R-4H56
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-4H56
S8405R4H56PJ/
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....................................................................................................................................... 32
CONTROL PANEL CIRCUIT .............................................................................................................................. 33
PRINTED WIRING BOARD ................................................................................................................................ 34
PARTS LIST........................................................................................................................................................ 35
R-4H56
R-4H56
1
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-4H56
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
GENERAL INFORMATION
WARNING
THIS APPLIANCE MUST BE EARTHED
IMPOTANT
THE WIRES IN THIS MAINS LEAD ARE COLOURED IN ACCORDANCE WITH THE FOLLOWING CODE:
GREEN-AND-YELLOW : EARTH
BLUE : NEUTRAL
BROWN : LIVE
ITEM DESCRIPTION
Power Requirements 240 Volts
50 Hertz
Single phase, 3 wire earthed
Power Consumption 1.4 kW
Power Output 900 watts nominal of RF microwave energy (IEC 705)
750 watts (2 litre water load)
Operating fequency 2450 MHz
Case Dimensions Width 550 mm
Height 312 mm
Depth 420 mm
Cooking Cavity Dimensions Width 381 mm
Height 210 mm
Depth 411 mm
Turntable diameter 360mm
Control Complement Touch Control System
Clock ( 1:00 - 12:59)
Timer (0 - 99 minutes 99 seconds)
Microwave Power for Variable Cooking
Repetition Rate;
HIGH............................................... Full power throughout the cooking time
MEDIUM HIGH ..................................................approx. 70% of Full Power
MEDIUM .............................................................approx. 50% of Full Power
MEDIUM LOW .................................................... approx. 30% of Full Power
LOW ................................................................... approx. 10% of Full Power
SENSOR COOK pad
REHEAT SENSOR pad
SENSOR INSTANT ACTION pads
NUMBER pads
POWER LEVEL pad
EASY DEFROST pad
MORE, LESS pads
STOP/CLEAR pad
AUTO START/CLOCK pad
INSTANT COOK/START pad
Set Weight Approx. 17 kg
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APPEARANCE VIEW
1. Ventilation openings
2. Oven lamp
3. Door hinges
4. Safety door 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.Menu label for Sensor Cook
14.Rating label
1
11
9
8
12
11
1
74
6
5
3
2
4
13
14
10
SMART
& EASY
REHEART
SENSOR
12345
67890
STOP
CLEAR
AUTO
START
CLOCK
INSTANT COOK
START
SENSOR
COOK
Fresh
Vegetables
Jacket
Potato
Frozen
Vegetables
Casseroles
Desserts
SENSOR COOK PAD
Press to select several popular menus.
REHEAT SENSOR PAD
Press to select 3 popular Reheat
menus.
SENSOR INSTANT ACTION PADS
Press to once to cook 1 of 6 popular
menus.
MORE( ), LESS( ) PADS
Press to increase/decrease the time
in one minute increments during
cooking or to alter the doneness for
the Sensor Instant Action, Reheat
Sensor, Sensor Cook or Easy Defrost
mode.
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 Microwave, Convection,
Grill or Mix cooking.
AUTO START/CLOCK PAD
Press to set clock or Auto Start time.
STOP/CLEAR PAD
Press to clear during programming.
Press once to stop operation of
oven during cooking; press twice
to cancel cooking programe.
NUMBER PADS
Press to enter cookling times, clock
time or to select the Sensor Cook
menus
EASY DEFROST PAD
Press to defrost meat by entering
weight only.
POWER LEVEL PAD
Press to select microwave power
setting. If not pressed, HIGH is
automatically selected.
Fish
Fillets
LESS MORE
POWER
LEVEL
EASY
DEFROST
TOUCH CONTROL PANEL
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OPERATION SEQUENCE
OFF CONDITION
Closing the door activates all door interlock switches
(Upper latch switch, Lower 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 flashes “88:88”.
2. To set any programs or set the clock, you must first touch
the STOP/CLEAR pad.
3. “ : “ appears in the display and the time counts up every
minute.
