R420LW
6 – 1
R420LW
Service Manual
CHAPTER 6.
OPERATION
[1] DESCRIPTION OF OPERATING SEQUENCE
The following is a description of component functions during oven operation.
1. OFF CONDITION
Closing the door activates the door sensing switch and primary inter-
lock 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 “ENJOY YOUR OVEN PRESS CLEAR AND
PRESS CLOCK”.
To set any program or set the clock, you must first touch the STOP/
CLEAR pad. The display will clear, and " : " will appear.
2. COOKING CONDITION
Program desired cooking time by touching the NUMBER pads. Pro-
gram the power level by touching the POWERLEVEL pad and then a
Number pad. When the START pad is touched, the following opera-
tions occur:
1) The contacts of relays are closed and components connected to
the relays are turned on as follows.
(For details, refer to Figure O-2)
2) 120 volts A.C. is supplied to the primary winding of the power trans-
former and is converted to about 3.3 volts A.C. output on the fila-
ment winding, and approximately 2370 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, the monitor witch,
door sensing switch, primary interlock switch, relay (RY1) and sec-
ondary interlock relay are activated with the following results. The
circuits to the turntable motor, the cooling fan motor, and the high
voltage components are de-energized, the oven lamp remains on,
and the digital read-out displays the time still remaining in the cook
cycle when the door was opened.
7) The monitor switch electrically monitors the operation of the pri-
mary interlock switch and secondary interlock relay and is mechan-
ically associated with the door so that it will function in the following
sequence.
a) When the door opens from the closed position, the secondary
interlock relay (RY2) and primary interlock switch open their
contacts. And contacts of the relay (RY1) remains closed. Then
the monitor switch contacts close.
b) When the door is closed from the open position, the monitor
switch contacts open first. Then the contacts of the primary
interlock switch and door sensing switch close. And contacts of
the relay (RY1) open.
If the primary interlock switch and secondary 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 monitor
fuse, primary interlock switch, relay (RY1) and secondary interlock
relay (RY2), causing the monitor fuse to blow.
3. POWER LEVEL P-0 TO P-90 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:
NOTE:
The ON/OFF time ratio does not correspond with the per-
centage of microwave power, because approx. 3 seconds
are needed for heating of the magnetron filament.
4. POWER OUTPUT REDUCTION
After 80%, 90% or 100% power cooking mode is carried out for more
than 30 minutes, the power out-put is automatically reduced to 70%.
5. SENSOR COOKING CONDITION
Using the SENSOR unction, the food is cooked without figuring time,
power level or quantity. When the oven senses enough steam from the
food, it relays the information to its microprocessor which will calculate
the remaining cooking time and power level needed for best results.
When the food is cooked, water vapor is developed. The sensor
“senses” the vapor and its resistance increases gradually. When the
resistance reaches the value set according to the menu, supplemen-
tary cooking is started. The time of supplementary cooking is deter-
mined by experiment with each food category and inputted into the
LSI.
An example of how sensor works: (POTATOES)
1. Potatoes at room temperature. Vapor is emitted very slowly.
2. Heat potatoes. Moisture and humidity is emitted rapidly. You can
smell the aroma as it cooks.;
RELAY CONNECTED
COMPONENTS
RY-1
oven lamp/turntable motor/fan motor
RY-2 power
transformer
VARI-MODE ON
TIME
OFF
TIME
P-HI (100% power)
32 sec.
0 sec.
P-90 (approx. 90% power)
30 sec.
2 sec.
P-80 (approx. 80% power)
26 sec.
6 sec.
P-70 (approx. 70% power)
24 sec.
8 sec.
P-60 (approx. 60% power)
22 sec.
10 sec.
P-50 (approx. 50% power)
18 sec.
14 sec.
P-40 (approx. 40% power)
16 sec.
16 sec.
P-30 (approx. 30% power)
12 sec.
20 sec.
P-20 (approx. 20% power)
8 sec.
24 sec.
P-10 (approx. 10% power)
6 sec.
26 sec.
P-0 (0% power)
0 sec.
32 sec.
MICROWA
VE
