Sharp R-2397, Service Manual

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4
R-2397
OFF CONDITION
Closing the door activates all door interlock switches
(1st latch switch, 2nd latch switch, 3rd latch switch and stop
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 (230 volts, 50Hz), the line voltage is
supplied to the point A5+A7 in the control panel.
Figure O-1 on page 30
1. The digital display shows .
NOTE: When the door is opened or after cooking, oven
lamp, blower motor and stirrer motors work for 1
minute.
MICROWAVE COOKING CONDITION
Touch MANUAL/ REPEAT key and enter a desired cooking
time with the touching NUMBER key. And then touch START
key.
Function sequence Figure O-2 on page 30
CONNECTED COMPONENTS RELAY
Oven lamp/ Blower motor/ Stirrer motors RY1
Power transformer (rear) RY3
Power transformer (front) RY4
1. The line voltage is supplied to the primary winding of the
high voltage transformer. The voltage is converted to
about 3.3 volts A.C. output 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 filament and the high voltage (2000 volts) is
sent to the voltage doubling circuit, where it is doubled
to negative voltage of approximately 4000 volts D.C..
3. The 2450 MHz microwave energy produced in the
magnetron 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 RY3+RY4 go back to their home position. The
circuits to the high voltage transformers. The relay RY1
remains and oven lamp, blower motor and stirrer motors
work for 1 minute.
5. When the door is opened during a cook cycle, the
switches come to the following condition.
CONDITION
DURING
DOOR OPEN
SWITCH CONTACT COOKING (NO COOKING)
1st latch switch COM-NO Closed Open
Monitor switch COM-NC Open Closed
2nd latch switch COM-NO Closed Open
Stop switch COM-NO Closed Open
3rd latch switch COM-NO Closed Open
The circuits to the high voltage transformers are cut off
when the 1st latch, 2nd latch, 3rd latch and stop switches
are made open. The blower motor, stirrer motors and
oven lamp remains on even if the oven door is opened
after the cooking cycle has been interrupted, because
OPERATION SEQUENCE
the relay RY1 stays closed. Shown in the display is the
remaining time, but the program is cancelled if the oven
is not started within 3 minutes.
6. MONITOR SWITCH CIRCUIT
The monitor switch is mechanically controlled by oven
door, and monitors the operation of the 1st latch switch.
6-1. When the oven door is opened during or after the cycle
of a cooking program, the 1st, 2nd, 3rd latch and stop
switches must open their contacts first. After that the
contacts (COM-NC) of the monitor switch can be
closed.
6-2. When the oven door is closed, the contacts (COM-NC)
of the monitor switch must be opened first. After that
the contacts (COM-NO) of the 1st, 2nd, 3rd latch and
stop switches must be closed.
6-3. When the oven door is opened and the contacts of the
1st latch switch remain closed, remains closed, the
fuse F6.3A will blow, because the monitor switch is
closed and a short circuit is caused.
MICROWAVE VARIABLE COOKING
When the microwave oven is preset for variable cooking
power, the line voltage is supplied to the high voltage
transformers intermittently within a 48 second time base
through the contacts of the relays RY3+RY4.
The following levels of microwaves power are given.
48 sec. ON
Number key
44sec. ON
Number key 9
40 sec. ON
Number key 8
36 sec. ON
Number key 7
32 sec. ON
Number key 6
26 sec. ON
Number key 5
22 sec. ON
Number key 4
16 sec. ON
Number key 3
12 sec. ON
Number key 2
8 sec. ON
Number key 1
0 sec. ON
Number key 0
NOTE: The ON/OFF time ratio does not exactly corre-
spond to the percentage of microwave power, be-
cause approx. 3 seconds are needed for heating up
the magnetron filament.
TWO MAGNETRON OPERATION SYSTEM
Two magnetrons MG1+MG2 are equipped in order to get
higher microwave power output. The primary windings of the
high voltage transformers T1+T2 are connected so that each
magnetron can be oscillated alternatively according to the
frequency of the power supply. Refer to the Figure 1 and 2.