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
1
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

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9
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
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.
Initial temperature .................................................................................................. T1 = 11°C
Temperature after (47 + 2) = 49sec. ...................................................................... T2 = 21°C
Temperature difference Cold-Warm.................................................................... ∆T1 = 10°C
Measured output power
The equation is “P = 90 x ∆T” ...................................................... P = 90 x 10°C = 900 Watts
JUDGMENT: The measured output power should be at least ±15 % of the rated output power.
CAUTION: 1°C CORRESPONDS TO 90 WATTS REPEAT MEASUREMENT IF THE POWER IS
INSUFFICIENT.
1000g
1000g
1000g
T1˚C T2˚C
Heat up for 49 sec.
B POWER TRANSFORMER TEST
WARNING: Highvoltagesandlargecurrentsarepresentatthesecondarywindingandfilament
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
secondarywindingconnectionsfromtherestoftheHVcircuitry.Usinganohmmeter,setonalowrange,
it is possible to check the continuity of all three windings. The following readings should be obtained:
a. Primary winding ....................approx. 1.13 Ω
b. Secondary winding ...............approx. 104.4 Ω
c. Filament winding...................less than 1Ω
Ifthereadingobtainedarenotstatedasabove,thenthepowertransformerisprobablyfaultyandshould
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 kΩin the other direction.

R-4A68
10
TEST PROCEDURES (CONT'D)
COMPONENT TEST
PROCEDURE
LETTER
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.
BC
HIGH VOLTAGE RECTIFIER
D HIGH VOLTAGE CAPACITOR TEST
CARRY OUT 3D CHECKS.
A. Isolate the high voltage capacitor from the circuit.
B. Continuity check must be carried out with measuring instrument which is set to the highest resistance
range.
C. Anormalcapacitorshowscontinuityforashorttime(kick)andthenaresistanceofabout10MΩafterithas
been charged.
D. A short-circuited capacitor shows continuity all the time.
E. An open capacitor constantly shows a resistance about 10 MΩbecause of its internal 10MΩresistance.
F. When the internal wire is opened in the high voltage capacitor shows an infinite resistance.
G. The resistance across all the terminals and the chassis must be infinite when the capacitor is normal.
If incorrect reading are obtained, the high voltage capacitor must be replaced.
CARRY OUT 4R CHECKS.
ESWITCH TEST
CARRY OUT 3D CHECKS.
Isolate the switch to be tested and using an ohmmeter check between the terminals as described in the
following table. Table: Terminal Connection of Switch
Plunger Operation COM to NO COM to NC
Released O.C. S.C.
Depressed S.C. O.C.
COM; Common terminal,
NO; Normally open terminal
NC; Normally close terminal
S.C.; Short circuit
O.C.; Open circuit
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
CARRY OUT 4R CHECKS.
FMONITOR RESISTOR TEST
CARRY OUT 3D CHECKS.
Disconnecttheleadsfromthemonitorresist.Usinganohmmeterandsetonalowrange.Checkbetween
the terminals of the monitor resistor.
The resistance of monitor resistor is approx. 0.8 ohms.
If incorrect readings are obtained, replace the monitor resistor.
CARRY OUT 4R CHECKS.
G TEMPERATURE FUSE OR THERMAL CUT-OUT TEST
CARRY OUT 3D CHECKS.
Disconnect the leads from the terminals of the temperature fuse or thermal cut-out. Then using an
ohmmeter, make a continuity test across the two terminals as described in the table below.
CARRY OUT 4R CHECKS.-

