Sharp R-4A52 Service Manual page 5

R-&u2
R-4E52
OPERATING SEQUENCE
OFF CONDITION
Closing the door activates all door interlock switches
(Upper latch switch, Lower 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
(240V 50Hz), 240 volts A.C. is supplied to the point
Al + A3 in the control unit.
Figure O-l on page 32 or 33
1 . The display flashes "88:88". --
2. To set any programmes or set the clock, you must
first touch the STOP/CLEAR key.
3. [lappears in the display and the time counts
up every minute.
NOTE: When the oven door is opened, the oven
lamp comes on at this time.
MICROWAVE COOKING CONDITION
HIGH COOKING
Enter a desired cooking time with the touching
NUMBER key and start the oven with touching
START key.
Function sequence Figure O-2 on page 32 or 33
CONNECTED COMPONENTS
RELAY
Oven lame, Fan motor, Turntable motor
RYI
Power transformer
RY2
1. 240 volts AC. is supplied to the primary winding
of the power transformer. The voltage is converted
to about
3.3
volts AC. 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 signal tone is heard
and the relays RYI + RY2 go back to their home
position.
The circuits to the oven lamp, power
transformer, fan motor and turntable motor are cut
off.
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)
Upper latch switch COM - NO Closed Open
Monitor switch
COM- NC
Open ' Closed
Lower latch switch COM - NO Closed Open
Stop switch COM- NO Closed Open
The circuits to the power transformer, fan motor and
turntable motor are cut off when the upper 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 inter-
rupted, because the relay RYI stays closed. Shown
in the display is the remaining time.
MONITOR SWITCH CIRCUIT
The monitor switch SW3 is mechanically controlled
by oven door, and monitors the operation of the
upper and lower latch switches SW1 + SW2.
6-2
When the oven door is opened during or after the
cycle of a cooking program, the upper latch and
lower latch switches SW1 + SW2 must open their
contacts first.
After that the contacts (COM -
NC) of the monitor switch SW3 can be closed
and then contacts of the stop switch SW4 can be
opened.
When the oven door is closed, the contacts
(COM-
NC) of the monitor switch SW3 must
be opened first, and the contacts (COM - NO)
of the stop switch SW4 must be closed. After that
the contacts of the upper latch switch SW1 latch
and lower latch switches SW1 + SW2 are closed.
6-3. When the oven door is opened and the contacts
of the upper and lower latch switches SW1 +
SW2 remain closed. The fuse E M8A will blow,
because the monitor switch is closed and a short
circuit is caused.
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