R-21AT - Sharp Home Appliance Service Manual (repair manual). Page 6

4

Closing the door activates the 1st. latch switch, 2nd. latch
switch and stop switch.

1. The oven display will show        .        .

Program desired cooking time by touching SELECT TIME
pad and the NUMBER pads. When the START pad is
touched, the following operations occur:

RELAY

CONNECTED COMPONENTS

RY-2

power transformer

RY-3

oven lamp/antenna motor/fan motor

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 2300 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 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 RY2 + RY3 go back to their home position.
The circuits to the oven lamp, high voltage transformer,
fan motor and antenna 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)

1st. interlock switch

COM-NO

Closed

Opened

Latch switch

COM-NO

Closed

Opened

2nd. interlock relay
control switch

COM-NO

Closed

Opened

Monitor Switch

COM-NC

Opened

Closed

The circuit to the high voltage transformer, fan motor, oven
lamp and antenna motor are cut off when the 1st. interlock
switch, latch switch and 2nd. interlock relay control switch
are made open. 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 1st.
interlock switch.

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

cycle of a cooking program, the  1st. interlock switch,
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.

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

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

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

1st. latch switch, 2nd. latch switch and the relay RY2
remain closed, the fuse M10A will blow, because the
monitor switch is closed  and a short circuit is caused.

When Variable Cooking Power is programmed, the line
voltage is supplied to the power transformer intermittently
through the contacts of relay (RY-2) which is operated by
the control unit within a 32 second time base. Microwave
power operation is as follows:

VARI-MODE

ON TIME

OFF TIME

Power 10(P-HI)

32 sec.

0 sec.

(100% power)
Power 9(P-90)

30 sec.

2 sec.

(approx. 90% power)
Power 8(P-80)

26 sec.

6 sec.

(approx. 80% power)
Power 7(P-70)

24 sec.

8 sec.

(approx. 70% power)
Power 6(P-60)

22 sec.

10 sec.

(approx. 60% power)
Power 5(P-50)

18 sec.

14 sec.

(approx. 50% power)
Power 4(P-40)

16 sec.

16 sec.

(approx. 40% power)
Power 3(P-30)

12 sec.

20 sec.

(approx. 30% power)
Power 2(P-20)

 8 sec.

24 sec.

(approx. 20% power)
Power 1(P-10)

 6 sec.

26 sec.

(approx. 10% power)
Power 0(P-0)

 0 sec.

32 sec.

(0% power)

Note:

The ON/OFF time ratio does not correspond with
the percentage of microwave power, because
approx. 2 seconds are needed for heating of the
magnetron filament.