Sharp R-3A55 User manual

R-3A55
SHARP SERVICE MANUAL S8304 R3A55PJ/
MICROWAVE OVEN
” -.- _~__ _ _ Momx R-3A55
In interests of user-safety the oven should be restored to its original condi-
TABLE OF CONTENTS page
GENERAL IMPORTANT INFORMATiON.. ................................................................................................... .I
WARNING ...................................................................................................................................................... 1
RODUCT SPECIFICATIONS ......................................................................................................................... 2
APPEARANCE VIEW .................................................................................................................................... 3
OPERATING SEQUENCE .............................................................................................................................
FUNCTION OF IMPORTANT COMPONENTS’ ............................................................................................ .:
TRABLESHOOTING CHART ......................................................................................................................... 7
TEST PROCEDURE ...................................................................................................................................... 9
TOUCH CONTROL PANEL ......................................................................................................................... 16
COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE ........................................................ 21
MICROWAVE MEASUREMENT .................................................................................................................. 26
WIRING DIAGRAM ...................................................................................................................................... 27
PICTORIAL DIAGRAM ............................................................................................................................. ...2 8
CONTROL PANEL CIRCUIT ....................................................................................................................... 29
PRINTED WIRING BOAD ........................................................................................................................... .30
PARTS LIST ................................................................................................................................................. 31
SHARP CORPORATION

SERVICE MANUAL
MICROWAVE OVEN
R-3A55
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 en-
tire text of this manual. so that they will be qualified to render sat-
isfactory customer service.
CAUTION
MICROWAVE RADIATION
Service engineers should not be exposed to the microwave en-
ergy which may radiate from the magnetron or other microwave
generating devices if it is improperly used or connected. All in-
put and output microwave connections, waveguides, flanges
andgaskets must be secured. Never operate the device without
a microwave energy absorbing load attached. Never look into
an open waveguide.
7
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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 25OV.
Removal of the outer wrap gives access to potentials above
25ov.
PRODUCT SPECIFICATION
OPEARTING SEQUENCE
TOUCH CONTROL PANEL
AND ADJUSTMENT PROCEDURE A
----- -P
MICROWAVE MESUREMENT
WIRING DIAGRAMS
PARTS LIST
SHARP CORPORATION
OSAKA, JAPAN

Fb3A55
PRODUCT SPECIFICATIONS
ITEM
Power Requirements 240 Volts
50 Hertz
DESCRIPTION
Power Consumption
Power Output
Case Dimensions
Single phase, 3 wire earthed
1.35 kW Approx. 6.1A
750 watts nominal of RF microwave energy (AS 2895 1986)
850 watts (IEC-705-1988 )
Operating frequency of 2450MHz
Width 520mm
Height 305mm
Depth 385mm
Cooking Cavity Dimensions Width 348mm
Height 197mm
Depth 368mm
Turntable diameter
Control Complement 325mm Touch Control System
Clock ( 1:00 - 12:59)
Timer (0 - 99 minutes 99 secinds)
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 (8 menu)
AUTO COOK pad
EASY DEFROST
NUMBER pads
POWER LEVEL pad
MORE. LESS pads
STOP/CLEAR pad
AUTO START/CLOCK pad
INSTANT COOK/START pad
A---a.* 4P I.-
nuurux. 13 KCI
GENERAL INFORMATION
WARNING
THIS APPLIANCE BE EARTHED
IMPORTANT
THE WIRES IN THIS MAINS LEAD ARE COLOURED IN ACCORDANCE WITH THE FOLLOWING CODE:
GREEN-AND-YELLOW : EARTH
BLUE : NEUTRAL
BROWN : LIVE
NOTE: Numbers and letters shown after sentences such as “RD44101 IJ” are for factory use only.
2

