R-879W (serv.man15) - Sharp Home Appliance User Guide / Operation Manual

R879(W)

5 – 1

R879(W)

Service Manual

 

Closing the door activates the monitored latch switch and the stop
switch.

IMPORTANT

                                            Figure O-1 on page 13-1 

1. The control unit is not energized. The display shows nothing (Fig.

O-1 (a)).

2. Open the door. The contacts (COM-NC) of the monitored latch

switch are closed and the control unit is energized. Then contacts
of relays RY1 and RY5 are closed, and the oven lamp will light and
the display will show “ENERGY SAVE MODE TO CANCEL
ENERGY SAVE MODE SET THE CLOCK” (Fig. O-1(b)).

3. Close the door. The contacts (COM-NC) of the monitored latch

switch are opened and the contacts of relay RY1 are opened and
the oven lamp will be turned off. The display will show “ . 0". (Fig.
O-1(c)).

NOTE: Energy save mode

1) If the oven has not been used for more than 3 minutes, the

contacts of the relay RY5 will be opened and the control
unit will be not energized. Open and close the door, the
control unit will resume.

2) If the clock is set, this energy save mode does not work.

Enter a desired cooking time by touching the TIME keys and start the
oven by touching START key.

Function sequence 

                           Figure O-2 on page 13-2

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

age 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 fila-

ment and the high voltage (2000 volts) is sent to the voltage dou-
bling circuit, where it is doubled to negative voltage of
approximately 4000 volts D.C..

3. The 2450 MHz microwave energy produced in the magnetron gen-

erates a wavelength of 12.24cm. 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 + RY6 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.

The circuit to the high voltage transformer is cut off when the contacts
of relay RY2, and the contacts (COM-NO) of the monitored latch
switch and monitor switch are made open. The circuit to the fan motor
is cut off when the relay RY6 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 relay RY2 and RY6 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 stays closed. Shown in the display is remaining time.

6. MONITOR SWITCH CIRCUIT

The monitor switch is mechanically controlled by the oven door,
and monitors the operation of the monitored latch switch.

1) When the oven door is opened during or after the cycle of a

cooking program, the monitored latch switch and stop switch
must open their contacts (COM-NO) first. After that the contacts
(COM-NC) of the monitor switch and monitored latch can be
closed.

2) When the oven door is closed, the contacts (COM-NC) of the

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

3) When the oven door is opened and the contacts (COM-NO) of

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

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

SETTING;

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.

CONNECTED COMPONENTS

RELAY

Oven lamp, Turntable motor 

RY1

High voltage transformer 

RY2

Fan motor, 

RY6

          CONDITION

SWITCH CONTACT 

DURING 

COOKING

DOOR OPEN 

(NO COOKING)

Monitored latch 
switch 

COM-NO
COM-NC 

Closed

Opened 

Opened

Closed

Stop switch   

COM-NO 

Closed 

Opened

Monitor switch        

COM-NO
COM-NC 

Closed

Opened   

Opened

Closed

100P (HIGH)

32 sec. ON

70P

(MEDIUM HIGH)

Approx. 70%

100%

24 sec. ON

8 sec. OFF

14 sec. OFF

20 sec. OFF

26 sec. OFF

50P

(MEDIUM)

Approx. 50%

18 sec. ON

50P

(MEDIUM LOW)

Approx. 30%

12 sec. ON

10P (LOW)

Approx. 10%

6 sec. ON

R879(W)

5 – 2

In this condition the food is cooked by the top grill heating element.
Programme the desired cooking time by touching the TIME keys and
touch the GRILL key once. When the START key is touched, the fol-
lowing 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 ener-

gized.

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

to the top grill heating element.

4. Now, the food is cooked by the top grill heating element.

In this condition the food is cooked by bottom grill heating element
energy. Programme the desired cooking time by touching the TIME
keys and touch the GRILL key twice. 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 ener-

gized.

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

to the bottom grill heating element.

