Sharp R-890SLM Service Manual download pdf (Page 12)

R-890SLM

6 - 2

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.

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 ele

ments

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

rised above 120°C, the fan motor remains rotating.

Automatically

the fan motor will be shut down at low temperature

(less than

105°C).

Figure D-2. Convection Cooking System

Door

Oven Cavity

Grill Heating

Elemen

Bottom Gril

Heating Element

Convection

Passag

Coolin

Fan

Convection

Moto

Convection

Fan

Turntabl

Insulation

Turntabl

Moto

[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.

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.

THERMISTOR

SENSING

VOLTAGE

OFF

32 (sec.)

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.

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Sharp R-890SLM Service Manual Page 12

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