Kenmore Microwave Repair Manual Model 721.66339
Kenmore Microwave Repair Manual Model 721.66339
Kenmore Microwave Repair Manual Model 721.66339
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-7-
6. OVERALL CIRCUIT DIAGRAM
A. SCHEMATIC DIAGRAM
B. MATRIX CIRCUIT FOR TOUCH KEY BOARD
-8-
Figure 4
Figure 5
-9-
7. OPERATING PROCEDURES
A. OVEN CONTROL PANEL
1. DISPLAY. The display includes a clock and indicators that tell you
time of day, cooking time settings, and cooking functions selected.
2. QUICK TOUCH SENSOR. This pad allows you to cook most of
your favorite foods without having to select cooking times and
power levels.
3. MORE / LESS. All of the one touch cook and Timed Cook can be
adjusted to cook food for a longer or shorter time.
MORE Press MORE will add 10 seconds to the cooking time.
LESS Press LESS will subtract 10 seconds to the cooking
time.
4. AUTO DEFROST. This pad is an accurate defrosting method for
frozen meat, poultry and fish up to 6.0 lbs.
5. TrueCookPlus
code.
6. NUMBER PADS. Touch Number Pads to enter cooking time,
power level, quantities, or food categories.
7. COOK TIME. Touch this pad to set a cooking time.
8. STOP/CLEAR. Touch this pad to stop the oven or clear entries.
9. EXPRESS DEFROST. This pad provides you with the quick
defrosting method for 1.0 pound frozen foods.
10. MELT. Touch this pad to melt chocolate, cheese, butter, or
marshmallows.
11. SOFTEN. Touch this pad to soften ice cream, cream cheese,
butter, or frozen juice.
12. AUTO COOK. Touch this pad to select programming food items.
13. KITCHEN TIMER. Touch this pad to use your microwave oven as
a kitchen timer.
14. CLOCK. Touch this pad to enter the time of day.
15. OPTION. Touch this pad to change the oven's default settings for
sound, clock, scroll speed and weight.
16. POWER. Touch this pad to set a cooking power.
17. ADD MINUTE. Touch this pad to cook at 100% cook power for
1 minute to 99 minutes and 59 seconds.
18. START. Touch this pad to start all entries (except the Quick
Touch Sensor, Express Defrost, Auto Cook and Add Minute
function which start automatically) and to turn Child Lock on or off.
NOTE: A beep sounds when you touch a key on the control panel, to indicate that you have entered
a setting.
B. EASY USE TABLE
(1) KITCHEN TIMER
1. Touch STOP/CLEAR.
2. Touch KITCHEN TIMER.
3. Touch correct number for time.
4. Touch START.
(2) CHILD LOCK
To set:
1. Touch STOP/CLEAR.
2. Touch START more than 4 seconds.
To cancel:
1. Touch STOP/CLEAR.
2. Touch START more than 4 seconds.
(3) SENSOR COOK
1. Touch STOP/CLEAR.
2. Touch SENSOR COOK Category.
(4) ADD MINUTE
1. Touch STOP/CLEAR.
2. Touch ADD MINUTE.
(5) AUTO DEFROST
1. Touch STOP/CLEAR.
2. Touch AUTO DEFROST.
Three different defrosting levels are provided.
(Touch 1 : Meat
Touch 2 : Poultry
Touch 3 : Fish)
3. Enter the weight of your food in decimal
increments from 0.1 to 6.0 pounds.
4. Touch START
5. At beeping, turn food over.
6. After turning food over, touch START to resume
defrosting.
(6) TIMED COOKING
1. Touch STOP/CLEAR.
2. Touch COOK TIME.
3. Touch number for cooking time.
4. Touch POWER.
5. Touch number for cooking power level.
6. Touch START.
(7) MULTI-STAGE COOKING
1. Touch STOP/CLEAR.
2. Touch COOK TIME.
3. Touch number for cooking time.
4. Touch POWER.
5. Touch number for cooking power level.
6. Repeat steps 2-5 to set 2nd cooking stage.
7. Touch START.
-10-
8. PROCEDURE FOR MEASURING MICROWAVE
ENERGY LEAKAGE
A. CAUTIONS
(1) Be sure to check a microwave emission prior to servicing
the oven if the oven is operative prior to servicing.
