. The insulation resistance should be more than 10 MΩ in the cold start.

If the results of above test 1 and/or 2 are out of above specifications, the heating element is probably faulty and should be replaced.

CARRY OUT 4R CHECKS.

The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore, unlike conventional microwave ovens, proper
maintenance can not be performed with only a voltmeter and ohmmeter.

In this service manual, the touch control panel assembly is divided into two units, Control Unit and Key Unit. Troubleshooting by unit replacement is
described according to the symptoms indicated.

The following symptoms indicate a defective key unit. Replace the key unit.

a) When touching the pads, a certain pad produces no signal at all.

b) When touching a number pad, two figures or more are displayed.

c) When touching the pads, sometimes a pad produces no signal.

The following symptoms indicate a defective control unit. Before replacing the control unit, perform the key unit test (Procedure M) to determine if con-
trol unit is faulty.

a) When touching the pads, a certain group of pads do not produce a signal.

b) When touching the pads, no pads produce a signal.

a) At a certain digit, all or some segments do not light up.

b) At a certain digit, brightness is low.

c) Only one indicator does not light up.

d) The corresponding segments of all digits do not light up; or they continue to light up.

e) Wrong figure appears.

f) A certain group of indicators do not light up.

g) The figure of all digits flicker.

a) Buzzer does not sound or continues to sound.

b) Clock does not operate properly.

c) Cooking is not possible.

If the display fails to clear when the STOP/CLEAR pad is depressed, first verify the flat ribbon cable is making good contact, verify that the stop switch
operates properly; that is the contacts are closed when the door is closed and open when the door is open. If the stop switch is good, disconnect the
flat ribbon cable that connects the key unit to the control unit and make sure the stop switch is closed (either close the door or short the stop switch
connector). Use the key unit matrix indicated on the control panel schematic and place a jumper wire between the pins that correspond to the STOP/
CLEAR pad making momentary contact.If the control unit responds by clearing with a beep the key unit is faulty and must be replaced. If the control
unit does not respond, it is faulty and must be replaced. If a specific pad does not respond, the above method may be used (after clearing the control
unit) to determine if the control unit or keypad is at fault.

G8

G9

G10

G1

1

G12

G7

G6

G5

G4

G3

G2

G1

GRILL

ROAST

POULTRY

ROAST

PORK

WHOLE

POULTRY

CHICKEN

QUARTERS

(WEIGHT)

(TIME)

(WEIGHT)

(TIME)

ROAST

BEEF/LAMB

DUAL

GRILL

KITCHEN

TIMER

MEAT

JOINT

MICRO

POWER

CLOCK

SET

AUTO

COOK

START

AUTO MINUTE

STOP

CLEAR

10 sec.

10 min.

1 min.

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CARRY OUT 3D CHECKS.

Remove the outer case and check voltage between Pin No. 1 and Pin No. 3 of the 3 pin connector (A) on the control unit with an A.C. voltmeter.

The meter should indicate rated voltage, if not check oven circuit.

RY1, RY2, RY3 and RY4 Relay Test

These relays are operated by D.C. voltage

        DC. voltage indicated ................................... Defective relay.

        DC. voltage not indicated ............................. Check diode which is connected to the relay coil. If diode is good, control unit is defective.

CARRY OUT 4R CHECKS.

To protect the electronic circuits, this model is provided with a fine foil pattern added to the input circuit on the PWB, this foil pattern acts as a fuse. If
the foil pattern is open, follow the troubleshooting guide given below for repair.

CARRY OUT 3D CHECKS.

NOTE: *At the time of these repairs, make a visual inspection of the varistor. Check for burned dam-

age. If any abnormal condition is detected, replace the control unit.

CARRY OUT 4R CHECKS.

RELAY SYMBOL

OPERATIONAL VOLTAGE

CONNECTED COMPONENTS

RY1

APPROX. 12V D.C.

Oven lamp / Turntable motor

RY2

APPROX. 12V D.C.

Grill heating element

RY3

APPROX. 12V D.C.

High voltage transformer

RY4

APPROX. 12V D.C.

Fan motor

STEPS

OCCURRENCE

CAUSE OR CORRECTION

1

The rated AC voltage is not present between Pin No. 1 of the 3-pin connec-
tor (A).

Check supply voltage and oven power cord.

2

The rated AC voltage is present at primary side of low voltage transformer.

Low voltage transformer or secondary circuit defective.
Check and replace control unit.

3

Only pattern at “a” is broken.

*Insert jumper wire J1 and solder. 
 (CARRY OUT 3D CHECKS BEFORE REPAIR)

4

Pattern at “a” and “b” are broken.

Replace control unit. 
(CARRY OUT 3D CHECKS BEFORE REPAIR)

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R657(W)

Service Manual

 

The control section consists of the following units as shown in the
touch control panel circuit.

(1) Key Unit

(2) Control Unit

The principal functions of these units and signals communicated
among them are explained below.

The key unit is composed of a matrix, signals generated in the LSI are
sent to the key unit through P30 - P37. When a key pad is touched, a
signal is completed through the key unit and passed back to the LSI
through P14 - P17 to perform the function that was requested.

Control unit consists of LSI, power source circuit, relay circuit, back
light circuit, synchronizing signal circuit, reset circuit, buzzer circuit,
and indicator circuit.

1) LSI

This LSI controls the tact switch strobe signal, relay driving signal,
for oven function and indicator signal.

2) Power Source Circuit

This circuit generates voltage necessary in the control unit.

3) Synchronizing Signal Circuit

The power source synchronizing signal is available in order to com-
pose a basic standard time in the clock circuit. It accompanies a
very small error because it works on commercial frequency.

4) Reset Circuit

A circuit to generate a signal which resets the LSI to the initial state
when power is supplied.

5) Buzzer Circuit

The buzzer is responsive to signals from the LSI to emit audible
sounds (key touch sound and completion sound).

6) Stop Switch

A switch to “tell” the LSI if the door is open or closed.

7) Relay Circuit

To drive the magnetron, fan motor, turntable motor, heating ele-
ment, and light the oven lamp.

8) Indicator Circuit

This circuit consists of 4-digits, 12-segments and 3-common elec-
trodes using a Liquid Crystal Display.

9) Back Light Circuit

A circuit to drive the back light (Light emitting diodes LD1 - LD4).

Symbol

Voltage

Application

VC

+5V

LSI(IC1)