R-3A55
APPEARANCE VIEW
.fi (Top)
/‘-
1. Ventilation openings
2. Oven lamp
3. Door hinges
4. Door safety latches
5. See through door
6. Coupling
7, Door open button
8. Touch control panel
9. Digital readout
10. Wave guide cover
11. Access cover for oven lamp replacement
12. Power supply cord
13. Rating label
DISPLAY
I REtiEAT 3E=ROST MED LOW rflGc; j
1KmI\r/lI\‘///I /TI .
/x/\I/ /x//\I /QiJ
?ldrcator
VA AUTO Kg COOK t
TOUCH CONTROL PANEL
INSTANTACTiONPADS
pCpdiTMU.
AUTOCOOKMENUS
ww.
3Jacket potato
4RoastLamb
5cornedMeat
z3,or4 SERVE OuANTTlY PAD
Toaxktw,three,orfourse~es,
AUTO press~padprior~pressing
COOK - ltlf2InslarltAdionpad.
-N-PADS
Presstoentercooldhgtines,dod<
, tine,weigMofquantih/offood,or
AUTOSTART/CLOCKPAD
Prtzsstoset~ofAutostalttime.
3

OPERATION
OFF CONDITION
Closing the door activates all door interlock switches
(1st. latch switch, 2nd. latch switch and stop 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.
The circuits to the power transformer, fan motor and
turntable motor are cut off when the 1st. latch switch,
2nd. latch switch, and stop 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 RYl stays closed. Shown in the display is the
remaining time.
Figure O-l on page 27
1. The display flashes “88:88”.
2. To set any programmes or set the clock, you must first
touch the STOP/CLEAR pad.
3. “88:88” appears in the display and the time counts up
every minute.
6. MONITOR SWITCH CIRCUIT
The monitor switch is mechanically controlled by oven
door, and monitors the operation of the 1st and 2nd.
latch switches.
6-1
NOTE:When the oven door is opened, the oven lamp
comes on at this time.
MICROWAVE COOKING CONDITION 6-2.
HIGH COOKING
Enter a desired cooking time with the touching NUMBER
Pad 6-3
and start the oven with touching START pad.
Function sequence
Figure O-2 on page 27
CONNECTED COMPONENTS
Oven lamp. Fan motor, Turntable motor
Power transformer
RELAY
RYl
RY2
MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW
COOKING
When the microwave oven is preset for variable cooking
power 240 volts AC. power is supplied to the power trans-
former 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.
1.
2
3.
4.
5.
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 secon-
dary winding.
The filament winding voltage (3.3 volts) heats the mag-
netron 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..
The 2450 MHz microwave energy produced in the
magnetron generates a wave length of 12.24 cm. This
energy is channeled through the waveguide (transport
channel) into the oven cavity, where the food is placed
to be cooked.
When the cooking time is up, a signal tone is heard and
the relays RYl+RY2 go back to their home position.
The circuits to the oven lamp, power transformer, fan
motor and turntable motor are cut off.
When the door is opened during a cook cycle, the
switches come to the following condition
CONDITION
SWITCH DURING
CONTACT DOOR OPEN
1st. latch switches CCXMNG (NO COOKING)
COM-NO Closed Open
2nd. latch switch COM-NO Closed Open
Monitor switch COM-NC Open Closed
Stop switch COM-NO Closed Open
SEQUENCE
When the oven door is opened during or after the
cycle of a cooking program, the 1st. latch switch, 2nd.
latch switch and stop switch must open their contacts
first.
After that the contacts (COM-NC) of the monitor
switch can be closed.
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, 2nd. latch switch
and stop switch are closed.
When the oven door is opened and the contacts of
thelst. latch switch, 2nd. latch switch remain closed.
The fuse M8A will blow, because the monitor switch
is closed and a short circuit is caused.
SETTING:
32 sec. ON
HIGH
24 sec. ON 8 sec. OFF
MEDIUM HIGH
MEDIUM 18 sec. ON 14 sec. OFF
N-1 Approx. 50% = 450 Watts
12 sec. ON 20 sec. OFF
MEDIUM LOW I] Approx. 30% = 270 Watts
6 sec. ON 26 sec. OFF
LOW m-1 Approx. 10% = 90 Watts
NOTE:The ON/OFF time ratio does not exactly corre-
spond to the percentage of microwave power, be-
cause approx. 2 seconds are needed for heating up
the magnetron filament.
4

