DAEWOO ELECTRONICS KOR-4125 User manual

Service Manual
Microwave Oven
Model : KOR-4125
DAEWOO ELECTRONICS CO., LTD.
OVERSEAS SERVICE DEPT.

2
PRECAUTIONS TO BE OBSERVED BEFORE AND
DURING SERVICING TO AVOID POSSIBLE
EXPOSURE TO EXCESSIVE MICROWAVE ENERGY
(a)Do not operate or allow the oven to be operated with the door opened.
(b)Make the following safety checks on all ovens to be serviced before activating the magnetron or other
micro-wave source, and make repairs if necessary: (1) Interlock operation, (2) proper door closing, (3)
seal and sealing surfaces (arcing, wear, and other damage), (4) damage to or loosening of hinges and
latches, and (5) evidence of dropping or abuse.
(c)Before turning on microwave power for any service test or inspection within the microwave generating
com-partments, check the magnetron, wave guide or transmission line, and cavity for proper
alignment, integrity, and connections.
(d)Any defective or misadjusted components in the interlock, monitor, door seal and microwave
generation and transmission systems shall be repaired, replaced, or adjusted by procedures described
in this manual before the oven is released to the owner.
(e)A microwave leakage check to verify compliance with the Federal performance standard should be
performed on each oven prior to release to the owner.
TABLE OF CONTENTS
PROPER USE AND SERVICE PRECAUTIONS 3
SPECIFICATIONS 4
SCHEMATIC DIAGRAM OF FEATURES 5
INSTALLATION 6
OPERATION 7
MEASUREMENT OF THE MICROWAVE OUTPUT POWER 8
MICROWAVE RADIATION TEST 9
WIRING DIAGRAM 10
CIRCUIT DESCRIPTION 11
PRECATIONS FOR DISASSEMBLY AND REPAIR 13
DISASSEMBLY AND ASSEMBLY 14
INTERLOCK MECHANISM 19
TROUBLE SHOOTING GUIDE 21
COMPONENT TEST PROCEDURE 23
SAFETY INTERLOCK CONTINUITY TEST 24
EXPLODED AND PARTS LIST 25

PROPER USE AND SERVICE PRECAUTIONS
CAUTION : This Device is to be Serviced Only by Properly Qualified Service Personnel. Consult the Service
Manual for Proper Service Procedures to Assure Continued Safety Operation and for Precautions
to be Taken to Avoid Possible Exposure to Excessive Microwave Energy.
1. For Safe Operation
Damage that allows the microwave energy (that cooks or heats the food) to escape will result in poor cooking and
may cause serious bodily injury to the operator.
IF ANY OF THE FOLLOWING CONDITIONS EXIST, OPERATOR MUST NOT USE THE APPLIANCE.
(Only a trained service personnel should make repairs.)
1) A broken door hinge.
2) A broken door viewing screen.
3) A broken front panel, oven cavity.
4) A loosened door lock.
5) A broken door lock.
The door seal area and oven cavity surface be kept clean.
No grease, soil or spatter should be allowed to build up on these surfaces or inside the oven.
DO NOT ATTEMPT TO OPERATE THIS APPLIANCE WITH THE DOOR OPEN. The microwave oven has
concealed switches to make sure the power is turned off when the door is opened. Do not attempt to defeat them.
DO NOT ATTEMPT TO SERVICE THIS APPLIANCE UNTIL YOU HAVE READ THIS SERVICE MANUAL.
2. For Safe Service Procedures.
1) If the oven to be serviced is operative, a microwave emission check should be performed prior to servicing the
oven.
2) If any ascertained oven unit is found to have excessive emission level 5mW/cm
2
, the service person should :
(a) inform the manufacturer, importer or assembler,
(b) repair the unit at no cost to the owner,
(c) attempt to ascertain the cause of the excessive leakage,
(d) tell the owner of the unit not to use it until the oven has been brought into compliance.
3) If the oven operates with the door opened, the service person should tell the user not to operate the oven and
contact the manufacturer immediately.
3
CAUTION
MICROWAVE RADIATION
PERSONNEL SHOULD NOT BE EXPOSED TO THE MICROWAVE ENERGY WHICH MAY RADIATE
FROM THE MAGNETRON OR OTHER MICROWAVE GENERATING DEVICE 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 IN IT. NEVER LOOK INTO AN OPEN
WAVEGUIDE OR ANTENNA WHILE THE DEVICE IS ENERGIZED.