4. Now, the food is cooked by the bottom grill heating element.

In this condition the food is cooked by top and bottom grill heating ele-
ments energy. Programme the desired cooking time by touching the
TIME keys and touch the GRILL key three times. 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 ener-

gized.

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

to the bottom grill heating element.

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

to the top grill heating element. 

5. Now, the food is cooked by the top and bottom grill heating ele-

ments.

Programme the desired convection temperature by touching CONV.
key. When the START key is touched, the following operations occur:

1. The coil shut-off relays RY1 and RY6 are energized, the oven lamp,

cooling fan motor and turntable motor are turned on.

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

and the main supply voltage is added to the top and bottom heating
elements.

3. When the oven temperature reaches the selected pre-heat temper-

ature, the following operations occur:

1) The coil shut-off relays RY3 and RY4 are energized by control

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

2) The oven will continue to function for 30 minutes, turning the top

and bottom heating elements on and off, as needed to maintain
the selected pre-heat temperature. The oven will shut-down
completely after 30 minutes.

When the pre-heat 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.
Programme the desired cooking time by touching the TIME keys and
program convection temperature by touching the CONV. key. 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.

NOTE: When the convection temperature 40

°C is selected, the con-

vection motor is not energized.

3. The relays RY3 and RY4 are energized (if the cavity temperature is

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

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

and the oven lamp, turntable motor, cooling fan motor, convection
motor, top and bottom heating elements are de-energized. At the
end of convection cycle, if the cavity air temperature rise above
120

°C, the circuit to the relay RY6 will be maintained (by the ther-

mistor circuit) to continue operation of the cooling fan motor until
temperature drops below 105

°C, at that time the relay RY6 will be

de-energized, turning off the fan motor.

Programme the desired cooking time by touching the TIME keys.
Touch the COMBI key once. Select the convection temperature by
touching the CONV. key. And select the microwave power level by
touching the MICRO POWER key. 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. The relay RY3 will be energized and the main supply voltage is

applied to the top grill heating element.

4. The relay RY4 is energized (if the cavity temperature is lower than

selected temperature) and the main supply voltage is applied to the
bottom heating element.

5. The relay RY2 is energized and the microwave energy is generated

by magnetron.

6. Now, the food is cooked by microwave and convection energy

simultaneously.

Programme the desired cooking time by touching the TIME keys.
Touch the COMBI key twice. And select the microwave power level by
touching the MICRO POWER key. 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 ener-

gized.

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

to the top grill heating element.

4. The relay RY2 is energized and the microwave energy is generated

by magnetron.

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

R879(W)

5 – 3

Programme the desired cooking time by touching the TIME keys.
Touch the COMBI key three times. Select the microwave power level
by touching the MICRO POWER key. 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 ener-

gized.

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

to the bottom grill heating element.

4. The relay RY2 is energized and the microwave energy is generated

by magnetron.

5. Now, the food is cooked by microwave and bottom grill simulta-

neously.

In grill cooking, convection cooking or dual cooking, the top heater,
bottom heater or magnetron operate within a 54 second time base.
The following table is the ON / OFF time ratio at each power output of
the top heaters, bottom heater or magnetron.

The magnetron, top or bottom heating elements, the fan motor or the convection motor will operate in accordance with following specification.

100%

54 sec.

0 sec.

90%

49 sec.

5 sec.

80%

45 sec.

9 sec.

70%

40 sec.

14 sec.

60%

36 sec.

18 sec.

50%

29 sec.

25 sec.

40%

24 sec.

30 sec.

30%

18 sec.

36 sec.

20%

13 sec.

41 sec.

10%

9 sec.

45 sec.

