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CHAPTER 5.

R990K(W)

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

[1] OFF CONDITION

Closing the door activates all door interlock switches: upper latch

switch, lower latch switch and stop switch. (In this condition, the moni-

tor switch contacts are closed.) When oven is plugged in a wall outlet

(230 - 240V, 50Hz), rated voltage is supplied to the control unit.

Figure O-1 on page 12-1

1. The display flashes "SHARP", "MICRO-", "WAVE",'OVEN".

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 now operates moving the damper to the open posi-

tion, 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.

[2] MICROWAVE COOKING CONDITION

1. HIGH COOKING

Enter cooking time by pressing the NUMBER pads and then select

microwave cooking and power level by pressing 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)

Figure O-2 on page 12-1

2. Rated voltage is supplied to the primary winding of the power trans-

former. The voltage is converted to about3.3 volts A.C. output on

the filament winding and high voltage of approximately 2260 volts

A.C. on the high voltage winding.

3. The filament winding voltage (3.3 volts) heats the magnetron fila-

ment and the high voltage (2260 volts) is sent to the voltage dou-

bling circuit.

4. The 2450 MHz microwave energy produced in the magnetron gen-

erates 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.

Service Manual

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 asso-

ciated 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.

2. MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW

COOKING

When variable cooking power is programmed, the rated voltage is sup-

plied to the power transformer intermittently through the contacts of

the relay (RY2) which is operated by the control unit within a 32-sec-

ond time base. Micro-wave power operation is follows:

SETTING;

VARI MODE

HIGH (100% power)

MED HIGH (approx. 70% power)

MED (approx. 50% power)

MED LOW (approx. 30% power)

LOW (approx. 10% power)

NOTE: The ON/OFF time ratio does not exactly correspond to the

percentage of microwave power, because approx. 3 seconds

are needed for heating up the magnetron filament.

[3] CONVECTION COOKING CONDITION

1. PREHEATING CONDITION

Press the PREHEAT pad and then select preheating temperature by

pressing the temperature 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.

2. he coil of relay (RY4) is energized by the CPU unit.The damper is

moved to the closed position, opening the damper switch contacts.

The opening of the dampers witch contacts sends a signal to the

LSI on the CPU unit de-energizing the relay (RY4) and opening the

circuit to the damper motor.

3. The coil of heater relay (RY3) is energized by the CPU unit and the

main supply voltage is added to the convection heater.

4. When the oven temperature reaches the selected preheat temper-

ature, the following operations occur:

1) The heater relay (RY3) is de-energized by the CPU unit temper-

ature circuit and thermistor, opening the circuit to the convection

heater.

5 – 1

R990K(W)

ON TIME

OFF TIME

32 sec.

0 sec.

24 sec.

8 sec.

18 sec.

14sec.

12 sec.

20 sec.

6 sec.

26 sec.