R-8000GK - Sharp Home Appliance Service Manual (repair manual). Page 6

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The following is a description of component functions during
oven operation.

Closing the door activates the door sensing switch and second-
ary interlock switch and 3rd. latch switch. (In this condition, the
monitor switch contacts are opened.)

1. The display will show "   .          ".
NOTE: When the door is opened, the oven lamp comes on.

HIGH COOKING
Press the MANUAL/REPEAT key. Program desired cooking
time by touching the NUMBER keys. Then press the MICRO-
WAVE key once. When the START key is touched, the following
operations occur:

1. The contacts of relays are closed and components connected

to the relays are turned on as follows.
(For details, refer to Figure O-2)

RELAY

CONNECTED COMPONENTS

RY-1

Oven lamp/Turntable motor

RY-2

High voltage transformer

RY-5

Fan motor

2. 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.

3. 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..

4. 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.

5. 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.

6. 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)

Secondary interlock
switch

COM-NO

Closed

Opened

Door sensing switch

COM-NO

Closed

Opened

3rd. latch switch

COM-NO

Closed

Opened

Monitor Switch

COM-NC

Opened

Closed

The circuit to the high voltage transformer is cut off when the
contacts of relay RY2, and the contacts (COM-NO) of the
secondary interlock switch are made open. The circuit to the
fan motor is cut off when the relay RY5 is made open. The
circuit to the turntable motor is cut off when the contacts
(COM-NO) of the secondary interlock 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.

7. MONITOR SWITCH CIRCUIT

The monitor switch is mechanically controlled by the oven
door, and monitors the operation of the secondary interlock
switch and the relay RY2.

7-1. When the oven door is opened during or after the cycle of

a cooking program, the secondary interlock switch and the
door sensing switch must open their contacts (COM-NO)
first. After that the contacts (COM-NC) of the monitor
switch can be closed and the contacts (COM-NO) of 3rd.
latch switch are made open.

7-2. When the oven door is closed, the contacts (COM-NC) of

the monitor switch must be opened and the contacts
(COM-NO) of 3rd. latch switch must be closed. After that
the contacts (COM-NO)  of the secondary interlock switch
and the door sensing switch are made closed.

7-3. When the oven door is opened and the contacts (COM-

NO) of  the secondary interlock switch remain closed, the
fuse F10A will blow. Because the relay RY2 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 coupled with the current-limiting relay RY2. The
following levels of microwave power are given.

Press the MANUAL/REPEAT key. Program desired convection
temperature by touching the OVEN(˚C) key. When the START
key is touched, the following operations occur: (Figure O-3)
1. The coil of shut-off relays (RY1, RY3 and RY5) are energized,

the oven lamp, cooling fan motor, turntable motor and jet
motor are turned on. The contacts (COM-NO) of relay RY6
are opened.

2.  The solid-state relays are energized by the control unit and

the main supply voltage is applied to the top and side heating
elements.

32 sec. ON

100%

30sec. ON

90%

26 sec. ON

80%

24 sec. ON

 70%

22 sec. ON

60%

18 sec. ON

50%

16 sec. ON

40%

12 sec. ON

30%

8 sec. ON

20%

6 sec. ON

10%

0 sec. ON

0%