R-962M - Sharp Home Appliance Service Manual (repair manual). Page 5

R-962M - 5

Damper position is set automatically by damper motor,
damper switch, damper cam and damper shaft.
These components are operated by a signal that judges if
microwave cooking or other cooking operation is selected by
the CPU unit.

Damper is in the open position, because a portion of cooling
air is channeled through the cavity to remove steam and
vapors given off from the heating foods.
It is then exhausted at the top of the oven cavity into a
condensation compartment.

Damper is in the closed position, so that no hot air will be
allowed to leak out the oven cavity.

1. When power supply cord is plugged in:
1-1. When power supply cord is plugged in, a signal is

sensed in the control unit, and operates shut-off relay
(RY7).

1-2. Contacts of shut-off relay (RY7) close, the damper

motor is energized, opening the damper door.

1-3. When the damper is moved to the open position by the

damper cam, damper switch is closed (ON position).

1-4. The signal of damper switch is re-sensed in the control

unit and shut-off relay (RY7) is turned off.

1-5. The A.C. line voltage A.C. to the damper motor is

stopped and the motor turns off.

2. When oven is microwave cooking:

Damper is in the open position

3. When oven is convection cooking:
3-1 Damper motor is energized right after the oven is

started.

3-2. When damper is in the closed position (damper switch

is OFF), its signal is sensed by the control unit, and
shut-off relay (RY7) is de-energized.

3-3. The damper is held in the closed position during the

cooking operation

3-4. At the end of any cooking, when the fan motor stops,

the relay (RY7) is energized and the damper is returned

to the open position.

NOTE: If the damper door is not in the proper position,

closed durining convection, grill or dual, or open
durning microwave, the control unit will stop oven
operation after 1 minute.

4. Operation of damper is shown below;

Damper operation

Cooking condition

Operation of Damper

Microwave

Convection

Grill; during backed up with con-

vection heater

Grill; after convection heater

back- up has stopped.

Dual (Microwave and Convection)

when oven temperature above
220˚C is programmed.

When oven  temperature be-
low 200˚C is programmed.

Dual (Microwave and Grill)

Fire sensing condition

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 accomplished by the LSI repeatedly measures the
voltage across the temperature measurement circuit (ther-
mistor) during it's 32-seconds time base comparing the
obtained voltage measurements. If the most recent  voltage
measured is 300mV grater than the previous voltage meas-
ured, the LSI judges it as a fire in the oven cavity and
switches off the relays to the high voltage transformer, fan
motor and convection 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 on page 4.

1. 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
one (21) seconds after the thermistor is cut off the LSI
turns on the cooling fan for six (6) seconds.

2. 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 300mV the LSI makes the judgment that
there is a fire in the oven cavity and will switch off the
relays to the high voltage transformer, fan motor and
convection motor. The LSI also stops counting down and
closes the damper door so that no fresh air will enter the
oven cavity.

The door can be opened by pushing the open button on the
control panel.  When the open button is pushed, the open
lever pushes lower latch head on the door upward.  The
upper latch head is linked with the lower latch head, so now,
the door can be opened.

Open

Close

Close

Open

Close but open
after 20 minutes.

Close

Open

Close

Upper latch head

Lower latch 
head

Door

SW3 Monitor switch

SW1 Monitored latch switch

SW2 Stop switch

Open lever