SHARP R241CWA, R-241CWAA, R-241CWAC, R-241CWAP Service Manual
SERVICE MANUAL
S7908R241CPA/
MICROWAVE OVEN
R-241CWAA
R-241CWAC
R-241CWAP
MODELS
R-241CW AA (Argentina)
R-241CWA C (Chile)
R-241CWAP (Peru)
In interests of user-safety the oven should be restored to its original
condition and only parts identical to those specified should be used.
TABLE OF CONTENTS
CAUTION, MICROWAVE RADIATION............................................................................................................... 1
WARNING............................................................................................................................................................1
PRODUCT SPECIFICATIONS ........................................................................................................................... 2
GENERAL INFORMATION..................................................................................................................................2
APPEARANCE VIEW ......................................................................................................................................... 3
OPERATION SEQUENCE.................................................................................................................................. 4
FUNCTION OF IMPORTANT COMPONENTS .................................................................................................. 5
SERVICING .........................................................................................................................................................6
TEST PROCEDURE........................................................................................................................................... 8
TOUCH CONTROL PANEL...............................................................................................................................14
COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE............................................................. 18
MICROWAVE MEASUREMENT ...................................................................................................................... 24
WIRING DIAGRAM........................................................................................................................................... 25
PICTORIAL DIAGRAM ..................................................................................................................................... 26
CONTROL PANEL CIRCUIT .............................................................................................................................27
PRINTED WIRING BOARD ...............................................................................................................................28
PARTS LIST ..................................................................................................................................................... 29
SHARP CORPORATION
R-241CWAA
R-241CWAC
R-241CWAP
SERVICE MANU AL
MICROWAVE OVEN
R-241CWAA
R-241CWAC
R-241CWAP
R-241CWAA (Argentina)
R-241CWAC (Chile)
R-241CWAP (Peru)
GENERAL IMPORTANT INFORMATION
This Manual has been prepared to provide Sharp Corp. Service
engineers with Operation and Service Information.
It is recommended that service engineers carefully study the
entire text of this manual, so they will be qualified to render
satisfactory customer service.
CAUTION
MICROWAVE RADIATION
DO NOT BECOME EXPOSED TO RADIATION FROM
THE MICROWAVE GENERATOR OR OTHER PARTS
CONDUCTING MICROWAVE ENERGY.
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.
PRODUCT SPECIFICATIONS
APPEARANCE VIEW
OPERATING SEQUENCE
FUNCTION OF IMPORTANT
COMPONENTS
SERVICING AND
TROUBLESHOOTING CHART
TEST PROCEDURE
TOUCH CONTROL PANEL
ASSEMBLY
WARNING
Never operate the oven until the following points are ensured.
(A) The door is tightly closed.
(B) The door brackets and hinges are not defective.
(C) The door packing is not damaged.
(D) The door is not deformed or warped.
(E) There is not any other visible damage with the oven.
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.
SHARP CORPORATION
OSAKA, JAPAN
COMPONENT REPLACEMENT
AND ADJUSTMENT PROCEDURE
MICROWAVE MEASUREMENT
WIRING DIAGRAM
PARTS LIST
1
R-241CWAA
R-241CWAC
R-241CWAP
PRODUCT SPECIFICATIONS
ITEM DESCRIPTION
Power Requirements 220 Volts / 50 Hertz
Power Consumption 1.2 kW
Power Output 800 watts nominal of RF microwave energy (IEC 705)
