R-216 (serv.man2). Complete - Sharp Home Appliance Service Manual (repair manual). Page 6

4

Closing the door activates all door interlock switches
(monitored latch switch and 2nd. interlock relay control
switch).

IMPORTANT
When the timer knob is at "0" the oven in the OFF
condition.
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 (230
- 240V 50Hz), the noise filter and the control panel are
energized.

HIGH COOKING
When the door is closed, the contacts (COM-NO) of the
monitored latch switch  and the monitor switch  are closed.
When the microwave power is set to HIGH position by
pressing the microwave power level button and cooking
time is selected by turning the timer knob, the following
components are energized: H.V. transformer, Magnetron,
Oven lamp, Turntable motor and Fan motor.

CONNECTED COMPONENTS

RELAY

Oven lamp, Fan motor, Turntable motor

RY1

High voltage transformer

RY2

1. The line voltage is supplied to the primary winding of

the high voltage 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 open. The circuits to the oven
lamp, high voltage transformer, fan motor and turnta-
ble 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)

Monitored latch switch

COM-NO

Closed

  Open

Monitor switch

COM-NC

Open

  Closed

2nd. interlock relay
control switch

COM-NO

Closed

  Open

The circuits to the 

high voltage

 transformer, fan motor

turntable motor, and the oven lamp are cut off when the

monitored latch switch  and 2nd. interlock relay control
switch are made open.

6. MONITOR SWITCH CIRCUIT

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

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

cycle of a cooking program, the monitored 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 (COM-NO) of the monitored latch
switch and 2nd. interlock relay control switch are
closed.

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

(COM-NO) of the monitored latch switch  remain
closed, the fuse T6.3A will blow, because the con-
tacts (COM-NC) of the monitor switch are closed and
a short circuit is caused.

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

SETTING;

NOTE: The ON/OFF time ratio does not exactly corre-

spond to the percentage of microwave power,
because approx. 3 seconds are needed for heat-
ing up the magnetron filament.

After 100% power cooking mode is carried out for more
than 20 minutes, the power output is automatically reduced
to 70%. Even if the cooking time is shorter than for 20
minutes, the power output is reduced to 70% after total
cooking time over 20 minutes when the oven is started in
100% power cooking mode again within 1 minute and 35
seconds.

HIGH

32 sec. ON

MEDIUM HIGH

Approx. 70%

100%

24 sec. ON

8 sec. OFF

14 sec. OFF

20 sec. OFF

26 sec. OFF

MEDIUM

Approx. 50%

18 sec. ON

MEDIUM LOW

Approx. 30%

12 sec. ON

LOW

Approx. 10%

6 sec. ON