Sharp R-2397 User Manual
SER VICE MANU AL
S5708R2397H/X
COMMERCIAL
MICROWAVE OVEN
R-2397
MODEL
R-2397
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
Page
CAUTION, MICROWAVE RADIATION ...................................................................................................... 1
WARNING................................................................................................................................................... 1
PRODUCT SPECIFICATIONS................................................................................................................... 2
GENERAL IMPORTANT INFORMATION ................................................................................................... 2
APPEARANCE VIEW................................................................................................................................. 3
OPERATION SEQUENCE ......................................................................................................................... 4
FUNCTION OF IMPORTANT COMPONENTS .......................................................................................... 5
SERVICING ............................................................................................................................................... 7
TEST PROCEDURE ................................................................................................................................ 10
TOUCH CONTROL PANEL ASSEMBLY .................................................................................................. 17
COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE..................................................... 24
MICROWAVE MEASUREMENT .............................................................................................................. 29
WIRING DIAGRAM .................................................................................................................................. 30
PICTORIAL DIAGRAM............................................................................................................................. 31
CONTROL PANEL CIRCUIT .................................................................................................................... 32
PRINTED WIRING BOARD ...................................................................................................................... 33
PARTS LIST............................................................................................................................................. 34
SHARP CORPORATION
R-2397
SERVICE MANUAL
COMMERCIAL
R-2397
GENERAL IMPORTANT INFORMATION
R-2397
PRODUCT SPECIFICATIONS
GENERAL 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.
APPEARANCE VIEW
OPERATING SEQUENCE
FUNCTION OF IMPORTANT
COMPONENTS
SERVICING AND
TROUBLESHOOTING CHART
TEST PROCEDURE
TOUCH CONTROL PANEL
ASSEMBLY
COMPONENT
REPLACEMENT AND
ADJUSTMENT PROCEDURE
MICROWAVE MEASUREMENT
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
OSAKA, JAPAN
1
WIRING DIAGRAM
PARTS LIST
R-2397
PRODUCT DESCRIPTION
SPECIFICATION
ITEM DESCRIPTION
Power Requirements 230 Volts
50 Hertz
Single phase, 3 wire grounded
Power Consumption 2.7 kW Approx. 13A
Power Output 1700 watts nominal of RF microwave energy (Method of IEC 705)
Operating frequency of 2450MHz
Outside Dimensions Width 510mm
Height 335 mm
Depth 470 mm
Cooking Cavity Dimensions Width 330 mm
Height 180 mm
Depth 330 mm
Control Complement Touch Control System
The combination of cooking time and microwave power
The oven can be programmed a series of up to 3 cookling stages.
The combination of microwave power and cooking time that can be input as
folllows.
Cooking Micrwave power level
Sequence that can be used. Cooking time that can be iused.
1 Stage only 0-100% Max. 30 minutes
2 or 3 Stage
NOTE:If the oven used with the power level above 40% on any stage, the
maximum cooking time is 30 minutes in total.
Microwave Power level
100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%
MANUAL / REPEAT key, NUMBER keys
MICROWAVE POWER SETTING key
STOP / CLEAR key, START Key
DOUBLE QUANTITY key, DEFROST key
SET key, CHECK key, VOLUME key
Set Weight Approx. 33kg
0-40% all stages Max. 30 minutes any stages
Max. 60 minutes for 2 stages
Max. 90 minutes for 3 stages
50-100% Max. 30 minutes for 3 stages
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
OVEN
1
2345
7
6
8
9
1011
12
13
15
16
14
18
19
17
1. Control panel
2. Hole for safety door latches
3. Ceramic floor
4. Splash cover
5. Oven light
6. Air intake filter
7. Air intake openings
8. Oven cavity
9. Door seals and sealing surfaces
10. Door hinges
11. Oven door with see-through window
12. Door safety latches
13. Door handle.
14. Outer cabinet
15. Removable cover over oven light bulb
16. Air vent openings
17. Power supply cord
18 Mounting plate
19 Screw for mounting plate
APPEARANCE VIEW
AUTO TOUCH CONTROL PANEL
34
DEF
DOUBLE
FILTER
CHECK
11
12
13
14
15
16
17
18
19
20
POWER
%
1
2
3
4
5
6
7
8
9
0
12
15
17
19
11
NUMBER
2
1 2 3
ON
1
10
x
2
6
5
7
8
9
13
14
16
18
20
R-2397
DISPLAY AND INDICATORS
Check indicators after the oven starts to
confirm the oven is operating as desired.
1. Heating indicator
This indicator shows cooking in progress.
