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R-8740M  - 5

Power Requirements

230-240V Volts / 50 Hertz / Single phase, 3 wire earthed

Power Consumption

Microwave cooking

1.45kW Approx. 6.3A

Dual cooking

(Microwave and Top Grill)

2.4kW Approx. 10.3A

(Microwave and Bottom Grill)

1.95kW Approx. 8.2A

(Top and Bottom Grill)                        1.5kW Approx. 6.3A

Convection cooking

1.525kW Approx. 6.4A

Bottom Grill cooking

550kW Approx. 2.3A

Top Grill cooking

1000kW Approx. 4.2A

Power Output

900 watts nominal of RF microwave energy (measured by method of IEC
60705) Operating fequency 2450 MHz

Top Grill heating element Power Output

 1000W

Bottom Grill heating element Power Output

500W

Case Dimensions

Width 520 mm

Height 309 mm (including foot)

Depth 488 mm

Cooking Cavity Dimensions

Width 349 mm

Height 207 mm

Depth 357 mm

Turntable diameter

325mm

Net Weight

Approx. 19 kg

Control Complement

These indicators will light corresponding with
below symbols

: Time reduce

: Memory

: Manual

: Percentage (for microwave
  power level)

: Lock (showing oven lock is set)

: Cook (showing oven in operation)

3. COOKING MODE indicator lights.

These indicator lights will light during
each cooking mode.

4. NUMBER keys for time and memory

programming

5. START key
6. STOP key
7. SOUND key
8. BOTTOM GRILL key
9. TOP GRILL key

10. CONVECTION key

To change the convection
temperature

11. MICROWAVE key

To change the microwave power
setting

12. MANUAL key
13. MEMORY key
14. TIME REDUCE key

R-8740M  - 6

These indicators will light corresponding with
below symbols

: Time reduce

: Memory

: Manual

: Percentage (for microwave
  power level)

: Lock (showing oven lock is set)

: Cook (showing oven in operation)

3. COOKING MODE indicator lights.

These indicator lights will light during
each cooking mode.

4. NUMBER keys for time and memory

programming

5. START key
6. STOP key
7. SOUND key
8. BOTTOM GRILL key
9. TOP GRILL key
10. CONVECTION key

To change the convection temperature

11. MICROWAVE key

To change the microwave power setting

12. MANUAL key
13. MEMORY key
14. TIME REDUCE key

14

13

12

11

10

9

8

7

6

1
2

3

4

5

9 

7

10

4

1

8

6

5

3

2

10

12

11

9. Door seals and sealing surfaces
10. Ventilation openings
11. Outer cabinet
12. Power supply cord
13. Turntable
14. Handle

1. Control panel
2. Oven lamp
3. Grill heating element (Top Grill)
4. Door opening button
5. Waveguide cover
6. Oven cavity
7. Turntable motor shaft
8. Grill heating element

(Bottom Grill)

14

13

R-8740M  - 7

Closing the oven door activates all door interlock switches
(Monitored latch switch and stop switch.

IMPORTANT:
When the oven door is closed, the contacts COM-NC of the
monitor switch SW2 must be open and the contacts (COM-
NO) must be closed. When the microwave oven is plugged
in a wall outlet (230V / 50Hz), 230 volts A.C. is supplied to
the point A9 + A11 in the control unit.

1. The display flashes ".0"
2. To set any programmes or set the clock, you must first

"put the oven in MANUAL MODE .  Press the MANUAL

key for 6-10 seconds. (oven will 'beep').  Press the

MANUAL key once more.  The oven is now in manual
mode (this will be indicated in the display window, above
the         symbol).

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

comes on at this time.

HIGH COOKING
Enter a desired cooking time with the number keys, press
the " MICROWAVE " 

  key, then press the START key 

.

CONNECTED COMPONENTS

RELAY

Oven lamp, Turntable motor

RY1

High voltage transformer

RY2

Fan motor

RY5

1. 230 volts A.C. is supplied to the primary winding of the

high voltage 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 channelled 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 signal tone is heard and

the relays RY1 + RY2 + RY5 go back to their home
position. The circuits to the oven lamp, high voltage
transformer, fan motor and turntable motor are cut off.

5. When the oven door is opened during a cooking cycle,

the switches come to the following condition.

Switch

Contact

          Condition
During

Oven Door

Cooking

Open(No cooking)

Monitored latch Switch COM-NO

Closed

Opened

Monitor Switch

COM-NO

Closed

Opened

Monitor Switch

COM-NC

Opened

Closed

Stop switch

COM-NO

Closed

Opened

The circuit to the high voltage transformer, is cut off when
the contact of relay RY2 contacts COM-NO of the monitored
latch switch, and monitor switch SW2 are made open. The

circuit to the fan motor is cut off when the relay RY5 is made
open. The circuit to the turntable motor is cut off when the
contacts COM-NO of the monitored latch switch are made
open. The relays RY2 and RY5 are made open when the
door is opened. The oven lamp remains on even if the oven
door is opened after the cooking cycle has been interrupted,
because the relay RY1  stay closed. Shown in the display is
remaining time.
6. MONITOR SWITCH CIRCUIT

The monitor switch SW2 is mechanically controlled by
the 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 their contacts (COM-
NO) first. After that the contacts (COM-NC) of the
monitor switch SW2 can be closed and the contacts
(COM-NO) of monitor switch SW2 are made open.

