R-341AM - Sharp Home Appliance Service Manual (repair manual). Page 4

R341M - 4

CONNECTED COMPONENTS

RELAY

Oven lamp, Fan motor, Turntable motor

RY1

Power transformer

RY2

Approx. 10% = 90 Watts

32 sec. ON

6 sec. ON

12 sec. ON

18 sec. ON

24 sec. ON

30 sec. OFF

20 sec. OFF

14 sec. OFF

8 sec. OFF

LOW

MEDIUM HIGH

MEDIUM

MEDIUM LOW

HIGH

Approx. 70% = 630 Watts

Approx. 50% = 450 Watts

Approx. 30% = 270 Watts

Closing the door activates all door interlock switches (latch
switch, monitored 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 pluged in a wall outlet (230 -
240V 50Hz), the line voltage is supplied to the point A3+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.

HIGH COOKING
Enter a desired cooking time by touching the Time pads and
start the oven by touching the 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 voltagedoubling 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.

The circuits to the power transformer,oven lamp fan
motor and turntable motor are cut off when the monitored
latch switch and stop switch are made open.   Shown in
the display is the remaining time.

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 cooking program, the monitored latch switch
(SW1), and stop switch (SW3) must open their 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.  After that the contacts of the monitored
latch switch (SW1) and stop switch (SW3) are closed.

6-3

When the oven door is opened and the contacts of the
monitored latch switch (SW1) remain closed, the fuse
(F1) 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

CONDITION

DURING

DOOR OPEN

SWITCH

CONTACT

COOKING

(NO COOKING)

Monitored latch switch

COM-NO

Closed

Open

Monitor switch

COM-NC

Open

Closed

Stop switch

COM-NO

Closed

Open

Monitor switch

COM-NO

Closed

Open

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.

100% = 900 Watts