DOOR OPEN MECHANISM
The door is opened by pushing the open button on the
control panel, refer to the Figure D-l.
When the open button is pushed, the open button pushes
up the switch lever, and then the switch lever pushes up
the the latch head. The latch heads are moved upward and
released from latch hook. Now the door will open.
LATCH dOOK
2ND LATCH
SW!TCH
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SWITCH --. MONITCR
Figure D-l. Door Open Mechanism
1ST. LATCH SWITCH, 2ND. LATCH SWITCH
AND STOP 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. latch switch 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.
LATCH SWITCH MONITOR SWITCH AND
MONITOR RESISTOR FOR PROPER OP-
ERATION.
MONITOR RESISTOR R 0.8R 20W
The monitor resistor prevents the fuse M8A bursting when
the fuse M8A blows due to the operation of the monitor
switch.
FUNCTION OF IMPORTANT COMPONENTS
ASYMMETRIC RECTIFIER
The asymmetric rectifier is a solid state device that pre-
vents current flow in both directions. And it prevents the
temperature rise of the power transformer by blowing the
fuse M8A when the high voltage rectifier is shorted.
/ HIGH VOLTAGE RECTIFIER
The rated peak reverse voltage of DI of the asymmetric
rectifier is 6 KV The rated peak reverse voltage of D2 of the
asymmetric rectifier is 1.7 KV. Dl and D2 of the asymmet-
ric rectifier or high voltage rectifier are shorted when the
each peak reverse voltage goes beyond the each rated
peak reverse voltage. (The process of blowing the fuse
MSA.)
1. The high voitage rectifier is shorted by any causes
when microwave cooking.
2. The peak reverse voltage oi Df of the rectifier goes
beyond the rated
peak reverse voltage i .7 KV in the voltage doubler cir-
cuit.
3. D2 of the rectifier is shorted.
4. The large electric currents flow through the high voltage
winding of the power transformer
5. The large electric currents beyond 8A flow through the
primary winding of the power transformer.
6. The fuse M8A blows by the large electric currents.
7. The power supply to the all electrical parts are cut off.
FUSE M8A
1. The fuse M8A blows when the contacts (COM-NO) of
the 1st. latch switch and 2nd. latch switch remain
closed with the oven door open and when the monitor
switch closes.
2. The fuse M8A also blows when asymmetric rectifier,
H.V. rectifier, H.V. wire harness, H.V.capacitor, magne-
tron or secondary winding of power transformer is
shorted.
3. If the wire harness or electrical components are short-
circuited, this fuse M8A blows to prevent an electric
shock or fire hazard.
THERMAL CUT-OUT TC 145°C (MG)
This thermal cut-out protects the magnetron against over-
heating. If the temperature goes up higher than 145°C
because the fan motor is interrupted, the ventilation open-
ings are blocked, the thermal cut-out will open and the line
voltages to the power transformer will be cut off and the
operation of the magnetron will be stopped.
The defective thermal cut-out must be replaced with new
one.
5

R-3A55
THERMAL CUT-OUT TC 145”@(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 ther-
mal cut-out must be replace with new one.
THERMAL CUT-OUT 95°C (FAN MOTOR)
The thermal cut-out protect the fan motor against over-
heating. If its temperature goes up higher than 95’C be-
cause the fan motor is locked or the ventilation operating
are blocked, the contacts of the thermal cut-out will open
and switch off the oven. When the oven cools itself down to
7523, the contacts of the thermal cut-out will close again.
TURNTABLE MOTOR
The turntable motor drives the turntable roller assembly 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 chan-
neled through the oven cavity to remove steam and vapors
given off from the heating foods. It is then exhausted
through the exhausting air vents at the oven cavity

