R-3H57
SHARP CORPORATION
SER VICE MANU AL
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-3H57
S8502R3H57PJZ
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 .......................................................................................................................................................... 7
TEST PROCEDURE ............................................................................................................................................ 9
TOUCH CONTROL PANEL ................................................................................................................................ 18
COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE............................................................... 24
MICROWAVE MEASUREMENT ........................................................................................................................ 30
WIRING DIAGRAM ............................................................................................................................................. 31
PICTORIAL DIAGRAM....................................................................................................................................... 33
CONTROL PANEL CIRCUIT .............................................................................................................................. 35
PRINTED WIRING BOARD ................................................................................................................................ 36
PARTS LIST........................................................................................................................................................ 37
R-3H57
R-3H57
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SER VICE 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-3H57
GENERAL IMPORTANT INFORMATION
This Manual has been prepared to provide Sharp Corp. Service
engineers with Operation and Service Information.
It is recommended that service engineers carefully study the
entire text of this manual, so they will be qualified to render
satisfactory customer service.
CAUTION
MICROWAVE RADIATION
DO NOT BECOME EXPOSED TO RADIATION FROM
THE MICROWAVE GENERATOR OR OTHER PARTS
CONDUCTING MICROWAVE ENERGY.
Service engineers should not be exposed to the microwave
energy which may radiate from the magnetron or other
microwave generating devices if it is improperly used or
connected. All input and output microwave connections,
waveguides, flanges and gaskets must be secured. Never
operate the device without a microwave energy absorbing
load attached. Never look into an open waveguide or
antenna while the device is energized.
WARNING
Never operate the oven until the following points are ensured.
(A) The door is tightly closed.
(B) The door brackets and hinges are not defective.
(C) The door packing is not damaged.
(D) The door is not deformed or warped.
(E) There is not any other visible damage with the oven.
Servicing and repair work must be carried out only by trained
service engineers.
All the parts marked "*" on parts list are used at voltages more
than 250V.
Removal of the outer wrap gives access to potentials above
250V.
All the parts marked "∆" on parts list may cause undue
microwave exposure, by themselves, or when they are damaged, loosened or removed.
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PRODUCT SPECIFICATIONS
ITEM DESCRIPTION
Power Requirements 240 Volts (for Australia) / 230 - 240 Volts (for New Zealand)
50 Hertz
Single phase, 3 wire earthed
Power Consumption 1.37kW
Power Output 900 watts nominal of RF microwave energy (IEC 705)
750 watts (2 litre water load)
Operating fequency 2450 MHz
Case Dimensions Width 520 mm
Height 305 mm including foot
Depth 389 mm
Cooking Cavity Dimensions Width 348 mm
Height 197 mm
Depth 368 mm
Turntable diameter 325mm
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
HELP pad
SENSOR COOK pads
SENSOR INSTANT ACTION pads
NUMBER pads
POWER LEVEL pad
EASY DEFROST pad
MEMORY pads
MORE, LESS pads
CLOCK pad
TIMER pad
STOP/CLEAR pad
AUTO START pad
INSTANT COOK/START pad
Set Weight Approx. 15 kg
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
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8
9
10
4
2
7
13
5
3
6
11144
1
12
APPEARANCE VIEW
1. Ventilation openings
2. Oven lamp
3. Door hinges
4. Door safety latches
5. See through door
6. Door seals and sealing
surfaces
7. Coupling
8. Door open button
9. Touch control panel
10.Digital readout
11.Waveguide cover
12.Power supply cord
13.Rating label
14.Menu label
Indicator
COOK KGSENSOR DEF HELP
HELP
SENSOR COOK
MEAT
Fresh Vegetables
Jacket Potato
Reheat Beverage
Fish Fillets
STOP
CLEAR
AUTO
START
DESSERTS
RICE
PASTA
VEGETABLES
Info Display
INSTANT COOK
START
POWER
LEVEL
EASY
DEFROST
TIMER
LESS MORE
CLOCK
MEMORY1MEMORY
2
1 2 3 4 5
6 7 8 9 O
SMART
&EASY
REHEAT
SENSOR COOK PADS
Press to select Sensor Cook
mode.
NUMBER PADS
Press to enter cooking times, clock
time, weight or quantity of food.
POWER LEVEL PAD
Press to select microwave power
setting. If not pressed, HIGH is
automatically selected.