MICROWAVE (100%) 
SINGLE OPERATION

Microwave

100% 20min, then 70%

TOP GRILL (100%) 
SINGLE OPERATION

Top heater

100% 15min, then 50%

BOTTOM GRILL (100%) 
SINGLE OPERATION

Bottom heater

100% 15min, then 50%

TOP(100%)/BOTTOM(100%)
DUAL OPERATION

Top heater

100% 6min then 70% and 70% 9min then 50%

Bottom heater

100% 6min then 70% and 70% 9min then 50%

MICRO(100%)/TOP GRILL(100%)
DUAL OPERATION

Microwave

100% 20min, then 70%

Top heater

100% 15min, then 50%

MICRO(70 - 10%)/TOP GRILL(100%)
DUAL OPERATION

Microwave

-

Top heater

100% 15min, then 50%

MICRO(100%)/BOTTOM GRILL(100%)
DUAL OPERATION

Microwave

100% 20min, then 70%

Bottom heater

100% 15min, then 50%

MICRO(70 - 10%)/BOTTOM GRILL(100%)
DUAL OPERATION

Microwave

-

Bottom heater

100% 15min, then 50%

Repeat Cook

Microwave
Top heater
Bottom heater

In case same cooking mode is repeated within 1min 15sec (including stop, end), 
oven calculates total cooking time and reduce the power level.

Repeat Auto Cook

Microwave

The power level is not reduced 1 time cooking. But only in case same menu is 
repeated within 1min 15sec, the power level of micro and grill is reduced from 
100% to 70% in 20mins after starting of last cooking. (Even if the time of the last 
cooking is longer than 20mins, the power level isn't reduced on the last cooking, 
and it is reduced from the beginning of the next cooking.) However, in time calcu-
lated from the start of the 1st cooking, even if the Cook mode changed, when rep-
etition cooking of the menu with which 100% of top & bottom heaters continues 
are performed, as shown in the following table, the power down of the cooking of 
the 2nd henceforth is carried out. (The 1st cooking is not applied)

R879(W)

5 – 4

NOTE:

✩The oven temp was checked by the thermometer when each stage is started.
If the oven temp is same or higher than 105

°C, the oven was judged as "with preheating".

When the oven temp is lower than 105

Micro and Top heating element can't be on at the same time.

PREHEAT

Cooling

60% 

CONV. (OVEN)

Cooling fan

60% 60 min. then 100%

Others

Cooling fan

100%

After cooking

Cooling fan

A cooling fan continues the rotation when Oven temperature is more than 120

°C. 

Then, it stops when it is less than 105

°C

Indication

NOW COOLING is indicated during the cooling fan movement after operation is 
finished. (It isn't indicated during a fan movement to stop on the way.)

°C, 230°C, 220°C, 200°C, 180°C, 160°C, 130°C, 100°C, 70°C, 40°C

HEATING ELEMENT 

TOP 100%
BOTTOM

100%

COOLING FAN 

60%

CONV. FAN 

0%

°C

°C

°C

°C

°C

°C

°C 100°C

°C

°C

✩WITHOUT PREHEATING

HEATING 
ELEMENT

TOP

50%

40%

40%

30%

20%

10%

10%

10%

10%

10%

BOTTOM

100%

90%

80%

70%

70%

60%

50%

40%

30%

20%

✩WITH PREHEATING

HEATING 
ELEMENT

TOP

50%

40%

40%

30%

20%

10%

10%

10%

10%

10%

BOTTOM

90%

70%

60%

50%

50%

50%

50%

40%

30%

20%

COOLING FAN

60% 60min, then 100%

CONV. FAN

100%

0%

°C

°C

°C

°C

°C

°C

°C

°C

°C

°C

✩WITHOUT PREHEATING

HEATING 
ELEMENT

TOP

50%

40%

40%

30%

20%

10%

10%

10%

10%

10%

BOTTOM

100%

90%

80%

70%

70%

60%

50%

40%

30%

20%

✩WITH PREHEATING

HEATING 
ELEMENT

TOP

50%

40%

40%

30%

20%

10%

10%

10%

10%

10%

BOTTOM

90%

70%

60%

50%

50%

50%

50%

40%

30%

20%

MICRO

10%, 30%, 50%

COOLING FAN

100%

CONV. FAN

100%

0%