R-555. R555 - 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 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.

1. The display shows flashing "88:88".
2. To set any programmes or set the clock, you must

first touch the STOP/CLEAR key.

3.        :        appears in the display.

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

comes on at this time.

HIGH COOKING
Enter a desired cooking time with the touching TIMER
keys and start the oven with touching START key.

CONNECTED COMPONENTS

RELAY

Oven lamp, Fan motor, Turntable motor

RY1

High voltage 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 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 signal tone is heard and

the relays RY1+RY2 go back to their home position.
The circuits to the oven lamp, high voltage 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)

Monitored 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 high voltage transformer, fan motor
and turntable motor are cut off when the monitored
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, 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 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. After that
the contacts of the monitored latch switch and 2nd.
interlock relay control switch are closed.

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

monitored latch switch remain closed. The fuse F10A
will blow, because the monitor switch is closed and a
short circuit is caused.

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 current-limiting
relay. The following levels of microwave power are given.

SETTING;

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.

100P

32 sec. ON

70P

Approx. 70%

100%

24 sec. ON

8 sec. OFF

14 sec. OFF

20 sec. OFF

26 sec. OFF

50P

Approx. 50%

18 sec. ON

30P

Approx. 30%

12 sec. ON

10P

Approx. 10%

6 sec. ON