DOWNLOAD Sharp R-8740 (serv.man17) Service Manual ↓ Size: 1.46 MB | Pages: 48 in PDF or view online for FREE

Model
R-8740 (serv.man17)
Pages
48
Size
1.46 MB
Type
PDF
Document
Service Manual
Brand
Device
Home Appliance / Microwave Oven / Complete
File
r-8740-sm17.pdf
Date

Sharp R-8740 (serv.man17) Service Manual ▷ View online

R-8740M  - 4
SERVICING
CAUTION
MICROWAVE RADIATION
Service engineers should not be exposed to the
microwave energy which may radiate from the magnetron
or other microwave generating devices if it is improperly
used or connected. All input and output microwave
connections, waveguides, flanges and gaskets must be
secured. Never operate the device without a microwave
energy absorbing load attached. Never look into an open
waveguide or antenna while the device is energized.
WARNING
THIS APPLIANCE MUST BE EARTHED
THE WIRES IN THIS MAINS LEAD ARE COLOURED IN
ACCORDANCE WITH THE FOLLOWING CODE:
GREEN-AND-YELLOW : EARTH        BLUE : NEUTRAL        BROWN : LIVE
WARNING
Servicing and repair work must be carried out only by
trained service engineers.
All the parts marked "*" on parts list are used at
voltages more than 250V.
Removal of the outer wrap gives access to potentials
above 250V.
All the parts marked "∆" on parts list may cause undue
microwave exposure, by themselves, or when they
are damaged, loosened or removed.
CAUTION/WARNING
REMEMBER TO CHECK 3D
1) Disconnect the supply.
2) Door opened, and wedged open.
3) Discharge high voltage capacitor.
WARNING: AGAINST THE CHARGE OF THE HIGH-
VOLTAGE CAPACITOR
The high-voltage capacitor remains charged about 60 sec-
onds after the oven has been switched off. Wait for 60
seconds and then short-circuit the connection of the high-
voltage capacitor (that is, of the connecting lead of the high-
voltage rectifier) against the chassis with the use of an
insulated screwdriver.
Sharp recommend that wherever possible fault-finding is
carried out with the supply disconnected. It may in, some
cases, be necessary to connect the supply after the outer
case has been removed, in this event carry out 3D checks and
then disconnect the leads to the primary of the High voltage
transformer. Ensure that these leads remain isolated from
other components and the oven chassis. (Use insulation tape
if necessary.) When the testing is completed carry out 3D
checks and reconnect the leads to the primary of the High
voltage transformer.
WARNING TO SERVICE PERSONNEL
Microwave ovens contain circuitry capable of producing very high voltage and current, contact with following parts will
result in electrocution.
High voltage capacitor, High voltage transformer, Magnetron, High voltage rectifier assembly, High voltage wires.
REMEMBER TO CHECK 4R
1) Reconnect all leads removed from components during
testing.
2) Replace the outer case (cabinet).
3) Reconnect the supply.
4) Run  the oven. Check all functions.
Microwave ovens should not be run empty. To test for the
presence of microwave energy within a cavity, place a cup of
cold water on the oven turntable, close the door and set the
power to HIGH and set the microwave timer for two (2) minutes.
When the two minutes has elapsed (timer at zero) carefully
check that the water is now hot. If the water remains cold carry
out 3D checks and re-examine the connections to the compo-
nent being tested.
When all service work is completed, and the oven is fully
assembled, the microwave power output should be checked and
a microwave leakage test should be carried out.
R-8740M  - 5
ITEM
DESCRIPTION
Power Requirements
230-240V Volts / 50 Hertz / Single phase, 3 wire earthed
Power Consumption
Microwave cooking
1.45kW Approx. 6.3A
Dual cooking
(Microwave and Top Grill)
2.4kW Approx. 10.3A
(Microwave and Bottom Grill)
1.95kW Approx. 8.2A
(Top and Bottom Grill)                        1.5kW Approx. 6.3A
Convection cooking
1.525kW Approx. 6.4A
Bottom Grill cooking
550kW Approx. 2.3A
Top Grill cooking
1000kW Approx. 4.2A
Power Output
900 watts nominal of RF microwave energy (measured by method of IEC
60705) Operating fequency 2450 MHz
Top Grill heating element Power Output
 1000W
Bottom Grill heating element Power Output
500W
Case Dimensions
Width 520 mm
Height 309 mm (including foot)
Depth 488 mm
Cooking Cavity Dimensions
Width 349 mm
Height 207 mm
Depth 357 mm
Turntable diameter
325mm
PRODUCT DESCRIPTION
Net Weight
Approx. 19 kg
Control Complement
1. DIGITAL DISPLAY
2. INDICATORS:
These indicators will light corresponding with
below symbols
: Time reduce
: Memory
: Manual
: Percentage (for microwave
  power level)
: Lock (showing oven lock is set)
: Cook (showing oven in operation)
3. COOKING MODE indicator lights.
These indicator lights will light during
each cooking mode.
SPECIFICATION
As part of our policy of continuous improvement, we reserve the right to
alter design and specifications without notice
4. NUMBER keys for time and memory
programming
5. START key
6. STOP key
7. SOUND key
8. BOTTOM GRILL key
9. TOP GRILL key
10. CONVECTION key
To change the convection
temperature
11. MICROWAVE key
To change the microwave power
setting
12. MANUAL key
13. MEMORY key
14. TIME REDUCE key
OPERATION KEYS:
Note:
Temperature measurements taken whilst the oven is in convection mode will differ from the displayed level.
This is due to the grill elements turning on and off in order to regulate the oven temperature.
This will not affect the cooking results as long as the operation manual and cook book are followed correctly.
R-8740M  - 6
APPEARANCE VIEW
OVEN
1. DIGITAL DISPLAY
2. INDICATORS:
