Sharp R-450H Service Manual Download Page 6

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R-450H

OPERATION SEQUENCE

because the relay (RY1) stays closed. Shown in the
display is the remaining time.

6. MONITOR SWITCH CIRCUIT

The monitor switch is mechanically controlled by oven
door, and monitors the operation of the 1st. latch switch
and 2nd. interlock relay.

6-1 When the oven door is opened during or after the

cycle of a cooking program, the 1st. latch switch and
2nd. interlock relay control switch must open their
contacts first. After that the contacts (COM-NC) of the
monitor switch can be closed.

6-2. When the oven door is closed, the contacts (COM-

NC) of the monitor switch must be opened first. After
that the contacts of the 1st. latch switch and 2nd.
interlock relay control switch are closed.

6-3. When the oven door is opened and the contacts of the

1st. latch switch and 2nd. interlock relay remain
closed. The fuse F10A will blow, because the monitor
switch is closed and a short circuit is caused.

VARIABLE COOKING

When the microwave oven is preset for variable cooking
power. Rated voltage is supplied to the power transformer
intermittently within a 32-second time base through the
relay contact which is coupled with the relay (RY2). The
following levels of microwave power are given.

SETTING;

OFF CONDITION

Closing the door activates all door interlock switches
(1st. latch switch, 2nd. interlock relay control switch)

IMPORTANT
When the oven door is closed, the monitor switch contacts
(COM-NC) must be open.
When the microwave oven is plugged in a wall outlet, rated
voltage is supplied to the noise filter and the control unit.

Figure O-1 on page 25

1. The display shows SHARP, MICRO-WAVE and OVEN.
2. To set any programs or set the clock, you must first

touch the STOP/CLEAR pad.

3. “ : “ appears in the display.
NOTE: When the oven door is opened, the oven lamp

comes on at this time.

MICROWAVE COOKING CONDITION

HIGH COOKING

Enter a desired cooking time with the touching Number
pads and start the oven with touching START pad.

Function sequence

Figure O-2 on page 25

CONNECTED COMPONENTS

RELAY

Oven lamp, Fan motor, Turntable motor

RY1

Power transformer

RY2

1. Rated voltage is supplied to the primary winding of the

power transformer. The voltage is converted to about
3.3 volts A.C. output on the filament winding and high
voltage of approximately 2000 volts A.C. on the
secondary winding.

2. The filament winding voltage (3.3 volts) heats the

magnetron filament and the high voltage (2000 volts) is
sent to the voltage doubling circuit, where it is doubled
to negative voltage of approximately 4000 volts D.C..

3. The 2450 MHz microwave energy produced in the

magnetron generates a wave length of 12.24 cm. This
energy is channelled through the waveguide (transport
channel) into the oven cavity, where the food is placed
to be cooked.

4. When the cooking time is up, a signal tone is heard and

the relays (RY1+RY2) go back to their home position
(off condition). The circuits to the oven lamp, power
transformer, fan motor and turntable motor are cut off.

5. When the door is opened during a cook cycle, the

switches come to the following condition

CONDITION
DURING

DOOR OPEN

SWITCH

CONTACT

COOKING

(NO COOKING)

1st. latch switch

COM-NO

Closed

Open

2nd. interlock relay
control switch

COM-NO

Closed

Open

Monitor switch

COM-NC

Open

Closed

The circuits to the power transformer, fan motor and
turntable motor are cut off when the 1st. latch switch
and 2nd. interlock relay control switch are made open.
The oven lamp remains on even if the oven door is
opened after the cooking cycle has been interrupted,

NOTE: The ON/OFF time ratio does not exactly correspond

to the percentage of microwave power, because
approx. 3 seconds are needed for heating up the
magnetron filament.

POWER OUTPUT REDUCTION

After 100% power cooking mode is carried out more than
40 minutes, the power output is automatically reduced to
70%.

HIGH

32 sec. ON

MEDIUM HIGH

Approx. 70%

24 sec. ON

8 sec. OFF

14 sec. OFF

20 sec. OFF