R-2397G (serv.man2). Complete (original copy) - Sharp Home Appliance Service Manual (repair manual). Page 6

4

Closing the door activates all door interlock switches
(1st latch switch, 2nd latch switch, 3rd latch switch and stop
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 (230 - 240  volts, 50Hz), the line
voltage is supplied to the point A5+A7 in the control panel.

1. The digital display shows      .
NOTE: When the door is opened or after cooking, oven

lamp, blower motor and stirrer motors work for 1
minute.

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/ Stirrer motors

RY1

Power transformer T1

RY3

Power transformer T2

RY4

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 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
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
stirrer 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)

1st latch switch

COM-NO

Closed

  Open

Monitor switch

COM-NC

Open

  Closed

2nd latch switch

COM-NO

Closed

  Open

Stop switch

COM-NO

Closed

  Open

3rd latch switch

COM-NO

Closed

  Open

The circuits to the high voltage transformers T1+T2 are
cut off when the 1st latch, 2nd latch, 3rd latch and stop
switches SW1+SW2+SW3+SW5 are made open. The
blower motor BM, stirrer 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
3 minutes.

6. MONITOR SWITCH CIRCUIT

The monitor switch SW4 is mechanically controlled by
oven door, and monitors the operation of the 1st latch
switch SW1.

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

of a cooking program, the 1st, 2nd, 3rd latch and stop
switches SW1+SW2+SW3+SW5 must open their con-
tacts first. After that the contacts (COM-NC) of the
monitor switch SW4 can be closed.

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

of the monitor switch SW4 must be opened first. After
that the contacts (COM-NO) of the 1st, 2nd, 3rd latch
and stop switches SW1+SW2+SW3+SW5 must be
closed.

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

1st latch switch SW1 remain closed, remains closed,
the fuse F2 F6.3A will blow, because the monitor switch
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.

48 sec. ON

Number key

44sec. ON

Number key 9

40 sec. ON

Number key 8

36 sec. ON

Number key 7

32 sec. ON

Number key 6

26 sec. ON

Number key 5

22 sec. ON

Number key 4

16 sec. ON

Number key 3

12 sec. ON

Number key 2

8 sec. ON

Number key 1

0 sec. ON

Number key 0

NOTE: The ON/OFF time ratio does not exactly corre-

spond to the percentage of microwave power, be-
cause approx. 3 seconds are needed for heating up
the magnetron filament.

Two magnetrons MG1+MG2 are equipped in order to get
higher microwave power output. The primary windings of the
high voltage transformers T1+T2 are connected so that each