R-3A55
TROUBLESHOOTING CHART
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.
REMEMBER TO CHECK 30 REMEMBER TO CHECK4FJ
1) Disconnect the supply.
2) Door opened, and wedged open.
3) Discharge high voltage capacitor.
1) Reconnect all leads removed from components during
testing.
2) Replace the outer case (cabinet).
3, Reconnect the supply-
WARNING AGAINST THE CHARGE OF THE 4) Run the oven. Check all functions.
The high-voltage capacitor remains charged Microwave ovens should not be run empty, To test for the 1
about 60 seconds after the oven has been I
/ switched off. Wait for 60 seconds and then short-
circuit the connection of the high-voltage capaci- 1
presence of microwave energy within a cavity, place a
cup of cold water on the oven turntable, close the door
and set the microwave timer for two (2) minutes. Set the
tor (that is, of the connecting lead of the high-volt- /
i age rectifier) against the chassis with the use of /
/ an insulated screwdriver.
I 1
Sharp recommend that wherever possible fault-find-
ing 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 30 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 3tJ checks and reconnect the leads to the
primary of the power transformer.
power level to HIGH and push the START button. When
the two minutes has elapsed (timer at zero) carefully
check that the water is now hot. If the water remains cold
carry out 30 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 reakage test carried out
TROUBLESHOOTING GUIDE
When troubleshooting the microwave oven, it is helpful IMPORTANT: If the oven becomes inoperative because of a
to follow the Sequence of Operation in performing the blown fuse M8A in the 1st. latch switch - 2nd.
checks. Many of the possible causes of trouble will re- latch switch - monitor switch - monitor resistor
quire that a specific test be performed. These tests are circuit, check the 1st. latch switch, 2nd. latch
given a procedure letter which will be found in the “Test switch, monitor switch and monitor resistor
Procedure”section. before replacing the fuse M8A.

R-3A55
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\ POSSIBLE CASE
AND DEFECTIVE
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CONDITION
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supply .cord is plugged intc
wall outle?.
“88:88” does not appear in drs
)FF
:ONDITION Display does not ooeratt
properly when STOPICLEAF
I pad IStouched.
1Oven iamp does not irah? a
I pears.!
ooor ooeped. iDlsp!aG ap
siay a,npeaf-si
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p av 293ears.i
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aoes nc: zoerate !Zsp!ah ap.
Gears. I
Over or any erectncai parts
aoes no: stop when cookrng
time 1s0 c- STOP/CLEAR pat
is touched.
OOKING
ONDITIOP Oven seem to be operatmg
but little or no heat is produced
;n oven load. iMIcrowave
power level IS se: at HIGH)
Oven Uoes not seems to be
operating properly when ME-
DIUM HIGH, MEDIUM, ME-
DIUM 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 cycie but
shuts down before end of
cooking cycle.
Oven stops as soon as when
the START pad is touched.
8

TEST PROCEDURES
PROCEDURE
LElTER COMPONENT TEST
A MAGNETRON TEST
1 NEVER TOUCH ANY PART IN THE CIRCUIT WITH YOUR HAND OR AN INSULATED TOOL /
WHILE THE OVEN IS IN OPERATION. I
I
,
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 Liter water load)
The foliowing test procedure should be carried out with the microwaveoven in a fully assembled condi-
tion (outer case fitted).Microwave output power from the magnetron can be measured by way oflEC
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/4.1 87calorie is generated. On the
other hand. if the temperature of the water with V(ml) rises AT (“C) during this microwave heating
period, the calorie of thewater is V x IT
/ The formula is as follows:
I Pxti4.187=Vx_l-T P(W)=4.l87xVxAT/t
1 Our condition for the water load is as follows: I
Room temperature ..........................around 20°C Power supply Voltage I
1Water load .....1000 g ...............Rated voltage Initial temperature ........... 10+2”C
/ Heating time I
.....................49 sec. j
P =‘85 x IT /
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 12)“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 ther-
mometer.
7. The water load must be (1000 f 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 Tl = 11“C)
2. Add the 1 litre water to the vessel.
3 Place the load on the centre of the shelf.
9

