6
R - 2 0 4 E W A
OPERATION
DESCRIPTION OF OPERATING SEQUENCE
The following is a description of component functions during
oven operation.
OFF CONDITION
Closing the door activates door sensing switch and second-
ary interlock switch. (In this condition, the monitor switch
contacts are opened.)
When oven is plugged in, 120 volts A.C. is supplied to the
control unit. (Figure O-1).
1. The display will show flashing "88:88".
2. To set any program or set the clock, you must first touch
the STOP/CLEAR pad. The display will clear, and " : "
will appear.
COOKING CONDITION
Program desired cooking time by touching the NUMBER
pads. And program the power level by touching the POWER
LEVEL pad.
When the START pad is touched, the following operations
occur:
1. The contacts of the relays are closed and components
connected to the relays are turned on as follows.
(For details, refer to Figure O-2)
RELAY
CONNECTED COMPONENTS
RY-1
oven lamp/turntable motor/fan motor
RY-2
power transformer
2. 120 volts A.C. is supplied to the primary winding of the
power transformer and is converted to about 3.4 volts
A.C. output on the filament winding, and approximately
2100 volts A.C. on the high voltage winding.
3. The filament winding voltage heats the magnetron
filament and the H.V. winding voltage is sent to a voltage
doubler circuit.
4. The microwave energy produced by the magnetron is
channelled through the waveguide into the cavity feed-
box, and then into the cavity where the food is placed to
be cooked.
5. Upon completion of the cooking time, the power
transformer, oven lamp, etc. are turned off, and the
generation of microwave energy is stopped. The oven
will revert to the OFF condition.
6. When the door is opened during a cook cycle, monitor
switch, door sensing switch, secondary interlock switch
and primary interlock relay are activated with the following
results. The circuits to the oven lamp, turntable motor,
the cooling fan motor, and the high voltage components
are de-energized, and the digital read-out displays the
time still remaining in the cook cycle when the door was
opened.
7. The monitor switch is electrically monitoring the operation
of the secondary interlock switch and primary interlock
relay (RY2) and is mechanically associated with the door
so that it will function in the following sequence.
(1) When the door opens from the closed position, the
secondary interlock switch, door sensing switch and
primary interlock relay (RY2) open their contacts. Then
the monitor switch contacts close.
(2) When the door is closed from the open position, the
monitor switch contacts open first. Then the contacts
of the secondary interlock switch and door sensing
switch close.
If the secondary interlock switch and primary interlock relay
(RY2) fail with the contacts closed when the door is opened,
the closing of the monitor switch contacts will form a short
circuit through the C/T fuse and primary interlock relay
(RY2), causing the C/T fuse to blow.
POWER LEVEL COOKING
When Variable Cooking Power is programmed, the 120
volts A.C. is supplied to the power transformer intermittently
through the contacts of relay (RY-2) which is operated by the
control unit within a 32 second time base. Microwave power
operation is as follows:
VARI-MODE
DISPLAY
ON TIME
OFF TIME
100% power
P-HI
32 sec.
0 sec.
approx. 90% power
P-90
30 sec.
2 sec.
approx. 80% power
P-80
26 sec.
6 sec.
approx. 70% power
P-70
24 sec.
8 sec.
approx. 60% power
P-60
22 sec.
10 sec.
approx. 50% power
P-50
18 sec.
14 sec.
approx. 40% power
P-40
16 sec.
16 sec.
approx. 30% power
P-30
12 sec.
20 sec.
approx. 20% power
P-20
8 sec.
24 sec.
approx. 10% power
P-10
6 sec.
26 sec.
0% power
P-0
0 sec.
32 sec.
Note:
The ON/OFF time ratio does not correspond with
the percentage of microwave power, because
approx. 3 seconds are needed for heating of the
magnetron filament.
POWER OUTPUT REDUCTION
If the oven is set for more than 20 minutes at 80, 90 or 100%
power level, after the first 20 minutes the power level will
automatically adjust itself to 70% power to avoid overcook-
ing.
