R-8000GK - Sharp Home Appliance Service Manual (repair manual). Page 7

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3. When the oven temperature reaches the selected preheat

temperature, the following operations occur:
3-1. The solid-state relays are de-energized by the control

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

3-2. The oven will continue to function for 30 minutes, turning

the heating elements on and off, as needed to maintain
the selected preheat temperature. The oven will
shutdown completely after 30 minutes

Press the MANUAL/REPEAT key. Enter the cooking time by
touching NUMBER key and select the temperature by touching
OVEN(˚C) key. When the START key is touched, the following
operations occur:

1. The numbers on the digital read-out start to count down to

zero.

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

motor are energized. The contacts (COM-NO) of relay RY6
are opened.

3.  The solid-state relays are energized (if the cavity temperature

is lower than the selected temperature) and the main supply
voltage is applied to the heating elements 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
jet motor are de-energized. At the end of the oven cycle, if the
cavity air temperature is above 111˚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 90˚C,
at which time the relay will be de-energized, turning off the fan
motor. Relay RY3 will however, open as soon as the convection
cycle has ended, turning off the jet motor.

Press the MANUAL/REPEAT key. Enter cooking time and then
touch the SPEED GRILL key once. Select the temperature by
pressing OVEN(˚C) key. Then select the microwave power level
by pressing MICROWAVE key.  When the START key is touched,
following operations occur;

1. The contacts of the relays RY1, RY3 and RY5 are closed, and

the oven lamp, turntable motor, jet motor and fan motors are
energized. The contacts (COM-NO) of relay RY6 are closed.

2. The solid-state relays are energized and the main supply

voltage is applied to the top and side heating elements.

Press the MANUAL/REPEAT key. Enter cooking time and then
touch SPEED GRILL key twice or 3 times. Select the tempera-
ture by pressing OVEN(˚C) key. Then select the microwave
power level by pressing MICROWAVE key. When the start key
is touched, following operations occur;

1. The contacts of the relays RY1, RY3 and RY5 are closed, and

the oven lamp,  turntable motor, jet motor and fan motors are
energized. The contacts (COM-NO) of relay RY6 are closed.

2. The solid-state relays are energized and the main supply

voltage is applied to the top and side heating elements.

3. The relay RY2 is energized and the microwave energy is

generated by magnetron.

Press the MANUAL/REPEAT key. Enter cooking time and then
touch SPEED CONV. key twice or 3 times. Select the tempera-
ture by pressing OVEN(˚C) key. Then select the microwave
power level by pressing MICROWAVE key. When the start key
is touched, following operations occur;

1. The contacts of the relays RY1, RY3 and RY5 are closed, and

the oven lamp, turntable motor, jet motor and fan motors are
energized. The contacts (COM-NO) of relay RY6 are opened.

2. The solid-state relays and relay RY2 are energized, and the

main supply voltage is applied to the top and side heating
elements and the high voltage transformer alternately.

This model incorporates a sensing feature which will stop the
oven's operation if there is a fire in the oven cavity during
microwave cooking. This fire sensing feature will operate when
the microwave power level is set to 80% or more. This is
accomplished by the LSI repeatedly measuring the voltage
across the temperature measurement circuit (thermistor) during
it's 32-seconds time base comparing the obtained voltage meas-
urements. If the most recent  voltage measured is 300 mV
greater than the previous voltage measured, the LSI judges it as
a fire in the oven cavity and switches off the relays to the power
transformer, fan motor and jet motor. The LSI also stops counting
down and closes the damper door so that no fresh air will enter
the oven cavity. Please refer to the following section for a more
detailed description.

Please refer to the timing diagrams below.

1. The fire sensing will start after 5 minutes when the oven is

started.

2. The thermistor operates within a 32-seconds time base and

it is energized for three (3) seconds and off for 29 seconds.
Two (2) seconds after the thermistor is energized, the voltage
across the temperature measurement circuit is sampled by
the LSI and twenty five (25) seconds after the thermistor is cut
off the LSI turns on the convection fan for three (3) seconds.

3. The above procedure is repeated. If the difference between the

first voltage measured (in step 1) and the voltage measured
when the procedure is repeated (step 2) is greater than 300 mV
the LSI makes the judgment that there is a fire in the oven cavity
and will switch off the relays to the power transformer, fan motor
and jet motor. The LSI also stops counting down and closes the
damper door so that no fresh air will enter the oven cavity.

4. Once the fire sensor feature has shut the unit down, the

programmed cooking cycle may be resumed by  pressing the
"START" key or the unit may be reset by pressing the STOP/
CLEAR key.

JET MOTOR

THERMISTOR

Sensing 

Voltage

ON

OFF

ON

OFF

ON

OFF

0 2 3

28

31

32 (sec.)

64 (sec.)

3 sec.

Sensing the voltage across temperature measurement circuit.

3 sec.