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R-244M - 5

1.  When the oven door is opened, the oven lamp comes on

at this time.

2. 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.

CONNECTED COMPONENTS

RELAY

Oven lamp, Fan motor, Turntable motor

RY1

Power transformer

RY2

CONDITION

DURING

DOOR OPEN

SWITCH

CONTACT

COOKING

(NO COOKING)

Monitor switch

COM-NC

Open

Closed

Monitored latch switch

COM-NO

Closed

Open

Stop switch

COM-NO

Closed

Open

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

switches come to the following condition.

The circuits to the power transformer, fan motor and
turntable motor are cut off when the monitored latch switch
and stop switch are made open.
The oven lamp remains on even if the oven door is opened
after the cooking cycle has been interrupted, because the
relay RY1 stays closed. Shown in the display is the remaining
time.

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

MEDIUM HIGH

MEDIUM LOW

Approx. 10% = 80 Watts

32 sec. ON

6 sec. ON

12 sec. ON

18 sec. ON

24 sec. ON

26 sec. OFF

20 sec. OFF

14 sec. OFF

8 sec. OFF

LOW

MEDIUM

HIGH

Approx. 70% = 560Watts

Approx. 50% = 400 Watts

Approx. 30% = 240 Watts

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.

Approx. 100% = 800 Watts

The door can be opened by pulling the door.

1. When the oven door is closed, the contacts (COM-NO)

must be closed.

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

must be opened.

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

NC) must be closed.

3. If the oven door is opened and he contacts (COM-NO)

of the monitored latch switch fail to open, the fuse F1
blows immediately after closing the contacts (COM-
NC) of the monitor switch.

CAUTION: BEFORE REPLACING A BLOWN FUSE  F1

TEST MONITORED LATCH SWITCH (SW1)
AND  MONITOR SWITCH FOR PROPER
OPERATION.  (REFER TO CHAPTER “TEST
PROCEDURE”).

1. The fuse F1 blows when the contacts (COM-NO) of the

monitored latch switch remain closed with the oven
door open and when the contacts (COM-NC) of the
monitor switch are closed.

2. If the wire harness or electrical components are short-

circuited, the fuse F1 blows to prevent an electric shock
or fire hazard.

The thermostat protects the high voltage transformer against
overheating. If the temperature goes up higher than 150˚C
because the fan motor is interrupted or the ventilation
openings are blocked, the thermostat will cycle, line volt-
age to the high voltage transformer will also cycle. (If
operated, check the magnetron for damage.)

Latch hook

SW3: Stop switch

Door

SW2: Monitor switch

SW1: Monitored latch switch

Latch heads

6

R-244M -

MICROWAVE OUTPUT POWER (IEC-60705)

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).

Using this procedure, the heating time to raise 1000g of water by 10

°

C is approximately 50 seconds.

The IEC-60705 procedure must be carried out using laboratory-type procedures and equipment.  These requirements
make the procedure unsuitable for routing performance checks.  An indication of the power being produced by the oven
can however be obtained using the procedure given below.

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 70.

MICROWAVE LEAKAGE TEST

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

The thermal cut-out located on the top of the oven cavity is
designed to prevent damage to the oven, if the food in the
oven catch fire due to over heating produced by improper
setting of cook time or failure of control unit. Under normal
operation, the thermal cut-out remains closed. However,
when abnormally high temperatures are reached within the
oven cavity, the thermal cut-out will open at 125˚C, causing
the oven to shut down. The defective thermal cut-out must be
replaced with a new one.

The turntable motor drives the turntable roller assembly to
rotate the turntable.

The fan motor drives a blade which draws external cool air.
This cool air is directed through the air vanes surrounding
the magnetron and cools the magnetron. This air is chan-
nelled through the oven cavity to remove steam and vapours
given off from heating food. It is then exhausted through the
exhaust vents at the rear of the oven cavity.

The noise filter assembly prevents radio frequency interfer-
ence that might flow back into the power circuit.

R-244M - 7

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.

Do not touch the electrical parts and the printed wiring board to prevent an electric

shock. Because the control unit is " TRANSLESS CIRCUIT " and all electrical parts
are used at A.C. line voltage.

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 M) 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.

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. 18.0V D.C.

Oven lamp / Turntable motor / Cooling fan motor

RY2

Approx.   7.0V D.C.

High voltage transformer

8

R-244M -

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 ab-
normal condition is detected, replace
the defective parts.

(J1) 

5

1

R70 

RY2

R1

D71

VRS1

ZD70 

RY1

If the display fails to clear when the STOP/CLEAR
key is depressed, first verify the lead wire harness
is making good contact, verify that the stop switch
operates properly; that is 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 indi-
cated on the switch unit circuit and place a jumper
wire between the pins that correspond to the
STOP/CLEAR 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
display unit) to determine if the display unit or
switch unit is at fault.

1

2

3

4

SW4

5

6

SW5

SW6

SW7

SW8

SW1

CN - C

CN - C

6Pin HARNESS

SW2

SW3