Noise Filter; Motor; Heating Element; Convection Cooking System - Sharp R-890SLM Service Manual

R-890SLM
2. The peak reverse voltage of D2 of the rectifier goes beyond
the rated peak reverse voltage 1.7 KV in the voltage doubler
circuit.
3. D2 of the rectifier is shorted.
4. The large electric currents flow through the high voltage
winding of the high voltage transformer.
5. The large electric currents beyond 8A flow through the
primary winding of the high voltage transformer.
6. The fuse F2 F8A blows by the large electric currents.
7. The power supplying to the high voltage transformer is cut off.

[7] NOISE FILTER

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

[8] MOTOR

1. TURNTABLE MOTOR
The turntable motor rotates the turntable.
2. FAN MOTOR
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. This air is channelled
through the oven cavity to remove steam and vapours given off
from heating food. It is then exhausted through the exhausting
air vents of the oven cavity.
3. CONVECTION MOTOR
The convection motor drives the convection fan and provide the
heated air.

[9] HEATING ELEMENT

1. TOP GRILL HEATING ELEMENT
The grill heating element is provided to brown the food and is
located on the top of the oven cavity.
2. BOTTOM GRILL HEATING ELEMENT
The grill heating element is provided to brown the food and is
located at the base of the oven cavity.

[10] CONVECTION COOKING SYSTEM

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
heating elements.
The air heated by the grill heating elements is circulated through
the convection passage provided on the outer casing of the oven
cavity by means of the convection fan which is driven by the
convection motor. It is then enters the inside of the oven through
the vent holes provided on the back side 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 circulates inside the oven cavity to raise
its temperature and, at the same time, comes into contact with
the food being 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 heating elements
are energized again. In this way, the inside of the oven cavity is
maintained at approximately the selected temperature.
When the convection time reaches "0", the heating elements
are de-energized and the convection fan stops operating and
the oven shuts off. At that time if the cavity air temperature has
Service_R-890SLM.indd 12
rised above 120°C, the fan motor remains rotating. Automatically
the fan motor will be shut down at low temperature (less than
105°C).
Door
Oven Cavity
Turntable
Motor
Insulation
Figure D-2. Convection Cooking System

[11] FIRE SENSING FEATURE

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 measurement
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 as a
fire in the oven cavity and stop the oven.
3. When LSI judges it as a fire in the oven cavity, LSI will switch
off the relays to high voltage transformer and fan motor and
LSI stops countering down.
ON
THERMISTOR
OFF
ON
SENSING
OFF
VOLTAGE
Sensing the voltage across temperature measurement circuit.

[12] OPEN JUDGE BY THERMISTOR

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 convection, grill (top and bottom grills) or combi
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.
6 - 2
Grill Heating
Element
Convection
Passage
Cooling
Fan
Convection
Motor
Convection
Fan
Turntable
Bottom Grill
Heating Element
32 (sec.)
30
4/25/09 10:55:06 AM