2. Memory number indicator
3. Defrost indicator
4. Check mode indicator
5. Power level display
6. Time display
7. Filter indicator
8. Double quantity mode indicator
9. 3rd. stage indicator
10. 2nd. stage indicator
11. 1st. stage indicator
OPERATING KEYS
12. DOUBLE QUANTITY key
13. DEFROST key
14. NUMBER keys
15. MANUAL/ REPEAT key
16. STOP/CLEAR key
17. MICROWAVE POWER SETTING key
18. START key
19. SET key
20. VOLUME key
21. CHECK key
21
INSTALLATION INFORMATION
When this commercial microwave oven is installed near other commercial electrical appliances, connect a lead wire
to each equivalent potential terminal with equipotential marking between them (insert a lead wire between a washer and
an earth angle, and screw them), as shown in Fig. A-1, to make sure that they are at equivalent potential.
If any lead wire is not connected between them, when person touch them he/she will get a electric shock.
COMMERCIAL MICROWAVE OVEN OTHER COMMERCIAL
Equipotential marking
Lead wire
Screw
Washer
Earth angle
(Equivalent potential terminal)
Lead wire
Figure A-1
3
ELECTRICAL APPLIANCE
Equivalent
potential terminal
R-2397
OPERATION SEQUENCE
OFF CONDITION
Closing the door activates all door interlock switches
(1st latch switch, 2nd latch switch, 3rd 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 (230 volts, 50Hz), the line voltage is
supplied to the point
A5+A7 in the control panel.
Figure O-1 on page 30
1. The digital display shows .
NOTE: When the door is opened or after cooking, oven
lamp, blower motor and stirrer motors work for 1
minute.
MICROWAVE COOKING CONDITION
Touch MANUAL/ REPEAT key and enter a desired cooking
time with the touching NUMBER key. And then touch START
key.
Function sequence Figure O-2 on page 30
CONNECTED COMPONENTS RELAY
Oven lamp/ Blower motor/ Stirrer motors RY1
Power transformer (rear) RY3
Power transformer (front) RY4
1. The line voltage is supplied to the primary winding of the
high voltage 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
circuits to the high voltage transformers. The relay
remains and oven lamp, blower motor and stirrer motors
work for 1 minute.
5. When the door is opened during a cook cycle, the
switches come to the following condition.
SWITCH CONTACT COOKING
1st latch switch COM-NO Closed Open
Monitor switch COM-NC Open Closed
2nd latch switch COM-NO Closed Open
Stop switch COM-NO Closed Open
3rd latch switch COM-NO Closed Open
The circuits to the high voltage transformers are cut off
when the 1st latch, 2nd latch, 3rd latch and stop switches
are made open. The blower motor, stirrer motors and
oven lamp remains on even if the oven door is opened
after the cooking cycle has been interrupted, because
RY3+RY4 go back to their home position. The
RY1
CONDITION
DURING DOOR OPEN
(NO COOKING)
the relay RY1 stays closed. Shown in the display is the
remaining time, but the program is cancelled if the oven
is not started within 3 minutes.
6. MONITOR SWITCH CIRCUIT
The monitor switch is mechanically controlled by oven
door, and monitors the operation of the 1st latch switch.
6-1. When the oven door is opened during or after the cycle
of a cooking program, the 1st, 2nd, 3rd latch and stop
switches 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
(COM-NO) of the 1st, 2nd, 3rd latch and
stop switches must be closed.
6-3. When the oven door is opened and the contacts of the
1st latch switch remain closed, remains closed, the
fuse F6.3A will blow, because the monitor switch is
closed and a short circuit is caused.
MICROWAVE VARIABLE COOKING
When the microwave oven is preset for variable cooking
power, the line voltage is supplied to the high voltage
transformers intermittently within a 48 second time base
through the contacts of the relays RY3+RY4.
The following levels of microwaves power are given.
48 sec. ON
Number key
44sec. ON
Number key 9
40 sec. ON
Number key 8
36 sec. ON
Number key 7
32 sec. ON
Number key 6
26 sec. ON
Number key 5
22 sec. ON
Number key 4
16 sec. ON
Number key 3
12 sec. ON
Number key 2
8 sec. ON
Number key 1
0 sec. ON
Number key 0
NOTE: The ON/OFF time ratio does not exactly corre-
spond to the percentage of microwave power, because approx. 3 seconds are needed for heating up
the magnetron filament.
TWO MAGNETRON OPERATION SYSTEM
Two magnetrons MG1+MG2 are equipped in order to get
higher microwave power output. The primary windings of the
high voltage transformers
magnetron can be oscillated alternatively according to the
frequency of the power supply. Refer to the Figure 1 and 2.
