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891M -

The oven will stop its operation when there is a fire in the
oven cavity in microwave cooking condition.
LSI measures the voltage across the temperature measure-
ment circuit intermittently within a 32-second time base once
the oven is started in the microwave cooking mode. The oven
will stop its operation when the difference of the voltages is
more than 0.69 volts in microwave cooking condition.

1. Within a 32-second base, first the thermistor is energized

for 3 seconds.  After 2 seconds since the thermistor is
energized, the voltage across the temperature
measurement circuit is measured. And after 21 seconds
since the thermistor is cut off, the convection motor
operates for 10 seconds.

2. The oven carries out the procedure above again. If the

second voltage is 0.69V higher than the first voltage, LSI
judges it is a fire in the oven cavity and stops the oven.

3. When sensor cooking, the sensing fire operation is not

carried out until the oven senses the steam from food.
Because food cannot be cooked well by rotating the
convection fan at that time. After sensing the steam, the
sensing fire operation is started.

4. When LSI judges it is fire in the oven cavity, LSI will switch

off the relays to the power transformer, fan motor and
convection motor and LSI stops counting down. And then
the damper is closed so that the fresh air does not come
into the oven cavity.

CONVECTION

MOTOR

THERMISTOR

Sensing 

Voltage

ON

OFF

ON

OFF

ON

OFF

0 2

20

30 32

64 (sec.)

3 sec.

Sensing the voltage across temperature measurement circuit.

10 sec.

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891M -

The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc.
Therefore, unlike conventional microwave ovens, proper maintenance cannot 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
Switch  Unit, and also the Control Unit is divided into two units, Display Unit and Power Unit, and
troubleshooting by unit replacement is described according to the symptoms indicated.
1.  Switch Unit.        Note : Check switch unit lead wire harness connection before replacement.

The following symptoms indicate a defective switch unit. Replace the switch unit.
a) When touching the buttons, a certain button produces no signal at all.
b) When touching a number button, two figures or more are displayed.
c) When touching the buttons, sometimes a button produces no signal.

2.  Control Unit

The following symptoms  indicate a defective control unit. Before replacing the control unit (power
unit and/or display unit), perform the Switch unit test (Procedure K) to determine if control unit is
faulty.

2-1  In connection with buttons.

a) When touching the buttons, a certain group of buttons do not produce a signal.
b) When touching the buttons, no buttons produce a signal.

2-2  In connection with indicators

a) At a certain digit, all or some dots do not light up.
b) At a certain digit, brightness is low.
c) Only one indicator does not light.
d) The corresponding dots 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 problems 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.

If the display fails to clear when the STOP/CLEAR button
is depressed, first verify the lead wire harness  is making
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 lead wire harness that connects the switch
unit to the display unit and make sure the door sensing
switch is closed (either close the door or short the door
sensing switch connecter). Use the Switch unit matrix
indicated on the switch unit circuit and place a jumper wire
between the pins that correspond to the STOP/CLEAR
button making momentary contact. If the display unit
responds by clearing with a beep the switch unit is faulty
and must be replaced. If the display 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 display unit) to determine if the display
unit or switch unit is at fault.

G 8

G 9

G 7

G 6

G 5

G 4

G 3

G 2

G 1

SW16

SW12

SW8

7

8

9

START

AUTO MINUTE

DUAL

BOOK MARK

BREAKFAST

CONVECTION

MICROWAVE

GRILL

PIZZA

INDEX

2

3

4

SW15

SW19

05

SW20

SW11

SW7

1

SW3

SW2

SW1

6

SW4

SW14

SW18

SW10

SW6

SW13

SW17

SW9

SW5

STOP

CLEAR

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891M -

1. CARRY OUT 3D CHECKS.
2. Disconnect the leads from the primary of the high voltage transformer. Make sure that the leads remain isolated

from other oven components and chassis. (Use insulation tape if necessary.)

3. Close the door.
4. Reconnect the supply.
5. Check the voltage between Pin Nos. 1 and 3 of the 4 pin connector (A) on the control unit with an A.C.

voltmeter. The meter should indicate 240 volts, if not check oven circuit.

6. Relay Test

These are operated by D.C. voltage. Check voltage at the relay coil with a D.C. voltmeter during the microwave
cooking operation.

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

RELAY SYMBOL

OPERATIONAL VOLTAGE

CONNECTED COMPONENTS

RY1

Approx. 19.5V D.C.

Oven lamp / Turntable motor

RY2

Approx. 18.0V D.C.

High voltage transformer

RY3

Approx. 18.6V D.C.

Top heater

RY4

Approx. 18.6V D.C.

Bottom heater

RY5

Approx. 24.2V D.C.

Cooling fan motor

RY6

Approx. 23.2V D.C.

Convection fan motor

7. CARRY OUT 4R CHECKS.

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

inspection of the varistor for burning dam-
age and examine the transformer with
tester for the presence of layer short-cir-
cuit (check primary coil resistance). If any
abnormal condition is detected, replace
the defective parts.

CARRY OUT 4R CHECKS.

1 2

( J 1 )

R Y 6

C N   -   B

C N   -   A

7

1

To protect the electronic circuits, this model is provided with a fine foil pattern added to the primary 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 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)

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891M -

OUTLINE OF TOUCH CONTROL PANEL

The touch control section consists of the following units.

(1) Switch Unit
(2) Control Unit (The Control Unit consists of Power

Unit and Display Unit).

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

Switch Unit
The switch unit is composed of a matrix, signals
generated in the LSI are sent to the switch unit through
P41, P42, P43 and P44.
When a switch button is touched, a signal is completed
through the switch unit and passed back to the LSI
through P91, P93, P94, P95 and P40 to perform the
function that was requested.

Control Unit
Control unit consists of LSI, IC, ACL circuit, indicator
circuit, LCD driver, power source circuit, relay circuit,
buzzer circuit, synchronizing signal circuit, switch unit
circuit and back light circuit.

This is a microcomputer, responsible for controlling
the entire control unit.

This is a read only memory IC, responsible for giving
IC1 the all programmes.

This is a memory IC.
This memorizes the contrast of LCD.

This is an amplifier IC.
This IC controls the contrast of LCD signal.

This IC drives the LCD.

This IC generates a signal which resets the LSI to
the initial state when power is supplied.

This circuit consists of 100 x 65 dots using a Liquid
Crystal Display.

This circuit generates voltages necessary in the
control unit from the AC line voltage.
In addition, the synchronizing signal is available in
order to compose a basic standard time in the clock
circuit.

Symbol

Voltage

Application

VC

-5.0V

LSI(IC1)

A circuit to drive the magnetron, fan motor, turntable
motor, convec. motor, heater and  light the oven
lamp.

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

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.

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

A circuit to drive the back light (Light emitting diodes
LD1- LD6 and Lamps LMP1, LMP2).

The switch circuit is composed of a matrix, signals
generated in the LSI are sent to the switch circuit
through PB6, PB7, P91, P93, P94, P95 and P40.
When a switch button is touched, a signal is
completed through the switch circuit and passed
back to the LSI through P41, P42, P43 and P44.

The temperature in the oven cavity is sensed by the
thermistor.
Tte variation of resistance according to sensed
temperature is detected by the temperature
measurement circuit and the result applied to LSI.
The result of detecting is given to LSI controlling the
relay and display.