Sharp R-880B Service Manual page 8

R-880B
energized.
4. The relay RY2 + RY4 are energized alternately within
a 48 seconds time base by the control unit.
5. The bottom heater operate through the relay RY4 is
energized. And the high voltage transformer operates
through the relay RY2 is energized.
6. The relationship between the top heating elements and
magnetron operations are as follows.
26 SEC.
ON
(MICRO.)
BOTTOM
HEATER OFF
HIGH MIX GRILL BOTTOM GRILL mode
8 SEC. 40 SEC.
ON
(MICRO.)
OFF
ON
BOTTOM
HEATER
OFF
LOW MIX GRILL BOTTOM GRILL mode
Note: The On/Off time ratio does not exactly correspond
to the percentage of microwave power, because
approx. 2 seconds are needed for heating up the
magnetron filament.
7. Upon completion of the selected cooking time, audible
signal sounds and the contacts of relays RY2 + RY4 +
RY6 are opened, then the bottom heater, high voltage
transformer, turntable motor and oven lamp are de-
energized. At the end of the convection cycle, if the
cavity air temperature is above 120˚C, the circuit to
RY5 will be maintained (by the thermistor circuit) to
continue operation of the cooling fan motor until the
temperature drops below 104˚C, at which time the
relay will be de-energized, turning off the fan motor.
AUTOMATIC OPERATIONS
This oven has the following automatic operations;
MULTI COOK
CONVIENIENCE/PIZZA
EASY DEFROST
Thease will automatically compute the cooking mode and
the cooking time. And the oven will cook or defrost the food
according to the special cooking sequence.
LIMITATIONS OF POWER OUTPUT IN MANUAL
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.
Specified cooking Limited power
Cooking mode time (minutes)
Microwave
20
100% Power
Top heaters 30
Bottom heater 15
Top browner and
10 (Top)
Bottom browner
10 (Bottom)
or Oven cooking
22 SEC.
MICROWAVE POWER
OFF
= APPROX. 50%
ON
MICROWAVE POWER
= APPROX. 10%
Time base
output (%) (seconds)
70 32
50 48
50 48
50 48
50 48
NOTE:
1. In case of Automatic operations, the limitations of
power output are not carried out.
2. In case that the STOP/CLEAR pad is pressed or the
oven door is opened during cooking, the limitations of
power output are 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 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.
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.
CONVECTION COOKING CONDITION
PREHEATING CONDITION
Press the PREHEAT pad and then select preheating
temperature by pressing the temperature pad. When the
START pad is touched, the following operations occur:
Figure O-4 on page 36
1. The coils of shut-off relays RY1+RY5+RY6 are ener-
gized, the oven lamp, cooling fan motor, turntable
motor and convection motor are turned on.
2. The coil of heater relays RY3+RY4 are energized by
the CPU unit and the main supply voltage is added to
the top and bottom heaters.
3. When the oven temperature reaches the selected
preheat temperature, the following operations occur:
3-1. The heater relays RY3+RY4 de-energized by the
CPU unit temperature circuit and thermistor, opening
the circuit to the top and bottom heaters.
3-2. The oven will continue to function for 30 minutes,
turning the top and bottom heaters on and off, as
needed to maintain the selected preheat tempera-
ture. The oven will shut-down completely after 30
minutes.
CONVECTION COOKING CONDITION
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. Press the CONVEC-
TION pad and then enter the cooking temperature by
pressing the temperature pad. And then enter the cooking
time by pressing the NUMBER pads. When the START
pad is touched, the following operations occur:
1. The numbers of the digital read-out start the count
down to zero.
2. The oven lamp, turntable motor, cooling fan motor and
convection motor are energized.
3. The 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 heating
element to return to the selected cooking temperature.
The top heaters and the bottom heater work in accord-
ance with the following table while the heaters are
energized.
6