R-82FBSTM (serv.man2) - Sharp Home Appliance Service Manual (repair manual). Page 11

R-82FBSTM - 11

The turntable motor rotates the turntable.

The fan motor drives a blade which draws external cool air, this
cool air is directed through the air vanes surrounding the
magnetron and cools the magnetron. Air is channelled through
the oven cavity to remove steam and vapours given off from
heating food. It is then exhausted through the air vents of the
oven cavity.

The convection motor drives the convection fan and provide the
heated air.

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

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 by forced circulation of the hot air produced by the grill
heaters.  The air heated by the grill heating elements is circulated
through the convectin passage provided on the outer casing of
the oven cavity by 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 heating elements are de-energized.
When the temperature inside the oven cavity drops below the
selected temperature, the elements are energized again.  In this
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 convection fan
stops operating and the oven shuts off.  At that time if the cavity
air temperature has risen above 120˚C, the fan remains rotating.
Automatically the fan motor will shut down at low temperature
(less than 105˚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 that there is a fire in the oven cavity and stops
the oven.

3. When LSI judges that there  is a fire in the oven cavity,

LSI will switch off the relays to high voltage transformer,
fan motor and LSI stops counting 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 thermistor 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

The noise filter assembly prevents radio frequency interference
that might flow back in the power circuit.