EASY DEFROST PAD
Press to defrost meat by entering
weight.
MORE ( ), LESS ( ) PADS
Press to increase/decrease the
time in one minute increments
during cooking or to alter the
doneness for the Convenience
Meals or Information Cook modes.
STOP/CLEAR PAD
Press to clear during programming.
Press once to stop operation of
oven during cooking; press twice
to cancel cooking programme.
HELP PAD
Press to select information guide
on/off, child lock or demonstration
modes.
Press to get cooking information.
SENSOR INSTANT ACTION PADS
Press once to cook 1 of 4 popular
menus.
MEMORY PADS
Press to enter two frequently used
cooking programmes.
Press to recall the memorized
programme.
TIMER PAD
Press to set Timer.
CLOCK PAD
Press to set Clock
INSTANT 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.
AUTO START PAD
Press to set Auto Start time.
TOUCH CONTROL PANEL
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OPERATION SEQUENCE
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.
Figure O-1 on page 31
1. The display shows SHARP , MICRO- , WAVE
and OVEN .
2. To set any programmes or set the clock, you must first
touch the STOP/CLEAR pad.
3. : appears in the display.
NOTE: When the oven door is opened, the oven lamp
comes on at this time.
MICROWAVE COOKING CONDITION
HIGH COOKING
Enter a desired cooking time with the touching NUMBER
pad and start the oven with touching START pad.
Function sequence
Figure O-2 on page 32
CONNECTED COMPONENTS RELAY
Oven lamp, Fan motor, Turntable motor RY1
Power transformer RY2
1. Rated voltage. is supplied to the primary winding of the
power transformer. The voltage is converted to about 3.3
volts A.C. output on the filament winding and high
voltage of approximately 2000 volts A.C. on the secondary
winding.
2. The filament winding voltage (3.3 volts) heats the
magnetron filament and the high voltage (2000 volts) is
sent to the voltage doubling circuit, where it is doubled to
negative voltage of approximately 4000 volts D.C..
3. The 2450 MHz microwave energy produced in the
magnetron generates a wave length of 12.24 cm. This
energy is channeled through the waveguide (transport
channel) into the oven cavity, where the food is placed to
be cooked.
4. When the cooking time is up, a signal tone is heard and
the relays RY1+RY2 go back to their home position. The
circuits to the oven lamp, power transformer, fan motor
and turntable motor are cut off.
5. When the door is opened during a cook cycle, the
switches come to the following condition
CONDITION
DURING DOOR OPEN
SWITCH CONTACT COOKING (NO COOKING)
1st. latch switches COM-NO Closed Open
2nd. latch switch COM-NO Closed Open
Monitor switch COM-NC Open Closed
Stop switch COM-NO Closed Open
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 RY1 stays closed. Shown in the display is the
remaining time.
6. MONITOR SWITCH CIRCUIT
The monitor switch is mechanically controlled by oven
door, and monitors the operation of the 1st and 2nd.
latch switches.
6-1 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.
6-2. When the oven door is closed, the contacts (COM-NC)
of the monitor switch must be opened. After that the
contacts of the 1st. latch switch, 2nd. latch switch and
stop switch are closed.
6-3. When the oven door is opened and the contacts of
the1st. latch switch, 2nd. latch switch remain closed.
The fuse M8A will blow, because the monitor switch is
closed and a short circuit is caused.
MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW
COOKING
When the microwave oven is preset for variable cooking
power, 230-240 volts A.C. power is supplied to the power
transformer intermittently within a 32-second time base
through the relay contact which is coupled with the currentlimiting relay. The following levels of microwave power are
given.
SETTING;
NOTE: The ON/OFF time ratio does not exactly correspond
to the percentage of microwave power, because
approx. 2 seconds are needed for heating up the
magnetron filament.
SENSOR COOKING CONDITION
Using the SENSOR COOK or SENSOR INSTANT ACTION
function, the foods are cooked or defrosted without figuring
time, power level or quantity. When the oven senses enough
steam from the food, it relays the information to its microprocessor which will calculate the remaining cooking time
and power level needed for best results.
When the food is cooked, water vapor is developed. The
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%
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sensor “senses” the vapor and its resistance increases
gradually. When the resistance reaches the value set according to the menu, supplementary cooking is started.
The time of supplementary cooking is determined by experiment with each food category and inputted into the LSI.
