DOWNLOAD Sharp R-246 (serv.man2) Service Manual ↓ Size: 1.06 MB | Pages: 32 in PDF or view online for FREE

3

7. Coupling
8. Control panel
9. Waveguide cover

10. Power supply cord
11. Turntable
12. Roller stay

1. Ventilation openings
2. Oven lamp
3. Door hinges
4. Door safety latches
5. See through door
6. Door seals sealing surfaces

DIGITAL READOUT

INDICATOR

EXPRESS COOK key

EXPRESS DEFROST key

START / AUTO MINUTE key

STOP / CLEAR key

POWER / WEIGHT key

TIME keys

9

2

5

4

4

7

11

3

6

8

12

10

1

4

Closing the door activates all door interlock switches
(monitored latch switch, 2nd. interlock relay control 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, rated
voltage is supplied to the noise filter and the control unit.

1. The display will show flashing "88:88".
2. To set any programmes or set the clock, you must

first touch the STOP/CLEAR pad.

3.        :        appears in the display.

HIGH COOKING
Enter a desired cooking time with the touching TIME keys
and start the oven with touching STARTkey.

CONNECTED COMPONENTS

RELAY

Oven lamp, Fan motors, Turntable motor

RY1

High voltage transformer

RY2

1. Rated 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 channeled 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 go back to their home position.
The circuits to the oven lamp, high voltage transformer,
fan motors and turntable motor are cut off.

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)

Monitored latch switch COM-NO

Closed

  Open

2nd. interlock relay
control switch

COM-NO

Closed

  Open

Monitor switch

COM-NC

Open

  Closed

The circuits to the high voltage transformer, fan mo-
tors, turntable motor and oven lamp are cut off when
the monitored latch switch  and 2nd. interlock relay
control switch are made open.

6.

MONITOR SWITCH CIRCUIT
The monitor switch is mechanically controlled by
oven door, and monitors the operation of the moni-
tored latch switch and the relay RY1.

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

cycle of a cooking program, the monitored 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 monitored latch switch and 2nd.
interlock relay control switch are closed.

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

the monitored latch switch remain closed, the fuse
T6.3A will blow, because the monitor switch is closed
and a short circuit is caused.

When the microwave oven is preset for variable cooking
power, rated voltage is supplied to the power 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.

SETTING;

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

spond to the percentage of microwave power,
because approx. 3 seconds are needed for heat-
ing up the magnetron filament.

After 100% power cooking mode is carried out for more
than 20 minutes, the power out-put is automatically re-
duced to 70%.  Even if the cooking time is shorter than for
20 minutes, the power output is reduced to 70% after total
cooking time over 20 minutes when the oven is started in
100% power cooking mode again within 1 minute and 35
seconds.

100P (HIGH)

32 sec. ON

70P (MEDIUM 

HIGH)

Approx. 70%

100%

24 sec. ON

8 sec. OFF

14 sec. OFF

20 sec. OFF

26 sec. OFF

50P (MEDIUM)

Approx. 50%

18 sec. ON

30P (MEDIUM 

LOW)

Approx. 30%

12 sec. ON

10P (LOW)

Approx. 10%

6 sec. ON

5

The thermal cut-out located on the top of the oven cavity
is designed to prevent damage to the oven if the foods in
the oven catch fire due to over heating produced by
improper setting of cook time or failure of control unit.
Under normal operation, the thermal cut-out remains
closed. However, when abnormally high temperatures are
reached within the oven cavity, the thermal cut-out will
open at 125˚C, causing the oven to shut down. The
defective thermal cut-out must be replaced with a new
one.

The thermal cut-out located on the top of the oven cavity
is designed to prevent damage to the magnetron if an over
heated condition develops in the tube due to cooling fan
failure, obstructed air guide, dirty or blocked air intake, etc.
Under normal operation, the thermal cut-out remains
closed. However, when abnormally high temperatures are
reached within the magnetron, the thermal cut-out will
open at  95˚C, causing the oven to shut down. When the
magnetron has cooled  to 75˚C, the thermal cut-out closes
and cook cycle will resume.

The turntable motor drives the roller stay to rotate the
turntable.