Case Dimensions Width 460 mm
Cooking Cavity Dimensions Width 314 mm
Turntable diameter 295 mm
Control Complement Touch Control System
R-241CWAA, R-241CWAC :
R-241CWAP (Peru) :
Single phase, 3 wire earthed
220 Volts / 60 Hertz
Single phase, 2 wire
Operating frequency 2450 MHz
Height 290 mm including foot
Depth 372 mm
Height 199 mm
Depth 321 mm
Timer (0 - 99 minutes 99 seconds)
Microwave Power for Variable Cooking
Repetition Rate;
HIGH....................................... Full power throughout the cooking time
MEDIUM HIGH ........................................ approx. 70% of FULL Power
MEDIUM .................................................. approx. 50% of FULL Power
MEDIUM LOW......................................... approx. 30% of FULL Power
LOW......................................................... approx. 10% of FULL Power
EASY DEFROST pad
INSTANT ACTION pads
Number pads
POWER LEVEL pad
TIMER/CLOCK pad
STOP/CLEAR pad
INSTANT COOK/START pad
Set Weight (Approx.) 14 kg
GENERAL INFORMATION
WARNING
THIS APPLIANCE MUST BE EARTHED
IMPORTANT
THE WIRES IN THIS MAINS LEAD ARE COLOURED IN ACCORDANCE WITH THE FOLLOWING CODE:
GREEN-AND-YELLOW (for R-241CWAA & R-241CWAC): EARTH
BLUE : NEUTRAL
BROWN : LIVE
2
APPEARANCE VIEW
R-241CWAA
R-241CWAC
R-241CWAP
OVEN
3
7
5
4
1. Ventilation openings
2. Oven lamp
3. Door hinges
4. Door safety latches
5. See through door
6. Door seals sealing surfaces
7. Coupling
6
2
9
1
11
8
10
13
4
12
8. Control panel
9. Waveguide cover
10.Power supply cord
11.Turntable
12.Roller stay
13. Earth wire [R-241CWAP]
TOUCH CONTROL PANEL
1. DIGITAL READOUT
2. INDICATOR
3. EASY DEFROST PAD
Press to select the Easy Defrost menu.
4. INSTANT ACTION PADS
Press to cook or reheat 6 popular menus.
5. NUMBER PADS
Press to enter cooking time, clock time, weight of
food.
6. POWER LEVEL PAD
Press to select microwave power setting.
If not pressed, HIGH is automatically selected.
Press to alter the cooking result for automatic
operations.
7. TIMER/CLOCK PAD
Press to set clock, timer, child lock or demonstration mode.
8. STOP/CLEAR PAD
Press to clear during programming.
Press once to stop operation of oven during cooking; press twice to cancel cooking programme.
9. INSTANT COOK/START PAD
Press once to cook for 1 minute at 100% or increase by 1 minute multiples each time this pad is
pressed during cooking.
Press to start oven after setting programmes.
1
2
3
4
5
6
8
7
9
3
R-241CWAA
R-241CWAC
R-241CWAP
OPERATION SEQUENCE
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
voltage is supplied to the control unit.
Figure O-1 on page 25
1. The display flashes "88:88".
2. To set any programmes or set the clock, you must first
touch the stop/ clear pad.
3. " : " appears in the display.
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 touching the number
keys and start the oven with touching the start key.
Function sequence
Figure O-2 on page 25
The circuits to the power transformer, fan motor and
turntable motor are cut off when the 1st. latch switch and
2nd. interlock relay control 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 the remaining time.
6. MONITOR SWITCH CIRCUIT
The monitor switch is mechanically controlled by oven
door, and monitors the operation of the 1st. latch switch
and the 2nd. interlock relay.
6-1 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 contacts (COM-NC) of the monitor
switch can be closed.
6-2. 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.
6-3. When the oven door is opened and the contacts of the
1st latch switch and 2nd. interlock relay remain closed.
The fuse M8A will blow, because the monitor switch is
closed and a short circuit is caused.
CONNECTED COMPONENTS RELAY
Oven lamp, Fan motor, Turntable motor RY1
Power transformer RY2
1. Rated voltage is supplied to the primary winding of the
power 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 go back to their home position. The
circuits to the oven lamp, power transformer, fan motor
and turntable motor are cut off.
5. When the door is opened during a cook cycle, the
switches come to the following condition.
MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW
COOKING
When the microwave oven is preset for variable cooking
power, rated voltage is supplied to the power transformer
intermittently within a 32-second time base through the relay
contact which is coupled with the current-limiting relay. The
following levels of microwave power are given.