TEST PROCEDURES
PROCEDURE
LElTER COMPONENT TEST
4. Operate the microwave oven at HIGH for the temperature of the water rises by a value A T of
(10 ?I2)“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.
Initial temperature ............................................................................................ Tl = 11°C
Temperature after (49+2)= 51 sec. ................................................................. T2=21C
Temperature difference Cold-Warm ............................................................. AT1 = 10°C
Measured output power
The equation is “P= 85 x AT” ................................................ P= 85 x 10°C = 850 Watts
JUDGMENT: The measured output power should be at least f 15 % of the rated output
power.
CAUTION: 1 C CORRESPONDS TO 85 WA-l-l-S. REPEAT MEASUREMENT IF THE POWER IS
INSUFFICIENT.
.
T2.C
Heat up for 51 sec.
MICROWAVE OUTPUT POWER (2 Liter water load)
The following test procedure should be carried out with the microwave oven in a fully assembled
condition (with outer case fitted).
Microwave output power from the magnetron can be measured by way of substitution, i.e. it can be
measured by using a 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.
On the other hand, if the temperature of the water with V(ml) rises AT (“C) during this microwave
heating period, the calorie of the water is V x AT.
The formulae is as follows;
P =8330xAT/t
Our condition for the water load is as follows:
Room temperature .................23* 2°C
Water load Power supply Voltage .......2000 ml Initial temperature ..................Rated voltage.
.......23 2 1“C
P = 75 x AT Heating time ....1min. 51 sec.
Measuring method:
A) The two water containers must be prepared.
The water container must be one (1) litre beaker made of Pyrex glass and its diameter approxi-
mately 12cm.
B) Put the one (1) litre water into each beaker (Each beaker has one litre water). The initial tempera-
ture of the water should be 23+2X.
C) Mark Tl on the one beaker and mark T2 on the other one. And stir the water and measure the
temperature of water the thermometer and note them. The graduation of the thermometer must be
scaled by 0.1% at minimum and an accurate mercury thermometer is recommended.
D) Place the two (2) beakers as touching each other in the centre of the oven cavity.
E) Set the timer to 1 minute and 51 seconds start the oven at HIGH.
10

TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
F) The time must be measured with stopwatch or wristwatch.
G) After 1 minute and 51 seconds, stop the oven by opening the door.
H) Put the two (2) beakers out of the oven cavity and measure the temperature of the water by stirring
the water with thermometer and note them.
Example
Initial temperature ...................................................................................Tl = 23°C T2 = 24°C
Temperature after 1 min. 51 sec. ...........................................................Tl = 33°C T2 = 34°C
Temperature difference Cold-Warm ...................................................111 = 10°C AT2 = 10°C
Mean temperature rise IT ..............................IT = (AT1 !I AT2) ; 2 = (1OcC+lO”C) / 2 = 10°C
Measured output power
The equation is P= 75 x AT ......................I....................................... P= 75 x 10°C = 750 Watts
NOTE: The measured output power should be at least z 15 % of the rated output power.
CAUTION: 1°C CORRESPONDS TO 75 WATTS.
REPEAT MEASUREMENT IF THE POWER IS INSUFFICIENT.
1 I
~
:
- -
- -
- -
--
1,1
7
I
1
- -
!$
I--
-
--
--
iT1 OC) (-EOC) (Tl OC;
tieatil3‘or:nn 5set
(T2OC)
B POWER TRANSFORMER TEST
WARNING: High voltages and large currents are present at the secondary winding and fila- 1
ment winding of the power transformer. It is very dangerous to work near this 1
part when the oven is on. NEVER make any voltage measurements at 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 :
a. Primary winding ......................... approximately 1.73 ohms.
b. Secondary winding ................... approximately 104.7ohms.
c. Filament winding ...................................... less than 1 ohm.
If the reading obtained are not as stated 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.
11

