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R-8740M  - 19

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 troubleshooting by unit replacement is described according to the symptoms indicated.
1.  Key Unit   Note : Check key unit ribbon connection before replacement.

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.

2. Control Panel

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

2-1  In connection with pads

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.

2-2  In connection with indicators

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.

2-3  Other possible troubles caused by defective control unit.

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.

CARRY OUT 3D CHECKS.
Remove the outer case and check voltage between Pin Nos. 11 and 9 of the 6 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, RY4, RY5 and RY7 Relay Test
These relays are operated by D.C. voltage
Check voltage at the relay coil with a D.C. voltmeter during the microwave cooking operation, grill cooking,
convection cooking or dual cooking.

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. 24.0V D.C.

Oven lamp / Turntable motor

RY2

Approx. 18.0V D.C.

High voltage transformer

RY3

Approx. 23.0V D.C.

Top heating element

RY4

Approx. 23.0V D.C.

Bottom heating element

RY5

Approx. 23.0V D.C.

Fan motor

RY7

Approx. 23.0V D.C.

Convection motor

CARRY OUT 4R CHECKS.

R-8740M  - 20

CARRY OUT 3D CHECKS.

STEPS

OCCURRENCE

CAUSE OR CORRECTION

1

The rated AC voltage is not present at

Check supply voltage and oven power cord.

power terminal of CPU connector (CN-A).

2

The rated AC voltage is present at primary

Low voltage transformer or secondary circuit defective.

side of low voltage transformer.

Check and repair.

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.

*Insert the coil RCILF2003YAZZ between "c" and "d".

(CARRY OUT 3D CHECKS BEFORE REPAIR)

NOTE: *At the time of these repairs, make a

visual inspection of the varistor for burn-
ing damage and examine the trans-
former with tester for the presence of
layer short circuit (check primary coil
resistance). If any abnormal condition
is detected, replace the defective parts.

CARRY OUT 3D CHECKS

Q20

RY5

FM

(J1)

B

PWR

CN - A

VRS1

T1

P

4

1

RY6

AC

D25

If the display fails to clear when the STOP 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 sensing 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 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 a 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 key pad is at fault.

CARRY OUT 4R CHECKS.

R-8740M

4

5

2

5

7

9

0

4

6

8

1

3

6

7

8

9

10

11

12

3

2

1

R-8740M  - 20

CARRY OUT 3D CHECKS.

STEPS

OCCURRENCE

CAUSE OR CORRECTION

1

The rated AC voltage is not present at

Check supply voltage and oven power cord.

power terminal of CPU connector (CN-A).

2

The rated AC voltage is present at primary

Low voltage transformer or secondary circuit defective.

side of low voltage transformer.

Check and repair.

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.

*Insert the coil RCILF2003YAZZ between "c" and "d".

(CARRY OUT 3D CHECKS BEFORE REPAIR)

NOTE: *At the time of these repairs, make a

visual inspection of the varistor for burn-
ing damage and examine the trans-
former with tester for the presence of
layer short circuit (check primary coil
resistance). If any abnormal condition
is detected, replace the defective parts.

CARRY OUT 3D CHECKS

Q20

RY5

FM

(J1)

B

PWR

CN - A

VRS1

T1

P

4

1

RY6

AC

D25

If the display fails to clear when the STOP 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 sensing 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 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 a 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 key pad is at fault.

CARRY OUT 4R CHECKS.

R-8740M

4

5

2

5

7

9

0

4

6

8

1

3

6

7

8

9

10

11

12

3

2

1

R-8740M  - 20

CARRY OUT 3D CHECKS.

STEPS

OCCURRENCE

CAUSE OR CORRECTION

1

The rated AC voltage is not present at

Check supply voltage and oven power cord.

power terminal of CPU connector (CN-A).

2

The rated AC voltage is present at primary

Low voltage transformer or secondary circuit defective.

side of low voltage transformer.

Check and repair.

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.

*Insert the coil RCILF2003YAZZ between "c" and "d".

(CARRY OUT 3D CHECKS BEFORE REPAIR)

NOTE: *At the time of these repairs, make a

visual inspection of the varistor for burn-
ing damage and examine the trans-
former with tester for the presence of
layer short circuit (check primary coil
resistance). If any abnormal condition
is detected, replace the defective parts.

CARRY OUT 3D CHECKS

Q20

RY5

FM

(J1)

B

PWR

CN - A

VRS1

T1

P

4

1

RY6

AC

D25

If the display fails to clear when the STOP 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 sensing 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 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 a 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 key pad is at fault.

CARRY OUT 4R CHECKS.

R-8740M

4

5

2

5

7

9

0

4

6

8

1

3

6

7

8

9

10

11

12

3

2

1