R-895M (serv.man15). Complete - Sharp Home Appliance Service Manual (repair manual). Page 11

R-895M - 11

The grill heating element is provided to brown the food and
is located at the base of the oven cavity.

This oven is designed with a hot air heating system where
food is heated be forced circulation of the hot air produced
by the grill heaters.  The air heated be the grill heating
elements is circulated through the convectin passage
provided on the outer casing of the oven cavity be means
of the convection fan which is driven by the convection
motor.  It then enters the inside of the oven through the
vent holes provided on the back of the oven. Next, the hot
air heats the food on the turntable and leaves the oven
cavity through the vent in the oven cavity rear wall.  In this
way, the hot air ciculates inside the oven cavity to raise its
temperature and at the same time, comes into contact
with the food cooked.  When the temperature inside the
oven cavity reaches the selected temperature, the heat-
ing elements are de-energized.  When the temperature
inside the oven cavity drops below the selected tempera-
ture, the elements are energized again.  In thia way, the
inside of the oven is maintained at approximately the
selected temperature.  When the convection time reaches
"0", the heating elements are de-energzed and the con-
vection fan stops operating and the oven shuts off.  At that
time if the cavity air temperature has rised above 120

o

C,

the fan remains rotating. Automatically the fan motor will
shut down at low temperature (less than 105

o

C).

The oven will stop its operation when there is a fire in the
oven cavity in microwave cooking condition.
LSI measures the voltage across the temperature meas-
urement circuit intermittently within 32-seconds time base
since the oven is started in microwave cooking condition.
The oven will stop its operation when the difference of the
voltage is more than 0.781 volts in microwave cooking
condition.
1. Within a 32-seconds base, the thermistor is energized

for 2 seconds.  At that time, the voltage across the
temperature measurement circuit is measured.

2. The oven carries out the procedure above again. If the

second voltage is 0.781V higher than first voltage, LSI
judges it  is a fire in the oven cavity and stop the oven.

3. When LSI judges it  is a fire in the oven cavity, LSI will

switch off the relays to high voltage transformer and fan
motor and LSI stops countring down.

1. If the temperature of the thermistor does not rise to

more than 40˚C after 4 minutes and 15 seconds from
when the oven is started in oven cooking mode, dual
cooking mode or grill (top and bottom) cooking mode,
the oven is turned off.

2. When the thermistor or the wire harness to the thermis-

tor is opened, the oven is turned off after 4 minutes and
15 seconds because this condition is same as above

THERMISTOR

SENSING

VOLTAGE

ON

OFF

ON

OFF

30

32 (sec.)

Sensing the voltage across temperature measurement circuit.

Door

Oven Cavity

Grill Heating
Element

Bottom Grill 
Heating Element

Convection
Passage

Cooling
Fan

Convection
Motor

Convection
Fan

Turntable

Insulation

Turntable
Motor