R-852 (serv.man2) - Sharp Home Appliance Service Manual (repair manual). Page 9

R-852 - 7

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

1. The control unit is not energized. The display shows

nothing (Fig. O-1 (a)).

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

tored latch switch are closed and the control unit is
energized. Then contacts of relays RY1 and RY5 are
closed, and the oven lamp will light and the display will
show "ENERGY SAVE MODE" (Fig. O-1(b)).

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

tored latch switch are opened and the contacts of relay
RY1 are opened and the oven lamp will be turned off.
The display will show "  .  

0

". (Fig. O-1(c)).

NOTE: Energy save mode
1. If the oven has not been used for more than 2 minutes,

the contacts of the relay RY5 will be opened and the
control unit will be not energized. Open and close the
door, the control unit will resume.

2. If the clock is set, this energy save mode does not work.

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

CONNECTED COMPONENTS

RELAY

Oven lamp, Turntable motor

RY1

High voltage transformer

RY2

Fan motor

RY6

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 wavelength 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 + RY6 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)

COM-NO

Closed

Opened

Monitored latch switch

COM-NC

Opened

Closed

Stop switch

COM-NO

Closed

Opened

COM-NO

Closed

Opened

Monitor Switch

COM-NC

Opened

Closed

The circuit to the high voltage transformer is cut off when
the contacts of relay RY2, and the contacts (COM-NO) of
the monitored latch switch SW1 and monitor switch SW3
are made open. The circuit to the fan motor is cut off when
the relay RY6 is made open. The circuit to the turntable
motor is cut off when the contacts (COM-NO) of the
monitored latch switch SW1 are made open. The relay RY2
and RY6 are made open when the door is opened. The
oven lamp remains on even if the oven door is opened after
the cooking cycle has been interrupted, because the relay
RY1  stay are closed. Shown in the display is remaining
time.
6. MONITOR SWITCH CIRCUIT

The monitor switch SW3 is mechanically controlled
by the 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 contacts (COM-NO)
of the monitored latch switch SW1 and stop switch
SW2 must open their contacts (COM-NO) first. And
the contacts (COM-NC) of the monitored latch switch
SW1 are made closed. After that the contacts (COM-
NC) of the monitor switch SW3 can be closed and the
contacts (COM-NO) of monitor switch SW3 are made
open.

6-2. When the oven door is closed, the contacts (COM-

NC) of the monitor switch SW3 must be opened and
the contacts (COM-NO) of monitor switch SW3 must
be closed. After that the contacts (COM-NO)  of the
monitored latch switch SW1 and the stop switch SW2
are made closed. And the contacts (COM-NC) of the
monitored latch switch SW1 are made open.

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

(COM-NO) of  the monitored latch switch SW1 remain
closed, the fuse F2 F8A will blow. Because the relay
RY1 and monitor switch SW3 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-second time base
through the relay contact which is coupled with the cur-
rent-limiting relay RY2. The following levels of microwave
power are given.

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.

TOP GRILL (Figure O-3a)
In this condition the food is cooked by the top grill heating
element . Programme the desired cooking time by touch-
ing the TIME keys and touh the GRILL key once. When the

900W

(HIGH)

32 sec. ON

630W  MEDIUM 

HIGH 

Approx. 70%

100%

24 sec. ON

8 sec. OFF

14 sec. OFF

20 sec. OFF

26 sec. OFF

450W (MEDIUM)

Approx. 50%

18 sec. ON

270W  MEDIUM 

LOW 

Approx. 30%

12 sec. ON

90W

(LOW)

Approx. 10%

6 sec. ON