An example of how sensor works:
NOTE: The oven should not be operated on SENSOR
COOK or SENSOR INSTANT ACTION immediately
after plugging in the unit. Wait five minutes before
cooking on SENSOR COOK or SENSOR INSTANT
ACTION.
2. The coil of shut-off relay (RY-1) is energized, the turntable
motor, oven lamp and cooling fan motor are turned on,
but the power transformer is not turned on.
3. After about 16 seconds, the cook relay (RY-2) is
energized. The power transformer is turned on,
microwave energy is produced and first stage is started.
The 16 seconds is the cooling time required to remove
any vapor from the oven cavity and sensor.
NOTE: During this first stage, do not open the door or touch
STOP/CLEAR pad.
4. When the sensor detects the vapor emitted from the
food, the display switches over to the remaining cooking
time and the timer counts down to zero.
At this time, the door may be opened to stir food, turn it
or season, etc.
5. When the timer reaches zero, an audible signal sounds.
The shut-off relay and cook relay are de-energized and
the power transformer, oven lamp, etc. are turned off.
6. Opening the door or touching the STOP/CLEAR pad, the
time of day will reappear on the display and the oven will
revert to an OFF condition.
DOOR OPEN MECHANISM
The door is opened by pushing the open button on the
control panel, refer to the Figure D-1.
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
HEADS
LATCH HOOK
2ND. LATCH
SWITCH
MONITOR
SWITCH
SWITCH
LEVER
STOP SWITCH
1ST. LATCH
SWITCH
Figure D-1. 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 OPERATION.
MONITOR RESISTOR R 0.8Ω 20W
The monitor resistor prevents the fuse M8A bursting when
the fuse M8A blows due to the operation of the monitor
switch.
1. Potatoes at room temperature.
Vapor is emitted very slowly.
2. Heat potatoes. Moisture and
humidity is emitted rapidly. You
can smell the aroma as it
cooks.
3. Sensor detects moisture and
humidity and calculates
cooking time and variable
power.
MICROWAVE
MICROWAVE
AH SENSOR
Cooking Sequence.
1. Touch each SENSOR COOK or SENSOR INSTANT
ACTION function pad to operating the sensor cooking.
FUNCTION OF IMPORTANT COMPONENTS
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ASYMMETRIC RECTIFIER
The asymmetric rectifier is a solid state device that prevents
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.
THERMAL CUT-OUT TC 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. However, 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 replace with new one.
THERMAL CUT-OUT 95˚C (FAN MOTOR)
The thermal cut-out protect the fan motor against overheating. If its temperature goes up higher than 95˚C because 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 75˚C, 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 channeled
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
NOISE FILTER (FOR NEW ZEALAND)
The noise filter prevents the radio frequency interference
that might flow back in the power circuit.
The rated peak reverse voltage of D1 of the asymmetric
rectifier is 6 KV The rated peak reverse voltage of D2 of the
asymmetric rectifier is 1.7 KV. D1 and D2 of the asymmetric
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 M8A.)
1. The high voltage rectifier is shorted by any causes when
microwave cooking.
2. The peak reverse voltage of D2 of the rectifier goes
beyond the rated peak reverse voltage 1.7 KV in the
voltage doubler circuit.
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 M8A 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,
magnetron or secondary winding of power transformer is
shorted.
3. If the wire harness or electrical components are shortcircuited, 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 overheating. If the temperature goes up higher than 145˚C
because the fan motor is interrupted, the ventilation openings 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.
D2 D1
ASYMMETRIC
RECTIFIER
HIGH VOLTAGE RECTIFIER
AB
C
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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 connection of the high-voltage capacitor (that is, of the
connecting lead of the high-voltage rectifier) against
the chassis with the use of an insulated screwdriver.
Sharp recommend that wherever possible fault-finding
is carried out with the supply disconnected. It may in,
some cases, be necessary to connect the supply after
the outer case has been removed, in this event carry out
3D checks and then disconnect the leads to the primary
of the power transformer. Ensure that these leads remain isolated from other components and the oven
chassis. (Use insulation tape if necessary.) When the
testing is completed carry out 3D checks and reconnect
the leads to the primary of the power transformer.
REMEMBER TO CHECK 4R
1) Reconnect all leads removed from components during
testing.
2) Replace the outer case (cabinet).
3) Reconnect the supply.
4) Run the oven. Check all functions.
