Sharp R-774M (serv.man2) Service Manual ▷ View online
R-774M - 5
APPEARANCE VIEW
9. Door seals and sealing surfaces
10.Ventilation openings
11.Outer cabinet
12.Power supply cord
13.Turntable
14.Low Rack
15.High Rack
10.Ventilation openings
11.Outer cabinet
12.Power supply cord
13.Turntable
14.Low Rack
15.High Rack
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
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)
CONTROL PANEL
OVEN
14
15
13
1
4
3
9
10
11
5
2
6
8
7
0
12
AUTO indicator.
DEFROST indicator.
TOP GRILL indicator.
BOTTOM GRILL indicator
COOK indicator.
MICROWAVE indicator.
WEIGHT indicators.
LESS/MORE indicators.
AUTO COOK key.
WEIGHT INCREASE/DECREASE keys.
INSTANT COOK keys.
DUAL GRILL key.
START/AUTO MINUTE key.
MICROWAVE POWER LEVEL indicator.
TIME keys.
STOP/CLEAR key.
KITCHEN TIMER/CLOCK SET key
WEIGHT CONVERSION key
MICROWAVE POWER LEVEL key.
OVEN (˚C) key.
GRILL key.
EXPRESS COOK keys.
EXPRESS DEFROST keys.
LESS/MORE keys.
DOOR OPEN button
R-774M - 6
OPERATION SEQUENCE
OFF CONDITION
Closing the door activates the monitored latch switch and
the stop switch.
the stop switch.
IMPORTANT:
When the oven door is closed, the contacts COM-NC
of the monitor switch must be open. When the micro-
wave oven is plugged in a wall outlet (230 - 240V /
50Hz), the line voltage is supplied to the noise filter.
When the oven door is closed, the contacts COM-NC
of the monitor switch must be open. When the micro-
wave oven is plugged in a wall outlet (230 - 240V /
50Hz), the line voltage is supplied to the noise filter.
Figure O-1 on page
29
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 moni-
tored 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" (Fig. O-1(b)).
energized. Then contacts of relays RY1 and RY5 are
closed, and the oven lamp will light and the display will
show "ENERGY SAVE MODE" (Fig. O-1(b)).
3. Close the door. The contacts (COM-NC) of the moni-
tored latch switch are opened and the contacts of relay
RY1 are opened and the oven lamp will be turned off.
The display will show " .
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 2 minutes,
1. If the oven has not been used for more than 2 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.
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.
MICROWAVE COOKING CONDITION
HIGH COOKING
Enter a desired cooking time by touching the TIME keys
and start the oven by touching START key.
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 30
CONNECTED COMPONENTS
RELAY
Oven lamp, Turntable motor
RY1
High voltage transformer
RY2
Fan motor
RY6
1. The line voltage 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.
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..
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 wavelength 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.
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.
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
During
Oven Door
Cooking
Open(No cooking)
COM-NO
Closed
Opened
Monitored latch switch
COM-NC
Opened
Closed
Stop switch
COM-NO
Closed
Opened
COM-NO
Closed
Opened
Monitor Switch
COM-NC
Opened
Closed
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 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 moni-
tored latch switch.
oven door, and monitors the operation of the moni-
tored latch switch.
6-1. 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. And the contacts (COM-NC) of the
monitored latch switch SW1 are made closed. After
that the contacts (COM-NC) of the monitor switch can
be closed and the contacts (COM-NO) of monitor
switch are made open.
switch and stop switch must open their contacts
(COM-NO) first. And the contacts (COM-NC) of the
monitored latch switch SW1 are made closed. After
that the contacts (COM-NC) of the monitor switch can
be closed and the contacts (COM-NO) of monitor
switch are made open.
6-2. When the oven door is closed, the contacts (COM-
NC) of the monitor switch 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.
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.
6-3. 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.
closed, the fuse F8A will blow. Because the relay RY1
and monitor switch are closed and a short circuit is
caused.
MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW
COOKING
COOKING
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 coupled with the cur-
rent-limiting relay RY2. The following levels of microwave
power are given.
power, the line voltage is supplied to the high voltage
transformer intermittently within a 32-second time base
through the relay contact which is coupled with the cur-
rent-limiting relay RY2. The following levels of microwave
power are given.
900W
(HIGH)
32 sec. ON
630W MEDIUM
HIGH
Approx. 70%
100%
24 sec. ON
8 sec. OFF
14 sec. OFF
20 sec. OFF
26 sec. OFF
450W (MEDIUM)
Approx. 50%
18 sec. ON
270W MEDIUM
LOW
Approx. 30%
12 sec. ON
90W
(LOW)
Approx. 10%
6 sec. ON
R-774M - 7
Note:
The On/Off time ratio does not exactly correspond
to the percentage of microwave power, because
approx. 3 seconds is needed for heating up the
magnetron filament.
to the percentage of microwave power, because
approx. 3 seconds is needed for heating up the
magnetron filament.
