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Model
R-8000GK
Pages
44
Size
1.16 MB
Type
PDF
Document
Service Manual
Brand
Device
Home Appliance / Microwave Oven
File
r-8000gk.pdf
Date

Sharp R-8000GK Service Manual ▷ View online

R-8000GK
4
OPERATION
DESCRIPTION OF OPERATING SEQUENCE
The following is a description of component functions during
oven operation.
OFF CONDITION
Closing the door activates the door sensing switch and second-
ary interlock switch and 3rd. latch switch. (In this condition, the
monitor switch contacts are opened.)
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 33
1. The display will show "   .          ".
NOTE: When the door is opened, the oven lamp comes on.
MICROWAVE COOKING CONDITION
HIGH COOKING
Press the MANUAL/REPEAT key. Program desired cooking
time by touching the NUMBER keys. Then press the MICRO-
WAVE key once. When the START key is touched, the following
operations occur:
1. The contacts of relays are closed and components connected
to the relays are turned on as follows.
(For details, refer to Figure O-2)
RELAY
CONNECTED COMPONENTS
RY-1
Oven lamp/Turntable motor
RY-2
High voltage transformer
RY-5
Fan motor
2. 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.
3. 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..
4. The 2450 MHz microwave energy produced in the magnetron
generates a wavelength 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.
5. When the cooking time is up, a signal tone is heard and the
relays RY1 + RY2 + RY5 go back to their home position. The
circuits to the oven lamp, high voltage transformer, fan motor
and turntable motor are cut off.
6. 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)
Secondary interlock
switch
COM-NO
Closed
Opened
Door sensing switch
COM-NO
Closed
Opened
3rd. latch switch
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
secondary interlock switch are made open. The circuit to the
fan motor is cut off when the relay RY5 is made open. The
circuit to the turntable motor is cut off when the contacts
(COM-NO) of the secondary interlock switch are made open.
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.
7. MONITOR SWITCH CIRCUIT
The monitor switch is mechanically controlled by the oven
door, and monitors the operation of the secondary interlock
switch and the relay RY2.
7-1. When the oven door is opened during or after the cycle of
a cooking program, the secondary interlock switch and the
door sensing switch must open their contacts (COM-NO)
first. After that the contacts (COM-NC) of the monitor
switch can be closed and the contacts (COM-NO) of 3rd.
latch switch are made open.
7-2. When the oven door is closed, the contacts (COM-NC) of
the monitor switch must be opened and the contacts
(COM-NO) of 3rd. latch switch must be closed. After that
the contacts (COM-NO)  of the secondary interlock switch
and the door sensing switch are made closed.
7-3. When the oven door is opened and the contacts (COM-
NO) of  the secondary interlock switch remain closed, the
fuse F10A will blow. Because the relay RY2 and monitor
switch are closed  and a short circuit is caused.
POWER LEVEL P-0 to P-90 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.
NOTE: The ON/OFF time ratio does not exactly correspond
the percentage of microwave power, because
approx. 3 seconds are needed for heating of the
magnetron filament.
PREHEATING CONDITION (CONVECTION MODE)
Press the MANUAL/REPEAT key. Program desired convection
temperature by touching the OVEN(˚C) key. When the START
key is touched, the following operations occur: (Figure O-3)
1. The coil of shut-off relays (RY1, RY3 and RY5) are energized,
the oven lamp, cooling fan motor, turntable motor and jet
motor are turned on. The contacts (COM-NO) of relay RY6
are opened.
2.  The solid-state relays are energized by the control unit and
the main supply voltage is applied to the top and side heating
elements.
32 sec. ON
100%
30sec. ON
90%
26 sec. ON
80%
24 sec. ON
 70%
22 sec. ON
60%
18 sec. ON
50%
16 sec. ON
40%
12 sec. ON
30%
8 sec. ON
20%
6 sec. ON
10%
0 sec. ON
0%
R-8000GK
5
3. When the oven temperature reaches the selected preheat
temperature, the following operations occur:
3-1. The solid-state relays are de-energized by the control
unit temperature circuit and thermistor, opening the
circuit to the heating elements.
3-2. The oven will continue to function for 30 minutes, turning
the heating elements on and off, as needed to maintain
the selected preheat temperature. The oven will
shutdown completely after 30 minutes
OVEN COOKING CONDITION
Press the MANUAL/REPEAT key. Enter the cooking time by
touching NUMBER key and select the temperature by touching
OVEN(˚C) key. When the START key is touched, the following
operations occur:
Figure O-3 on page 34
1. The numbers on the digital read-out start to count down to
zero.
2. The oven lamp, turntable motor, cooling fan motor and jet
motor are energized. The contacts (COM-NO) of relay RY6
are opened.
