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R-254M - 5

START

AUTO MINUTE

KG / LB

CONVERSION

DELAY START

CLOCK SET

DOWN

UP

TIMER

KITCHEN

STOP

CLEAR

R-254

KG LB

TURN

STIR

PCS MICRO COOK

POWER

LEVEL

LESS

MORE

1. Place the roller stay on the floor of the oven cavity, engaging

shaft into turntable motor shaft.

2. Then place the turntable on roller stay.

5. Control panel
6. Seal packing
7. Door latch openings
8. Oven cavity
9. Door seals and sealing surfaces
10.Safety door latches
11.Ventilation openings
12.Outer case
13.Power supply cord

OVEN
1. Door
2. Door hinges
3. Waveguide cover
4. Oven lamp

3

4

1

10

7

6

2

9

8

11

5

12

13

1. DIGITAL DISPLAY
2. TIME keys
3. EXPRESS COOK keys
4. EXPRESS DEFROST keys
5. MEAL IN ONE keys
6. AUTO COOK key
7.LESS/MORE keys
8. DELAY START /CLOCK SET key
9. START/AUTO MINUTE key
10.STOP/CLEAR key
11. POWER LEVEL
12. WEIGHT CONVERSION key
13. KITCHEN TIMER key
14. WEIGHT keys

Turntable 

Roller stay

Seal packing

2

3

4

5

6

7

8
9

10

1

14

13
12
11

R-254M - 6

Closing the door activates all door interlock switches
(monitored 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
- 240V 50Hz), the noise filter and the control panel are
energized.

100P (HIGH) COOKING
When the door is closed, the contacts (COM-NO) of the
monitored latch switch and the monitor switch are closed.
When the microwave power is set to 100P position by
pressing the power level pad and cooking time is entered
by touching the time pads, the following components are
energized: H.V. transformer, Magnetron, Oven lamp, Turn-
table motor and Fan motor.

CONNECTED COMPONENTS

RELAY

Oven lamp, Fan motor, Turntable motor

RY1

High voltage transformer

RY3

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 RY1+RY3 open. The circuits to the oven
lamp, 

high voltage

 transformer, fan motor 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 switch

COM-NO

Closed

  Open

COM-NO

Closed

  Open

Monitor switch

COM-NC

Open

  Closed

Stop switch

COM-NO

Closed

  Open

The circuits to the 

high voltage

 transformer, fan motor

turntable motor, and the oven lamp are cut off when the
monitored latch switch and stop switch are made open.

6. MONITOR SWITCH CIRCUIT

The monitor switch is mechanically controlled by oven
door, and monitors the operation of the monitored latch
switch.

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

cycle of a cooking program, the monitored latch
switch and stop 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 (SW2) must be opened first.
After that the contacts (COM-NO) of the monitored
latch switch (SW1) and stop switch (SW3) are closed.

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

(COM-NO) of the monitored latch switches (SW1)
remain closed, the fuse will blow, because the con-
tacts (COM-NC) of the 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-seconds time base
through the relay contact which is coupled with the cur-
rent-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.

32 sec. ON

24 sec. ON

18 sec. ON

12 sec. ON

6 sec. ON

8 sec. OFF

14 sec. OFF

20 sec. OFF

26 sec. OFF

HIGH

MEDIUM HIGH

MEDIUM

MEDIUM LOW

LOW

Approx. 70%

100%

Approx. 50%

Approx. 30%

Approx. 10%

R-254M - 7

The door can be opened by pulling the door.

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

must be closed.

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 F1
blows immediately after closing the contacts (COM-
NC) of the monitor switch.

CAUTION: BEFORE REPLACING A BLOWN FUSE  F1

TEST MONITORED LATCH SWITCH (SW1)
AND  MONITOR SWITCH FOR PROPER
OPERATION.  (REFER TO CHAPTER “TEST
PROCEDURE”).

1. The fuse F1 blows when the contacts (COM-NO) of the

monitored latch switch remain closed with the oven
door open and when the contacts (COM-NC) of the
monitor switch are closed.

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

circuited, the fuse F1 blows to prevent an electric shock
or fire hazard.

The thermostat protects the high voltage transformer
against overheating. If the temperature goes up higher
than 150˚C because the fan motor is interrupted or the
ventilation openings are blocked, the thermostat will open
circuit.  As the HV transformer cools, the thermostate will
then close again, causing the oven operation to cycle on
and off (If operated, check the magnetron for damage.)

Latch hook

SW3: Stop switch

Door

SW2: Monitor switch

SW1:Monitored latch switch

Latch heads

The thermal cut-out located on the top of the oven cavity
is designed to prevent damage to the oven, if the food 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 turntable motor drives the turntable roller assembly 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 heating food. It is then exhausted
through the exhaust vents at the rear of the oven cavity.

The noise filter assembly prevents radio frequency inter-
ference that might flow back into the power circuit.

R-254M - 8

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 proce-
dure letter which will be found in the “Test Procedure”
section.

IMPORTANT: If the oven becomes inoperative because

of a blown fuse. Check the monitored latch
switch and monitor switch before replac-
ing the F1 fuse.

CONDITION

PROBLEM

A

B

C

D

E

E E

F G

H

I

I

J

K

L

L

M

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

Fuse F1   blows when power cord 
is plugged into wall outlet. (Timer 
off)

All letters and indicators do not 
appear in display when power cord 
is first plugged into wall outlet.

Display does not operate properly 
when Stop/Clear pad is touched. 
(Buzzer should sound and "  ;  " or 
time of day should appear in display.

Oven lamp does not light, when in 
operation. 

Fan motor does not operate. 

Turntable motor does not operate. 

Oven or 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 operate properly during 
the variable cooking condition except 
100% (HIGH) cooking condition.

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

Oven stops as soon as the oven is 
started.

Fan motor, oven lamp and 
turntable motor do not operate at 
the same time.

OFF

CONDITION

COOKING

CONDITION

TEST PROCEDURE

POSSIBLE CAUSE

AND

DEFECTIVE PARTS

MAGNETRON

HIGH VOLTAGE  TRANSFORMER

H.V. RECTIFIER

HIGH VOLTAGE CAPACITOR

MONITORED LATCH SWITCH

STOP SWITCH

MONITOR SWITCH

THERMAL CUT-OUT 125

˚C

FUSE F1

NOISE FILTER

FAN MOTOR

TURNTABLE MOTOR

POWER SUPPLY CORD

OVEN LAMP OR SOCKET

SHORTED WIRE HARNESS

OPENED WIRE HARNESS

MIS-ADJUSTMENT SWITCHES

NO POWER AT WALL OUTLET

HVT THERMOSTAT

CONTROL UNIT

KEY UNIT

RELAY RY1

RELAY RY3

FOIL PATTERN ON P.W.B.