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11
TEST PROCEDURES (CONT'D)
PROCEDURE
LETTER COMPONENT TEST
.Table: Thermal cut-out Test
Temperature of "ON" condition Temperature of "OFF" condition Indication ofohmmeter
Parts Name (closed circuit) (˚C) (open circuit) (˚C) (When room temperature
is approx. 20˚C)
Thermal cut-out 145˚C This is not resetable type. Above 145˚C Closed circuit.
Temperature fuse 150˚C This is not resetable type. Above 150˚C Closed circuit.
If incorrect readings are obtained, replace the temperature fuse or thermal cut-out.
Anopencircuit temperaturefuse150˚C(MG) indicates thatthemagnetronhas overheated,thismaybe
due to restricted ventilation, cooling fan failure or a fault condition within the magnetron or HV circuit.
An open circuit thermal cut-out 145˚C (OVEN) indicates that the foods in the oven may catch fire, this
may be due to over heating produced by improper setting of the cooking time or failure of the control
panel.
CARRY OUT 3D CHECKS.
Disconnect the leads from the motor.
Using an ohmmeter, check the resistance between the two terminals as described in the table below.
HMOTOR WINDING TEST
Table: Resistance of Motor
Motors Resistance
Fan motor Approximately 295 Ω
Turntable motor Approximately 12.2 kΩ
If incorrect readings are obtained, replace the motor.
CARRY OUT 4R CHECKS.
IBLOWN FUSE M8A
CARRY OUT 3D CHECKS.
1. If the fuse M8A is blown, there could be shorts or ground in electrical parts or wire harness.
Check them and replace the defective parts or repair the wire harness.
2. If the fuse M8A is blown when the door is opened, check the 1st. latch switch, 2nd. interlock relay
control switch, 2nd. interlock relay, monitor switch and monitor resistor.
IfthefuseM8Aisblownbyincorrectdoorswitchingreplacethedefectiveswitch(s)andthefuseM8A.
CARRY OUT 4R CHECKS.
CAUTION: ONLY REPLACE FUSE M8A WITH THE CORRECT VALUE REPLACEMENT.
J TOUCH CONTROL PANEL ASSEMBLY TEST
The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore,
unlike conventional microwave ovens, proper maintenance cannot be performed with only a voltmeter
and ohmmeter.
In this service manual, the touch control panel assembly is divided into two units, Control Unit and Key
Unit, and troubleshooting by replacement is described according to the symptoms indicated.
1. Key Unit Note : Check key unit ribbon connection before replacement.
The following symptoms indicate a defective key unit. Replace the key unit.
a) When touching the pads, a certain pad produces no signal at all.
b) When touching a number pad, two figures or more are displayed.
c) When touching the pads, sometimes a pad produces no signal.
2. Control Panel
The following symptoms indicate a defective control unit. Before replacing the control unit,

R-4A68
12
PROCEDURE
LETTER COMPONENT TEST
TEST PROCEDURES (CONT'D)
perform the Key unit test (Procedure L) to determine if control unit is faulty.
2-1 In connection with pads.
a) When touching the pads, a certain group of pads do not produce a signal.
b) When touching the pads, no pads produce a signal.
2-2 In connection with indicators
a) At a certain digit, all or some segments do not light up.
b) At a certain digit, brightness is low.
c) Only one indicator does not light.
d) The corresponding segments of all digits do not light up; or they continue to light up.
e) Wrong figure appears.
f) A certain group of indicators do not light up.
g) The figure of all digits flicker.
2-3 Other possible troubles caused by defective control unit.
a) Buzzer does not sound or continues to sound.
b) Clock does not operate properly.
c) Cooking is not possible.
K KEY UNIT TEST
If the display fails to clear when the STOP/CLEAR pad is depressed, first verify the flat ribbon is marking
good contact, verify that the door sensing switch (stop switch) operates properly; that is the contacts are
closed when the door is closed and open when the door is open. If the door sensing switch (stop switch)
is good, disconnect the flat ribbon cable that connects the key unit to the control unit and make sure the
door sensing switch is closed (either close the door or short the door sensing switch connecter). Use the
Key unit matrix indicated on the control panel schematic and place a jumper wire between the pins that
correspond to the STOP/CLEAR pad marking momentary contact. If the control unit responds by clearing
with a beep the key unit is faulty and must be replaced. If the control unit does not respond, it is faulty and
must be replaced. If a specific pad does not respond, the above method may be used (after clearing the
control unit) to determine if the control unit or key pad is at fault.
G12
G11
G10
G 9
G 8 G 7 G 6 G 5 G 4 G 3 G 2 G 1
KEY UNIT
54321
09876
POWER
LEVEL INSTANT
COOK