T1+T2 are connected so that each
4
R-2397
COMMERCIAL
FREQUENCY
(50HZ)
POWER OUTPUT
BY MAGNETRON 1
POWER OUTPUT
BY MAGNETRON 2
OPERATION OF
MAGNETRON
T1: HIGH VOLTAGE
TRANSFORMER
(REAR)
C1: H.V. CAPACITOR
ASYMMETRIC
RECTIFIER
H. V. RECTIFIER
MG2: MAGNETRON (LOWER)
T2: HIGH VOLTAGE
TRANSFORMER
(FRONT)
C2: H.V. CAPACITOR
ASYMMETRIC
RECTIFIER
H. V. RECTIFIER
MG1: MAGNETRON (UPPER)
Figure B-1. High Voltage Circuit
FUNCTION OF IMPORTANT COMPONENTS
DOOR OPEN MECHANISM
1. The door release lever is pulled.
2. The upper latch head is lifted up by the linked door
release lever.
3. The latch lever is lifted up by the door release lever.
4. The joint lever is lifted up by the latch lever.
5. The lower latch head is lifted up by the joint lever.
6. Now both latch heads are lifted up, so they can be
released from the latch hook.
7. Now the door can be opened.
Door release
lever
Joint lever
Latch head
Figure D-1. Door Open Mechanism
Latch head
Monitor switch
Latch hook
2nd. latch switch
1st. latch switch
Stop switch
3rd. latch switch
Figure B-2. Operation of Magnetron
MONITOR SWITCH
The monitor switch is activated (the contacts opened) the
upper latch head and switch lever A while the door is
closed. The switch is intended to render the oven inoperative by means of blowing the fuse F6.3A when the
contacts of the 1st latch switch fail to open when the door
is opened.
Function
1. When the door is opened, the monitor switch contacts
close (to the ON condition) due to their being normally
closed. At this time the 1st latch switch is in the OFF
condition (contacts open) due to their being normally
open contact switches.
2. As the door goes to a closed position, the monitor
switch contacts are opened and 1st latch switch contacts are closed (On opening the door, each of these
switches operate inversely.)
3. If the door is opened and the 1st latch switch contacts
fail to open, the fuse F6.3A blows simultaneously with
closing of the monitor switch contacts.
CAUTION:BEFORE REPLACING A BLOWN FUSE
F6.3A TEST THE 1ST LATCH SWITCH,
MONITOR SWITCH AND MONITOR RESISTOR FOR PROPER OPERATION. (REFER
TO CHAPTER “TEST PROCEDURE”).
MONITOR RESISTOR
The monitor resistor prevents the fuse F6.3A 250V bursting when the fuse F6.3A 250V blows due to the operation
of the monitor switch.
1ST LATCH SWITCH, 2ND LATCH SWITCH, 3RD
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.
NOISE FILTER
The noise filter assembly prevents radio frequency interference that might flow back in the power circuit.
WEAK POINT
If the wire harness or electrical components make a shortcircuit, this weak point blows to prevent an electric shock
or fire hazard.
5
R-2397
FUSE F6.3A 250V
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 remains
closed with the oven door open and when the monitor
switch closes.
ASYMMETRIC RECTIFIER
The asymmetric rectifier is solid state device that prevents current flow is both directions. And it prevents the
temperature rise of the high voltage transformer by
blowing the weak point when the high voltage rectifier is
shorted.
AB
D2 D1
ASYMMETRIC
RECTIFIER
HIGH VOLTAGE RECTIFIER
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.
1. The high voltage rectifier is shorted by some fault
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 high voltage transformer.
5. The large electric currents flow through the primary
winding of the high voltage transformer.
6. The weak point blows by the large electric currents.
7. The power supplying to the high voltage transformer
is cut off.
EXHAUST THERMISTOR
The thermistor is a negative temperature coefficient type.
The temperature in the exhaust duct is detected through
the resistance of the thermistor.
If the temperature is high, the control panel will display
“EE7” and the oven will stop to avoid overheating and
catching fire.
If the thermistor is open, the control panel will display
"EE6" and the oven will stop.
MAGNETRON THERMISTOR
The air temperature around the lower magnetron is
detected through the resistance of the thermistor.
If the temperature is high, the control panel will display
"EE17" and the oven will stop to protect the lower
magnetron against overheat.
If the thermistor is open, the control panel will display
"EE16" and the oven will stop.
MAGNETRON THERMAL CUT-OUTS 145˚
These thermal cut-outs protect the magnetrons against
overheat. If their temperature go up higher than 145˚C
because the blower motor is interrupted, the ventilation
openings are blocked, the thermal cut-outs will open and
the line voltage to the high voltage transformer will be cut
off and the operations of the magnetrons will be stopped.
