R-242M - Sharp Home Appliance Service Manual (repair manual). Page 5

R-242M - 5

1.  When the oven door is opened, the oven lamp comes on

at this time.

2. When the cooking time is up, a single tone is heard and

the relays RY1 + RY2 go back to their home position.
The circuits to the oven lamp, power transformer, fan
motor and turntable motor are cut off.

CONNECTED COMPONENTS

RELAY

Oven lamp, Fan motor, Turntable motor

RY1

Power transformer

RY2

CONDITION

DURING

DOOR OPEN

SWITCH

CONTACT

COOKING

(NO COOKING)

Monitor switch

COM-NC

Open

Closed

Monitored latch switch

COM-NO

Closed

Open

Stop switch

COM-NO

Closed

Open

3. When the door is opened during a cook cycle, the

switches come to the following condition.

The circuits to the power transformer, fan motor and
turntable motor are cut off when the monitored latch switch
and stop switch are made open.
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.

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
relay contact which is coupled with the current-limiting relay
(RY2). The following levels of microwave power are given.
SETTING

MEDIUM HIGH

MEDIUM LOW

Approx. 10% = 80 Watts

32 sec. ON

6 sec. ON

12 sec. ON

18 sec. ON

24 sec. ON

26 sec. OFF

20 sec. OFF

14 sec. OFF

8 sec. OFF

LOW

MEDIUM

HIGH

Approx. 70% = 560Watts

Approx. 50% = 400 Watts

Approx. 30% = 240 Watts

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.

Approx. 100% = 800 Watts

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 he 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 closes.

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 cycle,
line voltage to the high voltage transformer will also cycle.
(If operated, check the magnetron for damage.)

Latch hook

SW3: Stop switch

Door

SW2: Monitor switch

SW1: Monitored latch switch

Latch heads