R-234 (serv.man4). Complete - Sharp Home Appliance Service Manual (repair manual). Page 9

R-234 - 9

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.

14 sec. OFF

8 sec. OFF

32 sec. ON

24 sec. ON

MEDIUM HIGH

HIGH

MEDIUM

MEDIUM LOW

LOW

18 sec. ON

6 sec. ON

12 sec. ON

26 sec. OFF

20 sec. OFF

Approx. 10% = 80 Watts

Approx. 30% = 240 Watts

Approx. 50% = 400 Watts

6. MONITOR SWITCH CIRCUIT

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

6-1

When the oven door is opened during or after the cycle
of a cooking program, the monitored latch switch
(SW1) must open its contacts first. After that the
contacts (COM - NC) of the monitor switch (SW2) can
be closed.

6-2

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

6-3

When the oven door is opened and the contacts of the
monitored latch switch (SW1) remain closed, the fuse
F1 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 26-second time base through the vari
contact. The following levels of microwave power are given.
SETTING

Closing the door activates the door interlock switch (moni-
tored latch switch).

IMPORTANT
When the oven door is closed, the monitor switch contacts
COM - NC must be open.
When the microwave oven is pluged in a wall outlet (220-
230V 50Hz), the noise filter is energised.

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

comes on at this time.

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

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 channeled 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.

CONDITION

DURING

DOOR OPEN

SWITCH

CONTACT

COOKING

(NO COOKING)

Monitor switch

COM-NC

Open

Closed

Monitored latch switch

COM-NO

Closed

Open

The circuits to the power transformer, fan motor and
turntable motor are cut off when the monitored latch
switch is opened.
The oven lamp remains on even if the oven door is
opened after the cooking cycle has been interrupted,
because the timer switch remains closed.

Oven lamp, Fan motor, Turntable motor

RY1

Power transformer

RY2

Approx. 70% = 560 Watts

100%          = 800 Watts