The defective thermal cut-out must be replaced with new
rated one.
BLOWER MOTOR THERMAL CUT-OUT 115˚C
This thermal cut-out protect the blower motor against
overheat. If its temperature goes up higher than 115˚C
because the blower motor is locked or the ventilation
openings are blocked, the contacts of the thermal cut-out
will open and the line voltage to the control unit will be cut
off and the operation of the oven will be stopped. The
defective thermal cut-out must be replaced with new rated
one.
OVEN THERMAL CUT-OUT 115˚C
This thermal cut-out protects the oven against overheat. If
the temperature goes up higher than 115˚C because the
food catches fire, the contacts of
and the line voltage to the control unit will be cut off and the
operation of the oven will be stopped. The defective
thermal cut-out will open
thermal
cut-out must be replaced with a new rated one.
BLOWER MOTOR
The blower motor drives a blade which draws external
cool air. This cool air is directed through the air vanes
surrounding the magnetrons and cools the magnetrons.
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.
STIRRER MOTOR
The stirrer motor drives a stirrer antenna to stir the
microwave radiation from the waveguide.
INTAKE THERMISTOR
This thermistor detects ambient air temperature.
6
R-2397
SERVICING
WARNING TO SERVICE PERSONNEL
Microwave ovens contain circuitry capable of producing very high voltage and current. Contact with following parts
will result in electrocution.
High voltage capacitor, High voltage 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 shortcircuit 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 high voltage 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 high voltage transformer.
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.
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 tray, close the door and
press Manual / Repeat key and set the microwave time
for one (1) minute. Set the power level to 100% and push
the START button. When the one 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.
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 F2 F6.3A in the 1st latch
switch - monitor switch - monitor resisitor
circuit, check the 1st latch switch, monitor
switch and monitor resistor before replacing the fuse F6.3A.
7
R-2397
CONDITION
OFF
CONDITION
ON
CONDITION
TEST PROCEDURE
POSSIBLE CAUSE
AND
DEFECTIVE PARTS
PPROBLEM
“ . “ does not appear on display when power
cord is plugged into wall outlet.
Control panel can not accept key in.
Fuse F6.3A blows when the door is opened.
Home fuse blowns when power cord is plugged
into wall outlet.
Weak point A017 blowns when power cord is
plugged into wall outlet.
Oven lamp, fan motor and stirrer motors do not
work for 1 minute whenever the door is opened
or after cooking.
Fuse F2 F6.3A blowns when power cord is
plugged into wall outlet.
Oven lamp does not light when door is opened.
(Blower and stirrer motors work)
Blower motor does not work when door is
opened. (Oven lamp lights and stirrer motors
work)
“EE 1” appear in display.
“EE 2” appear in display.
“EE 3” appear in display .
“EE 6” appear in display.
“EE 7” appear in display.
“EE 9” appear in display.
Oven lamp, blower motor and stirrer motors do
not work.
Oven lamp does not work.
Blower motor does not work.
Oven does not stop after end of cooking cycle or
when STOP/CLEAR key is touched. (Oven lamp,
blower motor and stirrer motors stop.)
Home fuse blows when starting the oven.
Oven goes into cook cycle but shuts down
before end of cooking cycle.
Oven seems to be operating but no heat is
produced in oven load.
It passed more than 1 minute after cooking but
oven lamp, blower motor and stirrer motors do
not stop.
“EE 0” appear in display .
“EE 16” appear in display.
“EE 17” appear in display.
“EE 8” appear in display .
“EE 10” appear in display .
Stirrer motors do not work.
