R-556D (serv.man2). Complete - Sharp Home Appliance Service Manual (repair manual). Page 7

R556D

5 – 1

R556D

Service Manual

 

Closing the door activates all door interlock switches (1st. latch switch
and 2nd. interlock relay control switch).

IMPORTANT

When the oven door is closed, the monitor switch contacts (COM-NC)
must be open.

When the microwave oven is plugged in a wall outlet, rated voltage is
supplied to the noise filter and the control unit.

                                            Figure O-1 on page 12-1 

1. The display will show flashing “88:88”.

2. To set any programmes or set the clock, you must first touch the

STOP/CLEAR button.

3. “  :  “ appears in the display.

NOTE: When the oven door is opened, the oven lamp comes on at

this time.

Enter a desired cooking time by pressing the TIME keys and start the
oven by pressing START button.

Function sequence 

                           Figure O-2 on page 12-1

1. Rated 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 fila-

ment and the high voltage (2000 volts) is sent to the voltage dou-
bling circuit, where it is doubled to negative voltage of
approximately 4000 volts D.C..

3. 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.

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

(RY1+RY2) 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 door is opened during a cook cycle, the switches come to

the following condition

The circuits to the high voltage transformer, fan motor, turntable motor
and oven lamp are cut off when the 1st. latch switch and 2nd. interlock
relay control switch are made open. The oven lamp remains on even if
the oven door isopened after the cooking cycle has been interrupted,
because the relay RY1 stays closed. Shown in the display is the
remaining time.

6. MONITOR SWITCH CIRCUIT

The monitor switch is mechanically controlled b yoven door, and
monitors the operation of the 1st. latch switch and 2nd. interlock
relay.

1) When the oven door is opened during or after the cycle of a

cooking program, the 1st. latch switch and 2nd. interlock relay
control switch must open their contacts first.

After that the contacts (COM-NC) of the monitor switch can be
closed.

2) When the oven door is closed, the contacts (COM-NC) of the

monitor switch must be opened. After that the contacts of the
1st. latch switch and 2nd. interlock relay control switch are
closed.

3) When the oven door is opened and the contacts of the 1st. latch

switch and 2nd. interlock relay remain closed. The fuse F10A
will blow, because the monitor switch is closed and a short cir-
cuit is caused.

When the microwave oven is preset for variable cooking power, rated
voltage is supplied to the high voltage transformer intermittently within
a 32-second time base through the relay contact which is coupled with
the current-limiting relay. The following levels of microwave power are
given.

SETTING;

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.

After 100% power cooking mode is carried out for morethan 40 min-
utes, the power out-put is automatically re-duced to 70%.

CONNECTED COMPONENTS

RELAY

Oven lamp, Fan motor, Turntable motor 

RY1

High voltage transformer 

RY2

          CONDITION

SWITCH CONTACT 

DURING 

COOKING

DOOR OPEN 

(NO COOKING)

1st. latch switch 

COM-NO 

Closed 

Open

2nd. interlock relay   
control switch   

COM-NO Closed 

Open

Monitor switch       

COM-NC 

Open   

Closed

100P

32 sec. ON

70P

Approx. 70%

100%

24 sec. ON

8 sec. OFF

14 sec. OFF

20 sec. OFF

26 sec. OFF

50P

Approx. 50%

18 sec. ON

30P

Approx. 30%

12 sec. ON

10P

Approx. 10%

6 sec. ON