R-1900M. Complete - Sharp Home Appliance Service Manual (repair manual). Page 5

R1900M

4 – 1

R1900M

Service Manual

 

The following is a description of component functions during oven operation.

(For details, refer to Figure O-1)

Closing the door activates the door sensing switch and secondary
interlock switches (1), (2). (In this condition, the monitor switches (1) &
(2) contacts are opened.) When the oven is plugged in, and the rated
voltage is supplied to the switching power supply unit through the
noise filter, (figure O-1). The switching supply unit supplies D.C. volt-
age (approx. 24V) to the relay unit. And the display will show “   .    “.

(For details, refer to Figure O-2)

Press MANUAL/ REPEAT pad. Enter cooking time by pressing the
number pads. Press the POWER LEVEL pad. Enter power level by
pressing the number pad. When the START pad is pressed, the follow-
ing operations occur: 

1. The contacts of relays are closed. And the oven lamp and the

antenna motors connected to the relays are turned on (For details,
refer to Figure O-2).

2. D.C. voltage is supplied to the fan motors, exhaust fan and exhaust

motor from the control unit.

3. Rated voltage is supplied to the primary winding of the power trans-

former and is converted to about 3.00 volts output on the filament
winding, and approximately 2320 volts on the high voltage winding.

4. The filament winding voltage heats the magnetron filament and the

H.V. winding voltage is sent to a voltage doubler circuit.

5. The microwave energy produced by the magnetron is channelled

through the waveguide into the cavity feed-box, and then into the
cavity where the food is placed to be cooked.

6. Upon completion of the cooking time, the oven will revert to the

OFF condition. The fan motors, exhaust fan and the exhaust motor
will operate at least for 1 minute.

7. When the door is opened during a cook cycle, monitor switches (1)

& (2), door sensing switch, secondary interlock switches (1), (2)
and primary interlock relay are activated with the following results.
The circuits to the high voltage components are de-energized. 

8. The monitor switch (1) is electrically monitoring the operation of the

secondary interlock switch (1) and primary interlock relay, and
monitor switch (2) is electrically monitoring the operation of the sec-
ondary interlock switch (2) and primary interlock relay, and monitor
switches (1), (2) are mechanically associated with the door so that
it will function in the following sequence.

1) When the door opens from a closed position, the contacts of the

primary interlock relay and secondary interlock switches (1), (2)
open. Then the monitor switch contacts close.

2) (When the door is closed from the open position, the monitor

switches (1), (2) contacts first open, and then the contacts of the
secondary interlock switches (1), (2) close.

If the secondary interlock switches (1), (2) and primary interlock relay
fail with their contacts closed when the door is opened, the closing of
the monitor switches (1), (2) contacts will form a short circuit through
the monitor fuse, secondary interlock switches (1), (2) and primary
interlock relay, causing the fuse F10 to blow.

When the door is opened, the contacts of the door sensing switch
open, initiating the following:

1. A signal is input to the control unit energizing the coil of shutoff

relay (RY-4).

2. The shut-off relay (RY-4) contacts close completing circuits to turn

on the oven lamp and antenna motors. 

3. If the door remains open, 60 seconds later the control unit de-ener-

gizes shut-off relay (RY-4) turning off the oven lamp and antenna
motors.

When Variable Cooking Power is programmed, the rated voltage A.C.
is supplied to the power transformer intermittently through the contacts
of relay (RY-2, RY-3). Relays RY-2 and RY-3 are operated by the con-
trol unit within an interval 54 second time base. Microwave power
operation is as follows:

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

Two magnetrons (1), (2) are equipped in order to get higher micro-
wave power output. The primary windings of the power transformers
(1), (2) are connected so that each magnetron can be oscillated alter-
natively according to the frequency of the power supply. Refer to the
Figure B-1.

Figure B-1. Operation of Magnetron

100% 54 

sec.

0 

sec.

90%      

49 sec.

5 sec.

80%      

45 sec.

9 sec.

70%      

40 sec.

14 sec.

60%      

36 sec.

18 sec.

50%      

29 sec.

25 sec.

40%      

24 sec.

30 sec.

30%      

18 sec.

36 sec.

20%      

 13 sec.

41 sec.

10%      

 9 sec.

45 sec.

0%      

 0 sec.

54 sec.

COMMERCIAL
FREQUENCY
(60HZ)

POWER OUTPUT
BY MAGNETRON 1

POWER OUTPUT
BY MAGNETRON 2

OPERATION OF
MAGNETRON