Service manual
R-204(W)
7
OPERATION SEQUENCE
OFF CONDITION
Closing the door activates all door interlock switches (1st.
interlock switch and 2nd. interlock relay control switch).
IMPORTANT
When the timer knob is at "0" the oven in the OFF
condition.
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
(230V 50Hz), the noise filter and the control panel are
energized.
Figure O-1 on page 25
MICROWAVE COOKING CONDITION
HIGH COOKING
When the door is closed, the contacts (COM-NO) of the
1st. interlock switch (SW1) and the monitor switch (SW2)
are closed. When the microwave power is set to 800W
position by pressing the microwave power level button and
cooking time is selected by turning the timer knob, the
following components are energized: H.V. transformer,
Magnetron, Oven lamp, Turntable motor and Fan motor.
Function sequence
Figure O-2 on page 25
CONNECTED COMPONENTS RELAY
Oven lamp, Fan motor, Turntable motor RY1
High voltage transformer RY2
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 RY1+RY2 open. The circuits to the oven
lamp, high voltage transformer, fan motor and turnta-
ble motor are cut off.
5. 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)
1st. interlock switch COM-NO Closed Open
Monitor switch COM-NC Open Closed
2nd. interlock relay
control switch
COM-NO Closed Open
The circuits to the high voltage transformer, fan motor
turntable motor, and the oven lamp are cut off when the
1st. interlock switch (SW1) and 2nd. interlock relay
control switch (SW3) are made open.
6. MONITOR SWITCH CIRCUIT
The monitor switch (SW2) is mechanically controlled
by oven door, and monitors the operation of the 1st.
interlock switch (SW1).
6-1 When the oven door is opened during or after the
cycle of a cooking program, the 1st. interlock switch
(SW1) and 2nd. interlock relay control switch (SW3)
must open their contacts first. After that the contacts
(COM-NC) of the monitor switch (SW2) can be closed.
6-2. When the oven door is closed, the contacts (COM-
NC) of the monitor switch (SW2) must be opened first.
After that the contacts (COM-NO) of the 1st. interlock
switch (SW1) and 2nd. interlock relay control switch
(SW3) are closed.
6-3. When the oven door is opened and the contacts
(COM-NO) of the 1st. interlock switch (SW1) remain
closed, the fuse F will blow, because the contacts
(COM-NC) of the monitor switch are closed and a
short circuit is caused.
560W, 400W, 240W, 80W 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-seconds time base
through the relay contact which is coupled with the cur-
rent-limiting relay RY2. The following levels of microwave
power are given.
SETTING;
NOTE: The ON/OFF time ratio does not exactly corre-
spond to the percentage of microwave power,
because approx. 3 seconds are needed for heat-
ing up the magnetron filament.
POWER OUTPUT REDUCTION
After 100% power cooking mode is carried out for more
than 20 minutes, the power output is automatically reduced
to 70%. Even if the cooking time is shorter than for 20
minutes, the power output is reduced to 70% after total
cooking time over 20 minutes when the oven is started in
100% power cooking mode again within 1 minute and 35
seconds.
32 sec. ON
Approx. 70%
100%
800W
560W
400W
240W
80W
24 sec. ON 8 sec. OFF
14 sec. OFF
10 sec. OFF
26 sec. OFF
Approx. 50%
18 sec. ON
Approx. 30%
12 sec. ON
Approx. 10%
6 sec. ON