R-895M (serv.man5). Operation sequence and function of important components - Sharp Home Appliance Service Manual (repair manual)

r-895m (serv.man5) service manual
Model
R-895M (serv.man5)
Pages
6
Size
490.54 KB
Type
PDF
Document
Service Manual
Brand
Device
Home Appliance / Microwave Oven / Operation sequence and function of important components
File
r-895m-sm5.pdf
Date

Read Sharp R-895M (serv.man5) Service Manual online

R-895M - 6
OPERATION SEQUENCE
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 micro-
wave oven is plugged in a wall outlet (230 - 240V /
50Hz), the line voltage is supplied to the noise filter.
Figure O-1 on page
 31
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 moni-
tored 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 moni-
tored 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 minutes,
the contacts of the relay RY5 will be opened and the
control unit will not be energized. Open and close the
door, the control unit will resume.
2. If the clock is set, this energy save mode does not work.
MICROWAVE COOKING CONDITION
HIGH COOKING
Enter a desired cooking time by touching the TIME keys
and start the oven by touching START key.
Function sequence Figure O-2 on page 32
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 12.24 cm. This
energy is channelled through the waveguide (trans-
port 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.
Switch
Contact
          Condition
During
Oven Door
Cooking
Open(No cooking)
COM-NO
Closed
Opened
Monitored latch switch
COM-NC
Opened
Closed
Stop switch
COM-NO
Closed
Opened
COM-NO
Closed
Opened
Monitor Switch
COM-NC
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 monitored 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 moni-
tored latch switch.
6-1. 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 latchcan be closed.
6-2. 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.
6-3. 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.
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 cur-
rent-limiting relay RY2. The following levels of microwave
power are given.
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.
GRILL COOKING CONDITION
TOP GRILL (Figure O-3a)
In this condition the food is cooked by the top grill heating
element . Programme the desired cooking time by touch-
ing the TIME keys and touh the GRILL key once. When the
STARTkey is touched, the following operations occur:
1. The numbers on the digital readout start the count
down to zero.
2. The oven lamp, cooling fan motor and turntable motor
are energized.
900W
(HIGH)
32 sec. ON
630W  MEDIUM 
HIGH 
Approx. 70%
100%
24 sec. ON
8 sec. OFF
14 sec. OFF
20 sec. OFF
26 sec. OFF
450W (MEDIUM)
Approx. 50%
18 sec. ON
270W  MEDIUM 
LOW 
Approx. 30%
12 sec. ON
90W
(LOW)
Approx. 10%
6 sec. ON
R-895M - 7
3. The relay RY3 is energized and the main supply
voltage is applied to the top grill heating element .
4. Now, the food is cooked by the top grill heating ele-
ment.
BOTTOM GRILL (Figure O-3b)
In this condition the food is cooked by bottom grill heating
element energy. Programme the desired cooking time by
touching the TIME keys and touch the GRILL key twice.
When the STARTkey is touched, the following operations
occur:
1. The numbers on the digital readout start the count
down to zero.
2. The oven lamp, cooling fan motor and turntable motor
are energized.
3. The relay RY4 is energized and the main supply
voltage is applied to the bottom grill heating element .
4. Now, the food is cooked by the bottom grill heating
element .
TOP AND BOTTOM GRILL (Figure O-3c)
In this condition the food is cooked by top and bottom grill
heating elements energy. Programme the desired cook-
ing time by touching the TIME keys and touch the GRILL
key three times. When the STARTkey is touched, the
following operations occur:
1. The numbers on the digital readout start the count
down to zero.
2. The oven lamp, cooling fan motor and turntable motor
are energized.
3. The relay RY4 is energized and the main supply
voltage is applied to the bottom grill heating element.
4. The relay RY3 is energized and the main supply
voltage is applied to the top grill heating element.
5. Now, the food is cooked by the top and bottom grill
heating elements.
CONVECTION COOKING CONDITION
PRE-HEATING (Figure O-4)
Programme the desired convection temperature by touch-
ing CONVECTION TEMPERATURE key. When the
STARTkey is touched, the following operations occur:
1. The coil shut-off relays RY1  and RY6 are energized,
the oven lamp, cooling fan motor and turntable motor
are turned on.
2. The coil shut-off relays RY3  and RY4 are energized by
control unit and the main supply voltage is added to the
top and bottom heating elements.
3. When the oven temperature reaches the selected pre-
heat temperature,  the following operations occur:
3-1. The coil shut-off relays RY3  and RY4 are energized
by control unit temperature circuit and thermistor,
opening the circuit to the top and bottom grill heating
elements.
3-2. The oven will continue to function for 30 minutes,
turning the top and bottom heating elements on and
off, as needed to maintain the selected pre-heat
temperature. The oven will shut-down completely
after 30 minutes.