TEST PROCEDURES
PROCEDURE
LEl-l-ER COMPONENT TEST
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 mor than 100 kL2in the other direction.
CARRY OUT 4R CHECKS A D2 Dl B
ASYMMETRIC RECTIFIER TEST ASYMMETRIC
CARRY OUT 3D CHECKS. +T@
RECTIFIER
c HIGH VOLTAGE RECTIFIER
Isolate the high voltage rectifier assembly from the HV circuit. The asymmetric rectifier can be tested
using an ohmmeter set to its highest range. Connect the ohmmeter across the terminals A+B of the
asymmetric rectifier and note the reading obtained. Reverse the meter leads and note this second
reading. If an open circuit is indicated in both directions then the asymmetric rectifier is good. If an
asymmetric rectifier is shorted in either direction, then the the asymmetric rectifier is probably faultly
and must be replaced with the high voltage rectifier. When the asymmetric rectifier is defective, check
whether magnetron, high voltage rectifier, high voltage wire or filament winding of the power trans-
former is shorted.
CARRY OUT @ 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.
D HIGH VOLTAGE CAPACITOR TEST
CARRY OUT m CHECKS.
A Isolate the high voltage capacitor from the circuit.
3. Continuity check must be carried out with measuring instrument which is set to the highest resis-
tance range.
C. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10 MR
after it has been charged.
D. A short-circuited capacitor shows continuity all the time.
E. An open capacitor constantly shows a resistance of about 10 MS1because of its internal 10 ML2
resistance.
F. When the internal wire is opened in the high voltage capacitor, the capacitor shows an infinite
resistance.
G. The resistance across all the terminals and the chassis must be inifinte when the capacitor is nor-
mal.
If incorrect readings are obtained, the high voltage capacitor must be replaced.
CARRY OUT 4R CHECKS
E SWITCH 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. SC.
Depressed S.C. O.C.
COM; Common terminal
NO; Normally open terminal
NC; Normally closed terminal
SC.; Short circuit
O.C.; Open circuit
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
CARRY OUT $J CHECKS.
12

R-3A55
TEST PROCEDURES
PROCEDURE
LElTER COMPONENT TEST
F THERMAL CUT-OUT TEST
CARRY OUT 3fJ CHECKS
Disconnect the leads from the terminals of the thermal cut-out. Then using an ohmmeter. make a
continuity test across the two terminals as described in the table below.
CARRY OUT 4J CHECKS
Table: Thermal cut-out Test
Parts Name
Thermal cut-out 145°C
Thermal cut-out 95°C
<
Temperature of “ON” condition Temperature of “OFF” condition lndicatron ofohmmeter I
(closed crrcuit) (‘Cl (open circuit) (‘C; i
(When room temperature f
is approx. 20-C‘, i
Below -20-C Above 14.5 C Ciosea e~rcu~: I
Below 75°C Above 95 C Closed c!rczif. J
If incorrect readings are obtained, replace the thermal cut-out.
An open circuit thermal cut-out 145’C (MG) indicates that the magnetron has overheated, This mad ke
due to resistricted ventilation, cooling fan failure or a fault condition within the magnetrcn or HV 3:1rzziT
An open circuit thermal cut-out 145°C (OVEN) indicates that the foods in the oven may catcn fire. ths
may be due to over heating produced by improper setting of the cooking time or faiiure of the contrc:
panel.
An open circuit thermal cut-out 95°C (FAN) indicates that the fan motor !Jvinding has overheated. this
may be due to blocked ventilation or locked cooling fan.
G MONITOR RESISTOR TEST
CARRY OUT =CHECKS.
Disconnect the leads from the monitor resist. Using an ohmmeter and set on a low range. Check
between 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.
H MOTOR WINDING TEST
CARRY OUT 3DCHECKS
Disconnect the leads from the motor.
Using an ohmmeter, check the resistance between the two terminals as described in the table below.
Motors
Fan motor
Table: Resistance of Motor
Resistance
Aonroximatelv 370 12
1 Turntable motor 1 Approximately 16.08 kQ
If incorrect readings are obtained, replace the motor.
CARRY OUT fi CHECKS
13

TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
BLOWN FUSE F 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 2nd. latch switch, monitor switch and
monitor resistor.
If the fuse M8A is blown by incorrect door switching replace the defective switch(s) and the fuse
M8A.
3. If the fuse M8A is blown, there could be a short in the asymmetric rectifier or
there could be a ground in wire harness. A short in the asymmetric rectifier may have occured due
to short or ground in H.V. rectifier, magnetron, power transformer or H.V. wire. Check them and re-
place the defective parts or repair the wire harness.
CARRY OUT 4R CHECKS
CAUTION: Only replace fuse M8A with the correct value replacement
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 symp-
toms indicated.
1 Key Unit
The following ^y ps m toms indicate a defective key unit. Replace the key unit.
aj 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. Replacing the control unit.
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.
dj 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 problems 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.
14

