R-24AT. R22AT and R24AT Alternative - Sharp Home Appliance Service Manual (repair manual). Page 6

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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 RY3+RY4 go back to their home position.
The circuits to the high voltage transformers T1+T2.
The relay RY1 remains and oven lamp, blower motor
and antenna motors work for 1 minute.

5. When the door is opened during a cook cycle, the

switches come to the following condition.

            CONDITION
DURING

DOOR OPEN

SWITCH

CONTACT

COOKING

(NO COOKING)

Interlock switches COM-NO

Closed

  Open

Monitor switches

COM-NC

Open

  Closed

Stop switch

COM-NO

Closed

  Open

The circuits to the high voltage transformers T1+T2
are cut off when the interlock and stop switches
SW1+SW2+SW5 are made open. The blower motor
BM, antenna motors and 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 the remaining time, but the
program is cancelled if the oven is not started within 1
minute.

6. MONITOR SWITCH CIRCUIT

The monitor switches SW3+SW4 are mechanically
controlled by oven door, and monitors the operation of
the interlock switches SW1+SW2.

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

cycle of a cooking program, the interlock switches
SW1+SW2 and stop switches SW5 must open their
contacts first. After that the contacts (COM-NC) of the
monitor switches SW3+SW4 can be closed.

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

NC) of the monitor switches SW3+SW4 must be
opened first. After that the contacts (COM-NO) of the
interlock switches SW1+SW2 and stop switch SW5
must be closed.

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

interlock switch SW1 (or SW2) remain closed, re-
mains closed, the fuse F1 F10A (or F2 F10A)  will
blow, because the monitor switch SW3 (or SW4) is
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
transformers T1+T2 intermittently within a 48 second time
base through the contacts of the relays RY3+RY4.
The following levels of microwaves power are given.

Closing the door activates all door interlock switches
(interlock switches and stop switch).

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 (230 - 240 volts, 50Hz), the line
voltage is supplied to the control unit through the noise
filter.

1. The digital display shows      .

When the door is opened, the contacts of the interlock
switches SW1+SW2 and stop switch SW5 open, initiating
the following:

1. A signal is input to the control unit energizing the coil of

shut-off relay RY-1.

2. The shut-off relay RY-1 contacts close completing

circuits to turn on the oven lamp, blower motor and
antenna motors.

3. If the door remains open, 60 seconds later the control

unit de-energizes shut-off relay RY-1 turning off the
oven lamp, blower motor and antenna motors.

When the door is closed, the contacts of the interlock
switches SW1+SW2 and stop switch SW5 close. With the
closing of the stop switch SW5 contacts, an additional
circuit is provided which will permit the operation of the
oven when one of the touch pads is depressed. Since the
control is enabled through the stop switch SW5, the door
must be closed before the touch pads will be effective.
When the door is closed, a full 60 second IDLE condition
is always provided for selecting and pressing the desired
touch pads. A 60 second IDLE condition will also follow the
end of each cook cycle.

Touch MANUAL/REPEAT key and enter a desired
cooking time with the touching NUMBER key. And then
touch START key.

CONNECTED COMPONENTS

RELAY

Oven lamp/ Blower motor/ Antenna motors

RY1

High voltage transformer T1

RY3

High voltage transformer T2

RY4

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

the two high voltage transformers. 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