SETTING;
HIGH
MEDIUM HIGH
MEDIUM
MEDIUM LOW
LOW
NOTE: The ON/OFF time ratio does not exactly correspond
to the percentage of microwave power, because
approx. 2 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
Approx. 70%
14 sec. OFF
Approx. 50%
20 sec. OFF
Approx. 30%
26 sec. OFF
Approx. 10%
CONDITION
DURING DOOR OPEN
SWITCH CONTACT COOKING
1st. latch switches COM-NO Closed Open
2nd. interlock relay
control switch
Monitor switch COM-NC Open Closed
COM-NO Closed Open
(NO COOKING)
4
FUNCTION OF IMPORTANT COMPONENTS
R-241CWAA
R-241CWAC
R-241CWAP
DOOR OPEN MECHANISM
The door is opened by pulling the door, refer to the Figure D-
1.
Door
Latch Heads
1st. Latch
Switch
Latch Hook
2nd. Interlock
Relay Control
Switch
Monitor
Switch
Figure D-1. Door Open Mechanism
1ST. LATCH SWITCH AND 2ND. INTERLOCK RELAY CONTROL 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 1st latch switch and 2nd. interlock relay fail to open,
the fuse blows simultaneously with closing the contacts
(COM-NC) of the monitor switch.
CAUTION: BEFORE REPLACING A FUSE TEST THE
1ST LATCH SWITCH, 2ND. INTERLOCK
RELAY(RY2), 2ND. INTERLOCK RELAY
CONTROL SWITCH, MONITOR SWITCH AND
MONITOR RESISTOR FOR PROPER OPERATION. (REFER TO CHAPTER "TEST
PROCEDURE".)
HIGH VOLTAGE FUSE
The high voltage fuse blows when the high voltage rectifier
or the magnetron is shorted.
THERMAL CUT-OUT 125˚C (OVEN)
The thermal cut-out located on the top of the oven cavity is
designed to prevent damage to the oven if the foods in the
oven catch fire due to over heating produced by improper
setting of cook time or failure of control unit. Under normal
operation, the thermal cut-out remains closed. However,
when abnormally high temperatures are reached within the
oven cavity, the thermal cut-out will open at 125˚C, causing
the oven to shut down. The defective thermal cut-out must
be replaced with a new one.
THERMAL CUT-OUT 95˚C (MAGNETRON )
The thermal cut-out located on the top of the oven cavity is
designed to prevent damage to the magnetron if an over
heated condition develops in the tube due to cooling fan
failure, obstructed air guide, dirty or blocked air intake, etc.
Under normal operation, the thermal cut-out remains closed.
However, when abnormally high temperatures are reached
to the thermal cut-out , it will open at 95˚C, causing the oven
to shut down. When the magnetron has cooled to 75˚C, the
thermal cut-out closes and cook cycle will resume.
TURNTABLE MOTOR
The turntable motor drives the roller stay to rotate the
turntable.
FAN MOTOR
The fan motor drives a blade which draws external cool air.
This cool air is directed through the air vanes surrounding
the magnetron 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.
MONITOR RESISTOR 0.8Ω 20W
The monitor resistor prevents the fuse bursting when the
fuse blows due to the operation of the monitor switch.
FUSE
1. The fuse blows when the contacts (COM-NO) of the 1st
latch switch and 2nd. interlock relay remain closed with
the oven door open and when the monitor switch closes.
2. If the wire harness or electrical components are shortcircuited, the fuse M8A blows to prevent an electric shock
of fire hazard.
5
R-241CWAA
R-241CWAC
R-241CWAP
SERVICING
WARNING TO SERVICE PERSONNEL
Microwave ovens contain circuitry capable of producing very high voltage and current, contact with any part of the high
voltage circuit will result in electrocution. High voltage capacitor, Power transformer, Magnetron, High voltage rectifier
assembly, High voltage fuse, High voltage harness.
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 seconds 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 power
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 power transformer.
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 level 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 component being
tested.
When all service work is completed and the oven is fully assembled, the microwave power output should be
checked and microwave leakage test should be carried out.
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 procedure letter which will be found in the "Test Procedure"section.
IMPORTANT: If the oven becomes inoperative because of
a blown fuse M8A in the 1st. latch switch 2nd. interlock relay - monitor switch - monitor resistor circuit, check the 1st. latch switch,
2nd. interlock relay, 2nd. interlock relay control switch, monitor switch and monitor
resistor before replacing the fuse M8A.