START
CLOCK
Pasta
Vegetable
STOP
CLEAR Steaks
/Chops Minced Meat
Dinner
Plate
( FROZEN
FOOD)
AUTO
START
Chicken
Pieces
Beverage
Dinner
Plate
( SNACKS &
REHEAT)
Jacket
Potato
Fresh
Veg.
Casseroles
Rice
L RELAY TEST
CARRY OUT 3D CHECKS.
Remove the outer case and check the voltage between Pin Nos. 3 and 5 of the 3 pin connector (A) on the
control unit with an A.C. voltmeter.
The meter should indicate 220 volts, if not check oven circuit.
RY1 and RY2 Relay Test
These relays are operated by D.C. voltage.
Check voltage at the relay coil with a D.C. voltmeter during the microwave cooking operation.
DC. voltage indicated .............. Defective relay.
DC.voltage not indicated........Check diodewhichis connectedtothe relay coil.If diode isgood,control

R-4A68
13
TEST PROCEDURES (CONT'D)
PROCEDURE
LETTER COMPONENT TEST
unit is defective.
RELAY SYMBOL OPERATIONAL VOLTAGE CONNECTED COMPONENTS
RY1 APPROX. 13.5V D.C. Oven lamp / Turntable motor / Cooling fan motor
RY2 APPROX. 13.0V D.C. Power transformer
CARRY OUT 4R CHECKS.
MPROCEDURES TO BE TAKEN WHEN THE FOIL PATTERN ON THE PRINTED WIRING BOARD
(PWB) IS OPEN
a
b
cd
13
P
RY1
VRS1
29
5
CN-A 1
(J4)
(J1)
T1
To protect the electronic circuits, this model is provided with a fine foil pattern added to the primary on the
PWB, this foil pattern acts as a fuse. If the foil pattern is open, follow the troubleshooting guide given
below for repair.
Problem: POWER ON, indicator does not light up.
CARRY OUT 3D CHECKS.
STEPS OCCURANCE CAUSE OR CORRECTION
1 The rated AC voltage is not present at Check supply voltage and oven power cord.
POWER terminal of CPU connector (CN-A).
2 The rated AC voltage is present at primary Low voltage transformer or secondary circuit defective.
side of low voltage transformer. Check and repair.
3 Only pattern at "a" is broken. *Insert jumper wire J1 and solder.
(CARRY OUT 3D CHECKS BEFORE REPAIR)
4 Pattern at "a" and "b" are broken. *Insert the coil RCILF2003YAZZ between "c" and "d".
(CARRY OUT 3D CHECKS BEFORE REPAIR)
NOTE: *At the time of making these repairs, make
avisualinspectionofthevaristor.checkfor
burned damage and examine the trans-
formerwithatesterforthepresenceoflayer
short-circuit(checkprimarycoilresistance).
If any abnormal condition is detected, re-
place the defective parts.
CARRY OUT 4R CHECKS.

14
R-4A68
The touch control section consists of the following units
as shown in the touch control panel circuit.
(1) Key Unit
(2) Control Unit
The principal functions of these units and the signals com-
municated among them are explained below.
Key Unit
The key unit is composed of a matrix, signals generated in
the LSI are sent to the key unit through R51, R52, R53, R60,
R61, R62 and R63.
When a key pad is touched, a signal is completed through
the key unit and passed back to the LSI through R81, R82,
R83 and R90 to perform the function that was requested.
Control Unit
Control unit consists of LSI, power source circuit, synchro-
nizing signal circuit, ACL circuit, buzzer circuit and indicator
circuit.
1) LSI
This LSI controls the key strobe signal, relay driving signal
for oven function and indicator signal.
2) Power Source Circuit
This circuit generates voltages necessary in the control
unit.
Symbol Voltage Application
VC -5V LSI(IC1)
TOUCH CONTROL PANEL ASSEMBLY
OUTLINE OF TOUCH CONTROL PANEL
3) Synchronizing Signal Circuit
Thepowersourcesynchronizingsignalisavailableinorder
to compose a basic standard time in the clock circuit. It
accompanies a very small error because it works on
commercial frequency.
4) ACL Circuit
A circuit to generate a signals which resets the LSI to the
initial state when power is supplied.
5) Buzzer Circuit
The buzzer is responsive to signals from the LSI to emit
audible sounds (key touch sound and completion sound).
6) Door Sensing Switch
A switch to “tell” the LSI if the door is open or closed.
7) Relay Circuit
To drive the magnetron, fan motor, turntable motor and
light the oven lamp.
8) Indicator Circuit
Indicator element is a Light-emitting diode.
Basically,a Light-emittingdiode istriode havinga cathode
and an anode.
The Light-emitting diode has 4-digits, 9-segments are
used for displaying figures.

