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R-959(SL)M-AA

8 – 2

3. Also, the high voltage transformer has the thermal cut-out in the primary coil. The thermal cut-out will open when the temperature of the thermal

cut-out in the primary coil reaches approximately 150

°C. The thermal cut-out resets automatically at 130°C. If an ohmmeter indicates an open cir-

cuit under normal condition, replace the high voltage transformer because the primary coil (thermal cut-out) has opened. An open primary coil
(thermal cut-out) indicates overheating of the high voltage transformer. Check for restricted air flow to the high voltage transformer, especially the
ventilation opening.

4. CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.

Isolate the high voltage rectifier assembly from the HV circuit. The high voltage rectifier can be tested using an ohmmeter set to its highest range.
Connect the ohmmeter across the terminal B+C of the high voltage rectifier and note the reading obtained. Reverse the meter leads and note this
second reading. The normal resistance is infinite in one direction and more than 100 k

Ω in the other direction.

CARRY OUT 4R CHECKS.

ASYMMETRIC RECTIFIER TEST

CARRY OUT 3D CHECKS.

Isolate the high voltage rectifier assembly from the HV circuit. The asymmetric rectifier can be
tested using an ohmmeter set to its highest range across the terminals A+B of the asymmetric
rectifier and note the reading obtained. Reverse the meter leads and note this second reading.
If an open circuit is indicated in both directions then the asymmetric rectifier is good. If the asymmetric rectifier is shorted in either direction, then the
asymmetric rectifier is faulty and must be replaced with high voltage rectifier. When the asymmetric rectifier is defective, check whether magnetron,
high voltage rectifier, high voltage wire or filament winding of the high voltage transformer is shorted.

CARRY OUT 4R CHECKS.

NOTE: FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIER, THE BATTERIES OF THE MEASURING INSTRUMENT MUST HAVE

A VOLTAGE AT LEAST 6 VOLTS, BECAUSE OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIRECTIONS.

CARRY OUT 3D CHECKS.

1. Isolate the high voltage capacitor from the circuit.

2. Continuity check must be carried out with measuring instrument which is set to the highest resistance range.

3. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10M

Ω after it has been charged.

4. A short-circuited capacitor shows continuity all the time.

5. An open capacitor constantly shows a resistance about 10 M

Ω because of its internal 10MΩ resistance.

6. When the internal wire is opened in the high voltage capacitor shows an infinite resistance.

7. The resistance across all the terminals and the chassis must be infinite when the capacitor is normal.

If incorrect reading are obtained, the high voltage capacitor must be replaced.

CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.

Isolate the switch to be tested and using an ohmmeter check between the terminals as described in the following table.

If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.

CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.

Disconnect the connector B from CPU unit. Measure the resistance of the thermistor with an ohmmeter. Connect the ohmmeter leads to Pin No's C1
and C3 of the thermistor harness.

If the meter does not indicate above resistance, replace the thermistor.

CARRY OUT 4R CHECKS.

Table: Terminal Connection of Switch

Plunger Operation

Common terminal to Normally open terminal

Common terminal to Normally close terminal

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D

Room Temperature

Resistance

20

°C - 30°C

Approximately 359.9 k

Ω - 152 kΩ

D2

D1

ASYMMETRIC
RECTIFIER

HIGH VOLTAGE
RECTIFIER

R-959(SL)M-AA

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.

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 (GRILL) indicates that the oven cavity has overheated, this may be due to no load operation.

An open circuit thermal cut-out (CONV.) indicates that the convection fan winding has overheated, this may be due to resistricted ventilation or locked
cooling fan or locked convection fan motor.

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.

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.

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 when the door is opened, check the monitored latch switch SW1 and monitor switch.

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

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

°

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C

C

Thermal cut-out 170

°C (GRILL)

Cuts back in at 155

°C.

Above 170

°

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C

Thermal cut-out 170

°C (CONV.)

Cuts back in at 155

°C.

Above 170

°

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Table: Resistance of Motor

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M

 

9

.

8

9

3

  

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A

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F

Ω

Turntable 
motor

RMOTDA255WRZZ

Approximately   14.5 k

Ω

RMOTDA189WRE0

Approximately   12.0 k

Ω

Convection fan motor

Approximately 183.7 k

Ω

Dumper 
motor

RMOTDA257WRZ1

Approximately   14.5 k

Ω

RMOTDA257WRZZ

Approximately   14.5 k

Ω

RMOTDA191WRE0

Approximately   11.0 k

Ω

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

F8A

20A

WHT

RED

R1

R2

N

Cx

Cy

L

L

L

L (min) Cx ± 20%

Cy ± 20%

1.0mH

0.22 uF

4700pF

R-959(SL)M-AA

8 – 4

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.

CAUTION: REPLACE NOISE FILTER.

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 termi-
nals of the heating element as described in the following table.

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, and also the Control unit is divided into
two units, CPU unit and Power unit, and troubleshooting by 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 N) 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.

d) Proper temperature measurement is not obtained.

Table: Resistance of heater

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P

Grill heating elements (Top)

Approximately 37.4 

Ω -39.7Ω [(18.7Ω - 19.85Ω) x 2]

Convection heating elements

Approximately 38.02 

Ω - 40.95Ω

R-959(SL)M-AA

8 – 5

If the display fails to clear when the STOP/
CLEAR pad is depressed, first verify the flat
ribbon cable is marking good contact, verify
that the door sensing switch (stop switch)
operates properly; that is the contacts are
closed when the door is closed and open
when the door is open. If the door sensing
switch (stop switch) is good, disconnect the
flat ribbon cable that connects the key unit to
the control unit and make sure the door sens-
ing switch is closed (either close the door or
short the door sensing switch connecter). 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
marking 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 deter-
mine if the control unit or key pad is at fault.

CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.

Remove the outer case and check voltage between Pin Nos. 1 and 3 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 dual 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.

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.

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.

RELAY SYMBOL

OPERATIONAL VOLTAGE

CONNECTED COMPONENTS

RY1

APPROX. 24.0V 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.

Convection heating element

RY5

APPROX. 24.0V D.C.

Fan motor

RY6

APPROX. 24.0V D.C.

Touch control transformer

RY7

APPROX. 24.0V D.C.

Convection motor

RY8

APPROX. 24.0V D.C.

Damper motor

N

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P

E

T

S

1

The rated AC voltage is not present between Pin No. 1 and 3 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 control unit.

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4

 CHECKS BEFORE REPAIR)

1

G

5

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6

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7

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8

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G2

G3

G4

G9

G10

G12

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11

MINCED

MEAT

10min.

1min.

10sec.

CHICKEN

PORTIONS

COMBI.

ROAST

PORK

AUTO

COOK

(TIME)

START

AUTO

MINUTE

(WEIGHT)

GRILL

KITCHEN

TIMER

STOP

CLEAR

ROAST

POULTRY

(TIME)

MICRO.

POWER

CONV.

(ºC)

(WEIGHT)

ROAST
BEEF/
LAMB

STEAK/
CHOPS

(J1)

(J2)

9

1

7

CN

-

E

CN

-

A

VRS1

a

c

d

b