Kenmore 721.68100 Service Manual

DIVISION 20

BASIC FIELD MANUAL

FOR

MICROWAVE OVEN

MODEL 721.68100790

September, 1997

MODEL 721.68100790

CAUTION

WARNING TO SERVICE TECHNICIANS

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 open. b. Make the following safety checks on all ovens to be serviced before activating the magnetron

or other microwave source, and make repairs as 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, (5) evidence of dropping or abuse.

c. Before turning on microwave for any service test or inspection within the microwave

generating compartments, 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 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.

¡ Proper operation of the microwave ovens requires that the magnetron be assembled to the wave

guide and cavity. Never operate the magnetron unless it is properly installed.

¡ Be sure that the magnetron gasket is properly installed around the dome of the tube whenever

installing the magnetron.

¡ Routine service safety procedures should be exercised at all times.

¡ Untrained personnel should not attempt service without a thorough review of the test procedures and

safety information contained in this manual.

-1-

MODEL 721.68100790

FOREWORD

Read this Manual carefully. Failure to adhere to or observe the information in this Manual may result in exposing yourself to the Microwave Energy normally contained within the oven cavity.

MODEL 721.68100790

MECHANICAL SERVICE INFORMATION

TABLE OF CONTENTS

1. Adjustment Procedures 3

2. Precautions on Installation 4

3. General Precautions in Use 4

4. Trial Operation 4

5. Specifications 5

6. Overall Circuit Diagram 6-7

7. Operating Procedures 8-10

8. Procedure for Measuring Microwave Energy Leakage 11-12

9. Disassembly Instructions 13-18

10. Interlock Continuity Test 19

11. Test and Checkout Procedures, and Troubleshooting A. Test Procedures 20-24 B. Checkout Procedures 25-27 C. Troubleshooting 28-32

-2-

MODEL 721.68100790

1. ADJUSTMENT PROCEDURES

To avoid possible exposure to microwave energy leakage, adjust the door latches and interlock switches, using the following procedure.

ONLY AUTHORIZED SERVICE PERSONNEL SHOULD MAKE THIS ADJUSTMENT.

The Interlock Monitor and Primary Interlock Switch acts as the final safety switch protecting the user from microwave energy. The terminals between “COM” and “NC” of the Interlock Monitor must close when the door is opened. After adjusting the Interlock Monitor Switch, make sure that it is correctly connected. See Figures 1-a and 1-b throughout this procedure.

CHECK THE DOOR LATCH AND SWITCH CLOSINGS.

NOTE: The outer cover of the microwave oven is

removed.

(1) Set the microwave oven on its side so that you can see

the latch board and the switches, as shown in Figure 1-a.

(2) Close the door tightly and check gaps A and B to be sure

they are no more than 1/64” (0.5 mm). See Figure 1-b

for close-up view of gaps A and B (door latches). If all gaps are less than 1/64” (0.5 mm), adjustment of the latch board may not be necessary. Go to Steps 5 and 6 to check the sequence of the switches.

NOTE: To correct sequence of the Primary Interlock

Switch, Secondary Interlock Switch and the Interlock Monitor Switch is very important.

If any gap is larger than 1/64” (0.5 mm), you will need to adjust the latch board-U, L. Go to step 3 and follow all steps in order.

ADJUST THE LATCH AND SWITCH CLOSINGS

(3) Loosen the two screws holding the plastic latch board as

shown.

(4) With the oven door closed tightly, move the latch board

upward toward the top of the oven and/or away from the door latch until the gaps are less than 1/64” (0.5 mm).

Hold the latch board tightly in this position until you check the sequence of the switches in steps 5 and 6.

TEST THE LATCH AND SWITCH SEQUENCE

(5) Open the oven door slowly. Watch the door latch, the

Primary Switch. Release Rod and Lever on the switches to make sure they are zero to the body of the switches in the following sequence:

- Primary Interlock Switch

- Secondary Interlock Switch

- Interlock Monitor Switch

Adjust the latch board until the switches operate in this sequence. See Steps 3 and 4.