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 pads
and start the oven with touching START pad.
Function sequence
Figure O-2 on page 31
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 channelled 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)
Upper latch switches COM-NO Closed Open
Lower 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 upper latch switch,
lower 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 upper and lower
latch switches.
6-1 When the oven door is opened during or after the cycle
of a cooking program, the upper latch switch, lower
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 upper latch switch, lower latch switch
and stop switch are closed.
6-3. When the oven door is opened and the contacts of the
upper latch switch and lower latch switch remain closed.
The fuse M8A will blow, because the monitor switch is
closed and a short circuit is caused.
VARIABLE COOKING
When the microwave oven is preset for variable cooking
power. Rated voltage is supplied to the power transformer
intermittently within a 32-second time base through the
relay contact which is coupled with the relay (RY2). The
following levels of microwave power are given.
SETTING;
32 sec. ON
24 sec. ON
18 sec. ON
12 sec. ON
6 sec. ON
8 sec. OFF
14 sec. OFF
20 sec. OFF
26 sec. OFF
HIGH
MEDIUM HIGH
MEDIUM
MEDIUM LOW
LOW
Approx. 70%
Approx. 50%
Approx. 30%
Approx. 10%
NOTE: 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, REHEAT SENSOR 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
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best results.
When the food is cooked, water vapor is developed. The
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:
ACTION immediately after plugging in the unit. Wait
five minutes before cooking on SENSOR COOK,
REHEAT SENSOR or SENSOR INSTANT ACTION.
2. Select desired Sensor setting.
3. Touch START pad (REHEAT SENSOR and SENSOR
INSTANT ACTION fuction are not neccessary to touch
START pad.) 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.
4. 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.
5. 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.
6. 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.
7. 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.
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.
Cooking Sequence.
1. Touch each SENSOR COOK function pad to operating
the sensor cooking.
NOTE: The oven should not be operated on SENSOR
COOK, REHEAT SENSOR or SENSOR INSTANT
MICROWAVE
MICROWAVE
AH SENSOR
FUNCTION OF IMPORTANT COMPONENTS
DOOR OPEN MECHANISM
The door can be opened by pushing the door open button on
the control panel. When the door open button is pushed, the
latch lever is moved upward, operating the latch head. The
latch head is moved upward, and released from the latch
hook. Now, the door can be opened.
MONITOR
SWITCH
UPPER
LATCH
SWITCH
STOP
SWITCH
LOWER
LATCH
SWITCH
LATCH
LEVER PLUNGER
SWICTH
LATCH
HEAD
DOOR
OPEN
BUTTON
LATCH
HEAD
LATCH
HOOK
DOOR
Figure D-1. Door Open Mechanism
UPPER LATCH SWITCH, LOWER 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 upper and lower latch switches 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 UPPER AND LOWER LATCH
SWITCHES, MONITOR SWITCH AND MONITOR RESISTOR FOR PROPER OPERATION.
(REFER TO CHAPTER “TEST PROCEDURE”.)
MONITOR RESISTOR (0.8Ω 20W)
The monitor resistor prevents the fuse (M8A) bursting when
the fuse blows due to the operation of the monitor switch.
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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.
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 thermal cut-out
will be close its contacts again when its temperature goes
down lower than -20˚C.
FUSE (M8A)
1. If the wire harness or electrical components are shortcircuited, this fuse blows to prevent an electric shock or
fire hazard.
2. The fuse blows when the asymmetric rectifier, H.V.
rectifier, H.V. wire harness, H.V. capacitor, magnetron or
secondary winding of power transformer is shorted.
3. The fuse also blows when upper and lower latch switches
remains closed with the oven door open and when the
monitor switch closes.
TEMPERATURE FUSE 150˚C (MG)
This fuse protects the magnetron against overheating. If the
temperature goes up higher than 150˚C because the fan
motor is interrupted, the air inlet duct is blocked or the
ventilation openings are obstructed, the fuse blows and puts
the oven out of operation.
The defective fuse must be replaced with new rated one.
