Sharp R-870B, Service Manual

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6
R-870B
CONVEC MIX HIGH MODE AND CONVEC MIX LOW
MODE
In these modes, the food is cooked by the convection and
the microwave energy. Press the MIX pad once for
CONVEC MIX HIGH mode. Press the MIX pad twice for
CONVEC MIX LOW mode. And then enter the cooking
time by pressing the number pads. When the START pad
is pressed, the following operations occur:
Figure O-5(a) on page 37
1. The relay RY1+ RY5 + RY6 are energized.
2. The numbers of the digital read-out start the count
down to zero.
3. The convection motor, turntable motor, oven lamp and
fan motor are energized.
4. The relay RY2 and the relays RY3 + RY4 are energized
alternately within a 48 seconds time base by the control
unit.
5. The relays RY3 + 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 selected cooking tempera-
ture. 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.
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 RY1 + RY2 +
RY3 + RY4 + RY6 are opened, then the top heaters,
bottom heater, high voltage transformer, turntable
motor, convection motor and oven lamp are de-ener-
gized. 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.
GRILL MIX HIGH MODE AND GRILL MIX LOW MODE
In these modes, the food is cooked by the top heaters and
the microwave energy. Press the MIX pad three times for
GRILL MIX HIGH mode. Press the MIX pad four times for
GRILL MIX LOW mode. And then enter the cooking time
by pressing the number pads. When the START pad is
pressed, the following operations occur:
Figure O-5(b) on page 37
1. The relay RY5 + RY6 are energized.
2. The numbers of the digital read-out start the count
down to zero.
3. The turntable motor, oven lamp and fan motor are
energized.
4. The relay RY2 + RY3 are energized alternately within
a 48 seconds time base by the control unit.
5. The top heaters operate through the relay RY3 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.
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 + RY3 +
RY6 are opened, then the top heaters, 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 de0energized, turning off the fan motor.
AUTOMATIC OPERATIONS
This oven has the following automatic operations;
CRISPY SNACK
PIZZA
AUTO GRILL
AUTO ROAST
AUTO BAKE
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.
16 SEC. 32 SEC.
22 SEC. 26 SEC.
22 SEC. 26 SEC.
CONVEC MIX LOW mode
CONVEC MIX HIGH mode
MICROWAVE POWER
= APPROX. 30%
MICROWAVE POWER
= APPROX. 10%
40 SEC. 8 SEC.
ON
ON
OFF
OFF
OFF
ON
OFF
ON
(MICRO.)
(MICRO.)
CONVEC
OPERATION
250˚C
CONVEC
OPERATION
250˚C
26 SEC. 22 SEC.
GRILL MIX LOW mode
GRILL MIX HIGH mode
MICROWAVE POWER
= APPROX. 50%
MICROWAVE POWER
= APPROX. 10%
40 SEC. 8 SEC.
ON
ON
OFF
OFF
OFF
ON
OFF
ON
(MICRO.)
(MICRO.)
TOP
HEATERS
TOP
HEATERS