R-3A55
K RELAY TEST
CARRY OUTm CHECKS
Remove the outer case and check 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 indicat 240 volts, if not check oven circuit.
RYl and RY2 Relay Test
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 diode which is connected to the relay coil. If diode is good, control
unit is defective.
t I
/ OPERATIONAL 1
RELAY SYMBOL j
I VOLTAGE / CONNECTED COMPONENTS
I
RYI 1Approx. 26.0 V.C.C. Ovenlamp/Turntablemotor/Coolingfan motor
I
RY2 / Approx. 25.0 V.D.C. Power transformer
CARRY OUT @ CHECKS
L PROCEDURES TO BE TAKEN WHEN THE FOIL PATTERN ON THE PRINTED WIRING
BOARD(PWB) IS OPEN.
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 30 CHECKS
STEPS j 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)
The rated AC voltage is present at primary
side of low voltage transformer.
Only pattern at “a” is broken.
Pattern at “a” and “b” are broken.
Low voltage transformer or secondary circuit defective.
Check and repair.
*Insert jumper wire Jl and solder. (CARRY OUT 30
CHECKS BEFORE REPAIR)
*Insert the coil RCILF2003YAZZ between “c” and “d”.
(CARRY OUTS CHECKS BEFORE REPAIR)
NOTE: At the time of these repairs, make a visual
inspection of the varistor for burning damage and
examine the transformer with tester for the pres-
ence of layer short-circuit (check primary coil resis-
tance). If any abnormal condition is detected, re-
place the defective parts.
CARRY OUT =CHECKS
15

9-3A55
TOUCH CONTROL PANEL ASSEMBLY
OUTRINE OF TOUCH CONTROL PANEL
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
communicated among them are explained below.
Key Unit
The key unit is composed of a matrix, signals gener-
ated in the LSI are sent to the key unit through RIO-
R13, R20 and R22. When a key pad is touched, a
signal is completed through the key unit and passed
back to the LSI through ROO-R03 to perform the func-
tion that was requested.
Control Unit
Control unit consists of LSI, power source circuit,
synchronizing 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)
3) Synchronizing Signal Circuit
The power source synchronizing signal is available in
order to compose a basic standard time in the clock cir-
cuit. 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
noticing sounds (key touch sound and completion-
sound).
6) Door Sensing Switch (Stop 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 Fluorescent Display.
Basically, a Fluorescent Display is triode having a
cathode, a grid and an anode. Usually. the cathode of a
Fluorescent Display is directly heated and the filament
serves as cathode.
The Fluorescent Display has 6-digits, 13-segments are
used for displaying figures.
VP
VFl
VF2
-30v
2.2Vac
Fluorescent display tube : Grid
and anode voltage
Filament of fluorescent display
tube
(VFl to VF2 voltage)
16