3.  The solid-state relays are energized (if the cavity temperature
is lower than the selected temperature) and the main supply
voltage is applied to the heating elements to return to the
selected cooking temperature.
4. Upon completion of the cooking time, the audible signal will
sound, and oven lamp, turntable motor, cooling fan motor and
jet motor are de-energized. At the end of the oven cycle, if the
cavity air temperature is above 111˚C, the circuit to RY5 will be
maintained (by the thermistor circuit) to continue operation of
the cooling fan motor until the temperature drops below 90˚C,
at which time the relay will be de-energized, turning off the fan
motor. Relay RY3 will however, open as soon as the convection
cycle has ended, turning off the jet motor.
SPEED GRILL COOKING (SG-1)
Press the MANUAL/REPEAT key. Enter cooking time and then
touch the SPEED GRILL key once. Select the temperature by
pressing OVEN(˚C) key. Then select the microwave power level
by pressing MICROWAVE key.  When the START key is touched,
following operations occur;
Figure O-4 on page 34
1. The contacts of the relays RY1, RY3 and RY5 are closed, and
the oven lamp, turntable motor, jet motor and fan motors are
energized. The contacts (COM-NO) of relay RY6 are closed.
NOTE : The rotate direction of the jet motor is reverse to one
of the oven cooking by the relay RY6.
2. The solid-state relays are energized and the main supply
voltage is applied to the top and side heating elements.
NOTE : After cooking, the operation of the fan motors is the
same as one of the oven cooking.
SPEED GRILL COOKING (SG-2, SG-3)
Press the MANUAL/REPEAT key. Enter cooking time and then
touch SPEED GRILL key twice or 3 times. Select the tempera-
ture by pressing OVEN(˚C) key. Then select the microwave
power level by pressing MICROWAVE key. When the start key
is touched, following operations occur;
Figure O-5 on page 35
1. The contacts of the relays RY1, RY3 and RY5 are closed, and
the oven lamp,  turntable motor, jet motor and fan motors are
energized. The contacts (COM-NO) of relay RY6 are closed.
NOTE : The rotate direction of the jet motor is revers to one
of the oven cooking.
2. The solid-state relays are energized and the main supply
voltage is applied to the top and side heating elements.
3. The relay RY2 is energized and the microwave energy is
generated by magnetron.
NOTE: After cooking, the operation of the fan motors is the
same as one of the oven cooking.
SPEED CONVECTION COOKING (SC-2, SC-3)
Press the MANUAL/REPEAT key. Enter cooking time and then
touch SPEED CONV. key twice or 3 times. Select the tempera-
ture by pressing OVEN(˚C) key. Then select the microwave
power level by pressing MICROWAVE key. When the start key
is touched, following operations occur;
Figure O-6 on page 35
1. The contacts of the relays RY1, RY3 and RY5 are closed, and
the oven lamp, turntable motor, jet motor and fan motors are
energized. The contacts (COM-NO) of relay RY6 are opened.
2. The solid-state relays and relay RY2 are energized, and the
main supply voltage is applied to the top and side heating
elements and the high voltage transformer alternately.
NOTE: After cooking, the operation of the fan motors is the
same as one of the oven cooking.
FIRE SENSING FEATURE (MICROWAVE MODE)
This model incorporates a sensing feature which will stop the
oven's operation if there is a fire in the oven cavity during
microwave cooking. This fire sensing feature will operate when
the microwave power level is set to 80% or more. This is
accomplished by the LSI repeatedly measuring the voltage
across the temperature measurement circuit (thermistor) during
it's 32-seconds time base comparing the obtained voltage meas-
urements. If the most recent  voltage measured is 300 mV
greater than the previous voltage measured, the LSI judges it as
a fire in the oven cavity and switches off the relays to the power
transformer, fan motor and jet motor. The LSI also stops counting
down and closes the damper door so that no fresh air will enter
the oven cavity. Please refer to the following section for a more
detailed description.
Operation
Please refer to the timing diagrams below.
1. The fire sensing will start after 5 minutes when the oven is
started.
2. The thermistor operates within a 32-seconds time base and
it is energized for three (3) seconds and off for 29 seconds.
Two (2) seconds after the thermistor is energized, the voltage
across the temperature measurement circuit is sampled by
the LSI and twenty five (25) seconds after the thermistor is cut
off the LSI turns on the convection fan for three (3) seconds.
3. The above procedure is repeated. If the difference between the
first voltage measured (in step 1) and the voltage measured
when the procedure is repeated (step 2) is greater than 300 mV
the LSI makes the judgment that there is a fire in the oven cavity
and will switch off the relays to the power transformer, fan motor
and jet motor. The LSI also stops counting down and closes the
damper door so that no fresh air will enter the oven cavity.