CONVECTION COOKING (Figure O-4)
When the pre-heat temperature is reached, a beep signal
will sound indicating that the holding temperature has
been reached in the oven cavity. Open the door and place
the food to be cooked in the oven. Program desired
cooking time by touching the TIME keys and program
convection temperature by touching the CONVECTION
TEMPERATURE key . When the START key is touched,
the following operations occur:
1. The numbers on the digital readout start the count
down to zero.
2. The oven lamp, cooling fan motor, turntable motor and
convection motor are energized.
NOTE: When the convection temperature 40˚C is se-
lected, the convection motor is not energized.
3. The relays RY3  and RY4 are energized (if the cavity
temperature is lower than selected temperature) and
the main supply voltage is applied to the top and
bottom heating elements to return to the selected
cooking temperature.
4. Upon completion of the cooking time, the audible sig-
nal will sound, and the oven lamp, turntable motor,
cooling fan motor, convection motor, top and bottom
heating elements are de-energized. At the end of
convection cycle, if the cavity air temperature rises
above 120˚C, the circuit to the relay RY6 will be main-
tained (by the thermistor circuit) to continue operation
of the cooling fan motor until temperature drops below
105˚C, at that time the relay RY6 will be de-energized,
turning off the fan motor.
DUAL COOKING CONDITION
MICROWAVE AND CONVECTION  (Figure O-5a)
Programme the desired cooking time by touching the
TIME keys. Touch the DUAL CONVECTION/GRILL key
once. Select the microwave power level by touching the
MICROWAVE POWER LEVEL key. And select the con-
vection temperature by touching the CONVECTION TEM-
PERATURE key.
When the STARTkey is touched, the following operations
occur:
1. The numbers on the digital readout start the count
down to zero.
2. The oven lamp, cooling fan motor, turntable motor and
convection motor are energized.
3. The relay RY3 will be energized and the main supply
voltage is applied to the top grill heatier.
4. The relay RY4 is energized (if the cavity temperature is
lower than selected temperature) and the main supply
voltage is applied to the bottom heating elementer.
5. The relay RY2 is energized and the microwave energy
is generated by magnetron.
6. Now, the food is cooked by microwave and convection
energy simultaneously.
MICROWAVE AND TOP GRILL  (Figure O-5b)
Programme the desired cooking time by touching the
TIME keys. Touch the DUAL CONVECTION/GRILL key
twice. Select the microwave power level by touching the
MICROWAVE POWER LEVEL key. When the STARTkey
is touched, the following operations occur:
1. The numbers on the digital readout start the count
down to zero.
2. The oven lamp, cooling fan motor and turntable motor
are energized.
3. The relay RY3 is energized and the main supply
voltage is applied to the top grill heating element.
4. The relay RY2 is energized and the microwave energy
is generated by magnetron.
5. Now, the food is cooked by microwave and top grill
simultaneously.
OPERATION SEQUENCE
R-895M - 8
MICROWAVE AND BOTTOM GRILL  (Figure O-5c)
Programme the desired cooking time by touching the
TIME keys. Touch the DUAL CONVECTION/GRILL three
times. Select the microwave power level by touching the
MICROWAVE POWER LEVEL key. When the STARTkey
is touched, the following operations occur:
1. The numbers on the digital readout start the count
down to zero.
2. The oven lamp, cooling fan motor and turntable motor
are energized.
3. The relay RY4 is energized and the main supply
voltage is applied to the bottom grill heating element.
4. The relay RY2 is energized and the microwave energy
is generated by magnetron.
5. Now, the food is cooked by microwave and bottom grill
simultaneously.
ON/OFF TIME RATIO
In grill cooking, convection cooking or dual cooking, the
top heater, bottom heater or magnetron operate whithin a
54 second time base. The following table is the ON / OFF
time ratio at each power output of the top heaters, bottom
heater or magnetron.
POWER OUTPUT
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.
AUTOMATIC COOKING
PIZZA
BREAKFAST
EXPRESS COOK
EXPRESS DEFROST
MEAL IN ONE
Above functions are automatic cooking. They automati-
cally work out the correct cooking mode and cooking time
and/or cooking temperature. They will cook according to
the special cooking sequence.
AUTO POWER CONTROL OPERATION
The magnetron, top or bottom heating elements, the fan
motor or the convection motor will operate in accordance
with following specification.
The power level is not reduced 1 time cooking. But only in case same menu is repeated within
1min 15sec, the power level of micro and grill is reduced from 100% to 70% in 20mins after
starting of last cooking. (Even if the time of the last cooking is longer than 20mins, the power
level isn't reduced on the last cooking, and it is reduced from the beginning of the next
cooking.) However, in time calculated from the start of the 1st cooking, even if the Cook mode
changed, when repetition cooking of the menu with which 100% of top & bottom heaters
continues are performed, as shown in the following table, the power down of the cooking of
the 2nd henceforth is carried out. (The 1st cooking is not applied)
In case same cooking mode is repeated within 1min 15sec (including stop, end), oven
calculates total cooking time and reduce the power level.