(2) The service personnel should inform the manufacturer,
importer, or assembler of any certified oven unit found to
have a microwave emission level in excess of
5mW/cm.sq. and should repair any unit found to have
excessive emission levels at no cost to the owner and
should ascertain the cause of the excessive leakage.
The service personnel should instruct the owner not to
use the unit until the oven has been brought into
compliance.
(3) If the oven operates with the door open, the service
personnel should;
- Tell the user not to operate the oven
- Contact the manufacturer and CDRH (Center for
Devices and Radiological Health) immediately.
NOTE: Address on CDRH
Office of Compliance (HFZ-312)
Center for Devices and Radiological Health
1390 Piccard Drive
Rockville, Maryland 20850
(4) The service personnel should check all surface and vent
openings for microwave emission testing.
(5) Check for microwave energy leakage after every
servicing. The power density of the microwave radiation
leakage emitted by the microwave oven should not
exceed 1mW/cm.sq. And always start measuring of an
unknown field to assure safety for operating personnel
from radiation leakage.
NOTE: The standard is 5mW/cm.sq. while in the
customers home. 1mW/cm.sq. stated here is
manufacturers own voluntary standard for units in
customers home.
EQUIPMENT
Electromagnetic energy leakage monitor (NARDA 8100B,
HOLADAY HI 1501)
600cc glass beaker
Glass thermometer 100C
B. MEASURING MICROWAVE ENERGY LEAKAGE
(1) Pour 27515cc of 205C water in a beaker which is
graduated to 600 cc, and place the beaker in the center
of the oven.
(2) Set the energy leakage monitor to 2,450 MHz and use it
following the manufacturers recommended test
procedure to assure correct result.
(3) When measuring the leakage, always use the 2 inch
(5cm) spacer supplied with the probe.
(4) Operate the oven at its maximum output.
(5) Measure the microwave radiation using and
electromagnetic radiation monitor by holding the probe
perpendicular to the surface being measured. (See
Figure 7)
C. MEASUREMENT WITH THE OUTER CASE REMOVED
(1) When you replace the magnetron, measure for
microwave energy leakage before the outer case is
installed and after all necessary components are
replaced or adjusted. Special care should be taken in
measuring the following parts.
- Around the magnetron
- The waveguide
WARNING: AVOID CONTACTING ANY HIGH VOLTAGE
PARTS.
-11-
Move probe along shaded area.
Probe scanning speed
less than 2.5 cm/sec.
Figure 7
Figure 6
D. MEASUREMENT WITH A FULLY ASSEMBLED OVEN
(1) After all components, including the outer panels, are
fully assembled, measure for microwave energy
leakage around the door viewing window, the exhaust
opening and air inlet openings.
(2) Microwave energy leakage must not exceed the values
prescribed below.
NOTES:
Leakage with the outer panels removed - less than
5mW/cm.sq. Leakage for a fully assembled oven
(Before the latch switch (primary) is interrupted) with the
door in a slightly opened position - less than
1 mW/cm .sq.
E. NOTE WHEN MEASURING
(1) Do not exceed meter full scale deflection.
(2) The test probe must be removed no faster than 1
inch/sec (2.5cm/sec) along the shaded area, otherwise
a false reading may result.
(3) The test probe must be held with the grip portion of the
handle. A false reading may result if the operators
hand is between the handle and the probe.
(4) When testing near a corner of the door, keep the probe
perpendicular to the surface making sure the probe
is moved horizontally along the oven surface.
F. RECORD KEEPING AND NOTIFICATION AFTER
MEASUREMENT
(1) After adjustment and repair of any microwave energy
interruption or microwave energy blocking device,
record the measured values for future reference. Also
enter the information on the service invoice.
(2) Should the microwave energy leakage not be more
than 1mW/cm.sq. after determining that all parts are in
good condition, functioning properly and genuine
replacement parts which are listed in this manual have
been used.
(3) At least once a year, have the electromagnetic energy
leakage monitor checked for calibration by its
manufacturer.
G. POWER OUTPUT MEASUREMENT
(1) Fill the test beaker with 59 F(15 C) ~ 75 F(24 C) 1 liter tap
water.
(2) Stir the water in the beaker with thermometer ( F or C) and
measure temperature as T1.
(3) Place the beaker on the center of turntable.
(4) Set for one (1) minute and three (3) seconds and operate
the oven at high power.
NOTE: The additional three (3) seconds is to allow the
magnetron to begin generating power.