4. Once the fire sensor feature has shut the unit down, the
programmed cooking cycle may be resumed by  pressing the
"START" key or the unit may be reset by pressing the STOP/
CLEAR key.
JET MOTOR
THERMISTOR
Sensing 
Voltage
ON
OFF
ON
OFF
ON
OFF
0 2 3
28
31
32 (sec.)
64 (sec.)
3 sec.
Sensing the voltage across temperature measurement circuit.
3 sec.
R-8000GK
6
FUNCTION OF IMPORTANT COMPONENTS
Monitor switch
Latch hook left
3rd. latch 
switch
Latch 
head
Secondary
interlock switch
(Monitored latch switch)
Door
sensing switch
(Primary interlock
  relay control switch)
Latch hook right
Latch 
head
FAN MOTOR OPERATION
After cooking is completed, the fan motors will continue for 1
minute. At the end of the cooking cycle, if the cavity air temperature
is above 111˚C, the circuit to RY5 will be maintained (by the
thermistor circuit) to continue operation of the cooling fan motor
until the temperature drops below 90˚C, at which time the relay will
be de-energized, turning off the fan motor.
DOOR OPEN MECHANISM
The door is opened by pulling the door handle down and forward,
referring to the figure D-1. When the door handle is pulled down,
the latch heads are moved upward. And then when the door
handle is pulled forward, the latch heads are released from the
latch hooks right and left. Now, the door will open.
Figure D-1. Door Open Mechanism
DOOR SENSING SWITCH, SECONDARY INTER-
LOCK SWITCH AND 3RD. LATCH SWITCH
1. When the oven door is closed, the contacts (COM-NO) must
be closed.
2. When the oven door is opened, the contacts (COM-NO) must
be opened.
MONITOR SWITCH
1. When the oven door is closed, the contacts (COM-NC) must
be opened.
2. When the oven door is opened, the contacts (COM-NC) must
be closed.
3. If the oven door is opened and the contacts (COM-NO) of the
secondary interlock switch and the relay RY2 fail to open, the
fuse F10A blows simultaneously with closing the contacts
(COM-NC) of the monitor switch .
CAUTION: BEFORE REPLACING A FUSE TEST THE SEC-
ONDARY INTERLOCK SWITCH, RELAY RY2 AND
MONITOR SWITCH   FOR PROPER OPERA-
TION. (REFER TO CHAPTER "TEST PROCE-
DURE".)
FUSE F10A
1. The fuse F10A blows when the contacts (COM-NO) of the
secondary interlock switch and relay RY2 remain closed with
the oven door open and when the monitor switch   closes.
2. If the wire harness or electrical components are short-
circuited, the fuse F10A blows to prevent an electric shock of
fire hazard.
HIGH VOLTAGE FUSE
The high voltage fuse blows when the high voltage rectifier or the
magnetron is shorted.
NOISE FILTER
The noise filter prevents the radio frequency interference that
might flow back in the power circuit.
THERMISTOR
The thermistor is a negative temperature coefficient type. The
temperature in the oven cavity is detected through the resistance
of the thermistor, and then the control unit causes the heater relay
to operate, thus the current to the heating elements is turned ON/
OFF. If the convection cooking or some cooking modes which use
the top / side heating elements is started and the oven temperature
does not rise above 37.8˚C, the control unit will stop the oven after
10 minutes. In this case, the thermistor may be opened.
MAGNETRON TEMPERATURE FUSE
The temperature fuse located on the waveguide flange is designed
to prevent damage to the magnetron if an over heated condition
develops in the magnetron due to cooling fan failure, obstructed air
guide, dirty or blocked air intake, etc. Under normal operation, the
temperature fuse remains closed. However, when abnormally
high temperatures are reached within the magnetron, the tempera-
ture fuse will open at 150˚C causing the oven to shut down.
HEATER TEMPERATURE FUSE
The temperature fuse located on the chassis support left is
designed to prevent damage to the chassis support left if an over
heated condition develops in the top and /or side heating
element unit
s due to convection fan failure, thermistor failure,
obstructed air ducts, dirty or blocked air intake, etc.
Under normal operation, the temperature fuse remains closed.
However, when abnormally high temperature are reached within
the top and /or side heating element unit
s, the temperature fuse
will open at 150˚C causing the oven to shut down.
TOP HEATER THERMAL CUT-OUT
The thermal cut-out located on the thermal cover upper is
designed to prevent damage to the top heating element unit if an
over heated condition develops in the top heating element unit
due to convection fan failure, thermistor failure, obstructed air
ducts, dirty or blocked air intake, etc.
Under normal operation, the thermal cut-out remains closed.
