Operation Sequence - Sharp R-3A56 Service Manual

R-3A56
OFF CONDITION
Closing the door activates all door interlock switches
(1st. latch switch, 2nd. 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 plugged in a wall outlet, rated
voltage is supplied to the point A3+A5 in the control unit.
Figure O-1 on page 27
1. The display flashes "88:88".
2. To set any programmes or set the clock, you must first
touch the STOP/CLEAR pad.
3. "88:88" appears 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
pad and start the oven with touching START pad.
Function sequence
Figure O-2 on page 28
CONNECTED COMPONENTS
Oven lamp, Fan motor, Turntable motor
Power transformer
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, power 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
SWITCH CONTACT
1st. latch switches COM-NO
2nd. latch switch COM-NO
Monitor switch COM-NC
Stop switch COM-NO

OPERATION SEQUENCE

RELAY
RY1
RY2
CONDITION
DURING DOOR OPEN
COOKING (NO COOKING)
Closed Open
Closed Open
Open Closed
Closed Open
The circuits to the power transformer, fan motor and
turntable motor are cut off when the 1st. latch switch,
2nd. 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 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 1st and 2nd.
latch switches.
6-1 When the oven door is opened during or after the cycle
of a cooking program, the 1st. latch switch, 2nd. 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 of the 1st. latch switch, 2nd. latch switch and
stop switch are closed.
6-3. When the oven door is opened and the contacts of
the1st. latch switch, 2nd. latch switch remain closed.
The fuse M8A will blow, because the monitor switch is
closed and a short circuit is caused.
MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW
COOKING
When the microwave oven is preset for variable cooking
power, 230-240 volts A.C. power 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;
HIGH
MEDIUM HIGH
MEDIUM
MEDIUM LOW
LOW
NOTE: The ON/OFF time ratio does not exactly correspond
to the percentage of microwave power, because
approx. 2 seconds are needed for heating up the
magnetron filament.
4
32 sec. ON
8 sec. OFF
24 sec. ON
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%