(6) Close the oven door slowly and be sure it is tightly

closed. Watch the three switches to make sure they are zero to the body of the switches in the following sequence:

- Interlock Monitor Switch

- Primary Interlock Switch

- Secondary Interlock Switch

NOTE: The Interlock Monitor Switch is an added safety

check on the Primary and Secondary Interlock Switches. If the Primary and Secondary Interlock Switches allow the oven to operate with the door open, the Monitor Switch will blow the fuse.

(7) When you achieve the proper sequence of switches in

Steps 5 and 6, tighten the latch board screws at that point.

TEST THE MICROWAVE ENERGY LEAKAGE

(8) Using a survey meter, make sure the microwave energy

is below 5 mW/cm.sq.

-3-

LATCH BOARD

INTERLOCK MONITOR SWITCH

PRIMARY INTERLOCK SWITCH

SECONDARY INTERLOCK SWITCH

SCREW

LATCH

LATCH BOARD

0-1/64"

DOOR LATCH

RELEASE LEVER

Figure 1-

Figure 1-b

MODEL 721.68100790

2. PRECAUTIONS ON INSTALLATION

(Figure 2)

A. Plug the power supply cord into a 120 V AC,

60 Hz, single-phase power source with a capacity

of at least 20 amperes.

B. Since the unit weights about 26 lbs, be sure to

place it on a sturdy and flat surface.

C. Avoid placing the unit in a location where there is

direct heat or splashing water.

D. Place the unit as far away as possible from TV,

radio, etc. to prevent interference.

CAUTION

3. GENERAL PRECAUTIONS IN USE

A. Never operate the unit when it is empty. Operating

the oven with no load may shorten the life of the

magnetron. Whenever cooking dry foods (dried

fish, bread, etc.) or a small amount of food, be sure

to put a glass of water into the cooking

compartment. The turntable tray may become hot

after operating, be careful when touching it.

B. Aluminum foil should be avoided because it will

disrupt cooking and may cause arcing. However,

small pieces may be used to cover some parts of

food to slow the cooking. Any aluminum foil used

should never be closer than 2.5 cm to any side wall

of the oven.

4. TRIAL OPERATION

After installation, the following sequences and results should be checked carefully. A. Put a container filled with water (about 1 liter) into

the oven, and close the door tightly.

B. Touch the STOP/CLEAR and the COOK TIME

keys. “0” appears in the display window.

C. Set cooking time for 10 minutes by touching “1”

and then “0” three times. “1000” appears in the display window.

D. Touch the START key.

Make sure the cavity light comes on. The unit will begin cooking and the display window will show the time counting down by seconds.

E. After about 5 minutes, make sure the primary

interlock switch, the secondary interlock switch and the interlock monitor and oven lamp switch operate properly by opening and closing the door several times. Touch the START key each time the door is closed.

F. Continue operating the unit. Two short and a long

beep sound signal is heard when the time is up.

The unit will shut off automatically. G. Confirm the water is hot. H. Finally, measure the output power according to

“POWER OUTPUT MEASUREMENT” on page 12.

5. FEATURES AND SPECIFICATIONS

A. The safety systems incorporated in this model are:

(1) Primary interlock switch (2) Secondary interlock switch (3) Interlock monitor switch (4) Choke system (5) Magnetron thermostat (6) Oven cavity thermostat

(Note: This thermostat located on the oven cavity will open and stop the unit from operation only if a high temperature is reached, such as, a fire created by overcooking food.)

B. Any one of 10 power output levels ranging 70W to

700W can be selected by the touch control and

electronic computer system. C. Cooking time can be displayed on the digital

readout. D. Three different cooking stages can be set. The

oven remembers three cooking stages and

changes from one cooking stage to another. This is

made possible with the memory function of the

microprocessor.

This unit is equipped with a 3-prong plug for your safety. If the wall outlet is a grounded 3-hole type, the unit will be grounded automatically.

