Sharp R-4A68 User manual

R-4A68
SHARP CORPORATION
SERVICE MANUAL
In interests of user-safety the oven should be restored to its original
condition and only parts identical to those specified should be used.
MODEL R-4A68
S3613R4A68PX/
MICROWAVE OVEN
TABLE OF CONTENTS Page
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 ........................................................................................................................ 23
WIRING DIAGRAM ............................................................................................................................................. 24
PICTORIAL DIAGRAM ....................................................................................................................................... 25
CONTROL PANEL CIRCUIT ...............................................................................................................................26
PRINTED WIRING BOARD .................................................................................................................................27
PARTS LIST ....................................................................................................................................................... 28

R-4A68

R-4A68
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SERVICE MANUAL
PRODUCT SPECIFICATIONS
SHARP CORPORATION
OSAKA, JAPAN
TEST PROCEDURE
SERVICING AND
TROUBLESHOOTING CHART
FUNCTION OF IMPORTANT
COMPONENTS
OPERATING SEQUENCE
APPEARANCE VIEW
MICROWAVE MEASUREMENT
WIRING DIAGRAM
PARTS LIST
TOUCH CONTROL PANEL
ASSEMBLY
COMPONENT REPLACEMENT
AND ADJUSTMENT PROCEDURE
MICROWAVE OVEN
R-4A68
GENERAL IMPORTANT INFORMATION
ThisManualhasbeenpreparedtoprovideSharpCorp.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.
Serviceengineersshouldnotbeexposedtothemicrowave
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
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 dam-
aged, loosened or removed.

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PRODUCT SPECIFICATIONS
GENERAL INFORMATION
WARNING
THIS APPLIANCE MUST BE EARTHED
IMPOTANT
THE WIRES IN THIS MAINS LEAD ARE COLOURED IN ACCORDANCE WITH THE FOLLOWING CODE:
GREEN-AND-YELLOW : EARTH
BLUE : NEUTRAL
BROWN : LIVE
ITEM DESCRIPTION
Power Requirements 220 Volts
50 Hertz
Single phase, 3 wire earthed
Power Consumption 1.45 kW
Power Output 900 watts nominal of RF microwave energy (IEC 705)
Operating fequency 2450 MHz
Case Dimensions Width 550 mm
Height 314.5 mm
Depth 446 mm
Cooking Cavity Dimensions Width 378 mm
Height 217 mm
Depth 425 mm
Turntable diameter 360mm
Control Complement Touch Control System
Clock ( 1:00 - 12:59)
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
INSTANT ACTION pads
EXPRESS DEFROST pads
NUMBER pads
POWER LEVEL pad
AUTO START/CLOCK pad
STOP/CLEAR pad
INSTANT COOK/START pad
Set Weight Approx. 17 kg

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APPEARANCEVIEW
1. Ventilation openings
2. Oven lamp
3. Door hinges
4. Door safety latches
5. See through door
6. Doorsealsandsealingsurfaces
7. Coupling
8. Door open button
9. Touch control panel
10.Digital readout
11.Waveguide cover
12.Power supply cord
8
9
10
4
2
7
5
3
6
11 1
12
TOUCH CONTROL PANEL
aINSTANT ACTION PADS
Press to cook or reheat 9 popular menus.
bEXPRESS DEFROST PADS
Press to defrost meat.
cNUMBER PADS
Press to enter cooking times, clock time, weight or
quantity of food.
Press to set Safety Lock.
dAUTO START /CLOCK PAD
Press to set Clock or Auto Start time.
ePOWER LEVEL PAD
Press to select microwave power setting.
If not pressed, HIGH is automatically selected.
fSTOP/CLEAR PAD
Press to clear during programming.
Press once to stop operation of oven during cooking;
press twice to cancel cooking programme.
gINSTANT COOK/START PAD
Press once to cook for 1 minute at HIGH or increase
by 1 minute multiples each time this pad is pressed
during cooking.
Press to start oven after setting programmes.
Beverage
Dinner Plate
Casseroles
SNACKS&REHEAT
Pasta
Vegetable
FROZEN FOOD
Dinner Plate
INSTANT ACTION
To adjust quantity-touch pad again
Jacket Potato
Rice
Fresh Veg.
COOKING
Minced Meat
Steaks/Chops
EXPRESSDEFROST
ChickenPieces
12345
6789
AUTOSTART
CLOCK POWER
LEVEL
STOP
CLEAR INSTANTCOOK START
a
a
a
b
c
d
f
e
g
COOK SERVE CHECK DEF g
Indicator

