R-772M (serv.man2) - Sharp Home Appliance Service Manual (repair manual). Page 5

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5
OPERATION SEQUENCE
OFF CONDITION
Closing the door activates the monitored latch switch and
the stop switch.
IMPORTANT:
When the oven door is closed, the contacts COM-NC
of the monitor switch  must be open. When the micro-
wave oven is plugged in a wall outlet (230 - 240V /
50Hz), the line voltage is supplied to the noise filter.
Figure O-1 on page 29
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.
MICROWAVE COOKING CONDITION
HIGH COOKING
Enter a desired cooking time by touching the TIME keys
and start the oven by touching START key.
Function sequence Figure O-2 on page 30
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 and monitor switch 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 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  stays 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 moni-
tored latch switch.
6-1. When the oven door is opened during or after the
cycle of a cooking program, the monitored latch
switch and stop switch 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 can
be closed and the contacts (COM-NO) of monitor
switch are made open.
6-2. When the oven door is closed, the contacts (COM-
NC) of the monitor switch must be opened and the
contacts (COM-NO) of monitor switch must be closed.
After that the contacts (COM-NO)  of the monitored
latch switch and the stop switch are made closed. And
the contacts (COM-NC) of the monitored latch switch
are made open.
6-3. When the oven door is opened and the contacts
(COM-NO) of  the monitored latch switch remain
closed, the fuse F8A will blow. Because the relay RY1
and monitor switch are closed  and a short circuit is
caused.
MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW
COOKING
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.
GRILL COOKING CONDITION
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-
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
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