Sharp R-480J User Manual
SERVICE MANUAL
S8406R480JPJ/
MICROWAVE OVEN
R-480J
MODEL
In interests of user-safety the oven should be restored to its original
condition and only parts identical to those specified should be used.
TABLE OF CONTENTS
CAUTION, MICROWAVE RADIATION ............................................................................................................. 1
WARNING .......................................................................................................................................................... 1
PRODUCT SPECIFICATIONS ......................................................................................................................... 2
GENERAL INFORMATION ................................................................................................................................ 2
APPEARANCE VIEW ....................................................................................................................................... 3
OPERATION SEQUENCE ................................................................................................................................ 4
FUNCTION OF IMPORTANT COMPONENTS ................................................................................................ 6
SERVICING ...................................................................................................................................................... 7
TEST PROCEDURE ......................................................................................................................................... 9
TOUCH CONTROL PANEL ............................................................................................................................. 16
COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE ........................................................... 22
MICROWAVE MEASUREMENT .................................................................................................................... 28
WIRING DIAGRAM ......................................................................................................................................... 29
PICTORIAL DIAGRAM ................................................................................................................................... 30
POWER UNIT CIRCUIT .................................................................................................................................. 31
CPU UNIT CIRCUIT ........................................................................................................................................ 32
PRINTED WIRING BOARD .............................................................................................................................33
PARTS LIST ................................................................................................................................................... 34
R-480J
Page
SHARP CORPORATION
R-480J
SERVICE MANUAL
MICROWAVE OVEN
R-480J
PRODUCT SPECIFICATIONS
R-480J
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.
APPEARANCE VIEW
OPERATING SEQUENCE
FUNCTION OF IMPORTANT
COMPONENTS
SERVICING AND
TROUBLESHOOTING CHART
TEST PROCEDURE
TOUCH CONTROL PANEL
ASSEMBLY
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.
SHARP CORPORATION
COMPONENT REPLACEMENT
AND ADJUSTMENT PROCEDURE
MICROWAVE MEASUREMENT
WIRING DIAGRAM
PARTS LIST
OSAKA, JAPAN
1
R-480J
PRODUCT SPECIFICATIONS
ITEM DESCRIPTION
Power Requirements 230 - 240 Volts
50 Hertz
Single phase, 3 wire earthed
Power Consumption 1.65 kW
Power Output 1200 watts nominal of RF microwave energy (IEC Test Procedure)
Operating frequency 2450 MHz
Case Dimensions Width 550 mm
Height 315 mm
Depth 446 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
HELP pad
SENSOR REHEAT pad
SENSOR COOK pads
HEALTHY MENU pads
EXPRESS MENUS pads
EASY DEFROST pad
MORE, LESS pads
QUICK & EASY pad
NUMBER pads
POWER LEVEL pad
CLOCK pad
TIMER pad
STOP/CLEAR pad
INSTANT COOK/START pad
Weight Approx. 19 kg
GENERAL INFORMATION
WARNING
THIS APPLIANCE MUST 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
2
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
15.Turntable
16.Roller stay
APPEARANCE VIEW
6
3
5
4
TOUCH CONTROL PANEL
14
7
11
4
2
13
10
R-480J
12
15
9
8
1
16
EXPRESS MENUS PADS
Press to select "Express Menus"
menus.
HEALTHY MENU PADS
Press to select "Healty Menu" menu.
EASY DEFROST PAD
Press to defrost frozen food by
entering quantity.
MORE, LESS PADS
Press to increase/ decrease the time
in one minute increments during cooking or to alter the cooking result for automatic operations.
POWER LEVEL PAD
Press to select microwave power
setting. If not pressed, HIGH is automatically selected.
CLOCK PAD
Press to set Clock.
STOP/CLEAR PAD
Press to clear during programming.
Press once to stop operation of oven
during cooking; press twice to cancel
cooking programme.
SENSOR DEFROST COOK
HELP
Display
Indicator
SENSOR COOK PADS
Press to select Sensor Cook menus.
QUICK AND EASY PAD
Press to select Quick and Easy
menus.
SENSOR REHEAT PAD
Press to select reheat menu.
HELP PAD
Press to select auto start, child lock,
demonstration modes or info on pads.
Press to get cooking information.
NUMBER PADS
Press to enter cooking times, clock
time, weight or quantity of food.
TIMER PAD
Press to set Timer
INSTANT COOK/START PAD
Press once to cook for 1 minute on
HIGH or increase by 1 minute multiples each time this pad is pressed
during cooking. Press to start the
oven after setting programmes.
