R-90GCK (serv.man17). Complete - Sharp Home Appliance Service Manual (repair manual). Page 11

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Usually, the damper is in the open position except during
convection cooking, preheat, grill, dual1, dual2 or all
cooking modes which use the top / side heating elements.
Damper position is set automatically by damper motor,
damper switch, motor cam and damper shaft. These
components are operated by a signal that judges if
microwave cooking, convection cooking operation or
other cooking operation is selected by the control unit.

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

Hot air

Hot air

Hot air

Convection
fan

Hot air

Oven cavity left side

Oven cavity   
top wall

Side heating
element unit

Side heating
element unit

Top heating element unit Top heating element unit

Turntable

at the top of the oven cavity into a condensation compart-
ment.

Convection, Preheat, Grill, Dual1, Dual2, or all cook-
ing modes which use the top / side heating elements:
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:

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

sensed in the control unit, and operates shut-off
relay (RY4).

1-2. Contacts of shut-off relay (RY4) 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 the damper switch is opened
(OFF position).

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

control unit and shut-off relay (RY4) is turned off.

1-5. The rated voltage to the damper motor is removed

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 by touching the CONV.

(˚C) and START keys.

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

switch is ON), its signal is sensed by the control
unit, and shut-off relay (RY4) 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, if the cavity

air temperature is below 121˚C, shut-off relay
(RY4) is energized, and the damper is returned to
the open position.

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 proce-
dure letter which will be found in the "Test Procedure
"section.

IMPORTANT: If the oven becomes inoperative because

of a blown fuse F10A in the secondary
interlock swith - monitor switch - primary
interlock relay RY2 circuit, check the moni-
tor switch, relay (RY1), primary interlock
relay (RY2) and secondary interlock switch
before replacing the fuse F10A.