(5) When the heating is finished, stir the water again with
thermometer and measure the temperature of water as T2.
(6) Subtract T1 from T2, this will give you the temperature rise.
(7) The microwave power output is within specification, if the
temperature rise is as shown below:
Temperature Rise
Line Voltage Degrees F Degrees C
120 V 18.9 ~ 25.2 10.5 ~ 14
108 V Min. 17.5 Min 9.7
(8) Power output will be influenced by line voltage of power
supply. Consequently, correct power output must be
measured within 120V AC 1 Volt while unit is operating.
-12-
SPECIAL TIP
This oven used the button head screws.
When you remove the screws, using the
tamper-resistant Torx driver have a
pin-in-head.
Button Head
(Torx style 2)
-13-
9. DISASSEMBLY INSTRUCTIONS
IMPORTANT NOTES:
UNIT MUST BE DISCONNECTED FROM ELECTRICAL
OUTLET WHEN MAKING REPAIRS, RE-PLACEMENTS,
ADJUSTMENTS AND CONTINUITY CHECKS. WAIT AT
LEAST ONE MINUTE, UNTIL THE HIGH VOLTAGE
CAPACITOR IN THE HIGH VOLTAGE POWER
SUPPLY HAS FULLY DISCHARGED. THE CAPACITOR
SHOULD BE DISCHARGED BY USING INSULATED
WIRE - I.E. TEST PROBE CONNECTED TO 10KOHM
RESISTOR IN SERIES TO GROUND. WHEN
RECONNECTING THE WIRE LEADS TO ANY PART,
MAKE SURE THE WIRING CONNECTIONS AND LEAD
COLORS ARE CORRECTLY MATCHED ACCORDING
TO THE OVERALL CIRCUIT DIAGRAM. (ESPECIALLY
SWITCHES AND HIGH VOLTAGE CIRCUIT.)
A. REMOVING OUTSIDE CASE (Figures 8)
(1) Remove three screws from the rear section.
(2) Remove one screw from the side section.
(3) Push the outer case back about 1 inch (3cm).
(4) Lift the case from the set.
B. REMOVING POWER AND CONTROL CIRCUIT
BOARD(Figure 9)
(1) Open the door.
(2) Remove two screws, securing the circuit board.
(3) Disconnect the lead wire from RELAY(RY2) on the
circuit board.
(4) Lift up and pull out control panel assembly carefully
from the cavity.
(5) Disconnect the lead wire from connector(CN1) on the
circuit board.
CAUTION: DISCHARGE THE HIGH VOLTAGE
CAPACITOR BEFORE SERVICING.
(6) Pull down and remove the circuit board from the control
panel.
(7) Remove the F.P.C connector from the terminal socket.
Lift up and pull out control panel
ground
screw
securing
screw
Remove screw
Figures 9
Figure 8
F.P.C.Connector
Control Panel
Circuit Board
C. DOOR ASSEMBLY / REMOVAL
(1) Open the door.
(2) Remove the choke cover very carefully with a flat-blade
screwdriver.
CAUTION : Be careful not to damage door seal plate by
screwdriver.
(3) Lift up and push the door.
NOTE:
1. After replacing the door, be sure to check that the primary
switch, monitor switch, and secondary switch operate
normally.
2. After replacing the door, check for microwave energy leakage
with a survey meter. Microwave energy must be below the
limit of 5 mW/cm.sq. (with a 275 ml water load)
3. When mounting the door assembly to the oven assembly, be
sure to adjust the door assembly parallel to the chassis. Also
adjust so the door has no play between the inner door surface
and oven frame assembly. If the door assembly is not
mounted properly, microwaves may leak from the clearance
between the door and the oven.
-14-
Remove choke cover
Remove Door
Figure 10
D. MAGNETRON REMOVAL
(1) Disconnect the wire lead from the magnetron.
(2) Carefully remove the mounting screws holding the
magnetron and the waveguide.
(3) Remove the magnetron assembly until the tube is clear
from the waveguide.
NOTE:
1. When removing the magnetron, make sure its dome
does not hit any adjacent parts, or it may be damaged.
2. When replacing the magnetron, be sure to install the
magnetron gasket in the correct position and be sure
that the gasket is in good condition.
3. After replacing the magnetron, check for microwave
leakage with a survey meter around the magnetron.
Microwave energy must be below the limit of 5 mW/cm
2
.