NOTE:
Some one-touch cooking features such as "Instant Cook" are disabled after three minutes when the
oven is not in use. These features are automatically enabled when the door is opened and closed or
the STOP/ CLEAR pad is pressed.
3
R-480J
OPERATION SEQUENCE
OFF CONDITION
Closing the door activates all door interlock switches
(1st. latch switch, 2nd. interlock relay control switch)
IMPORTANT
When the oven door is closed, the monitor switch contacts
(COM-NC) must be open.
When the microwave oven is plugged in a wall outlet, rated
voltage is supplied to the noise filter and the control unit.
Figure O-1 on page 29
1. The display shows SHARP, MICRO-WAVE and OVEN.
2. To set any programs 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
pads and start the oven with touching START pad.
Function sequence
Figure O-2 on page 29
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
(off condition)º. 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
1st. latch switch COM-NO Closed Open
2nd. interlock relay
control switch COM-NO Closed Open
Monitor switch COM-NC Open Closed
The circuits to the power transformer, fan motor and
turntable motor are cut off when the 1st. latch switch
and 2nd. interlock relay control switch are made open.
The oven lamp remains on even if the oven door is
opened after the cooking cycle has been interrupted,
(NO COOKING)
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. latch switch
and 2nd. interlock relay.
6-1 When the oven door is opened during or after the
cycle of a cooking program, the 1st. latch switch and
2nd. interlock relay control 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 first. After
that the contacts of the 1st. latch switch and 2nd.
interlock relay control switch are closed.
6-3. When the oven door is opened and the contacts of the
1st. latch switch and 2nd. interlock relay remain
closed. The fuse F10A 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
HIGH
24 sec. ON 8 sec. OFF
MEDIUM HIGH Approx. 70%
18 sec. ON
MEDIUM Approx. 50%
12 sec. ON
MEDIUM LOW Approx. 30%
6 sec. ON
LOW Approx. 10%
14 sec. OFF
20 sec. OFF
26 sec. OFF
NOTE: The ON/OFF time ratio does not exactly correspond
to the percentage of microwave power, because
approx. 3 seconds are needed for heating up the
magnetron filament.
SENSOR COOKING CONDITION
Using the SENSOR COOK or SENSOR INSTANT REHEAT function, the foods are cooked or reheated 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
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:
4
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.
AH SENSOR
MICROWAVE
R-480J
Cooking Sequence.
1. Touch each SENSOR COOK or SENSOR INSTANT
REHEAT function pad to operating the sensor cooking.
Refer to the operation manual for the proper procedure.
NOTE: The oven should not be operated on SENSOR
COOK or SENSOR INSTANT REHEAT
immediately after plugging in the unit. Wait two
minutes before cooking on SENSOR COOK or
SENSOR INSTANT REHEAT.
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.
POWER OUTPUT REDUCTION
After 100% power cooking mode is carried out more than
40 minutes, the power output is automatically reduced to
70%.
5
R-480J
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 latch hook. Now the door can be opened.
Door
Latch Hook
Latch
Heads
Switch
Lever
2nd. Interlock
Relay Control
Switch
Monitor
Switch
1st. Latch
Switch
Figure D-1. Door Open Mechanism
1ST. LATCH SWITCH AND 2ND. INTERLOCK RELAY CONTROL SWITCH
1. When the oven door is closed, the contacts (COM-NO)
must be closed.
2. When the oven door is opened, the contacts (COMNO) 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 (COMNC) must be closed.
3. If the oven door is opened and the contacts (COM-NO)
of the 1st. latch switch and 2nd. interlock relay fail to
open, the fuse (F10A) blows simultaneously with
closing the contacts (COM-NC) of the monitor switch.
CAUTION: BEFORE REPLACING A BLOWN FUSE
(F10A) TEST THE 1ST. LATCH SWITCH,
2ND. INTERLOCK RELAY AND MONITOR
SWITCH FOR PROPER OPERATION. (REFER TO CHAPTER "TEST PROCEDURE".)
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. However, when abnormally high temperature is
reached within the oven cavity, the oven thermal cut-out
will open at 145˚C, causing the oven to shut down. The
defective thermal cut-out must be replaced with new one.
THERMAL CUT-OUT 145˚C (MAGNETRON)
The thermal cut-out located near the magnetron is designed to prevent damage to the magnetron if an over
heated condition develops in the tube due to cooling fan
failure, obstructed air guide, dirty or blocked air intake, etc.
Under normal operation, the thermal cut-out remains
closed. However, when abnormally high temperatures are
reached within the magnetron, the thermal cut-out will
open at 145˚C causing the oven to shut down. The
defective thermal cut-out must be replaced with new one.
