Sharp R-4A55 User manual

R4A55
SHARP SERVICE MANUAL
MICROWAVE OVEN
MODEL R-4A55
in interests of user-safety the oven should be restored to its original condi-
t
, This is a supplimemental Service Manual For Model R-4A55. This model is Quite similar to Base Model R-4A53
(Refer No. is S7106R4A53PJZ). Use this supplimemental manual together with the Base Model Service Manual.
Refer to Base Model Service Manual for complete operation, service information, etc.
TABLE OF CONTENTS page
GENERAL IMPORTANT INFORMATION ...................................................................................................... 1
WARNING ...................................................................................................................................................... 1
RODUCT SPECIFICATIONS ......................................................................................................................... 2
APPEARANCE VIEW .................................................................................................................................... 3
SERVICING ................................................................................................................................................... 4
TEST PROCEDURE ...................................................................................................................................... 5
TOUCH CONTROL PANEL ........................................................................................................................... 9
COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE ....................................................... .I4
WIRING DIAGRAM ...................................................................................................................................... 17
PICTORIAL DIAGRAM .................................................. ..1................................................................~ .......... 18
CONTROL PANEL CIRCUIT ...................................................................................................................... .I9
PRINTED WIRING BOA0 ............................................................................................................................ 20
PARTS LIST ................................................................................................................................................. 21
SHARP CORPORATION

SERVICE MANUAL
SHAFZP
MICROWAVE OVEN
R-4A55
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.
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.
(0) 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.
SHARP CORPORATION
OSAKA, JAPAN
R4A55R4A55
APPEARANCE VIEW
TEST PROCEDUREST PROCEDURE

PRODUCT SPECIFICATIONS
ITEM
Power Requirements 240 Volts
50 Hertz
DESCRIPTION
Power Consumption
Power Output
Case Dimensions
Single phase, 3 wire earthed
1.4 kW
750 watts nominal of RF microwave energy (AS 2895 1986)
900 watts (IEC-705-1 988 )
Operating frequency of 2450MHz
Width 550mm
Height 312mm
Depth 420mm
Cooking Cavity Dimensions Width 381 mm
Height 21 I mm
Depth 411 mm
Turntable diameter
Control Complement 360mm
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
SERVE QUANTITY
INSTANT ACTION
AUTO COOK
EASY DEFROST
NUMBER pads
POWER LEVEL
MORE, LESS
STOP/CLEAR
Set Weight
AUTO START/CLOCK
INSTANT COOK/START
Approx. 17 kg
2

R4A55
APPEARANCE VIEW
8.Touch Control Panel
9.Digital readout
1O.Waveguide cover
11.Access cover for oven lamp replacement
12.Power supply cord
1.Ventilation openings
2.Oven lamp
3.Hinges
4.Safety door latches
5.See through door
6.Coupling
7.Door open button
TOUCH CONTROL PANEL
INSTANT ACTION PADS -
Press once to cook or reheat
8 popular menu.
AUTO COOK Chicken Reheat Ffoten
Press to select Auto Cook 1serve
Pieces Bevey;geSoup Dinner
1serve
mode.
AUTO COOK MENUS
NUMBER PADS
Press to enter
clock time, weight or quantity
of food, or to select the Auto
Cook menus.
Bacon Cy&es Fis~~~~ts
1 serve
.- Rice 8 Pasta Reheyt lW&sbie~
A
1
5seasonedRoast-
POWER LEVEL PAD-
Press to select microwave
power setting.
If not pressed, HIGH is auto-
matically selected.
STOP/CLEAR PAD
Press to clear during program
ming.
Press once to stop operation
of oven during cooking; press
twice to cancel cooking pro-
gramme.
- 2,3 or 4 SERVE QUANTITY
PADS
To cook two, three or four
serves, press required pad
prior to pressing the Instant
Action pad.
)I1u ,,q-q-qg
I
@q*y~ pj
Lp
I I I \
-MORE (A), LESS (r) PADS
Press to increase/decrease
the time in one minute incre-
ments during cooking or to
alter the doneness for the Al
Cook, Instant Action or Easy
Defrost modes.
- EASY DEFROST PAD
Press to defrost meat by en-
tering weight.
r INSTANT COOK/START
AUTO START/CLOCK PAD
Press to set clock or Auto
Start time. by 1 minute multiples each
time this pad is pressed dur-
ing cooking.
Press to start oven after set-
ting programmes.
3

