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R-734 - 17

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 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 keys, a certain key produces no signal at all.
b) When touching a key, two figures or more are displayed.
c) When touching the keys, sometimes a key produces no signal.

2.  Control Unit

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

2-1 In connection with keys.

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

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

Table: Resistance of heating element

Parts name

Resistance

Grill heating element

Approximately 56 

Ω

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 M

Ω

 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.

R-734 - 18

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 and RY3 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 or grill
cooking 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. 24.0V D.C.

Oven lamp / Turntable motor / Cooling fan motor

RY2

Approx. 18.0V D.C.

Heating element

RY3

Approx. 18.0V D.C.

High voltage transformer

If the display fails to clear when the STOP key is
depressed, first verify the lead wire harness is mak-
ing good contact, verify that the stop switch operates
properly; that  the contacts are closed when the door
is closed and open when the door is open. If the stop
switch is good, disconnect the lead wire harness that
connects the switch unit to the display unit and make
sure the stop switch is closed (either close the door
or short the stop switch connector). Use the Switch
unit matrix indicated on the switch unit circuit and
place a jumper wire between the pins that corre-
spond to the STOP key 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 key does not respond, the
above method may be used (after clearing the dis-
play unit) to determine if the display unit or switch unit
is at fault.

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)

1

2

3

4

SW2

5

6

SW3

SW4

SW5

SW6

SW7

SW1

R-734 - 19

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 con-
dition is detected, replace the defective parts.

CARRY OUT 4R CHECKS.

RY2

OL / FM
/ TTM

AC

5

1

D20 

VRS1

CN - A

D21 

RY1

(J1)

T1

R-734 - 20

The touch control section consists of the following units.

(1) Switch Unit
(2) Control 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 R60 and R61.
When a switch button is touched, a signal is completed
through the switch unit and passed back to the LSI through
R50, R51, R52 and R53 to perform the function that was
requested.

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

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

This circuit generates voltage necessary in the control
units.

Symbol

Voltage

Application

VC

+5V

LSI(IC1)

OUTLINE OF TOUCH CONTROL PANEL

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

The buzzer is responsive to signals from the LSI to emit
audible sounds (tact switch touch sound and comple-
tion sound).

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

To drive the magnetron, fan motor, turntable motor,
grill heating element and light the oven lamp.

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

The encoder converts the signal generated by LSI into
the pulse signal, and the pulse signal is returned to the
LSI.

A circuit to drive the back light (Light emitting diodes
LED1-LED4)