Three-Pronged(Grounding) Plug

Figure 2

-4-

Properly Polarized and Grounded Outlet

MODEL 721.68100790

SPECIFICATIONS

Rated Power Consumption 1050W maximum Output

700W maximum (*IEC 705 Rating standard) Adjustable 70W through 700W, 10 steps

Frequency 2,450 MHz

¡ 50 MHz

Power Supply 120V

¡ 12V AC, 60Hz

Rated Current 9.3 Amp. Magnetron Cooling Forced Air Cooling Microwave Stirring Turntable Rectification Rectification Voltage Doubler Half-Wave Door Sealing Choke System Safety Devices Thermostat:

Open at 90

C ¡ 5oC

Open at 75oC ¡ 5oC Fuse(15A) Primary Interlock Switch Secondary Interlock Switch Interlock Monitor

Magnetron 2M214 High Voltage Capacitor Capacitor: 0.76¥F, 1.9KV Ac High Voltage Diode 350mA, 9.0KV Cavity Lamp 125V, 20W Timer Digital, up to 99 mm. 99 sec. (in each cooking stage) Tray Tempered Safety Glass Overall Dimensions 19”(W) x 12

/8”(D) x 11”(H)

Oven Cavity Size 11

/4”(W) x 121/2”(D) x 75/8”(H)

Effective Capacity of Oven Cavity 0.7 Cu.ft. Accessories Use and Care Manual ,Turntable,

Rotating Ring Assembly.

SWITCH CHART

NOTE: Use the above switch chart with circuit diagram on page 6.

PRIMARY SECONDARY INTERLOCK INTERLOCK INTERLOCK MONITOR SWITCH SWITCH SWITCH

COM COM COM

NO NO NC

-5-

SWITCH MODE

CONDITIONS DOOR OPEN

DOOR CLOSED

MODEL 721.68100790

¡˜ ¡˜

¡˜

6. OVERALL CIRCUIT DIAGRAM A. SCHEMATIC DIAGRAM

-6-

PRIMARY

SWITCH

MAGNETRON

H.V.

CAPACITOR

H.V. DIODE

FUSE

15 A

AC 120V

60Hz

MICOM

CONTROLLER

F.M.

TRANSFORMER

H.V.

** NOTE : DOOR IS OPENED.

BK : BLACK BL : BLUE YL : YELLOW RD : RED

WH : WHITE PK : PINK GN : GREEN

T.T.M.

O.L.

CN1

PT1

BK BK

SECONDARY

SWITCH

OVEN

LAMP

MONITOR

SWITCH

TURN

TABLE

MOTOR

FAN

MO TOR

IMPORTANT SAFETY NOTE: THE SHADED AREAS ON THIS SCHEMATIC DIAGRAM INCORPORATE SPECIAL FEATURES

IMPORTANT FOR PROTECTION FROM MICROWAVE RADIATION, FIRE, ELECTRICAL SHOCK, AND

HAZARDS. WHEN SERVICING IT IS ESSENTIAL THAT ONLY MANUFACTURER'S SPECIFIED PARTS

BE USED FOR THE CRITICAL COMPONENTS IN THE SHADED AREAS OF THE SCHEMATIC DIAGRAM.

NOTICE: SINCE THIS IS BASIC SCHEMATIC DIAGRAM, THE VALUES OF COMPONENTS AND

SOME PARTIAL CONNECTIONS ARE SUBJECT TO CHANGE FOR IMPROVEMENT.

RY1

RY2

1' 1

MODEL 721.68100790

N.C

B. MATRIX CIRCUIT FOR TOUCH KEY BOARD

-7-

N.C

QUICK

N.C

COOK

TIME

N.C

AUTO

DEFROST

N.C

START

CLOCK

N.C

BEVE-

RAGE

STOP/

CLEAR

KITCHEN

TIMER

POPCORN

N.C

POWER

3 4 5 6 7

Figure 4

MODEL 721.68100790

7. OPERATING PROCEDURES A. OVEN CONTROL PANEL

-8-

ENTER POWER SENSOR AUTO WEIGHT

QUICK TOUCH

COOK Q'TY

DEF TIME

TEMP COW

COMBI

START REHEAT

POPCORN BEVERAGE

AUTO

DEFROST

CLOCK

KITCHEN

TIMER

QUICK

COOK

TIME

STOP/

CLEAR

START

123 456

7809

POWER

Indicator Lights-

Several Indicator Lights indicate which cooking operation you are using. (ENTER, POWER AUTO, WEIGHT, COOK, DEF, TIME, START REHEAT)

Quick Touch

Pre-set timing used for certain food items.

Kitchen Timer-

You can use your microwave oven as a timer.

Cook Time-

Used to set cooking time.

