R-653. Text - Sharp Home Appliance Service Manual (repair manual). Page 4

4

R-653M -

Closing the door activates all door interlock switches
(Monitored latch switch, and stop switch.)

When the microwave oven is preset for variable cooking
power, the 240 volts is supplied to the high voltage
transformer intermittently within a 32-second time base
through the relay contact which is coupled with the
current-limiting relay RY3. The following levels of micro-
wave power are given.

32 sec. ON

24 sec. ON

18 sec. ON

12 sec. ON

6 sec. ON

8.0 sec. OFF

14 sec. OFF

20 sec. OFF

26 sec. OFF

HIGH

MEDIUM 
HIGH

MEDIUM

MEDIUM 
LOW

LOW

Approx. 70%

Approx. 50%

Approx. 30%

Approx. 10%

100%

Note:

The On/Off time ratio does not exactly corre-
spond to the percentage of microwave power,
because  approx. 2 seconds  are needed for
heating up the magnetron filament.

SETTING

Latch hook

SW3: Stop switch

Door

SW2: Monitor switch

SW1:Monitored latch switch

Latch heads

The door can be opened by pulling the door.

Figure D-1. Door Open Mechanism

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) of each switch 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,
the fuse F1 blows immediately after closing the con-

1. If the wire harness or electrical components are

short-circuited, this fuse blows to prevent an electric
shock or fire hazard.

2. The fuse also blows when monitored latch switch

remains closed with the oven door open and when
the monitor switch contact (COM-NC) closes.

3. The fuse also blows when the H.V. rectifier, H.V. wire

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

The thermal cut-out protects the oven against the over
heat during grill cooking or combi grill cooking. If the
temperature rises above 150˚C because the fan motor
is interrupted, the air inlet duct is blocked or the ventila-
tion openings are obstructed, the thermal cut-out opens
and switches off the all electrical parts. The defective
thermal cut-out  makes the contact by cooling down.

This thermal cut-out protects the high voltage trans-
former against overheating. If the temperature goes up
higher than 150˚C because the fan motor is interrupted
or the ventilation openings are blocked, the thermal cut-
out  will open and line voltage to the high voltage
transformer will cut off and operation of the magnetron
will be stopped.  The defective thermal cut-out makes
the contact by cooling down.

tacts (COM-NC) of the monitor switch (SW2).

CAUTION: BEFORE REPLACING A BLOWN FUSE  F1

TEST MONITORED LATCH SWITCH (SW1)
AND  MONITOR SWITCH (SW2) FOR
PROPER OPERATION.  (REFER TO CHAP-
TER “TEST PROCEDURE”).