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 channelled through the oven cavity to remove steam and vapours given off from the heating foods. It is then exhausted
through the exhausting air vents at the oven cavity.
D2 D1
ASYMMETRIC
RECTIFIER
HIGH VOLTAGE RECTIFIER
AB
C
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 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 power transformer is cut off.
THERMAL CUT-OUT 145˚C (OVEN)
The thermal cut-out located on the top of the oven cavity is
designed to prevent damage to the oven if the foods in the
oven catch fire due to over heating produced by improper
setting of cook time or failure of control unit. Under normal
operation, the oven thermal cut-out remains closed. How-
R-4H56
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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 upper latch switch
- lower latch switch - monitor switch - monitor resistor circuit, check the upper latch
switch, lower latch switch, monitor switch
and monitor resistor before replacing the
fuse M8A.
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CK = Check / RE = Replace
MAGNETRON
POWER TRANSFORMER
H.V. RECTIFIER ASSEMBLY
HIGH VOLTAGE CAPACITOR
UPPER LATCH SWITCH
LOWER LATCH SWITCH
STOP SWITCH
MONITOR SWITCH
MONITOR RESISTOR
TEMPERATURE FUSE
THERMAL CUT-OUT
FAN MOTOR
TURNTABLE MOTOR
FUSE M8A
TOUCH CONTROL PANEL
RELAY (RY-1, RY-2)
FOIL PATERN ON P.W.B.
AH. SENSOR
POWER SUPPLY CORD
OVEN LAMP OR SOCKET
HIGH OLTAGE WIRE
SHORTED WIRE HARNESS
OPENED WIRE HARNESS
WALL OUTLET
HOME FUSE OR BREAKER
WRONG OPERATION
MISADJUSTMENT SWITCH
BLOCKED COOLING FAN
BLOCKED VENTILATION
OFF
CONDITION
POSSIBLE CAUSE
AND
DEFECTIVE PARTS
TEST PROCEDURE
ON
CONDITION
ABCDEEEEFG G H H I JLMNRERE CK CKCKCK CKCKCK CKCK
Home fuse blows when power
supply cord is plugged into wall
outlet.
FUSE M8A blows when power
supply cord is plugged into wall
outlet.
"88:88" does not appear in display but 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 1st
stage or cooking under the
Sensor Cooking condition
(Oven does not shuts off when
a cup of water is boiling by
Sensor Cooking.) or oven stop
soon.
CONDITION
PROBLEM
AH.
SENSOR
COOKING
CONDITION
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TEST PROCEDURES
PROCEDURE
LETTER
CARRY OUT 3D CHECKS.
Isolate the magnetron from high voltage circuit by removing all leads connected to filament terminal.
To test for an open circuit filament use an ohmmeter to make a continuity test between the magnetron
filament terminals, the meter should show a reading of less than 1 ohm.
To test for short filament to anode condition, connect ohmmeter between one of the filament terminals
and the case of the magnetron (ground). This test should be indicated an infinite resistance. If a low or
zero resistance reading is obtained then the magnetron should be replaced.
MICROWAVE OUTPUT POWER (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) = 49sec....................................................................... T2 = 21°C
Temperature difference Cold-Warm .................................................................... ∆T1 = 10°C
Measured output power
The equation is “P = 90 x ∆T”....................................................... P = 90 x 10°C = 900 Watts
JUDGMENT: The measured output power should be at least ± 15 % of the rated output power.
CAUTION: 1°C CORRESPONDS TO 90 WATTS REPEAT MEASUREMENT IF THE POWER IS
INSUFFICIENT.
1000g
1000g
1000g
T1˚C
T2˚C
Heat up for 49 sec.
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-4H56
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. 1.54 Ω
b. Secondary winding............... approx. 84.8 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.
1 litre
1 litre
1 litre 1 litre
R-4H56
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 circuit
O.C.; Open circuit
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
CARRY OUT
4R CHECKS.
F MONITOR RESISTOR TEST
CARRY OUT 3D 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.
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