Stop/Clear-

Stops the oven and clears all entries except CLOCK. Once cooking has begun, however, CLEAR will function only after STOP has been touched.

Display Window- Shows: * Time of day. * Cooking time. * Cooking power level. It also function as a countdown timer when cooking.

Quick On-

Used to set cooking time quickly and directly.

Numbers-

Used to enter the: * Time of day. * Cooking time. * Cooking power. * Food weight for defrost.

Power-

Used select cooking power level.

Start-

starts the oven.

NOTE: A "beep" sounds when you touch a "key" on the control panel, to indicate that you have entered a setting.

Figure 5

MODEL 721.68100790

B. PANEL INSTRUCTIONS (Figure 4)

The entire operation is done by simple touch control pads.

(1) Display Window

Numbers and letters explained in Figure 5 are shown in the display window (Vacuum Fluorescent Tube).

(a) The Time in six digits (12-hour indication):

00 Hour 00 Minute 00 Second.

(b) Cooking Time of Day in four digits 00 Minutes

00 Seconds. (c) Power Control Level in two digits: P-00 (d) Each Indicator Light shows which function is set

and involved in the course of cooking by turning

itself on. Indicator Lights automatically go out

upon completion of cooking.

(2) COOK TIME Key

The TIME key is used to set the cooking time. Touch the TIME key and then the number keys that correspond to the desired cooking time. The remaining time is continuously displayed during cooking.

(3) CLOCK Key

Used in setting Time of Day.

(4) AUTO DEFROST key (DEFROST MEAT,

POULTRY & FISH) Used in setting AUTO DEFROST.

(5) POWER Key

Used to select cooking power level.

(6) STOP/CLEAR Key

Used to stop the oven or clear all entries except CLOCK.

(7) START Key

Touch the START key after setting the desired cooking times etc. Also touch the START key to resume cooking after the cooking is temporarily stopped by opening the door. The key will not function unless the door is closed.

(8) QUICK ON Key

Used in setting cooking time quickly and directly.

(9) QUICK TOUCH COOKING key

Pre-set timing used for certain food item.

-9-

MODEL 721.68100790

C. EASY USE CHART

(1) CLOCK

1. Touch STOP/CLEAR.

2. Touch CLOCK.

3. Touch numbers for correct time of day.

4. Touch CLOCK.

(2) “HI-POWER” COOKING

1. Touch STOP/CLEAR.

2. Touch COOK TIME.

3. Touch numbers for desired cooking time.

(3) “MULTI-STAGE” COOKING

1. Touch STOP/CLEAR.

2. Touch COOK TIME.

3. Touch numbers 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.

(4) CHILD LOCK

To set:

1. Touch STOP/CLEAR.

2. Touch “0” more than 2 seconds. To cancel:

1. Touch STOP/CLEAR.

2. Touch “0” more than 2 seconds.

(5) KITCHEN TIMER

1. Touch STOP/CLEAR.

2. Touch KITCHEN TIMER.

3. Touch correct numbers for time.

4. Touch START.

(6) QUICK ON COOKING

1. Touch STOP/CLEAR.

2. Touch QUICK ON.

3. Touch number for desired minutes.

(7) AUTO DEFROST

1. Touch STOP/CLEAR.

2. Touch AUTO DEFROST. Three different defrosting levels are provided. (MEAT, POULTRY, 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 by following the instructions in the manual.

6. After turning food over, touch START to resume defrosting.

(8) QUICK TOUCH COOKING

1. Touch STOP/CLEAR.

2. Select one of categories, and then touch the key. NOTE: Do not leave oven unattended while popping corn.

-10-

MODEL 721.68100790

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 customer’s home. 1mW/cm.sq. stated here is manufacturer’s own voluntary standard for units in customer’s home.

EQUIPMENT

ƒU Electromagnetic energy leakage monitor (NARDA

8100B, HOLADAY HI 1501)

ƒU 600cc glass beaker ƒU Glass thermometer 1000C

B. MEASURING MICROWAVE ENERGY LEAKAGE

(1) Pour 275¡ 15cc of 20¡ 50C 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 manufacturer’s 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

MODEL 721.68100790

+ 28 hidden pages

Kenmore 721.68100 Service Manual

Specifications and Main Features

Frequently Asked Questions

User Manual