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R343M - 4

CONNECTED COMPONENTS

RELAY

Oven lamp, Fan motor, Turntable motor

RY1

Power transformer

RY2

Closing the door activates all door interlock switches (latch
switch, monitored latch switch and stop switch).

IMPORTANT
When the oven door is closed, the monitor switch contacts
COM - NC must be open.
When the microwave oven is pluged in a wall outlet (230 -
240V 50Hz), the line voltage is supplied to the point A3+A5
in the control unit.

1. The display flashes ”88:88”.
2. To set any programmes or set the clock, you must first

touch the STOP pad.

3. “  :  ” appears in the display.

Enter a desired cooking time by touching the Time pads and
start the oven by touching the START pad.

1. The line voltage is supplied to the primary winding of the

power transformer. The voltage is converted to about
3.3 volts A.C. output on the filament winding and high
voltage of approximately 2000 volts A.C. on the
secondary winding.

2. The filament winding voltage (3.3 volts) heats the

magnetron filament and the high voltage (2000 volts) is
sent to the voltagedoubling circuit, where it is doubled to
negative voltage of approximately 4000 volts D.C..

3. The 2450 MHz microwave energy produced in the

magnetron generates a wave length of 12.24 cm. This
energy is channeled through the waveguide (transport
channel) into the oven cavity, where the food is placed
to be cooked.

4. When the cooking time is up, a single tone is heard and

the relays RY1 + RY2 go back to their home position.
The circuits to the oven lamp, power transformer, fan
motor and turntable motor are cut off.

5. When the door is opened during a cook cycle, the

switches come to the following condition.

The circuits to the power transformer,oven lamp fan
motor and turntable motor are cut off when the monitored
latch switch and stop switch are made open.   Shown in
the display is the remaining time.

6. MONITOR SWITCH CIRCUIT

The monitor switch (SW2) is mechanically controlled by
oven door, and monitors the operation of the monitored
latch switch (SW1)

6-1

When the oven door is opened during or after the
cycle of cooking program, the monitored latch switch
(SW1), and stop switch (SW3) must open their contacts
first. After that the contacts (COM - NC) of the monitor
switch (SW2) can be closed.

6-2

When the oven door is closed, the contacts
(COM - NC) of the monitor switch (SW2) must be
opened first.  After that the contacts of the monitored
latch switch (SW1) and stop switch (SW3) are closed.

6-3

When the oven door is opened and the contacts of the
monitored latch switch (SW1) remain closed, the fuse
(F1) F8A will blow, because the monitor switch is
closed and a short circuit is caused.

When the microwave oven is preset for variable cooking
power, the line voltage is supplied to the power transformer
intermittently within a 32-second time base through the
relay contact which is coupled with the current-limiting relay
(RY2). The following levels of microwave power are given.
SETTING

CONDITION

DURING

DOOR OPEN

SWITCH

CONTACT

COOKING

(NO COOKING)

Monitored latch switch

COM-NO

Closed

Open

Monitor switch

COM-NC

Open

Closed

Stop switch

COM-NO

Closed

Open

Monitor switch

COM-NO

Closed

Open

NOTE: The ON/OFF time ratio does not exactly correspond

to the percentage of microwave power, because
approx. 3 seconds are needed for heating up the
magnetron filament.

32 sec. ON

24 sec. ON

18 sec. ON

12 sec. ON

6 sec. ON

8 sec. OFF

14 sec. OFF

20 sec. OFF

26 sec. OFF

HIGH

MEDIUM HIGH

MEDIUM

MEDIUM LOW

LOW

Approx. 70% = 630 Watts

100%

Approx. 50% = 450 Watts

Approx. 30% = 270 Watts

Approx. 10% = 90 Watts

 = 900 Watts

R343M - 5

LATCH
HEADS

LATCH HOOK

MONITOR
SWITCH (SW2)

MONITORED
LATCH
SWITCH (SW1)

STOP
SWITCH
(SW3)

DOOR OPEN BUTTON

OPEN LEVER

DOOR

1.  When the oven door is closed, the contacts (COM-

NO) must be closed.