4
SPECIFICATIONS
ITEM SPECIFICATION
POWER SUPPLY 230V~50HZ, SINGLE PHASE WITH EARTHING
POWER CONSUMPTION 920 W
MICROWAVE OUTPOWER 600 W (IEC 705) (FULL MICROWAVE POWER)
FREQUENCY 2450MHz
OUTSIDE DIMENSIONS (W X H X D) 444X235X337mm
CAVITY DIMENSIONS (W X H X D) 265X172X270mm
NET WEIGHT APPROX. 12kg
TIMER 35min. DUAL SPEED
POWER SELECTIONS 5 LEVELS
CAVITY VOLUME 0.4 Cu. Ft
* Specifications subject to change without notice.
337444
235

5
SCHEMATIC DIAGRAM OF FEATURES
2
3
5
76
84
9
10
11
1
¤Safety Interlock System
¤ŁDoor Viewing Screen - Allows viewing of food, the screen is designed so that light can pass through, but not
the microwave.
¤ØDoor Hook - When the door is closed, it will automatically shut. if the door is opened while the oven is
operating, the magnetro will immediately stop operating.
¤ŒOven Cavity
¤ºDoor Seal - Door seal maintains the microwave energy within the oven cavity and prevents microwave
leakage.
¤Glass Cooking Tray - Made of special heat resistant glass. Food in a proper receptacle is placed on this
tray for cooking.
¤Roller guide - This must always be used for cooking together with the glass cooking tray.
¤Coupler - This fits over the shaft in the center of the oven’s cavity floor. This is to remain in the oven for all
cooking.
¤Knob V.P.C - used to select a microwave power level.
¤Knob timer - used in setting cooking time for all functions.
¤æDoor Release Button - By pushing this button the latch system cut off all circuits and stops the oven before
the door is opened.

6
INSTALLATION
1. Steady, flat location.
This microwave oven should be set on a steady, flat surface.
2.Leave space behind and side.
All air vents should be kept a clearance. If all vents are covered during operation, the oven may be overheated
and, eventually, oven failure caused.
3.Away from radio, and TV sets
Poor television reception and radio interference may be resulted in, if the oven is located close to a TV, Radio, or
antenna, feeder and so on.
4.Away from heating appliances and water taps
Keep the oven away from hot air, steam or splash when choosing a place to position it, or the insulation might be
adversely affected and breakdowns occur.
5.power supply
• Check your local power source.
This microwave oven requires a current of approximately 5 amperes, 230V 50Hz.
use a receptacle that will accept the earth prong.
• Voltage Warning
The voltage used must be the same as specified on this Microwave Oven.
Using a higher voltage may result in a fire or other accident causing oven damage. Using low voltage will cause
slow cooking.
We are not responsible for damage resulted from use of this Microwave Oven with a voltage or amperage fruse
other than those specified.
• Power supply cord is about 1.0 meters long. Do not use an extension cord.
If the supply cord is damaged, it must be replaced by the manufacturer or its service agent or a similarly qualified
person in order to avoid a hazard;
IMPORTANT
6. Examine the oven after unpacking for any damage such as:
Dents, A misaligned door, Broken door, Dents in cavity.
If any of the above are visible, do not install this oven.
CAUTION : Do not be under any circumstances cut or remove the round earthing prong from this plug.
WARNING: This appliance must be earthed.
CAUTION : Maintenance work like the replacing the power cable must be made by a qualified technician of the
after-sales-services.
The wires in this main lead coloured in accordance with the following code.
Green-and-yellow : Earth
Blue : Neutral
Brown : Live
As the colours of the wires in the main lead of this appliance may not correspond with the coloured markings
identifying the terminals in your plug, proceed as follows:
The wire which is coloured green-and-yellow must be connected to the terminal in the plug which is marked
with the letter ‘E’ or by the earth symbol or green-and-yellow.
The wire which is coloured blue must be connected to the terminal which is marked with the letter ‘N’ or
coloured white.
The wire which is coloured brown must be connected to the terminal which is marked with the letter ‘L’ or
coloured red.