6
R-241CWAA
R-241CWAC
R-241CWAP
CK = Check / RE = Replace
CONDITION
OFF
CONDITION
ON
CONDITION
TEST PROCEDURE
POSSIBLE CAUSE
AND
DEFECTIVE PARTS
PROBLEM
Home fuse blows when power
supply cord is plugged into
wall outlet.
FUSE M8A blows when power
supply cord is plugged into
wall outlet.
"88:88" does not appear in display but power supply cord is
plugged into wall outlet.
Display does not operate properly when stop/clear pad is
touched.
Oven lamp does not light at
door opened. (Display appears.)
Oven does not start when the
start pad is touched. (Display
appears)
Oven lamp does not light (Display appears.)
Fan motor does not operate.
(Display appears.)
Turntable motor does not operate. (Display appears.)
Oven or any electrical parts
does not stop when cooking
time is 0 or stop/clear pad is
touched.
Oven seems to be operating
but little or no heat is produced
in oven load. (Microwave
power level is set at HIGH)
Oven does not seems to be
operating properly when MEDIUM HIGH, MEDIUM, MEDIUM LOW or LOW is set.
(Oven operates properly at
HIGH and then the stop/clear
pad is touched the oven
stops.)
Oven goes into cook cycle but
shuts down before end of cooking cycle.
ABC
MAGNETRON
CK D
EEEFGGHHIKMN
POWER TRANSFORMER
H.V. RECTIFIER ASSEMBLY
HIGH VOLTAGE WIRE
HIGH VOLTAGE CAPACITOR
RECK CK RE CK CK CK CK CK
1ST. LATCH SWITCH
2ND. INTERLOCK RELAY CONTROL SWITCH
MONITOR SWITCH
MONITOR RESISTOR
THERMAL CUT-OUT 125˚C (OVEN)
THERMAL CUT-OUT 95˚C (MG)
FAN MOTOR
TURNTABLE MOTOR
FUSE M8A
TOUCH CONTROL PANEL
RELAY (RY-1, RY-2)
FOIL PATERN ON P.W.B.
POWER SUPPLY CORD
SHORTED WIRE HARNESS
OPENED WIRE HARNESS
OVEN LAMP OR SOCKET
WALL OUTLET
MISADJUSTMENT SWITCH
HOME FUSE OR BREAKER
LJ
BLOCKED COOLING FAN
BLOCKED VENTILATION
KEY UNIT
H.V. FUSE
7
R-241CWAA
R-241CWAC
R-241CWAP
TEST PROCEDURES
PROCEDURE
LETTER
A MAGNETRON TEST
NEVER TOUCH ANY PART IN THE CIRCUIT WITH YOUR HAND OR AN INSULATED TOOL
WHILE THE OVEN IS IN OPERATION.
CARRY OUT 3D CHECKS.
Isolate the magnetron from the high voltage circuit by removing all leads connected to the filament
terminal.
To test for an open circuit filament use an ohmmeter to make a continuity test between the magnetron
filament terminals, the meter should show a reading of less than 1 ohm.
To test for a short circuit filament to anode condition, connect ohmmeter between one of the filament
terminals and the case of the magnetron (ground). This test should be indicated an infinite resistance. If
a low or zero resistance reading is obtained then the magnetron should be replaced.
MICROWAVE OUTPUT POWER (1 litre water load)
The following test procedure should be carried out with the microwave oven in a fully assembled condition
(outer case fitted). Microwave output power from the magnetron can be measured by way of IEC 705, i.e.
it can be measured by using water load how much it can be absorbed by the water load. To measure the
microwave output power in the microwave oven, the relation of calorie and watt is used. When P(W)
heating works for t(second), approximately P x t/4.187 calorie is generated. On the other hand, if the
temperature of the water with V(ml) rises ∆T (˚C) during this microwave heating period, the calorie of the
water is V x ∆T.
COMPONENT TEST
The formula is as follows;
P x t / 4.187 = V x ∆ T P (W) = 4.187 x V x ∆T / t
Our condition for water load is as follows:
Room temperature..............around 20˚C Power supply Voltage.........Rated voltage
Water load.........1000 g Initial temperature...........10±2°C Heating time.........52 sec.
