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R-24STM - 5

1. Place the roller stay on the floor of

the oven cavity, engaging shaft into
turntable motor shaft.

2. Then place the turntable on roller

stay.

Turntable

Seal packing

Roller stay

1

Digital Display

2

Indicators

The appropriate indicator will flash or light up,

just above each symbol according to the

instruction.  When an indicator is flashing, press

the suitable button (having the same symbol)

or do the necessary operation

Stir

Turn over

Weight

Portion Indicator

Microwave power level

Cooking in progress indicator

1.

DIGITAL DISPLAY

2.

EXPRESS COOK button

3.

EXPRESS DEFROST button

4.

START/AUTO MINUTE button

5

STOP/CLEAR button

6

TIME/WEIGHT button

7

POWER LEVEL button

KG

1

Door

2

Door hinges

3

Oven lamp

4

Waveguide cover

5

Control panel

6

Coupling

7

Door lock openings

8

Oven cavity

9

Door seals and sealing surfaces

10 Safety door latches
11 Ventilation openings
12 Outer cabinet
13 Rear plate
14 Power supply cord

10

11

12

13

14

7

R-24STM - 6

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.

14 sec. OFF

8 sec. OFF

32 sec. ON

24 sec. ON

MEDIUM HIGH

HIGH

MEDIUM

MEDIUM LOW

LOW

18 sec. ON

6 sec. ON

12 sec. ON

26 sec. OFF

20 sec. OFF

Approx. 10% = 80 Watts

Approx. 30% = 240 Watts

Approx. 50% = 400 Watts

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 a cooking program, the monitored latch switch
(SW1) and stop switch (SW3)must open its 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. The contacts (COM - NO) of the monitored
latch switch (SW1) and stop switch (SW3) are closed
after.

6-3

When the oven door is opened and the contacts of the
monitored latch switch (SW1) remain closed, the fuse
F1 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 vari
contact. The following levels of microwave power are given.
SETTING

Closing the door activates the door interlock switch (moni-
tored latch 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 noise filter is energised.

NOTE: When the oven door is opened, the oven lamp

comes on at this time.

Enter a desired cooking time with the touching TIME pad
and start the oven with touching 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 voltage doubling 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.

CONDITION

DURING

DOOR OPEN

SWITCH

CONTACT

COOKING

(NO COOKING)

Monitor switch

COM-NC

Open

Closed

Monitored latch switch

COM-NO

Closed

Open

The circuits to the power transformer, fan motor and
turntable motor are cut off when the monitored latch
switch is opened.

Oven lamp, Fan motor, Turntable motor

RY1

Power transformer

RY2

Approx. 70% = 560 Watts

100%          = 800 Watts

R-24STM - 7

1. The fuse F1 also blows when the H.V. rectifer, H.V. wire

harness, H.V. capacitor, magnetron or secondary
winding of power transformer is shorted.

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

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

°

°

The thermostat protects the magnetron against overheat-
ing. If this temperature goes up higher than 150

°C because

the fan motor is interrupted.  The ventilation openings are
blocked,or a HV short condition is created the thermostat
will open and line voltage to the power transformer and the
magnetron will cycle,preventing overheating

°

The thermal cut-out located on the top of the oven cavity is
designed to prevent damage to the oven if the foods 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 oven thermal cut-out remains closed. How-
ever, when abnormally high temperatures are reached
within the oven cavity, the oven thermal cut-out will open at
125

°C, causing the oven to shut down. The defective

thermal cut-out (TC2) 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 flows
through the oven cavity to remove steam and vapors given
off from the heating foods. It is then vented through the
exhaust air vents at the rear of oven cavity.

The noise filter prevents the radio frequency interference
that might flow back in the power circuit.

DOOR OPEN MECHANISM
The door can be opened by pulling the 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.

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 the contacts (COM - NO)

of the monitored latch switch (SW1) fail to open, fuse
F8A blows simultaneously with closing the contacts
(COM - NC) of the monitor switch (SW2).

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.

CAUTION: BEFORE REPLACING A BLOWN FUSE (F1)

TEST THE MONITORED LATCH SWITCH
(SW1) AND MONITOR SWITCH (SW2) FOR
PROPER OPERATION. (REFER TO
CHAPTER "TEST PROCEDURE".)

Latch hook

SW3: Stop switch

Door

SW2: Monitor switch

SW1:Monitored latch switch

Latch heads

R-24STM - 8

MICROWAVE OUTPUT POWER

The power output of this oven is rated using the method specified by IEC-60705.
Full details of how to carry out thisprocedure 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.

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