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OPERATION SEQUENCE
OFF CONDITION
Closing the door activates all door interlock switches
(1st. latch switch and 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 point (A3+A5) in the control unit.
Figure O-1 on page 24
1. The display shows 88:88 .
2. Tosetanyprogramsorsettheclock,youmustfirsttouch
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
EnteradesiredcookingtimewiththetouchingNumberpads
and start the oven with touching START pad.
Function sequence
Figure O-2 on page 24
CONNECTED COMPONENTS RELAY
Oven lamp, Fan motor, Turntable motor RY1
Power transformer RY2
1. Rated voltage is supplied to the primary winding of the
powertransformer.Thevoltageisconvertedtoabout3.3
volts A.C. output on the filament winding and high
voltageofapproximately2000voltsA.C.onthesecondary
winding.
2. The filament winding voltage (3.3 volts) heats the
magnetron filament and the high voltage (2000 volts) is
senttothevoltagedoublingcircuit,whereitisdoubledto
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)intotheovencavity,wherethefoodisplacedto
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
CONDITION
DURING DOOR OPEN
SWITCH CONTACT COOKING (NOCOOKING)
1st. latch switches COM-NO Closed Open
2nd. interlock relay
control switch COM-NO Closed Open
Monitor switch COM-NC Open Closed
The circuits to the power transformer, fan motor and
turntablemotorarecutoffwhenthe1st.latchswitchand
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
therelay(RY1)stays closed. Showninthedisplayisthe
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 2nd. interlock relay.
6-1 Whentheoven door isopenedduringorafter the cycle
of a cooking program, the 1st. latch switch and 2nd.
interlock relay control switch must open their contacts
first.
Afterthat thecontacts(COM-NC) ofthemonitor switch
can be closed.
6-2. Whentheoven dooris closed,the contacts(COM-NC)
of the monitor switch must be opened. After that the
contactsofthe1st.latchswitchand2nd.interlockrelay
control switch are closed.
6-3. When the oven door is opened and the contacts of the
1st.latchswitchand2nd.interlockrelayremainclosed.
The fuse M8A will blow, because the monitor switch is
closed and a short circuit is caused.
VARIABLE 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 relay (RY2). The
following levels of microwave power are given.
SETTING;
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%
Approx. 50%
Approx. 30%
Approx. 10%
NOTE: TheON/OFFtimeratiodoesnotexactlycorrespond
to the percentage of microwave power, because
approx. 2 seconds are needed for heating up the
magnetron filament.

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FUNCTION OF IMPORTANT COMPONENTS
DOOR OPEN MECHANISM
Thedoorcanbeopenedbypushingthedooropenbuttonon
thecontrolpanel.Whenthedooropenbuttonispushed,the
latch lever is moved upward, operating the latch head. The
latch head is moved upward, and released from the latch
hook. Now, the door can be opened.
LATCH
HEADS
LATCH HOOK
2ND. INTERLOCK
RELAY CONTROL 
SWITCH
MONITOR 
SWITCH
SWITCH LEVER
1ST. LATCH 
SWITCH
Figure D-1. Door Open Mechanism
1ST. LATCH SWITCH AND 2ND. INTERLOCK RE-
LAY CONTROL SWITCH
1. Whenthe oven door is closed,thecontacts(COM - NO)
must be closed.
2. Whentheovendoorisopened,thecontacts(COM-NO)
must be opened.
MONITOR SWITCH
1. When the oven door is closed, the contacts (COM- NC)
must be opened.
2. Whenthe ovendoorisopened,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 (M8A) blows simultaneously with closing
the contacts (COM-NC) of the monitor switch.
CAUTION: BEFORE REPLACING A BLOWN FUSE (M8A)
TEST THE 1ST. LATCH SWITCH, 2ND. IN-
TERLOCK RELAY, 2ND. INTERLOCK RELAY
CONTROL SWITCH, MONITOR SWITCH AND
MONITOR RESISTOR FOR PROPER OP-
ERATION. (REFER TO CHAPTER “TEST
PROCEDURE”.)
MONITOR RESISTOR (0.8Ω20W)
Themonitorresistorpreventsthefuse(M8A)burstingwhen
the fuse blows due to the operation of the monitor switch.
THERMAL CUT-OUT 145˚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 oven thermal cut-out remains closed. How-
ever, when abnormally high temperatures are reached
within the oven cavity, the oven thermal cut-out will open at
145˚C, causing the oven to shut down. The defective
thermal cut-out must be replaced with new one.
FUSE (M8A)
1. If the wire harness or electrical components are short-
circuited, this fuse blows to prevent an electric shock or
fire hazard.
2. Thefusealsoblowswhenthecontacts(COM-NO)ofthe
1st. latch switch and 2nd. interlock relay remain closed
with the oven door open and then the monitor switch
closes.
TEMPERATURE FUSE 150˚C (MG)
Thisfuseprotectsthemagnetronagainstoverheating.Ifthe
temperature goes up higher than 150˚C because the fan
motor is interrupted, the air inlet duct is blocked or the
ventilationopeningsareobstructed,thefuseblowsandputs
the oven out of operation.
The defective fuse must be replaced with new rated one.
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 chan-
nelled through the oven cavity to remove steam and va-
pours given off from the heating foods. It is then exhausted
through the exhausting air vents at the oven cavity.
TURNTABLE MOTOR
The turntable motor drives the turntable roller assembly to
rotate the turntable.