1. OUTPUT POWER CONTROL (MANUAL COOK)
OPERATION MODE
DEVICE
POWER CONTROL
MICROWAVE (100%)
SINGLE OPERATION
Microwave
100% 20min, then 70%
TOP GRILL (100%)
SINGLE OPERATION
Top heater
100% 15min, then 50%
BOTTOM GRILL (100%)
SINGLE OPERATION
Bottom heater
100% 15min, then 50%
TOP(100%)/BOTTOM(100%)
Top heater
100% 6min then 70% and 70% 9min then 50%
DUAL OPERATION
Bottom heater
100% 6min then 70% and 70% 9min then 50%
MICRO(100%)/TOP GRILL(100%)
Microwave
100% 20min, then 70%
DUAL OPERATION
Top heater
100% 15min, then 50%
MICRO(70 - 10%)/TOP GRILL(100%)
Microwave
-
DUAL OPERATION
Top heater
100% 15min, then 50%
MICRO(100%)/BOTTOM GRILL(100%)
Microwave
100% 20min, then 70%
DUAL OPERATION
Bottom heater
100% 15min, then 50%
MICRO(70 - 10%)/BOTTOM GRILL(100%)
Microwave
-
DUAL OPERATION
Bottom heater
100% 15min, then 50%
Microwave
Repeat Cook
Top heater
Bottom heater
2. OUTPUT POWER CONTROL (AUTO COOK)
Repeat Auto Cook
OPERATION SEQUENCE
R-895M - 9
FUNCTION OF IMPORTANT COMPONENTS
3. COOLING FAN OPERATION
OPERATION MODE
DEVICE
POWER CONTROL
PREHEAT
Cooling
60%
CONV.
Cooling fan
60% 60 min. then 100%
Others
Cooling fan
100%
After cooking
Cooling fan
Indication
4. CONVECTION POWER SETTING
PREHEATING
TEMP
250˚C, 230˚C, 220˚C, 200˚C, 180˚C, 160˚C, 130˚C, 100˚C, 70˚C, 40˚C
HEATING   TOP
100%
ELEMENT  BOTTOM
100%
COOLING FAN
60%
CONV. FAN
0%
CONVECTION
TEMP
250˚C
230˚C
220˚C
200˚C
180˚C
160˚C
130˚C
100˚C
70˚C
40˚C
WITHOUT
HEATING
TOP
50%
40%
40%
30%
20%
10%
10%
10%
10%
10%
PREHEATING ELEMENT  BOTTOM
100%
90%
80%
70%
70%
60%
50%
40%
30%
20%
WITH
HEATING
TOP
50%
40%
40%
30%
20%
10%
10%
10%
10%
10%
PREHEATING ELEMENT  BOTTOM
90%
70%
60%
50%
50%
50%
50%
40%
30%
20%
COOLING FAN
60% 60min, then 100%
CONV. FAN
100%
0%
DUAL CONVECTION
TEMP
250˚C
230˚C
220˚C
200˚C
180˚C
160˚C
130˚C
100˚C
70˚C
40˚C
WITHOUT
HEATING
TOP
50%
40%
40%
30%
20%
10%
10%
10%
10%
10%
PREHEATING ELEMENT  BOTTOM
100%
90%
80%
70%
70%
60%
50%
40%
30%
20%
WITH
HEATING
TOP
50%
40%
40%
30%
20%
10%
10%
10%
10%
10%
PREHEATING ELEMENT  BOTTOM
90%
70%
60%
50%
50%
50%
50%
40%
30%
20%
MICRO
10%,30%,50%
COOLING FAN
100%
CONV. FAN
100%
0%
NOTE
The oven temp was checked by the thermometer when each stages are started .
If the oven temp is same or higher than 105˚C, the oven was judged as "with preheating".
When the oven temp is lower than 105˚C or the cooling fan stops, the oven was judged as "without
preheating".
The  cooling fan continues to rotate when Oven temperature is more than 120˚C. Then,
it stops when it is less than 105˚C
NOW COOLING is indicated during the cooling fan movement after operation is finished.
(It isn't indicated during a fan movement to stop on the way.)
Latch hook
Door
SW2: Stop switch
Latch
Heads
SW3: Monitor switch
SW1: Monitored
latch switch
Tab
The door can be opened by pulling the door handle. When
the handle is pulled, the latch head is pulled, the latch head
is moved upward, and released from the latch hook now
the door can be opened.
MONITORED LATCH SWITCH
1. When the oven door is closed, the contacts (COM-NO)
of the switch must be closed. And the contacts (COM-
NC) must be opened.
2. When the oven door is opened, the contacts (COM-
NO) of the switch must be opened. And the contacts
(COM-NC) must be closed.
OPERATION SEQUENCE
Figure D-1. Door Open Mechanism
Page of 6
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