7
OPERATION
1
Connect the main lead to an electrical outlet.
2
After placing the food in a suitable container, open the oven door and put it on the glass tray.
The glass tray must always be in place during cooking.
3
CLOSE THE DOOR securely.
4
Choose cooking power level by setting V.P.C.
knob to the desired position.
Refer to cookbook for recommended power
levles.
5
Determine cooking time. Consult cookbook for
recipe timing.
¢”Oven light turns on and cooling fan starts to
operate. Microwave cooking starts.
6
You may open the door while the oven is
operating. As soon as the door is opened, the
safety mechanisms stop the generation of
microwave power and the operation of cooking
timer.
If you wish to change the time during cooking,
simply adjust the Timer to the desired time.
7
When the timer reaches zero, a bell will ring and
the unit will turn off.
¢”Oven light turns off.
If additional cooking time is needed and the
door is closed, the oven will automatically start
when the Timer is reset.
NOTE :
1. When setting Timer for less than 2 minutes, turn the
Timer past 2 minutes and then return to the correct
timer position.
2. Various clicking noises may be heard when turning
the V.P.C. Knob. This is normal and does not affect
the operation of your microwave oven.
Variable power cooking
ON and OFF cycle time of mechanicial V.P.C. switch is 30 seconds.
When the V.P.C. knob is set to the desired position and timer knob turns to the desired position, the V.P.C
switch has a cycle (ON/OFF time (sec)) listed below.
012
3
4
5
6
10
15
20
25
30
35
Variable power setting ON/OFF time (SEC) POWER
(HIGH) 30/0 100%
(MED HIGH) 23.2/6.8 77%
(MEDIUM) 16.5/13.5 55%
(DEFROST) 9.8/20.2 33%
(WARM) 5/25 17%

8
MEASUREMENT OF THE MICROWAVE OUTPUT POWER
Microwave output power can be checked by indirectly measuring the temperature rise of a certain amount of water
exposed to the microwave as directed below.
Procedure
1. Microwave power output measurement is made with the microwave oven supplied at rated voltage and operated at
its maximum microwave power setting with a load of 1,000¡5cc of potable water.
2. The water is contained in a cylindrical borosilicate glass vessel having a maximum material thickness of 3 mm and
an outside diameter of approximately 190 mm.
3. The oven and the empty vessel are at ambient temperature prior to the start of the test.
The initial temeprature of the water is 10¡2˚C (50¡3.6˚F).
It is measured immediately before the water is added to the vessel. After addition of the water to the vessel, the
load is immediately placed on the center of the shelf which is in the lowest notmal position.
4. Microwave power is switched on.
5. heating time should be exactly 70 seconds.
Heating time is measured while the microwave
generator is operating at full power.
The filament heat-up time for magnetron is not included.
6. The initial and final water temepratures are selected so
that the maximum difference between the ambient and
final water temperatures is 5K.
7. The microwave power output p in watt is calculated from the following formula:
•∆T is actual temperature rise.
• T is the heating time.
The power measured should be 600W¡10.0%
Water Load
Tray Fig. 14
P = 4187 X §T/t
CAUTION :
1. Water load should be measured exactly to 1 liter.
2. Input power voltage should be exactly 230 volts as specified.
3. Ambient temperature should be 20 ¡2˚C(68¡3.6˚F)

