Sharp R-4A68 Service Manual

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R-4A68

SHARP CORPORATION

SERVICE MANU AL

In interests of user-safety the oven should be restored to its original condition and only parts identical to those specified should be used.

MODEL

R-4A68

S3613R4A68PX/

MICROWAVE OVEN

TABLE OF CONTENTS

Page

CAUTION, MICROWAVE RADIATION................................................................................................................. 1

WARNING..............................................................................................................................................................1

PRODUCT SPECIFICATIONS ............................................................................................................................. 2

GENERAL INFORMATION....................................................................................................................................2

APPEARANCE VIEW ........................................................................................................................................... 3

OPERATION SEQUENCE.................................................................................................................................... 4

FUNCTION OF IMPORTANT COMPONENTS .................................................................................................... 5

SERVICING .......................................................................................................................................................... 6

TEST PROCEDURE ............................................................................................................................................. 8

TOUCH CONTROL PANEL .................................................................................................................................14

COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE ............................................................... 18

MICROWAVE MEASUREMENT ........................................................................................................................ 23

WIRING DIAGRAM ............................................................................................................................................. 24

PICTORIAL DIAGRAM ....................................................................................................................................... 25

CONTROL PANEL CIRCUIT ...............................................................................................................................26

PRINTED WIRING BOARD .................................................................................................................................27

PARTS LIST ....................................................................................................................................................... 28

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R-4A68

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R-4A68

SERVICE MANUAL

PRODUCT SPECIFICATIONS

SHARP CORPORATION

OSAKA, JAPAN

TEST PROCEDURE

SERVICING AND TROUBLESHOOTING CHART

FUNCTION OF IMPORTANT COMPONENTS

OPERATING SEQUENCE

APPEARANCE VIEW

MICROWAVE MEASUREMENT

WIRING DIAGRAM

PARTS LIST

TOUCH CONTROL PANEL ASSEMBLY

COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE

MICROWAVE OVEN

R-4A68

GENERAL IMPORTANT INFORMATION

This Manual has been prepared to provide Sharp Corp. Service engineers with Operation and Service Information.

It is recommended that service engineers carefully study the entire text of this manual, so they will be qualified to render satisfactory customer service.

CAUTION

MICROWAVE RADIATION

DO NOT BECOME EXPOSED TO RADIATION FROM THE MICROWAVE GENERATOR OR OTHER PARTS CONDUCTING MICROWAVE ENERGY.

Service engineers should not be exposed to the microwave energy which may radiate from the magnetron or other microwave generating devices if it is improperly used or connected. All input and output microwave connections, waveguides, flanges and gaskets must be secured. Never operate the device without a microwave energy absorbing load attached. Never look into an open waveguide or antenna while the device is energized.

WARNING

Never operate the oven until the following points are ensured. (A) The door is tightly closed. (B) The door brackets and hinges are not defective. (C) The door packing is not damaged. (D) The door is not deformed or warped. (E) There is not any other visible damage with the oven.

Servicing and repair work must be carried out only by trained service engineers.

All the parts marked "*" on parts list are used at voltages more than 250V.

Removal of the outer wrap gives access to potentials above 250V.

All the parts marked "∆" on parts list may cause undue microwave exposure, by themselves, or when they are damaged, loosened or removed.

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R-4A68

PRODUCT SPECIFICATIONS

GENERAL INFORMATION

WARNING

THIS APPLIANCE MUST BE EARTHED

IMPOTANT

THE WIRES IN THIS MAINS LEAD ARE COLOURED IN ACCORDANCE WITH THE FOLLOWING CODE:

GREEN-AND-YELLOW : EARTH BLUE : NEUTRAL BROWN : LIVE

ITEM DESCRIPTION

Power Requirements 220 Volts

50 Hertz

Single phase, 3 wire earthed Power Consumption 1.45 kW Power Output 900 watts nominal of RF microwave energy (IEC 705)

Operating fequency 2450 MHz Case Dimensions Width 550 mm

Height 314.5 mm

Depth 446 mm Cooking Cavity Dimensions Width 378 mm

Height 217 mm

Depth 425 mm Turntable diameter 360mm Control Complement Touch Control System

Clock ( 1:00 - 12:59)

