Sharp R-671 Service Manual download pdf (Page 10)

R-671 - 9

OPERATION SEQUENCE

OFF CONDITION

Closing the door activates the primary latch switch and the

stop switch.

IMPORTANT:

When the oven door is closed, the contacts COM-NC

of the monitor switch must be open. When the micro-

wave oven is plugged in a wall outlet (230V / 50Hz), the

line voltage is supplied to the noise filter.

Figure O-1 on page 32

1. The control unit is not energized. The display shows

nothing (Fig. O-1 (a)).

2. Open the door. The contacts (COM-NC) of the primary

latch switch are closed and the control unit is ener-

gized. Then contacts of relays RY1 and RY6 are

closed, and the oven lamp will light and the display will

flash (Fig. -1(b)).

3. Close the door. The contacts (COM-NC) of the primary

latch switch are opened and the oven lamp will be

turned off. The display will stop flashing (Fig. O-1(c)).

NOTE: Energy save mode

1. If the oven has not been used for more than 2 minutes,

the contacts of the relay RY6 will be opened and the

control unit will be not energized. Open and close the

door, the control unit will resume.

2. If the clock is set, this energy save mode does not work.

MICROWAVE COOKING CONDITION

HIGH COOKING

Select the microwave cooking mode with the COOKING

MODE selector. Enter a desired cooking time by turning

the TIME/WEIGHT dial and start the oven by pressing

START button.

Function sequence Figure O-2 on page 33

CONNECTED COMPONENTS RELAY

Oven lamp, Turntable motor RY1

High voltage transformer RY2

Grill heating element (Top) RY3

Bottom heating element RY4

Fan motor RY5

Control unit RY6

1. The line voltage is supplied to the primary winding of

the high voltage transformer. The voltage is converted

to about 3.3 volts A.C. output on the filament winding

and high voltage of approximately 2000 volts A.C. on

the secondary winding.

2. The filament winding voltage (3.3 volts) heats the

magnetron filament and the high voltage (2000 volts) is

sent to the voltage doubling circuit, where it is doubled

to negative voltage of approximately 4000 volts D.C..

3. The 2450 MHz microwave energy produced in the

magnetron generates a wavelength 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.

4. When the cooking time is up, a signal tone is heard and

the relays RY1 + RY2 + RY5 go back to their home

position. The circuits to the oven lamp, high voltage

transformer, fan motor and turntable motor are cut off.

5. When the oven door is opened during a cooking cycle,

the switches come to the following condition.

Switch Contact Condition

During Oven Door

Cooking Open(No cooking)

COM-NO Closed Opened

Primary latch Switch

COM-NC Opened Closed

Stop switch

COM-NO Closed Opened

Monitor Switch

COM-NC Opened Closed

The circuit to the high voltage transformer, fan motor and

turntable motor are cut off when the primary latch switch

and stop switch are made open. The oven lamp remains

on even if the oven door is opened after the cooking cycle

has been interrupted, because the relay RY1 stay closed.

Shown in the display is remaining time.

6. MONITOR SWITCH CIRCUIT

The monitor switch SW3 is mechanically controlled by

the oven door, and monitors the operation of the

primary latch switch SW1.

6-1. When the oven door is opened during or after the

cycle of a cooking program, the contacts (COM-NO)

of the primary latch switch SW1 and stop switch SW2

must open their contacts first. After that the contacts

(COM-NC) of the monitor switch SW3 can be closed.

6-2. When the oven door is closed, the contacts (COM-

NC) of the monitor switch SW3 must be opened. After

that the contacts (COM-NO) of the primary latch

switch SW1 and the stop switch SW2 are closed.

6-3. When the oven door is opened and the contacts

(COM-NO) of the primary latch switch SW1 remain

closed, the fuse F2 F8A will blow, because the moni-

tor switch is closed and a short circuit is caused.

MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW

COOKING

When the microwave oven is preset for variable cooking

power, the line voltage is supplied to the high voltage

transformer intermittently within a 32-second time base

through the relay contact which is coupled with the cur-

rent-limiting relay RY2. The following levels of microwave

power are given.

SETTING

800P100%

560P 70%

400P 50%

240P 30%

80P 10%

32 sec. ON

Approx. 100%

24 sec. ON 8 sec. OFF

Approx. 70%

18 sec. ON 14 sec. OFF

Approx. 50%

12 sec. ON 20 sec. OFF

Approx. 30%

6 sec. ON 26 sec. OFF

Approx. 10%

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.

GRILL COOKING CONDITION

The oven has three grill cooking condition. They are the

TOP GRILL mode, BOTTOM GRILL mode and TOP AND

BOTTOM GRILL mode.

1 2 ... 5 6 7 8 9 10 11 12 13 14 15 ... 44 45

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Sharp R-671 Service Manual Page 10

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