Sharp R-8320E, Service Manual

Page: 33 / 140

MICROWAVE COOKING CONDITION
1. HIGH COOKING
Program desired cooking time and Variable Cooking
Control by touching the NUMBER pads and the “HIGH”
pad of the Variable Cooking Control.
When the
“COOK” pad is touched, the following
operations occur: (Figure 2)
l - l
l-2
l-3
l-4
l-5
l-6
l-7
l-8
l-9
The COOK and HIGH indicators light.
The numbers of the digital readout start counting
down to zero.
The coil of shut-off relay (RY2) is energized.
A. The relay contacts (A) close to provide a
current path to the oven lamps.
B. The relay contacts (B) close to provide a
current path to the turntable motor.
The coil of shut-off relay (RY3) is energized.
The relay contacts close to provide a current path
to the cooling fan motor.
The coil of cook relay is energized by the con-
trol unit and relay unit.
The relay contacts close to provide a current
path to the power transformer.
The 240 volts A.C. is supplied to the primary
winding of the power transformer and is converted
to 3.15 volts A.C. output on the flament winding.
The 3.15 volts A.C. output from filament wind-
ing heats the magnetron filament.
The 2400 volts A.C. output from the high vottage
winding of the power transformer is sent to a
voltage doubler circuit consisting of a high voltage
capacitor and a rectifier.
The 2400 volts A.C. is converted to approximate-
ly 4000 negative. D.C. voltage (peak to peak) by
the voltage doubler circuit and sent to the
magnetron tube assembly.
The negative 4000 volts D.C. is applied to the
cathode of the magnetron tube. This causes the
magnetron to oscillate and produce the 2450
MHz cooking frequency.
The RF energy produced by the magnetron tube
is channeled through the waveguide into the
cavity
and then into the cavity where
the food is placed to be cooked.
l-10 Upon completion of the cooking time, the
following results will occur:
A. The shut-off relay
will be de-ener-
gized, de-energizing the oven lamps and the
turntable motor.
B. The shut-off relay (RY3) will be de-ener-
gized, de-energizing the cooling fan motor.
C. The cook relay will be de-energized, opening
the circuit to the power transformer stop-
ping the generation of microwave energy by
the magnetron.
D. The COOK and HIGH indicators will go out,
and the time of day will reappear.
The end of cooking signal will sound, and the
oven will revert OFF condition.
l-l 1. The monitor switch is electrically monitoring the
operation of the upper latch switch and is mecha-
nically associated with the door so that it will
function in the following sequence.
(1) When the door opens from closed position,
the upper and lower latch switches first
operate to open their contacts, and then the
monitor switch contacts close.
(2) When th e door is closed from open position,
the monitor switch contacts first open, and
then the contacts of the upper and lower latch
switches close.
In case the upper latch switch fail with it contacts closed
when the door is opened, closing of the monitor switch
contacts will form a short circuit through the fuse and
upper latch switch, causing the fuse to blow,
2. MEDIUM HIGH,
M E D I U M o r M E D I U M L O W /
DEFROST COOKING
Program disired cooking time by touching the number
pad or pads and “MED HIGH”, “MED” or “MED LOW/
DEFROST” pad of variable cooking control.
When the
“COOK” pad is touched, the following
operations occur:
2-1.
2-2.
2-3.
HIGH
MED
HIGH
MED
The shut-off relays (RY2 and RY3) and cook
relay are energized.
The COOK and selected
Cooking
Control indicators light.
The 240 volts A.C. is supplied to the power trans-
former intermittently through the cook relay
contacts which is operated by the control unit
within a 32 second time base.
The microwave power operation is as follows:
s e c . - - - - - - H
sec.
MICROWAVE POWER
OFF
=Approx. 70%
ON
sec.
14 sec.
MICROWAVE POWER
=Approx. 50%
MICROWAVE POWER
30%
Note: The ON/OFF time ratio does not correspond
with the percentage of microwave power,
approx. 2 seconds are needed for
heating of the magnetron filament.
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