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R239(W)

5 – 1

R239(W)

Service Manual

CHAPTER 5.

OPERATION SEQUENCE

[1] OFF CONDITION

Closing the door activates all door interlock switches (1st. 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.

Figure O-1 on page 14-1

1. The display will show flashing “88:88”.

2. To set any programmes or set the clock, you must first touch the

STOP button.

3. “ : “ appears in the display.

[2] MICROWAVE COOKING CONDITION

1. HIGH COOKING

Enter a desired cooking time by rotating the TIMER/WEIGHT knob
and start the oven with pressing START/+1 min button.

Function sequence

Figure O-2 on page 14-1

1. Rated voltage is supplied to the primary winding of the high voltage

transformer T. The voltage is converted to about 3.3 volts A.C. out-
put 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 fila-

ment and the high voltage (2000 volts) is sent to the voltage dou-
bling circuit, where it is doubled to negative voltage of
approximately 4000 volts D.C..

3. The 2450 MHz microwave energy produced in the magnetron MG

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+RY2) go back to their home position. The circuits to the oven
lamp OL, high voltage transformer T, fan motor FM and turntable
motor TTM are cut off.

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

the following condition

The circuits to the high voltage transformer T, fan motor FM, turntable
motor TTM and oven lamp OL are cut off when the 1st. latch switch
SW1 and 2nd. interlock relay control switch SW3 are made open.

6. MONITOR SWITCH CIRCUIT

The monitor switch SW2 is mechanically controlled by oven door,
and monitors the operation of the 1st. latch switch SW1, the relay
RY1 and the 2nd. interlock relay RY2.

1) When the oven door is opened during or after the cycle of a

cooking program, the 1st. latch switch SW1 and 2nd. interlock
relay control switch SW3 must open their contacts first. After
that the contacts (COM-NC) of the monitor switch SW2 can be
closed.

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

monitor switch SW2 must be opened. After that the contacts of
the 1st. latch switch SW1 and 2nd. interlock relay control switch
SW3 are closed.

3) When the oven door is opened and the contacts of the 1st. latch

switch SW1, the relay RY1 and the 2nd. interlock relay RY2
remain closed. The fuse F1 T6.3A will blow, because the moni-
tor switch SW2 is closed and a short circuit is caused.

2. MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW
COOKING

When the microwave oven is preset for variable cooking power, rated
voltage is supplied to the high voltage transformer T intermittently
within a 32-second time base through the relay contact which is cou-
pled with the current-limiting relay RY2. The following levels of micro-
wave power are given.

SETTING;

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.

[3] POWER OUTPUT REDUCTION

After 100% power cooking mode is carried out for more than 20 min-
utes, the power out-put is automatically reduced 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.

CONNECTED COMPONENTS

RELAY

Oven lamp, Fan motor, Turntable motor

RY1

high voltage transformer T

RY2

CONDITION

SWITCH CONTACT

DURING

COOKING

DOOR OPEN

(NO COOKING)