Microwave ovens should not be run empty. To test for
the presence of microwave energy within a cavity, place
a cup of cold water on the oven turntable, close the door
and set the 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 3D checks and re-examine the connections to
the component being tested.
When all service work is completed, and the oven is fully assembled, the microwave power output should be checked
and microwave leakage test 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: If the oven becomes inoperative because of
a blown fuse M8A in the 1st. latch switch 2nd. latch switch - monitor switch - monitor
resistor circuit, check the 1st. latch switch,
2nd. latch switch, monitor switch and monitor resistor before replacing the fuse M8A.
.
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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 properly
when STOP/CLEAR pad is
touched.
Oven lamp does not light at door
opened. (Display appears.)
Oven does not start when the
START pad is touched. (Display
appears)
Oven lamp does not light (Display
appears.)
Fan motor does not operate. (Display appears.)
Turntable motor assembly does
not operate. (Display appears.)
Oven or any electrical parts does
not stop when cooking time is 0 or
STOP/CLEAR pad is touched.
Oven seems to be operating but
little or no heat is produced in oven
load. (Microwave power level is
set at HIGH)
Oven does not seems to be operating properly when MEDIUM
HIGH, MEDIUM, MEDIUM LOW
or LOW is set. (Oven operates
properly at HIGH and then the
STOP/CLEAR pad is touched the
oven stops.)
Oven goes into cook cycle but shuts
down before end of cooking cycle.
Oven stops as soon as when the
START pad is touched.
AH sensor does not end during
Sensor Cooking condition. (Oven
does not shut off after a cup of
water is boiling by sensor cooking.
Oven stops at 16 sec. after starting.
OFF
CONDITION
PROBLEM
CONDITION
POSSIBLE CAUSE
AND
DEFECTIVE PARTS
TEST PROCEDURE
ON
CONDITION
MAGNETRON
POWER TRANSFORMER
H.V. RECTIFIER ASSEMBLY
HIGH VOLTAGE CAPACITOR
1ST. LATCH SWITCH
2ND. LATCH SWITCH
STOP SWITCH
MONITOR SWITCH
MONITOR RESISTOR
TEMPERATURE FUSE 95˚C
THERMAL CUT-OUT 145˚C
FAN MOTOR
TURNTABLE MOTOR
FUSE M8A
TOUCH CONTROL PANEL
KEY UNIT
RELAY (RY-1, RY-2)
FOIL PATERN ON P.W.B.
POWER SUPPLY CORD
SHORTED WIRE HARNESS
OPENED WIRE HARNESS
OVEN LAMP OR SOCKET
WALL OUTLET
MISADJUSTMENT SWITCH
HOME FUSE OR BREAKER
BLOCKED COOLING FAN
BLOCKED VENTILATION
NOISE FILTER (FOR N.Z.)
AH SENSOR
CK = Check / RE = Replace
ABCDEEEEGFFH HI JK LM RECK CKRECK CKCKCKCK NO
SENSOR
COOKING
CONDITION
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TEST PROCEDURES
PROCEDURE
LETTER
CARRY OUT 3D CHECK.
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 (1 Litre water load)
The following test procedure should be carried out with the microwave oven in a fully assembled
condition (outer case fitted). Microwave output power from the magnetron can be measured by way of
IEC 705, i.e. it can be measured by using water load how much it can be absorbed by the water load.
To measure the microwave output power in the microwave oven, the relation of calorie and watt is used.
When P(W) heating works for t(second), approximately P x t/4.187 calorie is generated. On the other
hand, if the temperature of the water with V(ml) rises ∆T (°C) during this microwave heating period, the
calorie of the water is V x ∆T.
NEVER TOUCH ANY PART IN THE CIRCUIT WITH YOUR HAND OR AN INSULATED TOOL
WHILE THE OVEN IS IN OPERATION.
A MAGNETRON TEST
The formula is as follows;
P x t / 4.187 = V x ∆ T P (W) = 4.187 x V x ∆T / t
Our condition for water load is as follows:
Room temperature..............around 20°C Power supply Voltage.........Rated voltage
Water load.........1000 g Initial temperature...........10±2°C Heating time.........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. 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 accurate thermometer.
7. The water load must be (1000±5) g.
8. “t” is measured while the microwave generator is operating at full power. Magnetron filament heatup 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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10
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) = 49 sec...................................................................... 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 for49 sec.