9
MICROWAVE RADIATION TEST
WARNING
•Make sure to check the microwave leakage before and after repair or adjustment.
• Always, start measuring of an unknown field to assure safety for operating personnel from microwave energy.
• Do not place your hands into any suspected microwave radiation field unless the safe density level is known.
• Card should be taken not to place the eyes in direct line with the source of microwave energy.
•Slowly approach the unit under test until the radiometer reads an appreciable microwave leakage from the unit
under the test.
Procedure
A) Prepare Microwave Energy Survey Meter, 600cc glass beaker, glass thermometer 100˚C or 212˚F.
B)Pour 275 ¡15cc of tap water initially at 20¡5˚C(68¡9˚F) in the 600cc neaker with an inside diameter of
approx. 9.5cm(3.5in).
C)Place it at the center of the tray and set it in a cavity.
D)Close the door and operate the oven.
E)Measure the leakage by using microwave energy survery meter with dual ranges, set to 2450 MHz.
- Measured radiation leakage must not exceed the values prescribed below.
• leakage for a fully assembled oven with door normally closed must be less than 4mW/cm
2
.
-When measuring the leakage, always use the 2 in(5cm) space cone with probe. Hold the probe perpendicular
to the cabinet, door. Place the space cone of the
probe on the door, cabinet, door seam, door viewing
screen, the exhaust air vents air vents and the suction
air vents.
- Measuring should be in a counter-clockwise direction
at a rate of 1 inch/sec. If the leakage of the cabinet
door seam is unknow, move the probe more slowly.
- When measuring near a corner of the door, keep the probe perpendicular to the areas making sure the probe
end at the base of the cone does not get closer than 2 inches from any metal.
if it does, erronous reading may be resulted.

10
WIRING DIAGRAM

11
CIRCUIT DESCRIPTION
1. When the food is placed in the oven cavity and door is closed.
•The contact of the interlock monitor switch is opened(NO).
• The contacts of the primary interlock switch and secondary interlock switch are closed.
2. When the timer is set to the time desired.
•The contact of the timer switch is closed.
• oven lamp turns on.
• 230V AC is applied to the hogh voltage transformer.
• Turntable motor start rotating and glass tray rotating.
• Fan motor rotaties and cools the magnetron by blowing air.
• Timer motor operates and points to passing cooking time.
•3.3 Volts AC is generated from the filamente winding of the high voltage transformer. This filament voltage is
applied to the magnetron to heat the magnetron filament through two noise preventing ckoke coils.
•A high voltage of 2000 Volts AC is generated in the secondary of high voltage transformer and this secondary
voltage is increase by the action of the diode and the charging of the high voltage transformer and this
secondary voltage is increased by the action of the diode and the charging of the high voltage capacitor. This
resultant D.C voltage is then applied to the anode of the magnetron. As shown in Fig. 2 the first half voltage
capacitor. Current flow is in the direction of the dotted-line during the second half cycle, the voltage produced by
the transformer secondary, and the charge of the high voltage capacitor are combined and applied to the
magnetron as shown by the solid line so that oscillations begins.
The disturbance wave generated by the magnetron is prevented by the choke coils of 1.5µH, filter capacitors of
500pF and the magnetron’s shielded case so that TV and radio programs are not impaired by noise.
TM
TM CL GM FM
CL GM FM
12A Fuse
Primary
Interlock
Switch Timer
Switch
COM NC
NO
Interlock
Monitor
Switch
Secondary
Interlock
Switch
Timer Motor Cavity Lamp Geared Motor Fan Motor
Fig. 1

12
3. When the door is opened during cooking.
•Primary interlock switch and secondary interlock switch open to cut off the primary voltage to the high voltage
transformer to stop microwave oscillation.
• Fan motor, timer motor and turntable motor stop rotating.
• Oven lamp turns off.
• As soon as the door is opened, monitor switch close(NC) to create the short circuit.
If the contacts of primary interlock switch and secondary interlock switch are both malfunction, the 12A fuse
blows open due to the large current surge caused by monitor switch activation.
HIGH VOLTAGE
TRANSFORMER
H.V.
CAPACITOR
H.V. DIODE
Fig. 2