15
R-4A68
DESCRIPTION OF LSI
LSI(IZA690DR)
The I/O signal of the LSI(IZA690DR) are detailed in the following table.
Pin No. Signal I/O Description
1 XOUT OUT Internal clock oscillation frequency control output.
Output to control oscillation input of XOUT.
2 XIN IN Internal clock oscillation frequency input setting.
Theinternalclockfrequencyissetbyinsertingtheceramicfilteroscillationcircuitwithrespect
to XIN terminal.
3 RESET IN Auto clear terminal.
Signal is input to reset the LSI to the initial state when power is supplied. Temporarily set to
“L” level the moment power is supplied, at this time the LSI is set. Thereafter set at “H” level.
4 R70 OUT Segment data signal.
Refer to the touch control panel circuit for the relationship between signals and indicators.
Normally, one pulse is output in every synchronized signal period, and input to the anode of
the light-emitting diode.
5 PULSE OUT Signal to sound buzzer.
A: key touch sound(0.12sec.).
B: Completion sound(2.4sec.).
6 R72 OUT Digit selection signal.
Refer to the touch control panel circuit about the relation between signals and digits.
Normally, one pulse is output in every synchronized signal period, and input to the light-
emitting diode.
7-9 R40-R42 OUT Digit selection signal.
Refer to the touch control panel circuit about the relation between signals and digits.
Normally, one pulse is output in every synchronized signal period, and input to the light-
emitting diode.
10 AIN3 IN Terminal to change cooking constant.
11 R50 OUT Segment data signal.
Signal similar to R70.
12 R51 OUT Segment data signal.
Signal similar to R70.
Key strobe signal.
Signalappliedtotouch-keysection.ApulsesignalisinputtoR81,R82,R83andR90terminal
while one of G2 line keys on key matrix is touched.
13 R52 OUT Segment data signal.
Signal similar to R70.
Key strobe signal.
Signalappliedtotouch-keysection.ApulsesignalisinputtoR81,R82,R83andR90terminal
while one of G3 line keys on key matrix is touched.
14 VSS IN Connected to VC.
15 R53 OUT Segment data signal.
Signal similar to R70.
Key strobe signal.
Signalappliedtotouch-keysection.ApulsesignalisinputtoR81,R82,R83andR90terminal
while one of G4 line keys on key matrix is touched.
16 R60 OUT Segment data signal.
Signal similar to R70.
Key strobe signal.
Signalappliedtotouch-keysection.ApulsesignalisinputtoR81,R82,R83andR90terminal
while one of G5 line keys on key matrix is touched.
17 R61 OUT Segment data signal.
Signal similar to R70.
Key strobe signal.
Signalappliedtotouch-keysection.ApulsesignalisinputtoR81,R82,R83andR90terminal
while one of G6 line keys on key matrix is touched.

16
R-4A68
18 R62 OUT Segment data signal.
Signal similar to R70.
Key strobe signal.
Signalappliedtotouch-keysection.ApulsesignalisinputtoR81,R82,R83andR90terminal
while one of G7 line keys on key matrix is touched.
19 R63 OUT Segment data signal.
Signal similar to R70.
Key strobe signal.
Signalappliedtotouch-keysection.ApulsesignalisinputtoR81,R82,R83andR90terminal
while one of G8 line keys on key matrix is touched.
20 INT2 IN Signal synchronized with commercial source frequency(50Hz).
This is basic timing for time processing of LSI.
21 R81 IN Signal coming from touch key.
WheneitheroneofG9linekeysonkeymatrixistouched,acorrespondingsignal outofR51,
R52, R53, R60, R61, R62, R63 will be input into R81. When no key is touched, the signal is
held at "L" level.
22 R82 IN Signal coming from touch key.
WheneitheroneofG10linekeysonkeymatrixistouched,acorrespondingsignaloutofR51,
R52, R53, R60, R61, R62, R63 will be input into R82.
23 R83 IN Signal coming from touch key.
WheneitheroneofG11linekeysonkeymatrixistouched,acorrespondingsignaloutofR51,
R52, R53, R60, R61, R62, R63 will be input into R83.
24 R90 IN Signal coming from touch key.
WheneitheroneofG12linekeysonkeymatrixistouched,acorrespondingsignaloutofR51,
R52, R53, R60, R61, R62, R63 will be input into R90.
25 R91 OUT Oven lamp, turntable motor and cooling fan motor driving signal. (Square Waveform
: 50Hz)
To turn on and off the control relay. The pulse signal (50Hz) is delivered to the control relay
driving circuit and cook relay control circuit.
26 R92 OUT Magnetron high-voltage circuit driving signal.
Toturn onand offthe cookrelay. In100% poweroperation, thesignals holds“L” levelduring
microwave cooking and “H” level while not cooking. In other cooking modes (70%,
50%,30%,10% power operation) the signal turns to “H” level and “L” level in repetition
according to the power level.
27 KEO IN Input signal which communicates the door open/close information to LSI.
Door closed; “H” level signal.
Door opened; “L” level signal.
28 VDD IN Connected to GND.
Pin No. Signal I/O Description

