Operation Sequence - Sharp R-880B Service Manual

R-880B
OFF CONDITION
Closing the door activates the 1st. latch switch, 2nd. latch
switch and stop switch.
IMPORTANT:
When the oven door is closed, the contacts COM-NC
of the monitor switch must be open. When the mi-
crowave oven is plugged in a wall outlet (230 - 240V
50Hz), the line voltage is supplied to the noise filter
and the control unit.
Figure O-1 on page 34
1. The oven display will show " SHARP MICRO- WAVE
OVEN " .
2. Press the STOP/CLEAR pad. The oven display will
show " : ".
3. Set the clock as follows.
3-1. Press the CLOCK pad once.
3-2. Enter the time of day by perssing the number
pads.
3-3. Start the clock by pressing the CLOCK pad.
NOTE:
1. If you do not set the clock, " : " will appear on the
display. When the operation of the oven is finished, " :
" will appear on the display instead of the time of day.
2. The oven can be also used when the clock is not set.
3. When the oven door is opened, the oven lamp does not
come on.
MICROWAVE COOKING CONDITION
100% (HIGH) COOKING
Enter a desired cooking time by pressing the number pads
and start the oven by pressing START pad.
Function sequence Figure O-2 on page 34
CONNECTED COMPONENTS
Convection motor
High voltage transformer
Grill heater (Top)
Bottom heater
Fan motor,
Oven lamp, Turntable motor
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 RY2 + RY5 + 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.

OPERATION SEQUENCE

Switch
1st. latch switch
2nd. latch switch
Stop switch
Monitor Switch
The circuit to the high voltage transformer, fan motor, oven
lamp and turntable motor are cut off when the 1st. latch
switch, 2nd. latch switch and stop switch are made open.
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 1st. latch
switch, the 2nd. latch switch and the relay RY2.
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 the
1st. latch switch, 2nd. latch switch and the relay RY2
remain closed, the fuse M10A will blow, because the
monitor switch is closed and a short circuit is caused.
70% (MEDIUM HIGH), 50% (MEDIUM), 30% (ME-
DIUM LOW), 10% (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-
RELAY
rent-limiting relay RY2. The following levels of microwave
RY1
power are given.
RY2
RY3
SETTING
RY4
RY5
RY6
Note: The On/Off time ratio does not exactly correspond
GRILL COOKING CONDITIONS
The oven has three grill cooking condition. They are the
TOP HEATER mode, BOTTOM HEATER mode and TOP
AND BOTTOM HEATER mode.
TOP
In this mode, the food is cooked by the top heaters. Press
the GRILL pad once and then enter the cooking time by
pressing the number pads. When the START pad is
pressed, the following operations occur:
4
Contact
COM-NO
COM-NO
COM-NO
COM-NC
32 sec. ON
100%
24 sec. ON
70%
18 sec. ON
50%
12 sec. ON
30%
6 sec. ON
10%
to the percentage of microwave power, because
approx. 2 seconds are needed for heating up the
magnetron filament.
HEATER
MODE
Figure O-3(a) on page 35
Condition
During Oven Door
Cooking Open(No cooking)
Closed Opened
Closed Opened
Closed Opened
Opened Closed
Approx. 100%
8 sec. OFF
Approx. 70%
14 sec. OFF
Approx. 50%
20 sec. OFF
Approx. 30%
26 sec. OFF
Approx. 10%