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R-890SLM

8 - 3

CARRY OUT 3D CHECKS.
Disconnect the leads from the terminals of the thermal cut-out. Then using an ohmmeter, make a continuity test across the two 

terminals as described in the below.

Table: Thermal Cut-out Test

Parts Name

Temperature of “ON” condition

(closed circuit).

Temperature of “OFF” condition

(open circuit).

Indication of ohmmeter (When 

room temperature is approx. 20°C.)

Thermal cut-out 125°C

This is not resetable type.

Above 125°C

Closed circuit

Thermal cut-out 145°C

Below 115°C.

Above 145°C

Closed circuit

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, or exces-

sive heat / fire inside the oven.
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.

Table: Resistance of Motor

Motors

Resistance

Fan motor

Approximately 399Ω

Turntable motor

Approximately 14.7kΩ

Convection fan motor

Approximately 288kΩ

If incorrect readings are obtained, replace the motor.
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.

MEASURING POINT

INDICATION OF OHMMETER

Between N and L

Approximately 680kΩ

Between terminal N and WHITE

Short circuit

Between terminal L and RED

Short circuit

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

CARRY OUT 3D CHECKS.
1. If the fuse F8A is blown when the door is opened, check the monitored latch switch and monitor switch.
2. If the fuse F8A is blown by incorrect door switching replace the defective switch(es) and the noise filter (fuse F8A).
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.

F8A

20A

WHT

RED

R1

R2

N

Cx

Cy

L

L

L

L (min) Cx ± 20% Cy ± 20%

R1

R2

1.0mH

0.22 uF

4700pF 10 M

680k

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R-890SLM

CARRY OUT 3D CHECKS.
Before carrying out the following tests make sure the heating element is cool completely.
1.  Resistance of heater.
  Disconnect the wire leads to the heating element to be tested. Using ohmmeter with low resistance range. Check the resistance 

  across the terminals of the heating element as described in the following table.

Table: Resistance of heater

Parts name

Resistance

Grill heating element (Top)

Approximately 48

Bottom heating element

Approximately 92Ω

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 - 100MΩ insulation tester. The insulation resistance should be more than 10MΩ 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 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 control panel assembly is divided into two units, Control Unit and Jog switch Unit, and troubleshooting by 

replacement is described according to the symptoms indicated.

The following symptoms indicate a defective Jog switch unit. Replace the Jog switch unit.
1.1. Tact switch
1) When touching the buttons, a certain button produces no signal at all.
2) When touching the buttons, sometimes a button produces no signal.
1.2. Potentiometer
1) When rotating the potentiometer, the cooking mode can not be selected.
1.3. Encoder
1) When rotating the encoder, the cooking time or the weight of food can not be entered.

The following symptoms indicate a defective control unit. Before replacing the control unit, perform the Jog switch unit test (Procedure N) 

to determine if control unit is faulty.
2.1. In connection with buttons
1) When touching the buttons, a certain group of buttons do not produce a signal.

2) When touching the buttons, no buttons produce a signal.
2.2. In connection with indicators
1) At a certain digit, all or some segments do not light up.

2) At a certain digit, brightness is low.

3) Only one indicator does not light up.

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

5) Wrong figure appears.

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

7) The figure of all digits flicker.
2.3. Other possible troubles caused by defective control unit.
1) Buzzer does not sound or continues to sound.

2) Clock does not operate properly.

3) Cooking is not possible.
4) Proper temperature measurement is not obtained.

If the display fails to clear when the STOP button is depressed, first verify the 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 cable that connects the Jog switch 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 Jog switch unit matrix indicated on the control panel schematic and place a jumper 

wire between the pins that correspond to the STOP button making momentary contact. If the control unit responds by clearing with a 

beep the Jog switch unit is faulty and must be replaced. If the control unit does not respond, it is a faulty and must be replaced. If a 

specific button does not respond, the above method may be used (after clearing the control unit) to determine if the control unit or Jog 

switch unit is at fault.

8 - 4

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R-890SLM

7

0P

J

1S

A-

N

C

CARRY OUT 3D CHECKS.
Remove the outer case and check voltage between Pin Nos. 5 and 7 of the 4 pin connector (E) on the control unit with an A.C. 

voltmeter. The meter should indicate 230-240 volts, if not check oven circuit.
Relay Test 
Check voltage at the relay coil with a D.C. voltmeter during the microwave cooking operation, grill operation, convection operation or 

combi operation.

