Sharp R-9H56, Service Manual

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R-9H56
4
OPERATION SEQUENCE
The following is a description of component functions during
oven operation.
Relay and Components Connection
RELAY CONNECTED COMPONENT
RY1 Oven lamp/ Turntable motor
RY2 Power transformer
RY3 Convection heater
RY4 Damper motor
RY5 Convection motor
RY6 Fan motor
OFF CONDITION
Closing the door activates all door interlock switches: upper
latch switch, lower latch switch and stop switch. (In this
condition, the monitor switch contacts are closed.)
When oven is plugged in a wall outlet (240V 50Hz), 240volts
A.C. is supplied to the control unit. (Figure O-1):
1. The display flashes “88:88”.
To set any programmes or set the clock, you must first
touch the STOP/CLEAR pad.
“ : “ appears in the display and the time counts up every
minute.
NOTE: When the oven door is opened, the oven lamp
comes on at this time.
2. A signal is input to the control unit, energizing the coil of
shut-off relay (RY4).
RY4 contacts close, completing a circuit to the damper
motor. The damper motor mow operates moving the
damper to the open position, thereby closing the contacts
of damper switch inputs a signal to the control unit.
The coil of relay RY4 is de-energized, opening its contacts,
thereby turning off the damper motor.
MICROWAVE COOKING CONDITION
HIGH COOKING
Program desired cooking time and Variable Cooking Con-
trol with the touching NUMBER pads and the POWER
LEVEL pad. When the START pad is touched, the following
operations occur:
1. The contacts of relays are closed and components
connected to relays are turned on (RY1, RY2, RY6).
(Figure O-2)
2. 240 volts A.C. is supplied to the primary winding of the
power transformer. The voltage is converted to about
3.35 volts A.C. output on the filament winding and high
voltage of approximately 2120 volts A.C. on the high
voltage winding.
3. The filament winding voltage (3.35 volts) heats the
magnetron filament and the high voltage (2120 volts) is
sent to the voltage doubling circuit.
4 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.
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 switch, upper latch switch, lower latch switch
and stop switch are activated with the following results.
The circuits to the turntable motor, cooling fan motor and
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 is electrically monitoring the operation
of the upper latch switch and lower latch switch and is
mechanically associated with the door so that it will
function in the following sequence.
1) When the door opens from a closed potion, the upper
latch switch and the lower latch switch open their contacts,
and then the monitor switch contacts close.
2) When the door is closed, from the open position, the
monitor switch contacts first open, and then the contacts
of the upper latch switch and lower latch switch must be
closed.
If the common and normal open contacts of upper latch
switch and the lower latch switch fail with their contacts
closed when the door is opened, the closing of the monitor
switch contacts will form a short circuit through the fuse,
upper latch switch and the lower latch switch, causing the
monitor fuse to blow.
MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW
COOKING
When variable cooking power is programmed, the 240 volts
A.C. is supplied to the power transformer intermittently
through the contacts of the relay (RY2) which is operated by
the control unit within a 32-second time base. Microwave
power operation is follows:
VARI MODE ON TIME OFF TIME
HIGH (100% power) 32 sec. 0 sec.
MED HIGH (approx. 70% power) 24 sec. 8 sec.
MED (approx. 50% power) 18 sec. 14sec.
MED LOW (approx. 30% power) 12 sec. 20 sec.
LOW (approx. 10% power) 6 sec. 26 sec.
NOTE: The ON/OFF time ratio does not exactly correspond
to the percentage of microwave power, because
approx. 2 seconds are needed for heating up the
magnetron filament.
CONVECTION COOKING CONDITION
PREHEATING CONDITION
Program desired convection temperature by touching the
CONVECTION pad and the temp. pad. When the START
pad is touched, the following operations occur:
1. The coil of shut-off relays RY1+RY5+RY6 are energized,
the oven lamp, cooling fan motor, turntable motor and
convection motor are turned on.