17
R-4A68
SERVICING
1. Precautions for Handling Electronic Components
This unit uses CMOS LSI in the integral part of the circuits.
Whenhandlingtheseparts,thefollowingprecautionsshould
bestrictlyfollowed.CMOSLSIhaveextremelyhighimped-
ance at its input and output terminals. For this reason, it is
easily influenced by the surrounding high voltage power
source, static electricity charge in clothes, etc. and some-
timesitisnotfullyprotectedbythebuilt-inprotectioncircuit.
In order to protect CMOS LSI.
1) When storing and transporting, thoroughly wrap them in
aluminiumfoil.Also wrapallPW boards containingthemin
aluminium foil.
2) When soldering, ground the technician as shown in the
figure and use grounded soldering iron and work table.
approx. 1M ohm
2. Shapes of Electronic Components
3
2
1ECB
3. Servicing of Touch Control Panel
Wedescribetheprocedurestopermitservicingofthetouch
control panel of the microwave oven and the precautions
you must take when doing so. To perform the servicing,
power supply to the touch control panel is available either
from the power line of the oven itself or from an external
power source.
(1) Servicingthetouchcontrolpanelwith power supplyof
the oven:
CAUTION:
THEHIGHVOLTAGE TRANSFORMEROFTHEMICRO-
WAVE OVEN IS STILL LIVE DURING SERVICING
PRESENTS A HAZARD.
Therefore, when checking the performance of the touch
control panel, put the outer cabinet on the oven to avoid
touching the high voltage transformer, or unplug the pri-
maryterminal(connector)ofthehighvoltagetransformerto
turn it off; and the end of such connector must be insulated
with an insulating tape. After servicing, be sure to replace
the leads to their original locations.
A.Onsome models,the powersupplycordbetweenthe touch
controlpanelandtheovenitselfissoshortthatthetwocan’t
be separated. For those models, check and repair all the
controls(sensor-relatedonesincluded)ofthetouchcontrol
panel while keeping it connected to the oven.
B.Onsome models,the powersupplycordbetweenthe touch
control panel and the oven proper is long enough that they
may be separated from each other. For those models,
therefore, it is possible to check and repair the controls of
thetouchcontrol panelwhilekeeping itapartfromtheoven
proper; in this case you must short both ends of the door
sensing switch (on PWB) of the touch control panel with a
jumper, which brings about an operational state that is
equivalenttotheovendoorbeingclosed.Asforthesensor-
related controls of the touch control panel, checking them
is possible if dummy resistor(s) with resistance is equal to
that of the controls are used.
(2) Servicing the touch control panel with power supply
from an external power source:
Disconnect the touch control panel completely from the
oven proper, and short both ends of the door sensing
switch (on PWB) of the touch control panel, which brings
about an operational state that is equivalent to the oven
doorbeingclosed.Connectanexternalpowersourcetothe
power input terminal of the touch control panel, then it is
possible to check and repair the controls of the touch
controlpanelitis also possible to check thesensor-related
controls of the touch control panel by using the dummy
resistor(s).
4. Servicing Tools
Toolsrequiredtoservicethetouchcontrolpanelassembly.
1) Soldering iron: 30W
(Itisrecommendedtouseasolderingironwithagrounding
terminal.)
2) Oscilloscope: Single beam, frequency range: DC-10MHz
type or more advanced model.
3) Others: Hand tools
5. Other Precautions
1) Before turning on the power source of the control unit,
remove the aluminium foil applied for preventing static
electricity.
2) After aluminium foil is removed, be careful that abnormal
voltageduetostaticelectricityetc.isnotappliedtotheinput
or output terminals.
3) Attach connectors, electrolytic capacitors, etc. to PWB,
making sure that all connections are tight.
4) Besureto use specified components wherehighprecision
is required.
IC
LM7905CT
Transistor
KRA101M
KRA222M
KRA223M
KRC101M
KRC243M