AA BB CCCDDEEEEE F FGH
MAGNETRON MG1
MAGNETRON MG2
HIGH VOLTAGE TRANSFORMER T1
HIGH VOLTAGE TRANSFORMER T2
H.V. RECTIFIER ASSEMBLY FOR MG1
H.V. RECTIFIER ASSEMBLY FOR MG2
H.V. WIRE HARNESS
H.V. CAPACITOR C1
H.V. CAPACITOR C2
1ST. LATCH SWITCH
2ND. LATCH SWITCH
3RD. LATCH SWITCH
MONITOR SWITCH
STOP SWITCH
WEAK POINT A018 F3
WEAK POINT A018 F4
WEAK POINT A017 F1
FUSE 6.3A F2
8
R-2397
IIIIJLKKK LM NPQ
MAGNETRON THERMAL CUT-OUT 145˚C TC1
MAGNETRON THERMAL CUT-OUT 145˚C TC2
B. MOTOR THERMAL CUT-OUT 115˚C TC3
OVEN THERMAL CUT-OUTT 115˚C TC4
MONITOR RESISTOR R1
STIRRER MOTOR
MAGNETRON THERMISTOR
EXHAUST THERMISTOR
INTAKE THERMISTOR
OVEN LAMP OR SOCKET
BLOWER MOTOR
NOISE FILTER
POWER SUPPLY CORD
FUSE HOLDER
SHORTED WIRE HARNESS
OPENED WIRE HARNESS
TOUCH CONTROL PANEL
RELAY RY-1, RY-3, RY-4
FOIL PATTERN
BLOCKED VENTILATION OPENINGS
BLOCKED BLOWER MOTOR
MIS ADJUSTMENT OF SWITCHES
HOME FUSE OR BREAKER
NO POWER AT WALL OUTLET
OVER THE MAX. COOKING TIME
DUE TO PROGRAMME LOCK
TEMPERATURE OF EXHAUST THERMISTOR IS HIGH
O
TEMPERATURE OF INTAKE THERMISTOR IS HIGH
TEMPERATURE OF MAGNETRON THERMISTOR IS HIGH
BLOCKED STIRRER ANTENNA
KEY UNIT
9
R-2397
PROCEDURE
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 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 (IEC-705-1988)
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 is measured by how much power the water load can absorb. 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.
TEST PROCEDURES
LETTER
COMPONENT 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 ............ 25 sec. P=170x∆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 5K.
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 can be 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
heat-up time is not included.
NOTE: The operation time of the microwave oven is “t + 3” sec. (3 sec. is magnetron filament heat-
up time.) Therefore total reheating time = 28 seconds.
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) K.
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.
10
PROCEDURE
1000g
1000g
1000g
T1˚C
T2˚C
AB
C
D2 D1
ASYMMETRIC
RECTIFIER
HIGH VOLTAGE RECTIFIER
R-2397
TEST PROCEDURES
LETTER
Initial temperature............................................................................................... T1 = 11°C
Temperature after (25 + 3) = 28 sec. ................................................................. T2 = 21°C
Temperature difference Cold-Warm ................................................................... ∆T = 10°C
Measured output power
The equation is “P = 170 x ∆T”.............................................. P = 170 x 10°C = 1700 Watts
JUDGMENT: The measured output power should be at least ± 15 % of the rated output power.
CAUTION: 1°C CORRESPONDS TO 170 WATTS. REPEAT MEASUREMENT IF THE POWER IS
INSUFFICIENT.
COMPONENT TEST
Heat up for 28 sec.
B HIGH VOLTAGE TRANSFORMER TEST
WARNING: High voltages and large currents are present at the secondary winding and
filament winding of high voltage 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 high voltage 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. 1.06 Ω
b. Secondary winding approx. 57.3 Ω
c. Filament winding less than 1 Ω
If the reading obtained are not stated as above, then the high voltage 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 infinity in one direction and more than 100 kΩ in the other direction.
CARRY OUT 4R CHECKS.
ASYMMETRIC RECTIFIER TEST
CARRY OUT 3D CHECKS.
11
R-2397
PROCEDURE
Isolate the high voltage rectifier assembly from the HV circuit. The asymmetric rectifier can be tested
using an ohmmeter set to its highest range. Contact the ohmmeter across the terminals A+B of the
asymmetric rectifier and note the reading obtained. Reverse the meter leads and note this second
reading. If an open circuit is indicated in both directions then the asymmetric rectifier is good. If an
asymmetric rectifier is shorted in either direction, then the 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 high voltage
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.
D HIGH VOLTAGE CAPACITOR TEST
CARRY OUT 3D CHECKS.
TEST PROCEDURES
LETTER
COMPONENT TEST
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 CHECK.
Isolate the switch to be tested and using an ohmmeter check between the terminals as described
in the following table.
Plunger Operation COM to NO COM to NC NO; Normally open terminal
Released O.C. S.C. NC; Normally close terminal
Depressed S.C. O.C. S.C.; Short circuit
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
Table: Terminal Connection of Switch COM;Common terminal
O.C.; Open circuit
CARRY OUT 4R CHECKS.
F WEAK POINT A018
CARRY OUT 3D CHECKS.
If the weak point A018 is blown, there could be a short in the asymmetric rectifier or there is a ground
in wire harness. A short in the asymmetric rectifier may have occured due to short or ground in H.V.
rectifier, magnetron, high voltage transformer or H.V. wire. Check them and replace the defective
parts or repair the wire harness.
CARRY OUT 4R CHECKS.
CAUTION: Only replace weak point
A018 with the correct value replacement.
12
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