LSI(IZA496DR)
DESCRIPTION OF LSI
The I/O signal of the LSl(lZA496DR) is detailed in the following table.
pi” No. ~ ;z;; ~ ; Description
Anode (seqment) of Fluorescent Displav illumination voltaqe: -30V I
Vp voltage of power source circuit input.
Siqnal cominq from touch kev. /
When either one of G12 line keys on key matrix is touched, a corresponding signal will
be input into ROo.
Siqnal cominq from touch kev.
When either one of Gl1 line keys on key matrix is touched, a corresponding signal will
be input into ROI.
4 1 R02 i IN Siqnal cominq from touch key.
When either one of GlO line keys on key matrix is touched. a corresponding signal will
be input into Ron.
5 Siqnal cominq from touch key.
When either one of G9 line keys on key matrix is toucned. a corresponding signal out
of R2o-R23, Rl c-R: s wiil be input into ROs. When no ke:’ is touched. the signal is held
at “L” level.
, I
6 / TEST ~ IN
/
7 j RESET i IN
/
Connected to VC.
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.
/ I
/ I
I
8 / OSCl / IN
9 osc2 \ OUT
Internal ciock oscillation frequencv input settinq.
The internal clock frequency is set by inserting the ceramic filter oscillation circuit with
respect to OSCl terminal.
Internal clock oscillation frequencv control output.
Output to control oscillation input of OSC2.
10/l 1 /GND/Avss/ IN/IN Connected to VC.
12 j AN0 / OUT Oven lampturntable motor and coolinq fan motor drivinq siqnal. (Square Wave- j
form : 50Hz) I
To turn on and off the control relay. The pulse signal (50Hz) is delivered to the control 1
relay driving circuit and cook relay control circuit. I
13 1 AN1 1 OUT Terminal not used.
OUT Maqnetron hiqh-voltaqe circuit drivinq siqnal. I
To turn on and off the cook relay. In low operation, the signals holds “L” level during 1
microwave cooking and “H” level while not cooking. In other cooking modes (MED 1
HIGH, MED,MED LOW,LOW) the signal turns to “H” level and “L” level in repetition
according to the power level. 1
I
15 1 AN3 ] OUT Terminal not used.
Input siqnal which communicates the door open/close information to LSI. I
Door closed; “H” level signal. I
Door opened; “L” level signal. I
17 AN5 IN
18-19 AN6-AN7 IN
Terminal to change cooking constant.
Connected to VC.
20/2 1 IAVCCNCCI IN/IN Connected to GND. t
A Siqnal svnchronized with commercial source freqencv(5OHz).
This is basic timing for time processing of LSI.
Terminal not used.
17

I I
) Pin No. ( Signal I/O
I !
124 iD2 j OUT
!
-r
/ Description
I
t
i 25 1 BUZZ 1 OUT
/ 27 j 05 OUT Diqit selection siqnal.
28 j D6 OUT
1
I
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 grid
of the fluorescent display.
Diqit selection siqnal.
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 grid
of the fluorescent display.
I
i
/ 29 ! D7 OUT
/ I I
I /
/ / I
j
I /
30 ID8 : OUT
t
-I-
Diqit selection sianai.
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 grid
of the fluorescent display.
Siqnal to sound buzzer.
A: key touch sound(0.12sec.).
B: Completion sound(2.4sec.).
Diqit 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 grid
of the fluorescent display.
Diqit selection siqnal.
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 grid
of the fluorescent display.
Seqment data siqnal.
Refer to the touch control panel circuit for the relationship between signals and indica-
tors. Normally, one pulse is output in every synchronized signal period, and input to
the anode of the fluorescent display.
R8c 1 OUT Seqment data siqnal.
: Refer to the touch control panel circuit for the relationship between signals and indica-
tors. Normally. one pulse is output in every synchronized signal period, and input to
the anode of the fluorescent display.
32 R8; ; OUT
33 j R82 , OUT
I
1
I I
I I
’ 34 I R83 I
/ OUT
I
/
I
/
/ 36 OUT
/
Seqment data siqnal.
Refer to the touch control panel circuit for the relationship between signals and indica-
tors. Normally, one pulse is output in every synchronized signal period, and input to
the anode of the fluorescent display.
Seqment data sianal.
Refer to the touch control panel circuit for the relationship between signals and indica-
tors. Normally, one pulse is output in every synchronized signal period, and input to
the anode of the fluorescent display.
Seqment data siqnal.
Refer to the touch control panel circuit for the relationship between signals and indica-
tors. Normally, one pulse is output in every synchronized signal period, and input to
the anode of the fluorescent display.
i
Seqment data siqnal.
Signal similar to 08.
Key strobe siqnal.
Signal applied to touch-key section. A pulse signal is input to ROo-ROsterminal while
one of G8 line keys on key matrix is touched.
Secament data siqnal.
Signal similar to D8.
Kev strobe siqnal.
Signal applied to touch-key section. A pulse signal is input to ROo-ROs terminal while
one of G7 line keys on key matrix is touched.
18
-