13
PRECAUTIONS FOR DISASSEMBLY AND REPAIR
- Cautions to be observed during troubleshooting.
Unlike many other appliances, the microwave oven is a high-current equipment. It is completely safe during normal
operation. However, carelessness in servicing the oven can result in an electric shock or possible dnager from a short
circuit.
You are asked to observe the following precautions carefully.
(1) Always remove the power plug from the outlet before servicing.
(2) use an insulated screwdriver and ware rubber golves when servicing the high voltage side.
(3) Discharge the high voltage capacitor before touching any oven components or wiring.
1. Check the earthed.
Do not operate with two wire extension cord.
The microwave oven is designed to be used when
earth.
It is imperative, therefore, to make sure it is earthed
properly before begining repair work.
2. Warning about the electric charge in the
high voltage capacitor.
For about 30 seconds after the operation stopped, and
electric charge remains in the high voltage capacitor.
When replacing or checking parts, short between oven
chassis and the negative high terminal of the high
voltage capacitor, by using a properly insulated screw
driver to discharge.
(4) When the 12A fuse is blown out due to the operation of the monitor switch;replace primary, secondary interlock
switch and monitor switch.
Refer to the next page for the necessary adjustment.
(5) After repair or replacement of parts, amke sure that the screws are properly tightened, and all electrical
connections are tightened.
(6) Do not operate without cabinet.
CAUTION : Sevice personnel should remove their watches whenever working close to the magnetron or
repairing it.
WARNING : When servicing the appliance, it is needed to give care to touching or replacing high potential parts
because of electrical shock or exposing microwave. These parts are same as follow - H.V.
Transformer, Magnetron, H.V. Capacitor, H.V. Diode.

14
DISASSEMBLY AND ASSEMBLY
1. To remove cabinet
Remove three screws on cabinet back.
2. To remove door assembly.
1) Remove two screws ¤Which secure the stopper
hinge top.
2) Remove the stopper hinge top ¤Ł and door
assembly ¤Øfrom top plate of cavity.
3) Remove the stopper hinge top ¤Ł from door
assembly.
4) Reverse the above steps for reassembly tasking
care to replace fixing glue.
3. To remove door parts.
2
3
1
5
4
6
Door Plate
32
1
NOTE : After replacing the door perform a check
of correct alignment with the hinge and
cavity front face.

15
(1) Remove the gasket door ¤from door plate.
(2) Remove the barrier screen inner ¤Łfrom door plate.
(3) Remove the door frame ¤Øfrom door plate.
(4) Remove the spring ¤ºand the hook ¤Œ.
(5) Remove the barrie screen outer ¤from door frame ¤Ø
(6) Reverse the above steps for reassembly.
4. Method to reduce the gap between the door seal and the oven front surface.
(1) To reduce gap located on part ‘ A ’.
1) Loosen twon screws on stopper hinge top, and then
push the door to contact the door seal to oven front
srface.
2) Tighten two screws.
(2) To reduce gap located on part ‘ B ’.
1) Loosen two screws on bottom hinge, and then push the door to oven front surface.
2) Tighten two screws.
(3) To reduce gap located on part ‘ C ’ (See Fig. A)
1) Loosen a screw on the interlock switch assembly located at the bottom of the oven body.
2) Draw the interlock switch assembly inward as possible to engage with hook on the bottom side.
3) Tighten a screw.
(4) To reduce gap lacated on part ‘ D ’ (See Fig. B)
1) Loosen a screw on the interlock switch assembly located at the top of the oven body.
2) Follow step 2) and 3) of (3).
NOTE : A small gap may be acceptable if the microwave leakage does not exceed 4mW/cm
2
PRIMARY
INTERLOCK
SWITCH
INTERLOCK
MONITOR
SWITCH
SECONDARY
INTERLOCK
SWITCH
HOOK
HOOK
B C
A D
Fig. A Fig. B

16
5. To remove control panel parts.
(1) Remove the screw which secure the control panel, push
up two snap fits and draw forward the control panel
assembly.
(2) Remove the door open lever ¤from the control panel.
(3) Remove two screws ¤Łwhich secure the timer assembly ¤Ø.
(4) Remove the timer assembly ¤Ø.
(5) Pull out the timer knob ¤Œfrom the timer assembly ¤Ø.
(6) Pull out the timer coupler ¤ºfrom the timer assembly ¤Ø.
(7) Remove the screw ¤which secure the V.P.C coupler ¤.
(8) Oull ou the V.P.C coupler ¤, V.P.V knob ¤, and flat spring ¤from the control panel.
(9) Remove the door open button ¤and button spring ¤æfrom the control panel.
(10) Reverse the above steps for reassembly.
11
Control Panel
1
45 3
2
9
8
10
7 6