(With a 275 ml. water load).
Make sure that gasket is rigidly attached to the
magnetron. To prevent microwave leakage, tighten the
mounting screws properly, making sure there is no gap
between the waveguide and the magnetron.
E. REMOVING THE TURNTABLE MOTOR
1) Remove the turntable and rotating ring.
2) Lay the unit down on its back.
3) Remove the turntable motor cover.
The turntable base cover is easily removed by pinching
the eight parts with a wire cutting.
4) Disconnect the leadwire from the turntable motor
terminals.
5) Remove the screw securing the turntable motor to the
oven cavity ASSEMBLY.
6) After repairing the motor, rotate the removed turntable
motor cover.
7) Fit the turntable motor cover
8) The taptite screw shall be used when a turntable motor
cover is secured with a screw.
s projecting part to the base
plate slit.
NOTE:
1. Remove the wire lead from the turntable motor VERY
CAREFULLY.
2. Be sure to grasp the connector, not the wires, when
removing.
-15-
Waveguide
Magnetron
Air duct
Magnetron
Gasket
Magnetron
Dome
Waveguide
Bracket
Figures 11
Wire Leads
Taptite Screw
Turntable Motor
Figures 12
F. HIGH VOLTAGE TRANSFORMER REMOVAL
1) Discharge the high voltage capacitor.
2) Disconnect the leadwire from magnetron, high voltage
transformer, and capacitor.
3) Remove the screw holding the high voltage transformer to
the baseplate.
G. FAN MOTOR ASSEMBLY / REMOVAL
1) Discharge the high voltage capacitor.
2) Disconnect the leadwire from fan motor and high voltage
capacitor.
3) Remove the two screws holding the the suction guide
ASSEMBLY to the oven cavity.
4) Remove the two screws holding the fan motor ASSEMBLY
to the suction guide ASSEMBLY.
H. HIGH VOLTAGE CAPACITOR AND DIODE REMOVAL
1) Discharge the high voltage capacitor.
2) Disconnect the leadwire from fan motor and high voltage
capacitor.
3) Remove the screw holding the suction guide ASSEMBLY to
the oven cavity.
4) Remove the screw holding the high voltage capacitor bracket
and remove the high voltage diode earth screw.
-16-
Figures 13
I. REMOVING SENSOR
1) Disconnect the leadwire from PCB Assembly.
2) Remove a screw securing the sensor duct.
Figures 14
J. INTERLOCK SYSTEM
1) INTERLOCK MECHANISM
The door lock mechanism is a device which has been
specially designed to eliminate microwave
activity when the door is opened during cooking and thus
to prevent the danger resulting from the microwave
leakage.
2) MOUNTING OF THE PRIMARY/MONITOR/
SECONDARY SWITCHES TO THE LATCH BOARD
3) INSTALLATION AND ADJUSTMENT OF THE LATCH
BOARD TO THE OVEN ASSEMBLY
Mount the latch board to the oven assembly.
Adjust the latch board in the arrow direction so that oven
door will not have any play in it when the door is closed.
Tighten the mounting screw.
Check for play in the door by pushing the door
release button. Door movement should be less than
0.5 mm. (1/64 inch)
Don't push the door release button while making this
adjustment. Make sure that the latch moves smoothly after
adjustment is completed and that the screws are tight.
Make sure the primary, monitor, and secondary switches
operate properly by following the continuity test
procedure.
-17-
Figures 15
-18-
A. PRIMARY INTERLOCK SWITCH TEST
When the door release button is depressed slowly with
the door closed, an audible click should be heard at
the same time or successively at intervals. When the
button is released slowly, the latches should activate
the switches with an audible click.
If the latches do not activate the switches when the
door is closed, the switches should be a adjusted in
accordance with the adjustment procedure. Disconnect
the wire lead from the primary switch. Connect the
ohmmeter leads to the common (COM) and normally
open (NO) terminal of the switch. The meter should
indicate an open circuit in the door open condition.
When the door is closed, the meter should indicate a
closed circuit.
When the primary switch operation is abnormal, make
the necessary adjustment or replace the switch only
with the same type of switch.
B. SECONDARY INTERLOCK SWITCH TEST
Disconnect the wire lead from the secondary switch.