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.

RELAY SYMBOL

OPERATIONAL VOLTAGE

CONNECTED COMPONENTS

RY1

APPROX. 18.0V D.C.

Oven lamp / Turntable motor

RY2

APPROX. 18.0V D.C.

High voltage transformer

RY3

APPROX. 24.0V D.C.

Grill (Top) heating element

RY4

APPROX. 24.0V D.C.

Bottom heating element

RY5

APPROX. 24.0V D.C.

Touch control transformer

RY6

APPROX. 24.0V D.C.

Fan motor

RY7

APPROX. 24.0V D.C.

Convection motor

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.
Problem: POWER ON, indicator does not light up.
CARRY OUT 3D CHECKS.

STEPS

OCCURRENCE

CAUSE OR CORRECTION

1

The rated AC voltage is not present between Pin Nos. 

5 and 7 of the 4-pin connector (E).

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 the touch control transformer or the 

control unit.

3

Pattern at “a” is broken.

Replace the control unit.

(CARRY OUT 3D CHECKS BEFORE REPAIR)

NOTE:   *At the time of these repairs, make a visual inspection of the varistor for burning

 

damage and examine the transformer with tester for the presence of layer short 

 

circuit (check primary coil resistance).

 

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

CARRY OUT 4R CHECKS.

8 - 5

W

H

3-

7

W

H

3-

8

W

H

3-

10

W

H

3-

9

4

-

3

H

W

3

-

3

H

W

2

-

3

H

W

1

-

3

H

W

S

S

E

R

P

X

E

K

O

O

C

SW1

/

P

O

T

S

R

A

E

L

C

SW13

KITCHEN TIMER
/ CLOCK SET

SW14

L

L

I

R

G

SW6

I

B

N

O

C

SW4

T

R

A

T

S

SW15

O

F

N

I

SW10

E

T

U

N

I

M

 

O

T

U

A

SW12

K

O

O

C

 

O

T

U

A

SW11

SHORT CUTS

SW9

SY

A

E

&

K

C

I

U

Q

SW8

)

(.

V ?

N

O

C

SW7

R

E

T

N

E

SW3

R

E

W

O

P

 

O

R

C

I

M

SW5

S

S

E

R

P

X

E

T

S

O

R

F

E

D

SW2

CARRY OUT 4R CHECKS.

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R-890SLM

9 - 1

The control section consists of the following units as shown in 

the control panel circuit.
(1) Jog Switch Unit
(2) Control Unit
The principal functions of these units and signals communicated 

among them are explained below.

The jog switch unit is composed of a matrix, signals generated 

in the LSI are sent to the jog switch unit from P42 – P45.
When a button is touched, a signal is completed through the jog 

switch unit and passed back to the LSI through P00, P20, P21 

and P22 to perform the function that was requested.

Control unit consists of LSI, power source circuit, synchronizing 

signal circuit, reset circuit, buzzer circuit, indicator circuit, 

encoder circuit, potentiometer circuit, temperature measurement 

circuit and back light circuit.
1)  LSI
 

This LSI controls the temperature measurement signal, 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.

Symbol

Voltage

Application

VC

-5.2V

LSI(IC1)

3)  Synchronizing Signal Circuit
 

The  power  source  synchronizing  signal  is  available  in 

order to compose 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 (tact switch 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, top and bottom heating element, 

convection motor, fan motor, turntable motor, touch control 

transformer and light the oven lamp.

8)   Encoder
 

The encoder converts the signal generated by LSI into the 

pulse signal, and the pulse signal is returned to the LSI.

9)   Potentiometer Circuit
 

The circuit makes setting of the cooking mode by variable 

resistance.

10) Back Light Circuit
 

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

LD10).

11) Indicator Circuit
 

This circuit consists 7-digits, 27-segments and 4-common 

electrodes using a Liquid Crystal Display.

12) Temperature Measurement Circuit: (OVEN THERMISTOR)
 

The  temperature  in  the  oven  cavity  is  sensed  by  the 

thermistor. The variation of resistance according to sensed 

temperature is detected by the temperature measurement 

circuit and the result applied to LSI. The LSI uses this 

information to control the relay and display units.

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