R-959SLMAA - Sharp Home Appliance Service Manual (repair manual). Page 8

R-959(SL)M-AA

5 – 1

R959(SL)MA

Closing the door activates the monitored latch switch and the stop
switch.

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 monitored latch

switch are closed and the control unit is energized. Then contacts
of relays RY1 and RY5 are closed, and the oven lamp will light and
the display will show “  . 0” . (Fig. O-1(b)).

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

switch are opened and the contacts of relay RY1 are opened and
the oven lamp will be turned off. The display will show " . 0". (Fig.
O-1(c)).

NOTE: Energy save mode

1) If the oven has not been used for more than 3 minutes, the

contacts of the relay RY5 will be opened and the control
unit will be not energized. Open and close the door, the
control unit will resume.

Enter a desired cooking time by touching the TIME keys and start the
oven by touching START key.

                           Figure O-2 on page 14-1

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

age 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 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 + RY6 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.

The circuit to the high voltage transformer is cut off when the contacts
of relay RY2, and the contacts (COM-NO) of the monitored latch
switch and monitor switch are made open. The circuit to the fan motor
is cut off when the relay RY6 is made open. The circuit to the turntable
motor is cut off when the contacts (COM-NO) of the monitored latch
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 stays closed. Shown in the display is remaining time.

6. MONITOR SWITCH CIRCUIT

The monitor switch is mechanically controlled by the oven door,
and monitors the operation of the monitored latch switch.

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

cooking program, the monitored latch switch and stop switch
must open their contacts (COM-NO) first. And the contacts
(COM-NC) of the monitored latch switch are made closed. After
that the contacts (COM-NC) of the monitor switch can be closed
and the contacts (COM-NO) of monitor switch are made open.

2) When the oven door is closed, the contacts (COMNC) of the

monitor switch must be opened and the contacts (COM-NO) of
monitor switch must be closed. After that the contacts (COM-
NO) of the monitored latch switch and the stop switch are made
closed. And the contacts (COM-NC) of the monitored latch
switch are made open.

3) 6-3. When the oven door is opened and the contacts (COM-NO)

of the monitored latch switch remain closed, the fuse F8A will
blow. Because the relay RY1 and monitor switch are closed and
a short circuit is caused.

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 cou-
pled with the current-limiting relay RY2. The following levels of micro-
wave 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.

CONNECTED COMPONENTS

RELAY

Oven lamp, Turntable motor 

RY1

High voltage transformer 

RY2

6

Y

R

 ,

r

o

t

o

m

 

n

a

F

          CONDITION

SWITCH CONTACT 

DURING

COOKING

DOOR OPEN 

(NO COOKING)

Monitored latch 
switch 

COM-NO
COM-NC 

Closed

Opened

Opened

Closed

Stop switch   

COM-NO 

Closed 

Opened

Monitor switch        

COM-NO
COM-NC 

Closed

Opened   

Opened

Closed

100% (HIGH)

32 sec. ON

70% (MEDIUM

HIGH)

Approx. 70%

100%

24 sec. ON

8 sec. OFF

14 sec. OFF

20 sec. OFF

26 sec. OFF

%

0

5

.

x

o

r

p

p

A

)

M

U

I

D

E

M

(

%

0

5

18 sec. ON

30% (MEDIUM

LOW)

Approx. 30%

12 sec. ON

%

0

1

.

x

o

r

p

p

A

)

W

O

L

(

%

0

1

6 sec. ON