6-2. When the oven door is closed. The contacts (COM-NC)

of the monitor switch SW2 must be opened and the
contacts (COM-NO) of monitor switch SW2 must be
closed.  After that the contacts of the monitored latch
switch SW1 and the stop switch SW3 are made closed.

6-3. When the oven door is opened and the contacts of the

monitored latch switch SW1 remain closed, the fuse F2
F8A will blow. Because the relay RY1 and monitor
switch SW2 are closed  and a short circuit is caused.

Program desired convection temperature by touching
"MANUAL", then the CONVECTION key. When the START key
is touched, the following operations occur:
1. The coil of shut-off relays RY1, RY5 and RY7 are energized,

the oven lamp, cooling fan motor, turntable motor and
convection motor are turned on.

2. The coil of shut-off relays RY3  and RY4 are energized by

the control unit and the main supply voltage is added to the

When the microwave oven is preset for variable cooking
power, the 230 volts A.C. power is supplied to the high voltage
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.

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

R-8740M  - 8

top and bottom heater.

3. When the oven temperature reaches the selected preheat

temperature, the following operations occur;

3-1. The shut-off relays RY3 and RY4 are de-energized by the

control unit temperature circuit and thermistor, opening
the circuit to the top and bottom heating elements.

3-2. The oven will continue to function for 15 minutes, turning

the convection heating elements on and off, as needed to
maintain the selected preheat temperature. The oven will
shut-down completely after 15 minutes.

When the preheat temperature is reached, a beep signal  will
sound indicating that the holding temperature has been reached
in the oven cavity. Open the door and place the food to be cooked
in the oven. Program desired cooking time  then touch the
CONVECTION key repeatedly to set the temperature.  When
the START key is touched, the following operations occur:
1. The numbers of the digital readout start the count down to

zero.

2. The oven lamp, cooling fan motor, turntable motor and

convection motor are energized.

3. Relays RY3 and RY4 are energized (if the cavity temperature

is lower than the selected temperature) and the main supply
voltage is applied to the top and bottom heaters to return to
the selected cooking temperature.

4. Upon completion of the cooking time, the audible signal will

sound, and oven lamp, turntable motor, cooling fan motor
and convection motor are de-energized. At the end of
convection cycle, if the cavity air temperature is above
104˚C, the circuit to RY5 will be maintained (by the thermistor
circuit) to continue operation of the cooling fan motor until
temperature drops below 104˚C, at that time the relay will
be de-energized, turning off the fan motor .

In this condition the food is cooked by grill heating element
energy. Programme the desired cooking time and top grill mode
by turning the mode select knob to           " TOP GRILL" and the
second rotary knob to set the time. When the START key is
touched, the following operations occur:
1. The numbers on the digital readout start the count down to

zero.

2. The oven lamp, cooling fan motor and turntable motor are

energized.

3. The relay RY3 is energized and the main supply voltage is

applied to the top grill heater.

4. Now the food is cooked by the top grill heater.

In this condition the food is cooked by bottom grill heating
element energy.  Program the desired cooking time and bottom
grill mode by turning the mode select knob to
 

  "BOTTOM  GRILL" and the second rotary knob to set

the time.  When the START key is touched, the following
operations occur:
1. The numbers on the digital readout start the count down to

zero.

2. The oven lamp, cooling fan motor and turntable motor are

energized.

3. The relay RY4 is energized and the main supply voltage is

applied to the bottom grill heater.

4. Now the food is cooked by the bottom grill heater.

In this condition the food is cooked by the top and bottom grill
heating element energy.  Program the desired cooking time
then set top+bottom grill mode by touching  

  "TOP GRILL"

and   

  "BOTTOM GRILL"keys.  (led's will light on the

display panel).

  "TOP & BOTTOM GRILL" .  When the

START key is touched, the following operations occur:
1. The numbers on the digital readout start the count down to

zero.

2. The oven lamp, cooling fan motor and turntable motor are

energized.

3. The relay RY4 is energized and the main supply voltage is

applied to the bottom grill heater.

4. The relay RY3 is energized and the main supply voltage is

applied to the top grill heater.

5. Now the food is cooked by the top+bottom grill heater.

Program the desired cooking time and then Dual cook mode
by touching the CONVECTION  

  and MICROWAVE keys.

(led's will light on the display panel).  When the START key is
touched, the following operations occur:
1. The numbers on the digital readout start the count down to

zero.

2. The oven lamp, cooling fan motor, turntable motor and

convection motor are energized.

3. Relay RY4 is energized (if the cavity temperature is lower

than the selected temperature) and the main supply voltage
is applied to the bottom heater.

4. Relay RY2 is energized and the microwave energy is

generated by the magnetron.

5. During operation relay RY2 will de-energize and relay RY3

will be energized and the main supply voltage is applied to
the top grill heater.  This will continue to cycle throughout
this mode.

6. Now the food is cooked by microwave and convection

energy simultaneously.

Program the desired cooking time and then Dual cook mode
by touching the "TOP GRILL"  

  and MICROWAVE keys

(led's will light on display panel).  When the START key is
touched, the following operations occur:
1. The numbers on the digital readout start the count down to

zero.

2. The oven lamp, cooling fan motor and turntable motor are

energized.

3. Relay RY3 is energized and the main supply voltage is

applied to the top heater.

4. Relay RY2 is energized and the microwave energy is

generated by the magnetron.

5. Now the food is cooked by microwave and top grill

simultaneously.