GRILL COOKING CONDITION
TOP GRILL (Figure O-3a)
In this condition the food is cooked by the top grill heating
element. Programme the desired cooking time by touch-
ing the TIME keys and touh the GRILL key once. When the
STARTkey is touched, the following operations occur:
In this condition the food is cooked by the top grill heating
element. Programme the desired cooking time by touch-
ing the TIME keys and touh the GRILL key once. When the
STARTkey 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 heating element.
4. Now, the food is cooked by the top grill heating ele-
ment.
BOTTOM GRILL (Figure O-3b)
In this condition the food is cooked by bottom grill heating
element energy. Programme the desired cooking time by
touching the TIME keys and touh the GRILL key twice.
When the STARTkey is touched, the following operations
occur:
In this condition the food is cooked by bottom grill heating
element energy. Programme the desired cooking time by
touching the TIME keys and touh the GRILL key twice.
When the STARTkey 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 heating element.
4. Now, the food is cooked by the bottom grill heating
element.
TOP AND BOTTOM GRILL (Figure O-3c)
In this condition the food is cooked by top and bottom grill
heating elements energy. Programme the desired cook-
ing time by touching the TIME keys and touh the GRILL
key three times. When the STARTkey is touched, the
following operations occur:
In this condition the food is cooked by top and bottom grill
heating elements energy. Programme the desired cook-
ing time by touching the TIME keys and touh the GRILL
key three times. When the STARTkey 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 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 elements.
OVEN COOKING CONDITION
PRE-HEATING (Figure O-4)
Programme the desired oven temperature by touching
OVEN (˚C) key. When the START key is touched, the
following operations occur:
1. The coil shut-off relays RY1 and RY6 are energized,
Programme the desired oven temperature by touching
OVEN (˚C) 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.
are turned on.
2. The coil shut-off relays RY3 and RY4 are energized by
the control unit and the mains supply voltage is applied
to the top and bottom heating elements.
to the top and bottom heating elements.
3. When the oven temperature reaches the selected pre-
heat temperature, the following operations occur:
3-1. The coil shut-off relays RY3 and RY4 are de-ener-
gised by control unit temperature circuit and thermis-
tor, switching to the top and bottom grill heating
elements off.
tor, switching to the top and bottom grill heating
elements off.
3-2. The oven will then 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.
off, as needed to maintain the selected pre-heat
temperature. The oven will shut-down completely
after 30 minutes.
NOTE: The fan motor will be turned on and off at
preheating. And the convection motor will be turned
off at preheating. See "Power setting" on page 9.
off at preheating. See "Power setting" on page 9.
OVEN COOKING (Figure O-4)
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 cooked in the oven. Program desired cooking
time by touching the TIME keys and program oven tem-
perature by touching the OVEN (˚C) key . When the
START key is touched, the following operations occur:
1. The numbers on the digital readout start the count
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 cooked in the oven. Program desired cooking
time by touching the TIME keys and program oven tem-
perature by touching the OVEN (˚C) 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 energized.
3. The relays RY3 and RY4 are energized (if the cavity
temperature is lower than selected temperature) and
the mains supply voltage is applied to the top and
bottom heating elements to return to the selected
cooking temperature.
the mains 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 sig-
nal will sound, and the oven lamp, turntable motor,
cooling fan motor, top and bottom heating elements
are de-energized. At the end of cooking cycle, if the
cavity air temperature rises above 120˚C, the power to
the relay RY6 will be maintained (by the thermistor
circuit) to continue operation of the cooling fan motor
until the temperature drops below 105˚C. At that time
the relay RY6 will be de-energized, turning off the fan
motor.
cooling fan motor, top and bottom heating elements
are de-energized. At the end of cooking cycle, if the
cavity air temperature rises above 120˚C, the power to
the relay RY6 will be maintained (by the thermistor
circuit) to continue operation of the cooling fan motor
until the temperature drops below 105˚C. At that time
the relay RY6 will be de-energized, turning off the fan
motor.
DUAL COOKING CONDITION
MICROWAVE AND TOP GRILL (Figure O-5a)
Programme the desired cooking time by touching the
TIME keys. Touch the DUAL GRILLL key once. Select the
microwave power level by touching the MICROWAVE
POWER LEVEL key. When the STARTkey is touched, the
following operations occur:
Programme the desired cooking time by touching the
TIME keys. Touch the DUAL GRILLL key once. Select the
microwave power level by touching the MICROWAVE
POWER LEVEL key. When the STARTkey 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 heating element.
4. The relay RY2 is energized and microwave energy is
OPERATION SEQUENCE
R-774M - 8
generated by magnetron.
5. Now, the food is cooked by microwave and top grill
simultaneously.