However, when abnormally high temperature are reached within
the top heating element unit, the thermal cut-out will open at
170˚C causing the oven to shut down. When the thermal cut-out
has cooled, the thermal cut-out closes at 155˚C.
SIDE HEATER THERMAL CUT-OUT
The thermal cut-out located on the thermal cover left is designed
to prevent damage to the side heating element unit if an over
heated condition develops in the side heating element unit due
to convection fan failure, thermistor failure, obstructed air ducts,
dirty or blocked air intake, etc.
Under normal operation, the thermal cut-out remains closed.
However, when abnormally high temperature are reached within
the side heating element unit, the thermal cut-out will open at
150˚C causing the oven to shut down. When the thermal cut-out
has cooled, the thermal cut-out closes at 130˚C.
TOP HEATING ELEMENT
The top heating element is located at the top of the oven cavity.
R-8000GK
7
It is intended to heat air driven by the convection fan. The heated
air is kept in the oven and force-circulated and reheated by the
top heating element.
SIDE HEATING ELEMENT
The side heating element is located at the left side of the oven
cavity. It is intended to heat air driven by the convection fan. The
heated air is kept in the oven and force-circulated and reheated
by the top heating element.
TURNTABLE MOTOR
The turntable motor rotates the turntable located in the bottom of
the oven cavity, so that the food on the turntable is cooked evenly
during cooking. The turntable may turn in either direction.
FAN MOTOR (MAGNETRON SIDE)
The fan motor drives a blade which draws external cool air. This
cool air is directed through the air vents surrounding the magn-
etron and cools the magnetron. This air is channelled through the
oven cavity to remove steam and vapours given off from the
heating foods. It is then exhausted through the exhausting air
vents at the oven cavity.
FAN MOTOR (HIGH VOLTAGE TRANSFORMER
SIDE)
The fan motor drives a blade which draws external cool air. This
cool air is directed through the air vents surrounding the power
transformer and cools the power transformer. This air is chan-
nelled through the oven cavity to remove steam and vapours
given off from the heating foods. It is then exhausted through the
exhausting air vents at the oven cavity.
CONVECTION COOKING SYSTEM
This oven is designed with a hot air heating system where food is
not directly heated by the heating element, but is heated by forced
circulation of the hot air produced by the heating elements. The air
heated by the heating elements is circulated through the convec-
tion passage provided on the outer casing of the oven cavity by
means of the convection fan which is driven by the jet motor. It then
enters the inside of the oven through the vent holes provided on the
top and left sides of the oven. Next, the hot air heats the food on the
turntable and leaves the oven cavity through the vent in the centre
of the oven cavity back side wall. Without leaving the oven, this hot
air is reheated by the heating elements, passes through the
convection passage and enters the inside of the oven cavity again,
in a continuing cycle. In this way, the hot air circulates inside the
oven cavity to raise its temperature and, at the same time, comes
into contact with the food being cooked. When the temperature
inside the oven cavity reaches the selected temperature, the
heating elements are de-energized. When the temperature inside
the oven cavity drops below the selected temperature, the heating
elements are energized again. In this way, the inside of the oven
cavity is maintained at approximately the selected temperature.
When the convection time reaches 0, the heating elements are de-
energized and the convection fan stops operating and the oven
shuts off.
Flow of hot air:
The rotation direction of the jet motor is controlled by relay RY6.
When the convection fan rotates clockwise, the hot air from the
oven cavity left side wall blows stronger than one from the oven
cavity top wall. ( This mode is called “Convection mode”.) When
the convection fan rotates counterclockwise, the hot air from the
oven cavity top wall blows stronger than one from the oven cavity
left side wall. (This mode is called “JET mode”.)
Figure D-2. Rotation direction of convection fan
Figure D-3. Flow of hot air
Side heating
element unit
Top heating
element unit
Convection 
fan
Convection mode
JET 
mode
FRONT VIEW
Hot air
Hot air
Hot air
Convection
fan
Hot air
Oven cavity left side
Oven cavity   
top wall
Side heating
element unit
Side heating
element unit
Top heating element unit Top heating element unit
Turntable
Convection Mode
JET Mode
TROUBLESHOOTING GUIDE
When troubleshooting the microwave oven, it is helpful to
follow the Sequence of Operation in performing the checks.
Many of the possible causes of trouble will require that a
specific test be performed. These tests are given a proce-
dure letter which will be found in the "Test Procedure
"section.
IMPORTANT:
If the oven becomes inoperative because of a
blown fuse F10A in the secondary interlock
swith - monitor switch - primary interlock relay
RY2 circuit, check the monitor switch, relay
(RY1), primary interlock relay (RY2) and sec-
ondary interlock switch before replacing the
fuse F10A.
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