R-334 (serv.man4). Complete - Sharp Home Appliance Service Manual (repair manual). Page 9

R-334 - 9

Closing the door activates all door interlock switches (moni-
tored latch switch and stop 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
(220-230V 50Hz), the line voltage is supplied to the point.
Relay COM terminal + A5 in the control unit.

1. The display flashes ”88:88”.
2. To set any programmes or set the clock, you must first

touch the STOP pad.

3. “   :   ” appears in the display and the time counts up every

minute.

NOTE: When the oven door is opened, the oven lamp does

not come on at this time.

HIGH COOKING
Enter a desired cooking time with the ROTARY KNOB and
start the oven with touching START pad.

Oven lamp, Fan motor, Turntable motor

RY1

Power transformer

RY2

1. The line 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 single tone is heard and

the relays RY1 + RY2 go back to their home position.
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.

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.

CONDITION

DURING

DOOR OPEN

SWITCH

CONTACT

COOKING

(NO COOKING)

Monitor switch

COM-NC

Open

Closed

COM-NO

Closed

Open

Monitored latch switch

COM-NO

Closed

Open

Stop switch

COM-NO

Closed

Open

The circuits to the power transformer, fan motor and
turntable motor are cut off when the monitored   latch
switch and stop switch are made open.

6. MONITOR SWITCH CIRCUIT

The monitor switch SW2 is mechanically controlled by
oven door, and monitors the operation of the monitored
switch SW1

6-1

When the oven door is opened during or after the cycle
of cooking program, the monitored latch and stop
switches SW1 + SW3 must open their contacts first.
After that the contacts (COM - NC) of the monitor
switch SW2 should close.

6-2

When the oven door is closed, the contacts
(COM - NC) of the monitor switch SW2 must be
opened first and  the contacts (COM - NO) of the
monitored latch switch SW1  and stop switch SW3
must close after.

6-3

When the oven door is opened and the contacts of the
monitored latch switch SW1 remain closed, the
fuse F8A will blow, because the monitor switch is
closed and a short circuit is caused.

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

SETTING

32 sec. ON

24 sec. ON

18 sec. ON

12 sec. ON

6 sec. ON

8 sec. OFF

14 sec. OFF

20 sec. OFF

26 sec. OFF

HIGH

MEDIUM 
HIGH

MEDIUM

MEDIUM 
LOW

LOW

Approx. 70% = 630Watts

Approx. 50% = 450Watts

Approx. 30% = 270Watts

Approx. 10% = 90Watts

100% = 900Watts