18
R-4A68
COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE
WARNING: Avoid possible exposure to microwave energy. Please follow the instructions below before
operating the oven.
1. Door does not close firmly.
2. Door hinge, support or latch hook is damaged.
3. The door gasket or seal or damaged.
4. The door is bent or warped.
5. There are defective parts in the door interlock system.
6. There are defective parts in the microwave generating
and transmission assembly.
7. There is visible damage to the oven.
Do not operate the oven:
1. Without the RF gasket (Magnetron).
2. If the wave guide or oven cavity are not intact.
3. If the door is not closed.
4. If the outer case (cabinet) is not fitted.
1. Disconnect the oven from the power supply.
2. Make sure that a definite” click” can be heard when the
microwave oven door is unlatched. (Hold the door in a
closed position with one hand, then push the door open
button with the other, this causes the latch leads to rise,
it is then possible to hear a “click’ as the door switches
operate.)
3. Visuallycheckthedoorandcavityfaceplatefordamage
(dents, cracks, signs of arcing etc.).
Carry out any remedial work that is necessary before
operating the oven.
Do not operate the oven if any of the following conditions
exist;
Please refer to ‘OVEN PARTS, CABINET PARTS, CONTROL PANEL PARTS, DOOR PARTS’, when carrying out any of
the following removal procedures: OUTER CASE REMOVAL
To remove the outer case, proceed as follows.
1. Disconnect oven from power supply.
2. Open the oven door and wedge it open.
3. Removethefour(4)screwsfromrearandalongtheside
edge of case.
4. Slide the entire case back about 1 inch (3 cm) to free it
from retaining clips on the cavity face plate.
5. Lift the entire case from the oven.
6. Discharge the H.V. capacitor before carrying out any
further work.
7. Do not operate the oven with the outer case removed.
N.B.; Step 1,2 and 6 from the basis of the 3D checks.
CAUTION: DISCHARGE HIGH VOLTAGE CAPACITOR
BEFORE TOUCHING ANY OVEN COMPO-
NENTS OR WIRING.
1. CARRY OUT 3D CHECKS.
2. Disconnect wire leads from power transformer,
magnetron and capacitor terminals.
3. Remove four (4) screws holding transformer to bottom
plate.
4. Remove transformer from bottom plate.
Re-install
1. Rest transformer on the bottom plate with its primary
Removal
1. CARRY OUT 3D CHECKS.
2. Disconnect wire leads from magnetron.
3. Remove the two (2) screws holding the magnetron air
ducttomagnetron. And slide magnetron air duct slightly
so that two (2) screws at left hand side of magnetron
appear.
4. Carefullyremovethe four (4)screwsholdingmagnetron
to waveguide flange.
5. Removemagnetronwithcaresothatmagnetronantenna
is not hit by any metal object around antenna.
6. Now, the magnetron is free.
Re-install
1. Re-install the magnetron to waveguide flange with care
POWER TRANSFORMER REMOVAL
terminals toward front side.
2. Secure the transformer with four (4) screws to bottom plate.
3. Re-connect wire leads (primary and high voltage) to
power transformer and filament leads of transformer to
magnetron and high voltage capacitor. Refer to
"PICTORIAL DIAGRAM".
4. Re-install outer case and check that oven is operating
properly.
MAGNETRON REMOVAL
so that magnetron antenna is not hit by any metal
object.
2. Secure the magnetron with four (4) screws.
3. Hold the magnetron air duct to the magnetron and
secure the magnetron air duct with two (2) screw.
4. Re-connect the wire leads to the magnetron. Refer to
"PICTORIAL DIAGRAM".
5. Re-install outer case and check that the oven is
operating properly.
CAUTION: WHEN REPLACING MAGNETRON, BE
SURE THE R.F. GASKET IS IN PLACE AND
MOUNTING SCREWS ARE TIGHTENED
SECURELY.