Sharp R-820BK, Service Manual

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6
R-820BK
R-820BW
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 , , ,
, , , , ,
and .
To set any program or set the clock, you must first touch
the STOP/CLEAR pad. The display will clear, and " : "
will appear.
MICROWAVE COOKING CONDITION
Program desired cooking time by touching the NUMBER
pads. Program the power level by touching the POWER
LEVEL pad and then a Number pad. When the START pad
is touched, the following operations 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)
RELAY CONNECTED COMPONENTS
RY-2 Power transformer
RY-5 Fan motor
RY-6 Oven lamp/ Turntable motor
2. 120 volts A.C. is supplied to the primary winding of the
power transformer and is converted to about 3.1 volts
A.C. output on the filament winding, and approximately
2260 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,
relay (RY5), relay (RY6) and primary interlock relay(RY2)
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 secondary interlock switch and primary interlock
relay 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 relay
(RY5), primary interlock relay(RY2) and secondary
interlock switch open their contacts. And contacts of the
relay(RY6) remains closed. 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. And contacts of the relay(RY6) open.
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 monitor fuse, secondary interlock switch,
relay(RY6) and primary interlock relay(RY2), causing the
monitor fuse to blow.
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:
VARI-MODE ON TIME OFF TIME
Power 10(P-HI) 32 sec. 0 sec.
(100% power)
Power 9(P-90)
30 sec. 2 sec.
(approx. 90% power)
Power 8(P-80)
26 sec. 6 sec.
(approx. 80% power)
Power 7(P-70)
24 sec. 8 sec.
(approx. 70% power)
Power 6(P-60)
22 sec. 10 sec.
(approx. 60% power)
Power 5(P-50)
18 sec. 14 sec.
(approx. 50% power)
Power 4(P-40)
16 sec. 16 sec.
(approx. 40% power)
Power 3(P-30)
12 sec. 20 sec.
(approx. 30% power)
Power 2(P-20)
8 sec. 24 sec.
(approx. 20% power)
Power 1(P-10)
6 sec. 26 sec.
(approx. 10% power)
Power 0(P-0)
0 sec. 32 sec.
(0% power)
Note: The ON/OFF time ratio does not correspond with
the percentage of microwave power, because
approx. 2 seconds are needed for heating of the
magnetron filament.
GRILL COOKING CONDITIONS
The oven has two grill cooking conditions. They are the TOP
HEATER mode and TOP AND BOTTOM HEATER mode.