Connect the ohmmeter leads to the common (COM)
and normally open (NO) terminals of the switch. The
meter should indicate a open circuit in the door open
condition. When the door is closed, meter should
indicate an closed circuit. When the secondary switch
operation is abnormal, make the necessary adjustment
or replace the switch only with the same type of switch.
C. MONITOR SWITCH TEST
Disconnect the wire lead from the monitor switch.
Connect the ohmmeter leads to the common (COM)
and normally closed (NC) terminals of the switch. The
meter should indicate closed circuit in the door open
condition. When the door is closed, meter should
indicate an open circuit. When the monitor switch
operation is abnormal, replace with the same type of
switch.
NOTE: After repairing the door or the interlock system,
it is necessary to do this continuity test before
operating the oven.
WARNING : FOR CONTINUED PROTECTION AGAINST EXCESSIVE RADIATION
EMISSION, REPLACE ONLY WITH IDENTICAL REPLACEMENT PARTS.
TYPE NO. SZM-V 16-FA-63 OR VP-533A-OF OR V-5230Q FOR PRIMARY SWITCH
TYPE NO. SZM-V 16-FA-62, VP-532A-OF OR V-5220Q FOR MONITOR SWITCH
TYPE NO. SZM-V 15-FA-63, VP-533A-OFF OR SECONDARY SWITCH
COMPONENTS TEST PROCEDURE RESULTS
SWITCHES Check for continuity of the Door Door
(Wire leads removed) switch with an Ohm-meter open closed
Primary
Switch
Monitor
Switch
Secondary
Switch
NOTE : After checking for the continuity of switches, make sure that they are
connected correctly.
NO
COM
NC
COM
NO
COM
10. INTERLOCK CONTINUITY TEST
-19-
CAUTIONS
1. DISCONNECT THE POWER SUPPLY CORD FROM THE OUTLET WHENEVER REMOVING THE OUTER CASE
FROM THE UNIT. PROCEED WITH THE TEST ONLY AFTER DISCHARGING THE HIGH VOLTAGE CAPACITOR
AND REMOVING THE WIRE LEADS FROM THE PRIMARY WINDING OF THE HIGH VOLTAGE
TRANSFORMER.
2. ALL OPERATIONAL CHECKS WITH MICROWAVE ENERGY MUST BE DONE WITH A LOAD (1 LITER OF
WATER IN CONTAINER) IN THE OVEN.
COMPONENTS TEST PROCEDURE RESULTS
HIGH VOLTAGE
TRANSFORMER
(Wire leads removed)
MAGNETRON
(Wire leads removed)
1. Measure the resistance.
(Ohm-meter scale: Rx1 and Rx100)
Primary winding
Secondary winding
Filament winding
2. Measure the resistance.
(Ohm-meter scale: Rx1000)
Primary winding to ground
Filament winding to ground
1. Measure the resistance.
(Ohm-meter scale: Rx1)
Filament terminal
2. Measure the resistance.
(Ohm-meter scale: Rx1000)
Filament to chassis
Approx.: 0.2 ~ 0.4 ohm
Approx.: 70 ~ 100 ohm
Less than: 1 ohm
Normal: Infinite
Normal: Infinite
Normal: Less than 1 ohm
Normal: Infinite
FILAMENT
WINDING
PRIMARY
TERMINAL
11. TEST AND CHECKOUT PROCEDURES, AND TROUBLESHOOTING
A. TEST PROCEDURES
-20-
COMPONENTS TEST PROCEDURE RESULTS
HIGH VOLTAGE
CAPACITOR
HIGH VOLTAGE
DIODE
NOTE :
Some inexpensive meters
may indicate infinite
resistance in both direction.
Measure the resistance.
(Ohm-meter scale: Rx1000)
Terminal to terminal.
Measure the resistance.
(Ohm-meter scale: Rx1000)
Terminal to case.
Measure the continuity (Forward).
(Ohm-meter scale: Rx10000)
Measure the continuity (Reverse).
(Ohm-meter scale: Rx10000)
Normal: Momentarily indicates
several ohms, and
then gradually returns
to infinite.
Normal: Infinite.
Normal: Continuity.
Abnormal: Infinite.
Normal: Infinite.
Abnormal: Continuity.
NOTE: When testing the magnetron, be sure to install the magnetron gasket in the
correct position and be sure that the gasket is in good condition.