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.
NOISE FILTER
The noise filter prevents the radio frequency interference
that might flow back in the power circuit.
FUSE (F10A)
1. If the wire harness or electrical components are shortcircuited, this fuse blows to prevent an electric shock or
fire hazard.
2. The fuse also blows when 1st. latch switch and 2nd.
interlock relay remains closed with the oven door open
and when the monitor switch closes.
HIGH VOLTAGE FUSE 0.75A
The high voltage fuse blows when the high voltage rectifier
or magnetron is shorted.
6
SERVICING
WARNING TO SERVICE PERSONNEL
R-480J
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 fuse, 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 reexamine 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 should be carried out.
TROUBLESHOOTING GUIDE
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.
IMPORTANT: If the oven becomes inoperative because
of a blown fuse F10A in the 1st. latch
switch - 2nd. interlock relay - monitor switch
circuit, check the 1st. latch switch, 2nd.
interlock relay and monitor switch before
replacing the fuse F10A.
7
R-480J
CK = Check / RE = Replace
CONDITION
OFF
CONDITION
ON
CONDITION
SENSOR
COOKING
CONDITION
TEST PROCEDURE
ABCDEEEFG GHHIJKLMN
POSSIBLE CAUSE
AND
DEFECTIVE PARTS
PROBLEM
Home fuse blows when power
supply cord is plugged into wall
outlet.
FUSE F10A 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 when 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.
MAGNETRON
POWER TRANSFORMER
H.V. RECTIFIER ASSEMBLY
HIGH VOLTAGE CAPACITOR
1ST. LATCH SWITCH
2ND. N D. INTERLOCK RELAY
CONTROL SWITCH
MONITOR SWITCH
NOISE FILTER
RE RE CK CK CK CK CK CK CK CK O
THERMAL CUT-OUT (MAGNETRON)
THERMAL CUT-OUT (OVEN)
FAN MOTOR
TURNTABLE MOTOR
FUSE F10A
HIGH VOLTAGE FUSE
TOUCH CONTROL PANEL
KEY UNIT
RELAY (RY-1, RY-2)
FOIL PATERN ON P.W.B.
POWER SUPPLY CORD
OVEN LAMP OR SOCKET
SHORTED WIRE HARNESS
OPENED WIRE HARNESS
WALL OUTLET
HOME FUSE OR BREAKER
WRONG OPERATION
BLOCKED VENTILATION OPENING
MISADJUSTMENT SWITCH
AH SENSOR
BLOCKED COOLING FAN
8
TEST PROCEDURES
R-480J
PROCEDURE
LETTER
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 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 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 microwave oven in a fully assembled
condition (outer case fitted). Microwave output power from the magnetron can be measured by IEC
test procedure, 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.
COMPONENT TEST
The formula is as follows;
P x t / 4.187 = V x ∆ T+ 0.55 x mc (T2-T0)/
4.187P (W) = 4.187 x V x ∆T / t + 0.55 x mc (T2-T0)/t
Our condition for water load is as follows:
Room temperature (T0) ... around 20°CPower supply Voltage .............. Rated voltage
Water load..................................1000 g Initial temperature (T1) ...................... 10±1°C
Heating time .............................. 35 sec. Mass of container (mc) ......................... 330 g
T2 ................ Final Temperature ∆T = T2 - T1 P = 120 x ∆T + 0.55 x mc (T2-T0)/35
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±1)˚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
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 + 3” sec. 3 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 ˚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.
9
R-480J
TEST PROCEDURES
PROCEDURE
LETTER
Room temperature .................. To = 21˚C Initial temperature ................. T1 = 11°C
Temperature after (35 + 3) = 38 sec. ................................................................ T2 = 21°C
Temperature difference Cold-Warm (∆T = T2 - T1) ......................................... ∆T = 10°C
Measured output power
The equation is “P = 120 x ∆T” ........................................... P = 120 x 10°C = 1200 Watts
JUDGEMENT: The measured output power should be at least ± 15 % of the rated output power.
CAUTION: 1°C CORRESPONDS TO 120 WATTS REPEAT MEASUREMENT IF THE POWER IS
INSUFFICIENT.
1000g
T1˚C
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.
COMPONENT TEST
1000g
Heat up for 38 sec.
1000g
T2˚C
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. 1.0 Ω
b. Secondary winding .............. approx. 84 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.
CARRY OUT 4R CHECKS.
B
HIGH VOLTAGE RECTIFIER
C
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
A. Isolate the high voltage capacitor from the circuit.
3D CHECKS.
10
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