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 3D
1) Disconnect the supply.
2) Door opened, and wedged open.
3) Discharge high voltage capacitor.
WARNING AGAINST THE CHARGE OF THE
HIGH-VOLTAGE CAPACITOR
The high-voltage capacitor remains charged
about 60 seconds after the oven has been
switched off. Wait for 60 seconds and then short-
circuit the connection of the high-voltage capaci-
tor (that is, of the connecting lead of the high-volt-
age rectifier) against the chassis with the use of
an insulated screwdriver.
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 3D checks and then disconnect
the leads to the primary of the power transformer.
Ensure that these leads remain isolated from other
components and the oven chassis. (Use insulation
tape if necessary.) When the testing is completed
carry out 3lJ checks and reconnect the leads to the
primary of the power transformer.
REMEMBER TO CHECK%
1) Reconnect all leads removed from components during
testing.
2) Replace the outer case (cabinet).
3) Reconnect the supply.
4) Run the oven. Check all functions.
Microwave ovens should not be run empty. To test for the
presence of microwave energy within a cavity, place a
cup of cold water on the oven turntable, close the door
and set the microwave timer for two (2) minutes. Set the
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 a 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

TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
A MAGNETRON TEST
NEVER TOUCH ANY PART IN THE CIRCUIT WITH YOUR HAND OR AN INSULATED TOOL ’
WHILE THE OVEN IS IN OPERATION.
CARRY OUT 3D CHECKS
Isolate the magnetron from the high voltage circuit by removing all leads connected to the filament
terminal.
To test for an open circuit filament use an ohmmeter to make a continuity test between the magnetron
filament terminals, the meter should show a reading of less than 1 ohm.
To test for a short circuit filament to anode condition, connect ohmmeter between one of the filament
terminals and the case of the magnetron (ground). This test should be indicated an infinite resistance.
If a low or zero resistance reading is obtained then the magnetron should be replaced.
MICROWAVE OUTPUT POWER (1 Litre water load)
The following test procedure should be carried out with the microwaveoven in a fully assembled condi-
tion (outer case fitted).Microwave output power from the magnetron can be measured by way of IEC
705, i.e. it can be measured by using water load how much it can be absorbed by the water load. To
measure the microwave output power in the microwave oven, the relation of calorie and watt is
used.When P(W) heating works for t(second), approximately P x t/4.187calorie 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 AT
The formula is as follows;
Pxt/4.187=VxAT P(W)=4.187xVxAT/t
Our condition for the water load is as follows:
Room temperature ..........................around 20°C Power supply Voltage ...............Rated voltage
Water load ..... 1000 g Initial temperature ...........10%X Heating time ......................47sec.
P=9OxAT
Measuring condition:
1. Container
The water container must be a cylindrical borosilicate glass vessel having a maximum material
thickness of 3 mm and an outside diameter of approximately 190 mm.
2. Temperature of the oven and vessel
The oven and the empty vessel are at ambient temperature prior to the start of the test.
3. Temperature of the water
The initial temperature of the water is (10 + 2)X.
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.X at minimum and an accurate ther-
mometer.
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 Tl = 11“C)
2. Add the 1 litre water to the vessel.
3 Place the load on the centre of the shelf.
5

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 I!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 (47+2)= 49 sec. .................................................................T2 = 21 “C
Temperature difference Cold-Warm ...................................*....................*.... AT1 = 10°C
Measured output power
The equation is “P= 90 x AT” ................................................P= 90 x 10°C = 900 Watts
JUDGEMENT: The measured output power should be at least + 15 % of the rated output
power.
CAUTION: 1°C CORRESPONDS TO 90 WA-ITS. REPEAT MEASUREMENT IF THE POWER IS
INSUFFICIENT.
-- -
-- -
T2.C
Heat up for 49 sec.
MICROWAVE OUTPUT POWER (2 Litre water ioad)
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 Power supply Voltage ..................Rated voltage.
Water load .......2000 ml Initial temperature .......23 + 1“C Heating time ....1min. 51 sec.
P = 75 x AT
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 239°C.
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 “C 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.
6