The fan motor drives a blade which draws external cool air.
This cool air is directed through the air vanes surrounding
the magnetron and cools the magnetron. This air is chan-
nelled through the oven cavity to remove steam and
vapours given off from the heating foods. It is then ex-
hausted through the exhausting air vents at the oven
cavity.

The noise filter prevents the radio frequency interference
that might flow back in the power circuit.

The door is opened by pulling the door, refer to the Figure
D-1.

1. When the oven door is closed, the contacts (COM-NO)

must be closed.

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

NO) must be opened.

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

must be opened.

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

NC) must be closed.

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

of the monitored latch switch fail to open, the fuse
T6.3A blows simultaneously with closing the contacts
(COM-NC) of the monitor switch .

CAUTION: BEFORE REPLACING A FUSE TEST THE

MONITORED LATCH SWITCH AND
MONITOR SWITCH   FOR PROPER OP-
ERATION. (REFER TO CHAPTER "TEST
PROCEDURE".)

1. The fuse T6.3A blows when the contacts (COM-NO) of

the monitored latch switch remain closed with the oven
door open and when the monitor switch   closes.

2. If the wire harness or electrical components are short-

circuited, the fuse T6.3A blows to prevent an electric
shock of fire hazard.

The high voltage fuse blows when the high voltage rectifier
or the magnetron is shorted.

Latch Heads

Latch Hook

Door

Monitor
Switch

Monitored
Latch
Switch

2nd. Interlock
Relay Control
 Switch

6

When troubleshooting the microwave oven, it is helpful to
follow the Sequence of Operation in performing the
checks. Many of the possible causes of trouble will require
that a specific test be performed. These tests are given a
procedure letter which will be found in the "Test Procedure
"section.

IMPORTANT: If the oven becomes inoperative because

of a blown fuse T6.3A in the monitored
latch switch  - monitor switch  circuit, check
the monitored latch switch and monitor
switch  before replacing the fuse T6.3A.

CK = Check / RE = Replace

MAGNETRON

HIGH VOLTAGE TRANSFORMER

H.V. RECTIFIER ASSEMBLY

HIGH VOLTAGE WIRE

HIGH VOLTAGE CAPACITOR

MONITORED. LATCH SWITCH

2ND. INTERLOCK RELAY CONTROL

SWITCH

MONITOR SWITCH

THERMAL CUT-OUT 125˚C (OVEN)

THERMAL CUT-OUT 95˚C (MG)

FAN MOTOR

TURNTABLE MOTOR

FUSE T6.3A

TOUCH CONTROL PANEL

RELAY (RY-1)

RELAY (RY-2)

FOIL PATERN ON P.W.B.

POWER SUPPLY CORD

SHORTED WIRE HARNESS

OPENED WIRE HARNESS

OVEN LAMP

WALL OUTLET

MISADJUSTMENT SWITCH

HOME FUSE OR BREAKER

BLOCKED COOLING FAN

BLOCKED VENTILATION

NOISE FILTER

KEY UNIT

H.V. FUSE

Home fuse blows when power
supply cord is plugged into
wall outlet.

FUSE T6.3A blows when
power supply cord is plugged
into wall outlet.

"88:88" does not appear in
display but power supply cord
is plugged into wall outlet.

Display  does not operate
properly when STOP/CLEAR
pad is touched.

Oven does not start when the
START pad is touched.
(Display appears)

Oven lamp does not light
(Display appears.)

Fan motor does not operate.
(Display appears.)

Turntable motor does not
operate. (Display appears.)

Oven or any electrical parts
does not stop when cooking
time is 0 or STOP/CLEAR pad
is touched.

Oven seems to be operating
but little or no heat is produced
in oven load. (Microwave
power level is set at HIGH)

Oven does not seems to be
operating properly when 70%,
50%, 30% or 10% is set. (Oven
operates properly at 100%
when the STOP/CLEAR pad
is touched the oven stops.)

Oven goes into cook cycle but
shuts down before end of
cooking cycle.

OFF
CONDITION

PROBLEM

CONDITION

POSSIBLE CAUSE

AND

DEFECTIVE PARTS

TEST PROCEDURE

ON
CONDITION

A B C

CK

D E

E E F F G G H K M   M N

RECKCKRE CKCKCKCKCK

I L J