P = 80 x ∆ T
Measuring condition:
1. Container
The water container must be a cylindrical borosilicate glass vessel having a maximum material
thickness of 3 mm and an outside diameter of approximately 190 mm.
2. Temperature of the oven and vessel
The oven and the empty vessel are at ambient temperature prior to the start of the test.
3. Temperature of the water
The initial temperature of the water is (10±2)˚C.
4. Select the initial and final water temperature so that the maximum difference between the final water
temperature and the ambient temperature is 5˚C.
5. Select stirring devices and measuring instruments in order to minimize addition or removal of heat.
6.
The graduation of the thermometer must be scaled by 0.1˚C at minimum and an accurate thermometer.
7. The water load must be (1000±5) g.
8. “t” is measured while the microwave generator is operating at full power. Magnetron filament heat-up
time is not included.
NOTE: The operation time of the microwave oven is “t + 2” sec. 2 sec. is magnetron filament heat-up time.
Measuring method:
1. Measure the initial temperature of the water before the water is added to the vessel.
(Example: The initial temperature T1 = 11˚C)
2. Add the 1 litre water to the vessel.
3. Place the load on the centre of the shelf.
4. Operate the microwave oven at HIGH for the temperature of the water rises by a value ∆ T of
(10 ± 2)˚C.
5. Stir the water to equalize temperature throughout the vessel.
6. Measure the final water temperature. (Example: The final temperature T2 = 21°C)
7. Calculate the microwave power output P in watts from above formula.
8
TEST PROCEDURES
B
C
HIGH VOLTAGE RECTIFIER
R-241CWAA
R-241CWAC
R-241CWAP
PROCEDURE
LETTER
Initial temperature .................................................................................................. T1 = 11°C
Temperature after (52 + 2) = 54 sec. ..................................................................... T2 = 21°C
Temperature difference Cold-Warm.................................................................... ∆T1 = 10°C
Measured output power
The equation is “P = 80 x ∆T” ...................................................... P = 80 x 10°C = 800 Watts
JUDGMENT: The measured output power should be at least ± 15 % of the rated output power.
CAUTION: 1°C CORRESPONDS TO 80 WATTS. REPEAT MEASUREMENT IF THE POWER IS
INSUFFICIENT.
1000g
T1˚C
B POWER TRANSFORMER TEST
COMPONENT TEST
1000g
Heat up for 54 sec.
1000g
T2˚C
WARNING: High voltages and large currents are present at the secondary winding and filament
winding of the power transformer. It is very dangerous to work near this part when the
oven is on. NEVER make any voltage measurements of the high-voltage circuits,
including the magnetron filament.
CARRY OUT 3D CHECKS.
Disconnect the leads to the primary winding of the power transformer. Disconnect the filament and
secondary winding connections from the rest of the HV circuitry. Using an ohmmeter, set on a low range,
it is possible to check the continuity of all three windings. The following readings should be obtained:
R-241CWAA/241CWAC R-241CWAP (Peru)
Primary winding 1.6 ohms approximately 1.35 ohms approximately
Secondary winding 128 ohms approximately 123 ohms approximately
Filament winding less than 1 ohm
If the reading obtained are not stated as above, then the power transformer is probably faulty and should
be replaced.
CARRY OUT 4R CHECKS.
C HIGH VOLTAGE RECTIFIER ASSEMBLY TEST
HIGH VOLTAGE RECTIFIER TEST
CARRY OUT 3D CHECKS.
Isolate the high voltage rectifier assembly from the HV circuit. The high voltage rectifier can be tested
using an ohmmeter set to its highest range. Connect the ohmmeter across the terminal B+C of the high
voltage rectifier and note the reading obtained. Reverse the meter leads and note this second reading.
The normal resistance is infinite in one direction and more than 100 kΩ in the other direction.
CARRY OUT 4R CHECKS.
NOTE: FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIER, THE BATTERIES OF THE
MEASURING INSTRUMENT MUST HAVE A VOLTAGE AT LEAST 6 VOLTS, BECAUSE
OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIRECTIONS.
9
Loading...