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R-21FBSTM/R-22FBSTM - 5

Turntable

Seal packing

Roller stay

1

2

The appropriate indicator will flash or light up,

just above each symbol according to the

instruction.  When an indicator is flashing, press

the required button (having the same symbol)

or do the necessary operation

Stir

Turn over

Weight

Microwave power level

Cooking in progress indicator

3.

AUTOMATIC button

Press to select one of the 12 automatic programmes.

4.

MICROWAVE POWER LEVEL button

5.

STOP button

6

START/+1 MIN button

7

TIMER/WEIGHT knob

1

Front trim

2

Oven lamp

3

Waveguide cover

4

Oven cavity

5

Door seals and sealing surfaces

6

Door opening handle

7

Fixing points(4 points)

8

Ventilation openings

9

Outer cover

10 Rear intake duct
11 Power supply cord support clip
12 Power supply cord
13 Top exhaust duct

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.

R-21FBSTM/R-22FBSTM - 6

NOTE: The ON/OFF time ratio does not exactly correspond

to the percentage of microwave power, because
approx. 3 seconds are needed for heating up the
magnetron filament.

6-1

When the oven door is opened during or after the cycle
of a cooking program, the monitored latch switch
(SW1)and stop switch (SW3) must open their
contacts(COM-NO) first. After that the contacts (COM
- NC) of the monitor switch (SW2) can be closed.

6-2

When the oven door is closed, the contacts
(COM - NC) of the monitor switch (SW2) must be
opened first. The contacts (COM - NO) of the monitored
latch switch (SW1) and stop switch (SW3) are closed
after.

6-3

When the oven door is opened and the contacts of the
monitored latch switch (SW1) remain closed, the fuse
F1 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 power transformer
intermittently within a 32-second time base through the vari
contact. The following levels of microwave power are given.
SETTING

Closing the door activates the door interlock switch (moni-
tored latch switch).

IMPORTANT
When the oven door is closed, the monitor switch contacts
COM - NC must be open.
When the microwave oven is pluged in a wall outlet (230-
240V 50Hz), the noise filter is energised.

NOTE: When the oven door is opened, the oven lamp

comes on at this time.

Enter a desired cooking time  by rotating the time/weight
knob and start the oven by touching START pad.

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

power 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 single tone is heard and

the relays RY1 + RY3 + RY4 go back to their home
position. The circuits to the oven lamp, power 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)

Monitor switch

COM-NC

Open

Closed

COM-NO

Closed

Open

Monitored latch switch

COM-NO

Closed

Open

Stop switch

COM-NO

Closed

Open

The circuits to the power transformer, fan motor and
turntable motor are cut off when the monitored latch
switch is opened. 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 the remaining time.

6. MONITOR SWITCH CIRCUIT

The monitor switch (SW2) is mechanically controlled by
oven door, and monitors the operation of the monitored
latch switch (SW1)

Oven lamp, Turntable motor

RY1

Power transformer

RY3

Fan motor

RY4

32 sec. ON

Approx. 70% = 560 Watts

100% = 800 Watts

HIGH

MEDIUM HIGH

MEDIUM

MEDIUM LOW

LOW

24 sec. ON

8 sec. OFF

14 sec. OFF

20 sec. OFF

26 sec. OFF

Approx. 50% = 400 Watts

18 sec. ON

Approx. 30% = 240 Watts

12 sec. ON

Approx. 10% = 80 Watts

6 sec. ON

R-21FBSTM/R-22FBSTM - 7

1. The fuse F1 also blows when the H.V. rectifer, H.V. wire

harness, H.V. capacitor, magnetron or secondary
winding of power transformer is shorted.

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

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

°

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 oven thermal cut-out remains closed. How-
ever, when abnormally high temperatures are reached
within the oven cavity, the oven thermal cut-out will open at
125

°

C, causing the oven to shut down. The defective ther-

mal cut-out must be replaced with a new one.

°

This thermal cut-out protects the magnetron against
overheat.
If the temperature goes up higher than 125

°

C

 because

the fan motor is interrupted or the ventilation openings are
blocked, the thermal cut-out TC02 will open and line
voltage to the high voltage transformer T will cut off and
operation of the magnetron MG will be stopped. 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 flows
through the oven cavity to remove steam and vapors given
off from the heating foods. It is then vented through the
exhaust air vents at the rear of oven cavity.

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

DOOR OPEN MECHANISM
The door can be opened by pulling the door.

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 (SW1) fail to open, fuse
F8A blows simultaneously with closing the contacts
(COM - NC) of the monitor switch (SW2).

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.

CAUTION: BEFORE REPLACING A BLOWN FUSE (F1)

TEST THE MONITORED LATCH SWITCH
(SW1) AND MONITOR SWITCH (SW2) FOR
PROPER OPERATION. (REFER TO
CHAPTER "TEST PROCEDURE".)

Latch hook

SW3: Stop switch

Door

SW2: Monitor switch

SW1:Monitored latch switch

Latch heads

R-21FBSTM/R-22FBSTM - 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 procedure
letter which will be found in the “Test Procedure” section.

IMPORTANT:

If the oven becomes inoperative because of
a blown fuse F1. Check the monitored latch
switch and monitor switch before replacing
the F8A fuse.

CONDITION 

PROBLEM

A

B

C

E

D E

E F

F

J  

I

L

J

K

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

"88:88"does not operate in display 
when power cord is plugged into wall 
outlet.

Display does not operate properly 
when STOP button is touched.

Oven lamp does not light, when door 
is opened.  (Display operates).

Oven does not start when START               

button is touched.(Display operates).

Fan motor does not operate (Oven 
lamp lights). 

Turntable motor assembly does not 
operate (Oven lamp lights). 

Oven or electrical parts does not stop 
when timer knob is at "0" or STOP 
button is touched. 

Display operates properly but all 
electrical parts do not  operate.

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

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

Oven does not seem to be operating 
properly during variable cooking 
condition(Oven operates properly at 
HIGH).

Fuse F8A blows (F1)

OFF

CONDITION

COOKING

CONDITION

TEST PROCEDURE

POSSIBLE CAUSE

AND

DEFECTIVE PARTS

MAGNETRON

HIGH VOLTAGE  TRANSFORMER

H.V. RECTIFIER ASSY

H.V.HARNESS

HIGH VOLTAGE CAPACITOR

MONITORED LATCH SWITCH

STOP SWITCH

MONITOR SWITCH

MAG THERMAL CUT--OUT 125

0

C

THERMAL CUT-OUT 125

0

C (OVEN)

FUSE F1

NOISE FILTER

TURNTABLE MOTOR

FAN MOTOR

TC TRANSFORMER

CONTROL UNIT

SWITCH UNIT

RELAY RY1,3,4

FOIL PATTERN ON P.W.B.

POWER SUPPLY CORD

SHORTED WIRE HARNESS

OPENED WIRE HARNESS

OVEN LAMP  

BLOCKED VENTILATION OPENINGS

 

WRONG OPERATION

MIS-ADJUSTMENT OF SWITCHES

HOME FUSE OR BREAKER

NO POWER AT WALL OUTLET

BLOCKED COOLING FAN

I

G H

M