R-671M - Sharp Home Appliance Service Manual (repair manual). Page 6

R-671M  -  6

Closing the door activates the primary latch switch and the
stop switch.

1. The control unit is not energized.

The display shows nothing. (Fig0-1a)

2. Open the door. The contacts (COM-NC) of the primary

latch switch are closed and the control unit is energized.
Then contacts of relays RY1 and RY6 are closed, the
oven lamp will light and the display will flash:  
(Fig 0-1b).

3. Close the door. The contacts (COM-NC) of the primary

latch switch are opened and the oven lamp will be
turned off. The display will stop flashing (Fig 0-1c).

NOTE 1.  If the oven has not been used for more than two

minutes, the contacts of the relay RY6 will be
opened and the control unit will not be energized.
Open and close the door, the control unit will
resume.

NOTE 2.  If the clock is set, this energy save mode does

not work.

Enter a desired cooking time by pressing the TIME keys,
and select the power level by pressing the MICROWAVE
POWER LEVEL key and start the oven by pressing
START key.

CONNECTED COMPONENTS

RELAY

Oven lamp, Turntable motor

RY1

High voltage transformer

RY2

Grill heating element

RY3

Bottom heating element

RY4

Fan motor,

RY5

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 + RY5 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 oven door is opened during a cooking cycle,

the switches come to the following condition.

Switch

Contact

          Condition
During

Oven Door

Cooking

Open(No cooking)

Monitored latch Switch COM-NO

Closed

Opened

COM-NO

Opened

Closed

Stop switch

COM-NO

Closed

Opened

Monitor Switch

COM-NO

Closed

Opened

COM-NC

Opened

Closed

The circuit to the high voltage transformer, fan motor and
turntable motor are cut off when the monitored latch switch
and stop 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  stay closed.
Shown in the display is remaining time.
6.   MONITOR SWITCH CIRCUIT

  The monitor switch is mechanically controlled by the

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 contacts (COM-NO)
of the monitored latch switch and stop 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 (COM-NO) of the monitored latch switch
and the stop switch are closed.

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 high voltage
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

800P 100%

560P

70%

400P

50%

240P

30%

80P

10%

32 sec. ON

Approx. 100%

24 sec. ON

8 sec. OFF

Approx. 70%

18 sec. ON

14 sec. OFF

Approx. 50%

12 sec. ON

20 sec. OFF

Approx. 30%

6 sec. ON

26 sec. OFF

Approx. 10%

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.

The oven has three grill cooking condition. They are the
TOP GRILL mode, BOTTOM GRILL mode and TOP AND
BOTTOM GRILL mode.