R-963 (serv.man2) - Sharp Home Appliance Service Manual (repair manual). Page 12

R-953/963M - 10

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 dual 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.

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

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

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

Damper Operation
1. When power supply cord is plugged in or when the

control unit resumes after energy save mode finishes:

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

sensed in the control unit, and operates shut-off relay
(RY8).

1-2. Contacts of shut-off relay (RY8) 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 posi-
tion).

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

control unit and shut-off relay (RY8) is turned off.

1-5. The rated voltage 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 (RY8) is de-energized.

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

convection cooking operation.

3-4. At the end of the convection cooking, when the fan

motor stops, shut-off relay (RY8) is energized, and
the damper is returned to the open position.

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

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

4. Operation of damper is shown below.

Cooking Mode

Operation of Damper

Microwave cooking

Open

Convection cooking

Closed

Grill; during backed up with

convection heating element

Closed

Grill; after convection heating

element backed up has stopped

Open

Dual (Microwave and Convection)

Closed

Dual  (Microwave and Grill)

Open

Fir sensing condition

Closed

When troubleshooting the microwave oven, it is helpful to follow the Sequence of Operation in performing the checks.
Many of the possible causes of trouble will require that a specific test be performed. These tests are given a procedure
letter which will be found in the “Test Procedure” section.

IMPORTANT: If the oven becomes inoperative because of a blown fuse F8A in the monitored latch switch - monitor

switch circuit, check the monitored latch switch and monitor switch before replacing the fuse F8A.