MICROWAVE OUTPUT POWER (2 Litre 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 ∆T (˚C) during this microwave heating
period, the calorie of the water is V x ∆T.
The formula is as follows;
P = 8330 x ∆ T/t
Our condition for 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......1 min. 51sec.
P = 75 x ∆T
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 approximately
12cm.
B) Put the one (1) litre water into each beaker (Each beaker has one litre water). The initial temperature
of the water should be 23±1˚C.
C) Mark T1 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 minutes and 51 seconds, start the oven at 100% power.
F) The time must be measured with stopwatch or wristwatch.
G) After 1 minutes 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.
R-3H57
11
TEST PROCEDURES (CONT'D)
B POWER TRANSFORMER TEST
WARNING: High voltages and large currents are present at the secondary winding and filament
winding of the power transformer. It is very dangerous to work near this part when
the oven is on. NEVER make any voltage measurements of the high-voltage
circuits, including the magnetron filament.
CARRY OUT 3D CHECKS.
Disconnect the leads to the primary winding of the power transformer. Disconnect the filament and
secondary winding connections from the rest of the HV circuitry. Using an ohmmeter, set on a low range,
it is possible to check the continuity of all three windings. The following readings should be obtained:
a. Primary winding ................... approx. 1.4 Ω
b. Secondary winding............... approx. 98 Ω
c. Filament winding .................. less than 1Ω
If the reading obtained are not stated as above, then the power transformer is probably faulty and should
be replaced.
CARRY OUT 4R CHECKS.
C HIGH VOLTAGE RECTIFIER ASSEMBLY TEST
HIGH VOLTAGE RECTIFIER TEST
CARRY OUT 3D CHECKS.
Isolate the high voltage rectifier assembly from the HV circuit. The high voltage rectifier can be tested
using an ohmmeter set to its highest range. Connect the ohmmeter across the terminal B+C of the high
voltage rectifier and note the reading obtained. Reverse the meter leads and note this second reading.
The normal resistance is infinite in one direction and more than 100 kΩ in the other direction.
Example
Initial temperature .............................................................................T1 = 23˚C T2 = 24˚C
Temperature after 1 min. 51 sec. ..................................................... T1 = 33˚C T2 = 34˚C
Temperature difference Cold-Warm.............................................. ∆T1 = 10˚C ∆T2 = 10˚C
Mean temperature rise ∆T.........................∆T = (∆T1 ± ∆T2) / 2 = (10˚C+10˚C) / 2 = 10˚C
Measured output power
The equation is P= 75 x ∆T ........................................................ P= 75 x 10˚C = 750 Watts
NOTE: The measured output power should be at least ± 15 % of the rated output power.
CAUTION: 1˚C CORRESPONDS TO 75 WATTS. REPEAT MEASUREMENT IF THE POWER IS
INSUFFICIENT.
COMPONENT TEST
PROCEDURE
LETTER
1 l 1 l
(T1 C) (T2 C)
1 l 1 l
(T1 C) (T2 C)
Heat up for 1min. 51 sec.
R-3H57
12
TEST PROCEDURES (CONT'D)
CARRY OUT
4R CHECKS.
ASYMMETRIC RECTIFIER TEST
CARRY OUT
3D CHECKS.
Isolate the high voltage rectifier assembly from the HV circuit. The asymmetric can be tested using an
ohmmeter set to its highest range 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 direction then the asymmetric rectifier is good. If an asymmetric rectifier is shorted in either
direction, then the asymmetric rectifier is probably faulty and must be replaced with high voltage rectifier.
When the asymmetric rectifier is defective, check whether magnetron, high voltage rectifier, high voltage
wire or filament winding of the power transformer is shorted.
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.
PROCEDURE
LETTER
COMPONENT TEST
AB
C
D2 D1
ASYMMETRIC
RECTIFIER
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. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10MΩ after it has
been charged.
D. A short-circuited capacitor shows continuity all the time.
E. An open capacitor constantly shows a resistance about 10 MΩ because of its internal 10MΩ resistance.
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.
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. S.C.
Depressed S.C. O.C.
COM; Common terminal,
NO; Normally open terminal
NC; Normally close terminal
S.C.; Short,
O.C.; Open circuit
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
CARRY OUT
4R CHECKS.
E THERMAL CUT-OUT TEST
CARRY OUT 3D 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 4R CHECKS
.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.
Thermal cut-out 95˚C Below 75˚C Above 95˚C Closed circuit.
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