These indicators will light corresponding with
below symbols
: Time reduce
: Memory
: Manual
: Percentage (for microwave
  power level)
: Lock (showing oven lock is set)
: Cook (showing oven in operation)
3. COOKING MODE indicator lights.
These indicator lights will light during
each cooking mode.
OPERATION KEYS:
4. NUMBER keys for time and memory
programming
5. START key
6. STOP key
7. SOUND key
8. BOTTOM GRILL key
9. TOP GRILL key
10. CONVECTION key
To change the convection temperature
11. MICROWAVE key
To change the microwave power setting
12. MANUAL key
13. MEMORY key
14. TIME REDUCE key
14
13
12
11
10
9
8
7
6
1
2
3
4
5
7
10
4
1
8
6
5
3
2
10
12
11
9. Door seals and sealing surfaces
10. Ventilation openings
11. Outer cabinet
12. Power supply cord
13. Turntable
14. Handle
1. Control panel
2. Oven lamp
3. Grill heating element (Top Grill)
4. Door opening button
5. Waveguide cover
6. Oven cavity
7. Turntable motor shaft
8. Grill heating element
(Bottom Grill)
14
13
R-8740M  - 7
 OPERATION SEQUENCE
OFF CONDITION
Closing the oven door activates all door interlock switches
(Monitored latch switch and stop switch.
IMPORTANT:
When the oven door is closed, the contacts COM-NC of the
monitor switch SW2 must be open and the contacts (COM-
NO) must be closed. When the microwave oven is plugged
in a wall outlet (230V / 50Hz), 230 volts A.C. is supplied to
the point A9 + A11 in the control unit.
Figure O-1 on page 35
1. The display flashes ".0"
2. To set any programmes or set the clock, you must first
"put the oven in MANUAL MODE .  Press the MANUAL
key for 6-10 seconds. (oven will 'beep').  Press the
MANUAL key once more.  The oven is now in manual
mode (this will be indicated in the display window, above
the         symbol).
NOTE: When the oven door is opened, the oven lamp
comes on at this time.
MICROWAVE COOKING CONDITION
HIGH COOKING
Enter a desired cooking time with the number keys, press
the " MICROWAVE " 
  key, then press the START key 
.
Function sequence Figure O-2 on page 35
CONNECTED COMPONENTS
RELAY
Oven lamp, Turntable motor
RY1
High voltage transformer
RY2
Fan motor
RY5
1. 230 volts A.C. 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 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.
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)
Monitored latch Switch COM-NO
Closed
Opened
Monitor Switch
COM-NO
Closed
Opened
Monitor Switch
COM-NC
Opened
Closed
Stop switch
COM-NO
Closed
Opened
The circuit to the high voltage transformer, is cut off when
the contact of relay RY2 contacts COM-NO of the monitored
latch switch, and monitor switch SW2 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 monitored latch switch are made
open. The relays RY2 and RY5 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  stay closed. Shown in the display is
remaining time.
6. MONITOR SWITCH CIRCUIT
The monitor switch SW2 is mechanically controlled by
the oven door, and monitors the operation of the
monitored latch switch SW1.
6-1. When the oven door is opened during or after the cycle
of a cooking program, the monitored latch switch SW1
and stop switch SW3 must open their contacts (COM-
NO) first. After that the contacts (COM-NC) of the
monitor switch SW2 can be closed and the contacts
(COM-NO) of monitor switch SW2 are made open.
6-2. When the oven door is closed. The contacts (COM-NC)
of the monitor switch SW2 must be opened and the
contacts (COM-NO) of monitor switch SW2 must be
closed.  After that the contacts of the monitored latch
switch SW1 and the stop switch SW3 are made closed.
6-3. When the oven door is opened and the contacts of the
monitored latch switch SW1 remain closed, the fuse F2
F8A will blow. Because the relay RY1 and monitor
switch SW2 are closed  and a short circuit is caused.
CONVECTION COOKING CONDITION
PREHEATING CONDITION (Figure O-4)
Program desired convection temperature by touching
"MANUAL", then the CONVECTION key. When the START key
is touched, the following operations occur:
1. The coil of shut-off relays RY1, RY5 and RY7 are energized,
the oven lamp, cooling fan motor, turntable motor and
convection motor are turned on.
2. The coil of shut-off relays RY3  and RY4 are energized by
the control unit and the main supply voltage is added to the
MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW
COOKING
When the microwave oven is preset for variable cooking
power, the 230 volts A.C. power 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 to the
percentage of microwave power, because approx. 3
seconds  are needed for heating up the magnetron
filament.
32 sec. ON
24 sec. ON
18 sec. ON
12 sec. ON
6 sec. ON
8 sec. OFF
14 sec. OFF
20 sec. OFF
26 sec. OFF
HIGH
MEDIUM HIGH
MEDIUM
MEDIUM LOW
LOW
Approx. 70% = 630 Watts
100%
Approx. 50% = 450 Watts
Approx. 30% = 270 Watts
Approx. 10% = 90 Watts
 = 900 Watts
Page of 48
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  • DOWNLOAD Sharp R-8740 (serv.man17) Service Manual ↓ Size: 1.46 MB | Pages: 48 in PDF or view online for FREE
  • Here you can View online or download the Service Manual for the Sharp R-8740 (serv.man17) in PDF for free, which will help you to disassemble, recover, fix and repair Sharp R-8740 (serv.man17) Microwave Oven. Information contained in Sharp R-8740 (serv.man17) Service Manual (repair manual) includes:
  • Disassembly, troubleshooting, maintenance, adjustment, installation and setup instructions.
  • Schematics, Circuit, Wiring and Block diagrams.
  • Printed wiring boards (PWB) and printed circuit boards (PCB).
  • Exploded View and Parts List.