Sharp R-27STM, Service Manual

Page: 5 / 28

R-27STM
5
COOK MICRO PCS KG TURN STIR
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TOUCH CONTROL PANEL
1. DIGITAL DISPLAY
2. INDICATORS
BUTTONS :
3. AUTO COOK
4. EXPRESS COOK
5. EXPRESS DEFROST
6. START/AUTO MINUTE
7. STOP/CLEAR
8. POWER LEVEL
9. TIME/WEIGHT KNOB
NOTE: Some one-touch cooking features such as "START/AUTO MINUTE" are
disabled after three minutes when the oven is not in use. These fea-
tures are automatically enabled when the door is opened and closed
or the STOP button is pressed.
OFF CONDITION
Closing the door activates all door interlock switches (1st. latch
switch, 2nd. interlock relay control 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, rated volt -
age is supplied to the noise filter and the control unit.
Figure O-1 on page 20
The display will show flashing "88:88".
To set any programmes or set the clock, you must first touch the
STOP/CLEAR button.
" : " appears in the display.
MICROWAVE COOKING CONDITION
HIGH COOKING
Enter a desired cooking time by rotating the TIME/WEIGHT
knob and start the oven with pressing START/AUTO MINUTE
button.
Function sequence
Figure O-2 on page 20
CONNECTED COMPONENTS RELAY
Oven lamp, Fan motor, Turntable motor RY1
High voltage transformer RY2
Rated voltage is supplied to the primary winding of the high volt -
age 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
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 ap -
proximately 4000 volts D.C..
The 2450 MHz microwave energy produced in the magnetron
generates a wave length of 12.24 cm. This energy is channelled
OPERATION SEQUENCE
through the waveguide (transport channel) into the oven cavity,
where the food is placed to be cooked.
When the cooking time is up, a signal tone is heard and the re
-
lays (RY1+RY2) go back to their home position. The circuits to
the oven lamp, high voltage transformer, fan motor and turntable
motor are cut off.
When the door is opened during a cook cycle, the switches
come to the following condition
SWITCH CONTACT
CONDITION
DURING
COOKING
DOOR OPEN
(NO COOKING)
1st. latch switch COM -NO Closed Open
2nd. interlock relay
control switch
COM -NO Closed Open
Monitor switch COM -NC Open Closed
The circuits to the high voltage transformer, fan motor, turntable
motor and oven lamp are cut off when the 1st. latch switch and
2nd. interlock relay control switch are made open.
MONITOR SWITCH CIRCUIT
The monitor switch is mechanically controlled by oven door, and
monitors the operation of the 1st. latch switch, the relay (RY1)
and the 2nd. interlock relay (RY2).
When the oven door is opened during or after the cycle of a
cooking program, the 1st. latch switch and 2nd. interlock relay
control switch must open their contacts first. After that the con
-
tacts (COM -NC) of the monitor switch can be closed.
When the oven door is closed, the contacts (COM -NC) of the
monitor switch must be opened. After that the contacts of the
1st. latch switch and 2nd. interlock relay control switch are
closed.
When the oven door is opened and the contacts of the 1st. latch
switch, the relay (RY1) and the 2nd. interlock relay (RY1) remain
closed. The fuse T6.3A will blow, because the monitor switch is
closed and a short circuit is caused.
R27STM.indd 5 11/3/08 2:04:25 PM