MICROWAVE AND BOTTOM GRILL (Figure O-5b)
Programme the desired cooking time by touching the
TIME keys. Touch the DUAL GRILL three twice. Select the
microwave power level by touching the MICROWAVE
POWER LEVEL key. When the STARTkey is touched, the
following operations occur:
TIME keys. Touch the DUAL GRILL three twice. Select the
microwave power level by touching the MICROWAVE
POWER LEVEL key. When the STARTkey 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 mains supply
voltage is applied to the bottom grill heating element.
4. The relay RY2 is energized and microwave energy is
generated by magnetron.
5. Now, the food is cooked by microwave and bottom grill
simultaneously.
POWER SETTING
Following table shows each power setting of the top
heating element, bottom heating element, magnetron and
fan motor on Oven cooking mode and Oven preheating
mode.
heating element, bottom heating element, magnetron and
fan motor on Oven cooking mode and Oven preheating
mode.
ON/OFF TIME RATIO
In grill cooking, oven cooking or dual cooking, the top
heater, bottom heater or magnetron operate whithin a 48
second time base. The following table is the ON / OFF time
ratio at each power output of the top heaters, bottom
heater or magnetron.
heater, bottom heater or magnetron operate whithin a 48
second time base. The following table is the ON / OFF time
ratio at each power output of the top heaters, bottom
heater or magnetron.
POWER OUTPUT
ON TIME
OFF TIME
100%
48 sec.
0 sec.
90%
44 sec.
4 sec.
80%
40 sec.
8 sec.
70%
36 sec.
12 sec.
60%
32 sec.
16 sec.
50%
26 sec.
22 sec.
40%
22 sec.
26 sec.
30%
16 sec.
32 sec.
20%
12 sec.
36 sec.
10%
8 sec.
40 sec.
O
VEN PREHEATING
OVEN COOKING
TOP
BOTTOM
FAN
TOP
BOTTOM
FAN
HEATER
HEATER
MOTOR
HEATER HEATER
MOTOR
200˚C
100%
100%
100%
100%
100%
100%
180˚C
100%
100%
100%
100%
100%
100%
160˚C
100%
100%
100%
100%
100%
100%
130˚C
100%
100%
100%
100%
100%
100%
100˚C
100%
100%
100%
100%
100%
100%
70˚C
100%
100%
100%
100%
100%
100%
40˚C
100%
100%
100%
100%
100%
100%
NOTE:
1. In case of Automatic operations, the limitations of
1. In case of Automatic operations, the limitations of
power output are not carried out.
2. In case that the stop key is touched or the oven door is
opened during cooking, the limitations of power output
are not carried out after the total cooking time beyond
the specified cooking time.
are not carried out after the total cooking time beyond
the specified cooking time.
3. In case of the two or more same cooking modes are
carried out, the limitations of power output are not
carried out after the total cooking time beyond the
specified cooking time.
carried out after the total cooking time beyond the
specified cooking time.
4. In case of the two or more different cooking modes are
carried out, the specified cooking time is started to
count from the point when the cooking mode is changed.
count from the point when the cooking mode is changed.
5. If the cooking mode has the power level display, the
power level is also displayed when the limitations of
power output are carried out.
power output are carried out.
Specified cooking
Limited power
Time base
Cooking mode
time (minutes)
output (%)
(seconds)
Microwave (100%)
20
70
32
Top grill
30
50
48
Bottom grill
45
50
48
Top grill and
15 (Top)
50
48
Bottom grill
15(Bottom)
50
48
Micro. (100%)
20 (Micro.)
70
48
+ Top grill
15 (Grill)
50
48
Micro. (100%)
20 (Micro.)
70
48
+ Bottom grill
15 (Heater)
50
48
D
U
A
L
OPERATION SEQUENCE
AUTOMATIC COOKING
CHILLED READY MEALS
FROZEN READY MEALS
CHICKEN QUARTERS
CRISPY CRUMB FOODS
OVEN CHIPS
BAKED POTATOES
Above functions are automatic cooking. They automati-
cally work out the correct cooking mode and cooking time
and/or cooking temperature. They will cook according to
the special cooking sequence.
FROZEN READY MEALS
CHICKEN QUARTERS
CRISPY CRUMB FOODS
OVEN CHIPS
BAKED POTATOES
Above functions are automatic cooking. They automati-
cally work out the correct cooking mode and cooking time
and/or cooking temperature. They will cook according to
the special cooking sequence.
LIMITATIONS OF POWER OUTPUT IN MANUAL
OPERATION
OPERATION
After the same cooking mode is carried out for more than
the specified cooking time, the power output is automati-
cally reduced by turning the control relays on and off
intermittently, as shown in the table below. This is to
protect the oven door against temperature rising.
the specified cooking time, the power output is automati-
cally reduced by turning the control relays on and off
intermittently, as shown in the table below. This is to
protect the oven door against temperature rising.
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