2.  When the oven door is opened, the contacts (COM-

NO) must be opened.

f the oven door is opened and the contacts

(COM-NO) of the monitored latch switch SW1
fail to open, the fuse F8A blows
simultaneously with closing the contacts
(COM-NC) of the monitor switch SW2.

CAUTION:  BEFORE REPLACING A BLOWN

FUSE F8A TEST THE MONITORED
LATCH SWITCH SW1, MONITOR
SWITCH SW2.

The power output of this oven is rated using the method specified by IEC-60705.  Full details of how to carry out this
procedure can be found in the Sharp Technical Training notes which is available from Sharp Parts Centre
(part number SERV-LITMW01).

The IEC-60705 procedure must be carried out using laboratory-type procedures and equipment.  These requirements
make the procedure unsuitable for routine performance checks.

Note: The following test method gives an indication of the output power only, it cannot be used to establish the actual/

rated output power.  If the true output power is required, then the IEC-60705 test method must be used.

Alternative simplified method:
1. Place 2 litres of cold water (between 12

°

C and 20

°

C) in a suitable container.

2. Stir the water and measure the temperature in 

°

C.  Note temperature as T1.

3. Place the container in the microwave and heat the water for 2 minutes on full power.
4. When the 2 minutes is completed, remove the container and stir the water.  Note the water temperature as T2.
5. Calculate the output power using the following formula:

R.F. Power Output = (T2 - T1) x 80.

This oven should be tested for microwave leakage on completion of any repair or adjustment, following the procedure
described in the Sharp Technical Training notes (part number SERV-LITMW01).  The maximum leakage permitted in
BS EN 60335-2-25 is 50W/m

2 

(equivalent to 5mW/cm

2

), however it is not normal to detect any significant leakage,

therefore, any leakage which is detected should be investigated.

It is essential that only leakage detectors with current calibration traceable to the National Physical Laboratories are

used.

Suitable leakage detectors :

CELTEC A100
APOLLO X1

R343M - 6

Remove the outer case and check voltage between Pin No 5 of the 3 pin connector (A) and common terminal
of the relay (RY2) on the control unit with an A.C. voltmeter.
The meter should indicate rated voltage, if not check oven circuit.

RY1 and RY2 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.

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. 19.0V D.C.

Oven lamp / Turntable motor / Cooling fan motor

RY2

Approx.   7.5V D.C.

Power transformer

To prevent an electric shock. Do not touch the electrical parts and the printed wiring
board. Because the control unit is " TRANSLESS CIRCUIT " and all electrical parts
are used at A.C. line voltage.

   

1. Disconnect the oven from the power supply.
2. Discharge the high voltage capacitor.
3. Remove the control unit from the control panel.
4. By using an ohmmeter, check the tact switch operation.
5. When the tact switch is not depressed, an ohmmeter should indicate an open circuit. When the tact

switch is depressed, an ohmmeter should indicate a short circuit. If improper operation is indicated,
the tact switch is probably defective and should be checked.

    

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 in one unit and troubleshooting by unit replacement
is described according to the symptoms indicated.
Control Panel.

The following symptoms indicate a defective control unit.

1.  Tact Switch.

The following symptoms indicate a defective tact switch. Replace the tact switch.

a) When touching a tact switch, a certain tact switch produces no signal at all.
b) When touching a tact switch, sometimes a tact switch produces no signal.

2. In connection with tact switches.

a) When touching a tact switch, a certain group of tact switch do not produce a signal.
b) When touching a tact switch, no tact switch produce a signal.

3. Display problems.

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.
h)  When touching a tact switch, the control unit does not respond.

4. Other possible problems caused by defective control unit.

a) Buzzer does not sound or continues to sound.

R343M - 7

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.

STEPS

OCCURRENCE

CAUSE OR CORRECTION

1

The rated voltage is not applied between Pin

Check supply voltage and oven power cord.

No. 5 of the 3 pin connector (A) and the

common terminal of the relay RY2.

2

Only pattern at "a" is broken.

*Insert jumper wire J1 and solder.

3

Pattern at "a" and "b" are broken.

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

NOTE: *At the time of making these repairs, make a visual inspection of the varistor. Check for burned damage. If

any abnormal condition is detected, replace the defective parts.

1

5

RY2

(J1)

CN-A 

RY1

D1

VRS1

D71

ZD71