Antenna
Gasket
Chassis
Filament
-21-
COMPONENTS TEST PROCEDURE RESULTS
RELAY 2
FAN MOTOR
(Wire leads removed)
TURNTABLE
MOTOR
(Wire leads removed)
SENSOR
Check for continuity of relay 2 with an ohm-
meter.
(Remove wire leads from relay 2 and operate
the unit.)
Measure the resistance.
(Ohm-meter scale: R x 1)
Measure the resistance.
(Ohm-meter scale: R x 1)
1) Disconnect sensor connector from micom
computer board.
2) Measure resistance terminal to terminal
(ohm meter scale: R X 1000)
POWER
LEVEL
1 4 sec 18 sec
2 6 sec 16 sec
3 8 sec 14 sec
4 10 sec 12 sec
5 12 sec 10 sec
6 14 sec 8 sec
7 16 sec 6 sec
8 18 sec 4 sec
9 20 sec 2 sec
10 22 sec 0 sec
Normal:
A: Approx. 85 ~ 100 ohm.
B: Approx. 10 ~ 25 ohm.
Abnormal: Infinite or several
ohm.
Normal: Approx.100~150 ohm
Abnormal: Infinite or several
ohm.
Normal: Approximately
BK - RD: 5.2 Kohm
RD - WH: 2.1 Kohm
BK - WH: 2.1 Kohm
Abnormal: Infinite or several.
* Sensor cooking condition
1. Oven should be plugged in at least
5 minutes before sensor cooking.
2. Room temperature should not
exceed 95F .
3. Be sure the exterior of the cooking
container and the interior of the oven
are dry. Wipe each off with paper
towel.
4. The oven will not generate
microwave energy for the first 28
seconds of the sensor cooking cycle.
NOTE : A MICROWAVE LEAKAGE TEST MUST ALWAYS BE PERFORMED
WHEN THE UNIT IS SERVICED FOR ANY REASON.
MAKE SURE THE WIRE LEADS ARE IN THE CORRECT POSITION.
WHEN REMOVING THE WIRE LEADS FROM THE PARTS, BE SURE
TO GRASP THE CONNECTOR, NOT THE WIRES.
Relay 2
A
B
RD
BK
WH
1
2
3
-22-
B. CHECKOUT PROCEDURES
(1) CHECKOUT PROCEDURES FOR FUSE BLOWING
CAUTION: REPLACE BLOWN FUSE WITH 20 AMPERE FUSE.
Fuse blows immediately after
the door is closed.
Fuse blows immediately after
the door is opened.
Fuse blows when the door is closed and START key
is touched.
Improper operation of the primary interlock,
secondary interlock switches and/or the interlock
monitor switch.
Malfunction of the high voltage transformer; the high
voltage capacitor including the diode, the magnetron,
the blower motor or the circuit board.
PROBLEMS CAUSES
NOTES:
- If the fuse is blown by an improper switch operation, replace the defective switches and the fuse at the same time.
After replacing the defective switches with new ones, make sure that they are correctly connected.
- Check for microwave energy leakage according to 1. ADJUSTMENT PROCEDURES on page 3, when the
primary interlock, secondary interlock switches and/or the interlock monitor switches are adjusted or replaced.
-23-
(2) CHECKOUT PROCEDURES FOR RELAY
- PROBLEM (A) -
FAN motor and oven lamp turn on without touching
START key when the door is closed.
Remove the mate connector of I/O
CON from the circuit board does
the unit still operate?
GOOD
GOOD
Replace the
circuit board
- PROBLEM (B) -
FAN motor and oven lamp turn on When the door is
closed and START key is touched.
Check the interlock switches
Replace the
micro switches.
Defective
RELAY or poor
connection of
relay
Replace
RELAY or correct
the connection.
NO
NO
YES
NO
NO
YES
YES
-24-
NOTE: A MICROWAVE ENERGY LEAKAGE TEST MUST ALWAYS BE PERFORMED WHEN THE UNIT IS
SERVICED FOR ANY REASON.
(3) CHECKOUT PROCEDURES FOR CIRCUIT BOARD
The following symptoms indicate a defective circuit
board.
(1) The start function fails to operate but the high
voltage Systems, the interlock switches, the door
sensing and the relay check good.
(2) The unit with a normal relay continuously operates.
(3) The buzzer does not sound or continues to sound.
(4) Some segments of one or more digits do not light up, or
they continue to light up, or segments light when they
should not.
(6) Wrong figures appear.