17
6. To remove high voltage capacitor
(1) Remove a screw ¤which secure the grounding ring
terminal of the H.V. diode ¤Łand the capacitor holder ¤Ø.
(2) Remove the H.V. diode ¤Łfrom the capacitor holder ¤Ø.
(3) Reverse the above steps for reassembly.
High voltage circuit wiring
7. To remove magnetron.
(1) Remove three screws ¤which secure the
magnetron ¤Ł.
(2) Remove the magnetron ¤Ł.
(3) Reverse the abvove steps for reassembly.
1
3
2
Magnetron
H.V. Capacitor
H.V.
Diode
H.V. Transformer
2
1

18
8. To remove fan motor assembly.
(1) Remove screw ¤from the rear panel of cavity. (2) Remove screw ¤from the rear panel of cavity.
(3) Pull out the guide wind assembly. (4) Pull out the fan ¤ºfrom the fan motor ¤Ø.
(5) Remove two screws ¤Łfrom the fan motor ¤Ø.(6) Remove the fan motor ¤Øout of guide wind ¤Œ.
(7) Remove the filter ¤out of guide wind ¤Œ.(8) Reverse the above steps for reassemble.
9. To remove transformer.
(1) Remove the four screw ¤holding the H.V.
transformer ¤Ł.
(2) Remove the transformer ¤Ł.
(3) Reverse the above steps for reassembly.
CAUTION : Never install the magnetron without the metallic gasket plate which is packed with each magnetron
to prevent microwave leakage. Whenever repair work is carried out on magnetron, check the
microwave leakage. It shall nor exceed 4mW/cm2 for a fully assembled oven with door normally
closed.
2
1
Metallc Gasket Plate
Magnetron AntennaWave Guide
54
6
3
2
71
Magnetron
antenna
Metallic
gasket
plate
Cooling fin
Magnetron
Filament
terminal

19
INTERLOCK MECHANISM
The door lock mechanism is a device which has been specially designed to completely eliminate microwave radiation
when the door is opened during operation, and thus to perfectly prevent the danger resulting from the leakage of
microwave.
(1) primary interlock switch
when the door is closed, the hook the oven door. If the door is not closed properly, the oven will not operate. When
the door is properly closed, the hook pushes the button of the micro switch. Then the button of the primary interlock
switch bring it under “NO” condition.
Adjustment 1.
When the door is closed, the switch button is pushed
by the hook.
The movement of the switch button should exceed
1.2 mm measured at the top of the button.
PRIMARY
INTERLOCK
SWITCH
HOOK
1 .2mm

20
(2) Secondary interlock switch and interlock monitor switch
When the door is closed, the hook
pushes the lock lever downward, the
lock lever presses the button of the
monitor interlock switch to bring it under
“NO” , condition and presses the button
of the secondary interlock switch to
bring it under “NO” , condition.
Adjustment 2.
Interlock monitor switch
When the door is closed, the interlock monitor switch should be opened before other switches close.
When the door is opened, the interlock monitor switch should be closed after other switches open.
Secondary interlock switch
The movement of the switch button should exceed 1.2 mm measured at the top of the button.
(3) Adjustment steps
a)Loosen the two mounting screws.
b) Adjust interlock switch assembly position.
c) Confirm the gap (1.2mm) described above.
d) Make sure that lock lever moves smoothly after adjustments are completed.
e) Completely tighten the two mounting screws.
(4) Interlock switch replacement
Whenever safety interlock switch are replaced.
1) Refer to the following diagram.
2) Check the connection of monitor switch after replacement.
3) Perform the electrical continuity check of interlock switches and microwave emission test mentioned in this
manual.
SECONDARY
INTERLOCK
SWITCH
INTERLOCK
MONITOR
SWITCH
HOOK
NOTE : Micorwave emission test should be performed after adjusitng interlock machanism. If the microwave
emission exceed 4mW/cm
2
, readjust interlock mechanism.
Secondary
Interlock
Switch
RD
WH
WH BL BK
WH
WH
RD
Interlock
Monitor
Switch
Primary
Interlock
Switch
SYMBOL COLOR
RD RED
WH WHITE
BK BLACK
BL BLUE