R-4A55
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 set I
. *.......................................................... Tl = 33°C T2 = 34°C
Temperature difference Cold-Warm ...................................................ATI = 10°C ?,T2 = 10°C /
Mean temperature rise AT ..............................AT /
Measured output power = (AT1 31AT2) /2 = (1O”C+1O”C) / 2 = 10°C I
The equation is P= 75 x AT I
..............................................................
P= 75 x 10°C = 750 Watts /
NOTE: The measured output power should be at least i 15 % of the rated output power.
CAUTION: 1°C CORRESPONDS TO 75 WATTS.
REPEAT MEASUREMENT IF THE POWER IS INSUFFICIENT. I
II
d
x
- -
- -
-
- -
--
(Tl “C) (Tl “C)
Heat up for mtn. 5 set
II
Eli
7
--
--
--
--
(T2 “C)
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 symp-
toms indicated.
1. Key Unit
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. 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.
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 problems caused by defective control unit.
a) Buzzer does not sound or continues to sound.
7

TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
b) Clock does not operate properly.
c) Cooking is not possible.
d) Proper temperature measurement is not obtained.
M RELAY TEST
1. CARRY OUT 3D CHECKS
2. Disconnect the leads from the primary of the power transformer. Make sure that the leads remain
isolated from other oven components and chassis. (Use insulation tape if necessary)
3. Close the door.
4. Reconnect the supply.
5. Check the voltage between Pin Numbers 3 and 5 of 4-pin connector (A) on the control unit with an
A.C. voltmeter. The meter should indicated 240 volts, if no check oven circuit.
6. RYl AND RY2 Test
These are operated by D.C. voltage. Check voltage at 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.
RELAY SYMBOL OPERATIONAL
VOLTAGE CONNECTED COMPONENTS 1
RYl Approx. 26.5V.D.C. Oven lampnurntable motor/Cooling fan motor
RY2 Approx. 25.8V.D.C. Power transformer
N PROCEDURES TO BE TAKEN WHEN THE FOIL PAlTERN 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.
STEPS OCCURANCE CAUSE OR CORRECTION
1 The rated AC voltage is not present at Check supply voltage and oven power cord. Please use
POWER terminal of CPU connector (CN-A) term “Low voltage transformer” when refering to
transformer Tl .
The rated AC voltage is present at primary Low voltage transformer or secondary circuit defective.
side of low voltage transformer. Check and repair.
Only pattern at ‘a” is broken. *insert jumper wire Jl and solder. (CARRY OUT 3D
CHECKS BEFORE REPAIR)
Pattern at “a” and “b” are broken. ‘Insert the coil RCILF2003YAZZ between “c” and “d”.
(CARRY OUT 3D CHECKS BEFORE REPAIR)
is- i hi -- I I- . I i
b
NOTE:*At the time of these repairs, make a v
ual inspection of the varistor for burning
damage and test the T/C transformer
with an ohmmeter for the presence of
layer short-circuit (check primary coil re-
sistance). If any abnormal condition is
detected, replace the defective parts.
CARRY OUT @ CHECKS RYI c#-
8

TOUCH CONTROL PANEL ASSEMBLY
OUTLINE OF TOUCH CONTROL PANEL
The touch control section consists of the following unit 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 generated
in the LSI are sent to the key unit through ROo - RO3, Rio
- R13. When a key pad is touched, a signal is completed
through the key unit and passed back to the LSI through
R23, R30 - R32 to perform the function 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 for generates voltage necessary in the control
unit.
Symbol
VC
VP
VFl
VF2
Voltage
-5V
-29v
3Vac
Application
LSI(IC1)
Fluorescent display tube : Grid
and anode voltage
Filament of fluorescent display
tube
(VFl to VF2 voltage)
3) Synchronizing Signal Circuit
This power source synchronizing signal is available in
order 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 generat a signal which resets the LSI to the
initial state when power is supplied.
5) Buzzer Circuit
The buzzer responsive to signals from the LSI to emit
noticing 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 Fluorescent Display.
Basically, a Fluorescent Display is a 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, 13segments are
used for displaying figures.