(7) The figures of all digits flicker.
(8) Some of the indicators do no light up.
(9) The clock does not keep time properly.
-25-
C. TROUBLE SHOOTING
WHEN YOU GET A COMPLAINT FROM YOUR CUSTOMER, EVALUATE THE COMPLAINT CAREFULLY. IF THE
FOLLOWING SYMPTOMS APPLY, PLEASE INSTRUCT THE CUSTOMER IN THE PROPER USE OF THE MICROWAVE
OVEN. THIS CAN ELIMINATE AN UNNECESSARY SERVICE CALL.
CAUTIONS
1. Check grounding before checking for trouble.
2. Be careful of the high voltage circuit.
3. Discharge the high voltage capacitor.
4. When checking the continuity of the switches or of the high voltage transformer, disconnect one lead wire from these
parts and then check continuity with the AC plug removed. To do otherwise may result in a false reading or damage
to your meter.
5. Do not touch any part of the circuit on the PCB since static electric discharge may damage this control panel.
Always touch yourself to ground while working on this panel to discharge any static charge built up in your body.
(Micom model only)
CONDITION
Microwave oven
does not work.
Inserting many plugs into one
outlet and using them at the
same time.
(blown fuse or breaker)
Microwave oven plug is not
inserted tightly.
Output power is too low. Low AC input voltage.
Food temperature is too low.
Using metallic ware and
allowing it to touch the oven
wall.
Sparks occur.
Inconsistent intensity of
microwave by their
characteristics.
1. Use plastic wrap or lid.
2. Stir once or twice while
cooking soup, cocoa or
milk, etc.
Uneven cooking.
Ceramic ware trimmed in
gold or silver powder is used.
Avoid using other electrical
appliances when you use the
microwave oven.
Insert microwave oven plug
securely.
Use the microwave oven at
adequate line voltage.
This may not be a defect.
It is possible that the food
should be cooked for a
longer time period.
Do not use metallic ware for
cooking except where noted
in the cooking guide.
Do not use any type of
cookware with metallic
trimming.
CAUSE REMEDY
-26-
1. Incomplete segments.
Segment missing.
Partial segment missing.
Digit flickering (NOTE: Slight flickering is normal.)
2. Colon does not turn on or blink.
3. A distinct change in the brightness of one or more numbers in display.
4. One or more digits in the display are not lighting.
5. Display indicates a number different from one touched, for example, key in 5 and 3 appears in the display.
6. Specific numbers (for example 7 or 9) will not display when key pad is touched.
7. Display does not count down with time blinking or up with clock operation.
8. Display obviously jumps in time while counting down.
9. Display counts down too fast while cooking.
10. Each indicator light does not turn on after setting cooking cycle.
11. Display time of day does not reappear when cooking is finished.
(TROUBLE 1) The following visual conditions indicate a probable defective control circuit.
CONDITION CHECK RESULT CAUSE REMEDY
1. No input can be
programmed.
Continuity
No continuity
Defective PCB
assembly.
Loose
connection.
Replace PCB
assembly.
Connect them
tightly.
Check the conn-
ection between
membrane key
assembly and
PCB assembly.
2. Some inputs
cannot be
programmed.
3. Display shows a
number or figure
different from one
touched.
4. Random
programming
when touching
other pads.
5. Display is fixed
at some figure
and can not
accept any
input.
Everything works
as specified.
Still have trouble.
Defective key
membrane
assembly.
Defective PCB
assembly.
Replace key
membrane
assembly.
Replace PCB
assembly.
Replace key
membrane
assembly and
check operation.
-27-
CONDITION CHECK RESULT CAUSE REMEDY
1. Fuse blows. Continuity.
No continuity.
Continuity.
Shorted contact at
the primary switch.
Replace fuse,
primary, monitor
switches, and
RELAY(RY2) of
P.C.B Assembly.
No continuity.
Normal.
Defective high
voltage capacitor.
Replace high
voltage capacitor.
Fuse blows again
Defective high volt-
age transformer.
Replace high volt-
age transformer.
Malfunction of the
monitor switch.
Replace fuse,
primary, monitor
switches, and
RELAY(RY2) of
P.C.B Assembly.
Check continuity
of monitor
switch (with
door closed).
Check continuity
of primary
switch (with
door opened).
Disconnect one
side of the wire
lead connected
from transformer
to the high
voltage
capacitor and
operate the unit.