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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 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 con-
nection of the high-voltage capacitor (that is, of the
connectingleadof thehigh-voltagerectifier)against
thechassiswith theuseofan 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
theouter casehasbeen removed,inthis eventcarryout
3D checks and then disconnect the leads to the primary
of the power transformer. Ensure that these leads re-
main 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) Reconnectallleadsremovedfromcomponentsduring
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
thepresenceofmicrowave energy withinacavity,place
acupofcoldwateronthe oven turntable, close the door
andset the microwavetimerfor two(2)minutes.Setthe
powerleveltoHIGHand push the START button. When
the two minutes has elapsed (timer at zero) carefully
checkthatthewaterisnowhot.Ifthewaterremainscold
carry out3D checks and re-examine the connections to
the component being tested.
Whenallserviceworkiscompleted,andtheoven isfullyassembled,themicrowavepoweroutputshouldbechecked
and microwave leakage test carried out
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.
TROUBLESHOOTING GUIDE
IMPORTANT: Iftheovenbecomesinoperativebecauseof
a blown fuse M8A in the 1st. latch switch -
2nd.interlockrelay -monitorswitch - moni-
torresistorcircuit,checkthe1st.latchswitch,
2nd. interlock relay, 2nd. interlock relay
control switch, monitor switch and monitor
resistor before replacing the fuse M8A.

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MAGNETRON POWER TRANSFORMER
H.V. RECTIFIER ASSEMBLY HIGH VOLTAGE CAPACITOR 1ST. LATCH SWITCH 2ND. INTERLOCK RELAY CONTROL SWITCH MONITOR SWITCH
MONITOR RESISTOR TEMPERATURE FUSE THERMAL CUT-OUT FAN MOTOR TURNTABLE MOTOR
FUSE M8A TOUCH CONTROL PANEL RELAY (RY-1, RY-2) FOIL PATTERN ON P.W.B. POWER SUPPLY CORD OVEN LAMP OR SOCKET
HIGH OLTAGE WIRE SHORTED WIRE HARNESS OPENED WIRE HARNESS WALL OUTLET HOME FUSE OR BREAKER
WRONG OPERATION MISADJUSTMENT SWITCH BLOCKED COOLING FAN BLOCKED VENTILATION OPENING
Home fuse blows when power
supply cord is plugged into wall
outlet.
FUSE M8A blows when power
supply cord is plugged into wall
outlet.
Display does not show anything
when power supply cord is
plugged into wall outlet.
Display does not operate prop-
erly 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 (Dis-
play appears.)
Fanmotordoesnotoperate.(Dis-
play appears.)
Turntable motor assembly does
not operate. (Display appears.)
Ovenoranyelectricalpartsdoes
notstopwhencookingtimeis0or
TOP / 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)
Ovendoesnotseemstobeoper-
ating properly when MEDIUM
HIGH, MEDIUM, MEDIUM LOW
or LOW is set. (Oven operates
properly at HIGH and when the
TOP/CLEAR pad istouchedthe
oven stops.)
Oven goes into cook cycle but
shuts down before end of cook-
ing cycle.
OFF
CONDITION
TEST PROCEDURE
ON
CONDITION
CK = Check / RE = Replace
ABC D EEEFGGHHIJLMRE RECKCK CKCK CKCK CKCK CK
PROBLEM
CONDITION
POSSIBLE CAUSE
AND
DEFECTIVE PARTS

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TEST PROCEDURES
PROCEDURE
LETTER
CARRY OUT 3D CHECKS.
Isolate the magnetron from high voltage circuit by removing all leads connected to 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 short 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 (IEC705)
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.
Tomeasurethemicrowaveoutputpower inthemicrowaveoven, therelationof calorieandwattis 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.
NEVER TOUCH ANY PART IN THE CIRCUIT WITH YOUR HAND OR AN INSULATED TOOL
WHILE THE OVEN IS IN OPERATION.
AMAGNETRON 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 PowersupplyVoltage.........Ratedvoltage
Water load.........1000 g Initial temperature...........10±2°C Heating time.........47 sec.
P = 90 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 the test.
3. Temperature of the water
The initial temperature of the water is (10±2)°C.
4. Selecttheinitialandfinalwatertemperaturesothatthemaximumdifference 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. Thegraduation ofthethermometermustbescaledby 0.1°Cat minimumandaccurate 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.
COMPONENT TEST