Sharp R-890SLM, Service Manual

Page: 7 / 47

R-890SLM
[1] OFF CONDITION
Closing the door activates the monitored latch switch and the
stop switch.
IMPORTANT
When the oven door is closed, the contacts COM-NC of the
monitor switch must be open. When the microwave oven is
plugged in a wall outlet (230 - 240V / 50Hz), the line voltage
is supplied to the noise filter.
Figure O-1 on page 13-1
1. The control unit is not energized. The display shows nothing
(Fig. O-1 (a)).
2. Open the door. The contacts (COM-NC) of the monitored
latch switch are closed and the control unit is energized.
Then contacts of relays RY1 and RY5 are closed, and the
oven lamp will light and the display will show “ENERGY
SAVE MODE TO CANCEL ENERGY SAVE MODE SET THE
CLOCK” (Fig. O-1(b)).
3. Close the door. The contacts (COM-NC) of the monitored
latch switch are opened and the contacts of relay RY1 are
opened and the oven lamp will be turned off. The display will
show “ . 0”. (Fig. O-1(c)).
NOTE: Energy save mode
1) If the oven has not been used for more than 3 min-
utes, the contacts of the relay RY5 will be opened
and the control unit will be not energized.
Open and close the door, the control unit will resume.
2) If the clock is set, this energy save mode does not work.
[2] MICROWAVE COOKING CONDITION
1. HIGH COOKING
Press MICRO POWER button. And enter the cooking time by
rotate ENCODER dial. And start the oven by press START button.
Function sequence
Figure O-2 on page 13-2
CONNECTED COMPONENTS RELAY
Oven lamp, Turntable motor RY1
High voltage transformer RY2
Fan motor, RY6
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 wavelength of 12.24cm. 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 RY1 + RY2 + RY6 go back to their home position. The
circuits to the oven lamp, high voltage transformer, fan motor
and turntable motor are cut off.
5. When the oven door is opened during a cooking cycle, the
switches come to the following condition.
CHAPTER 5. OPERATION SEQUENCE
SWITCH CONTACT
CONDITION
DURING
COOKING
DOOR OPEN
(NO COOKING)
Monitored latch
switch
COM-NO
COM-NC
Closed
Opened
Opened
Closed
Stop switch COM-NO Closed Opened
Monitor switch
COM-NO
COM-NC
Closed
Opened
Opened
Closed
The circuit to the high voltage transformer is cut off when the
contacts of relay RY2, and the contacts (COM-NO) of the moni-
tored latch switch and monitor switch are made open. The circuit
to the fan motor is cut off when the relay RY6 is made open.
The circuit to the turntable motor is cut off when the contacts
(COM-NO) of the monitored latch switch are made open. The
relay RY2 and RY6 are made open when the door is opened.
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 remaining time.
6. MONITOR SWITCH CIRCUIT
The monitor switch is mechanically controlled by the oven
door, and monitors the operation of the monitored latch switch.
1) When the oven door is opened during or after the cycle of
a cooking program, the monitored latch switch and stop
switch must open their contacts (COM-NO) first. After that
the contacts (COM-NC) of the monitor switch and monitored
latch can be closed.
2) When the oven door is closed, the contacts (COM-NC) of
the monitor switch SW3 must be opened and the contacts
(COM-NO) of monitor switch must be closed. After that the
contacts (COM-NO) of the monitored latch switch and the
stop switch are made closed, and the contacts (COM-NC)
of the monitored latch switch are made open.
3) When the oven door is opened and the contacts (COM-NO)
of the monitored latch switch remain closed, the fuse F8A
will blow. Because the relay RY1 and monitor switch are
closed and a short circuit is caused.
2. MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW
COOKING
When the microwave oven is preset for variable cooking power,
the line voltage 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 RY2. The
following levels of microwave power are given.
SETTING;
100P (HIGH)
32 sec. ON
70P
(MEDIUM HIGH)
Approx. 70%
100%
24 sec. ON 8 sec. OFF
14 sec. OFF
20 sec. OFF
26 sec. OFF
18 sec. ON
30P
(MEDIUMLOW)
10P
(LOW)
50P
(MEDIUMLOW)
Approx. 30%
Approx. 50%
Approx. 10%
12 sec. ON
6 sec. ON
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.
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