Replace fuse
2. Fuse does not
blow.
No continuity.
Continuity.
No continuity.
Defective power
supply cord.
Replace power
supply cord.
Defective
thermostat.
Replace
thermostat.
Check continuity
of thermostat.
Check continuity
of power supply
cord.
(TROUBLE 2) Oven does not operate at all, Display window does not display any figures,
and no input is accepted.
-28-
CONDITION CHECK RESULT CAUSE REMEDY
1. Setting time
does not count
down when
touching START
pad.
2. Fan motor or
oven lamp do
not turn on.
No continuity.
Continuity.
Continuity
Defective PCB
assembly.
Loose connection.
Replace PCB
assembly.
Connect them
tightly.
No continuity
Abnormal Check fan motor. Defective fan motor. Replace fan motor.
Abnormal
Normal
Check oven lamp. Defective oven lamp. Replace oven lamp.
Defective
secondary switch.
Replace
secondary switch.
Check continuity
of secondary
switch (with
door closed).
Check the con-
nection between
CN1 connector
and PCB
assembly.
(TROUBLE 3) Display shows all figures set, but oven does not start cooking while desired
program times are set and START pad is touched.
(TROUBLE 4) Oven seems to be operating but little heat is produced in oven load.
NOTE : Simple test of power output-conducted by heating one liter water for one min. if available.
Minimum 8.5C temperature rise is normal condition.
CONDITION CHECK RESULT CAUSE REMEDY
Output is low
Lower than 90% of
rating voltage.
Normal
Abnormal
Defective PCB
assembly.
Replace PCB
assembly.
Normal
Abnormal
Measure the
output power.
Defective
magnetron.
Replace
magnetron.
Decrease in power
source voltage
with load.
Suggest customer
contact local
electric power
utility co. or
qualified
electrician.
Check the
power source
voltage.
Disconnect the
wire leads from
relay 2 and
check on and off
time with
multitester.
-29-
CONDITION CHECK RESULT CAUSE REMEDY
No microwave
oscillation.
No continuity.
Continuity.
Abnormal
Defective high
voltage
transformer.
Replace high
voltage
transformer.
Normal
Defective PCB
assembly.
Replace PCB
assembly.
Disconnect the
wire leads from
relay 2 and
check continuity
of relay 2.
(Operate the unit)
Check high vol-
tage transformer
Output is full power
when you set lower
power level.
Abnormal.
Defective PCB
assembly.
Replace PCB
assembly.
Disconnect the
wire leads from
relay 2 and check
continuity relay 2.
(Operate the unit)
Abnormal
Defective high
voltage capacitor.
Replace high
voltage capacitor.
Normal
Check high vol-
tage capacitor.
Abnormal
Defective high
voltage diode.
Replace high
voltage diode.
Normal
Check high vol-
tage diode.
Abnormal
Defective
magnetron.
Replace
magnetron.
Check
magnetron.
(TROUBLE 5) No microwave oscillation even though oven lamp and fan motor run.
(Display operates properly)
NOTE : Make sure the wire leads are in the correct position.
When Removing the wire leads from the parts, be sure to grasp the connector, not the wires.
When removing the magnetron, be sure to install the magnetron gasket in the correct position
and in good condition.
EXPLODED VIEW
INTRODUCTION
-30-
DOOR
CONTROL PANEL
BASE PLATE
OUTER CASE
LATCH BOARD
INTERIOR
SENSOR
#EV#
-31-
DOOR PARTS
1004
1000
1005
1007
1006
1002
1013
1003
1001
#EV#
-32-
CONTROLLER PARTS
2000
2002
2006
W106
2004
2381
#EV#
-33-
OVEN CAVITY PARTS
3002
W107
W103
3001
3003
3008
3009
W105
3034
#EV#
-34-
LATCH BOARD PARTS
W102
4002
4003
4002
4004
4000
4001
#EV#
#EV#
5014
5016
5010
5003
5012
W109
W208
W101
W109
5007
3006
W101
W110
5009
5006
W101
5015
9000
5000
5002
3007
5018
W109
W101
5001
5041
W208
-35-
INTERIOR PARTS
-36-
BASE PLATE PARTS
5008
W101
W108
6000
6007
6001
#EV#
-37-
SENSOR PARTS
W136
5011
5004
W108
#EV#
P/NO: MFL30502909 Printed in Korea