Sharp R-1500AT, Service Manual

Page: 10 / 56

R1500AT
4 – 1
R1500AT
Service Manual
CHAPTER 4.
OPERATION
[1] DESCRIPTION OF OPERATING SEQUENCE
The following is a description of component functions during oven operation.
1. OFF CONDITION
1. When the oven is plugged in with the door closed, the line voltage
is supplied to the noise filter. And the display shows nothing.
(Refer to Figure O-1(a))
2. When the door is opened with plugged in, the contacts (COM-NC)
of the secondary interlock switch (1) SW1 are closed. And the line
voltage is supplied to the switching power supply unit (power unit),
the oven lamp and antenna motors. Then the switching power sup-
ply unit supplies D.C. voltage (approx.24V) to the relay unit. And
the contacts of the relay RY-4 on the relay unit are closed. The dis-
play shows “0”.
(Refer to Figure O-1(b))
3. When the door is closed, the contacts (COM-NC) of the secondary
interlock switch SW1 are opened. Because the contacts of the relay
RY-4 has been closed, the line voltage is kept supplying to the
switching power supply unit, oven lamp and antenna motors. And
the switching power supply unit keeps supplying D.C. voltage to the
relay unit. The display shows ”0”.
(Refer to Figure o-1(c))
NOTE: The contacts of the relay RY-4 will open if the oven is not oper-
ated for 3 minutes or more. And the oven condition will go
back to one of Figure O-1(a).
2. COOKING CONDITION
(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. Because the contacts of RY4
have been closed. And also the oven lamp and antenna motors will
operated at the same time.
7. When the door is opened during a cook cycle, monitor switches
SW3 & SW4, door sensing switch SW5, secondary interlock
switches SW1, SW2 and primary interlock relay RY1 are activated
with the following results. The circuits to the high voltage compo-
nents are de-energized.
8. The monitor switch SW3 is electrically monitoring the operation of
the secondary interlock switch SW1 and primary interlock relay
RY1, and monitor switch SW4 is electrically monitoring the opera-
tion of the secondary interlock switch SW2 and primary interlock
relay RY1, and monitor switches SW3, SW4 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 RY1 and the contacts (COM-NO) of sec-
ondary interlock switches SW1, SW2 open. Then the monitor
switches SW3, SW4 contacts close.
2) (When the door is closed from the open position, the monitor
switches SW3, SW4 contacts first open, and then the contacts
(COM-NO) of the secondary interlock switches SW1, SW2
close.
If the secondary interlock switches SW1, SW2 and primary interlock
relay RY1 fail with their contacts closed when the door is opened, the
closing of the monitor switches SW3, SW4 contacts will form a short
circuit through the secondary interlock switches SW1, SW2 and pri-
mary interlock relay RY1, causing the fuse F8 to blow.
3. VARIABLE POWER COOKING
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
the percentage of microwave power, because approx. 3
seconds are needed for heating of the magnetron fila-
ment.
4. TWO MAGNETRON OPERATION SYSTEM
Two magnetrons MG1, MG2 are equipped in order to get higher micro-
wave power output. The primary windings of the power transformers
T1, T2 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
VARI-MODE ON TIME OFF TIME
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 MG1
POWER OUTPUT
BY MAGNETRON MG2
OPERATION OF
MAGNETRON