Timer (0 - 99 minutes 99 seconds)

Microwave Power for Variable Cooking

Repetition Rate;

HIGH ............................................... Full power throughout the cooking time

MEDIUM HIGH ..................................................approx. 70% of Full Power

MEDIUM .............................................................approx. 50% of Full Power

MEDIUM LOW ....................................................approx. 30% of Full Power

LOW....................................................................approx. 10% of Full Power

INSTANT ACTION pads

EXPRESS DEFROST pads

NUMBER pads

POWER LEVEL pad

AUTO START/CLOCK pad

STOP/CLEAR pad

INSTANT COOK/START pad Set Weight Approx. 17 kg

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R-4A68

APPEARANCE VIEW

1. Ventilation openings

2. Oven lamp

3. Door hinges

4. Door safety latches

5. See through door

6. Door seals and sealing surfaces

7. Coupling

8. Door open button

9. Touch control panel

10.Digital readout

11.Waveguide cover

12.Power supply cord

3

TOUCH CONTROL PANEL

a INSTANT ACTION PADS

Press to cook or reheat 9 popular menus.

b EXPRESS DEFROST PADS

Press to defrost meat.

c NUMBER PADS

Press to enter cooking times, clock time, weight or quantity of food. Press to set Safety Lock.

d AUTO START /CLOCK PAD

Press to set Clock or Auto Start time.

e POWER LEVEL PAD

Press to select microwave power setting. If not pressed, HIGH is automatically selected.

f STOP/CLEAR PAD

Press to clear during programming. Press once to stop operation of oven during cooking; press twice to cancel cooking programme.

g INSTANT COOK/START PAD

Press once to cook for 1 minute at HIGH or increase by 1 minute multiples each time this pad is pressed during cooking. Press to start oven after setting programmes.

Beverage

Dinner Plate

Casseroles

SNACKS & REHEAT

Pasta

Vegetable

FROZEN FOOD

Dinner Plate

INSTANT ACTION

To adjust quantity-touch pad again

Jacket Potato

Rice

Fresh Veg.

COOKING

Minced Meat

Steaks/Chops

EXPRESS DEFROST

Chicken Pieces

12345 6789

AUTO START

CLOCK

POWER

LEVEL

STOP

CLEAR

I NSTANT COOK

START

COOK SERVE CHECK DEF

Indicator

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R-4A68

OPERATION SEQUENCE

OFF CONDITION

Closing the door activates all door interlock switches (1st. latch switch and 2nd. interlock relay control switch).

IMPORTANT When the oven door is closed, the monitor switch contacts (COM-NC) must be open. When the microwave oven is plugged in a wall outlet, rated voltage is supplied to the point (A3+A5) in the control unit.

Figure O-1 on page 24

1. The display shows 88:88 .

2. To set any programs or set the clock, you must first touch the STOP/CLEAR pad.

3. : appears in the display.

NOTE: When the oven door is opened, the oven lamp

comes on at this time.

MICROWAVE COOKING CONDITION

HIGH COOKING

Enter a desired cooking time with the touching Number pads and start the oven with touching START pad.

Function sequence

Figure O-2 on page 24

CONNECTED COMPONENTS RELAY Oven lamp, Fan motor, Turntable motor RY1 Power transformer RY2

1. Rated voltage is supplied to the primary winding of the power transformer. The voltage is converted to about 3.3 volts A.C. output on the filament winding and high voltage of approximately 2000 volts A.C. on the secondary winding.

2. The filament winding voltage (3.3 volts) heats the magnetron filament and the high voltage (2000 volts) is sent to the voltage doubling circuit, where it is doubled to negative voltage of approximately 4000 volts D.C..

3. The 2450 MHz microwave energy produced in the magnetron generates a wave length of 12.24 cm. This energy is channelled through the waveguide (transport channel) into the oven cavity, where the food is placed to be cooked.

4. When the cooking time is up, a signal tone is heard and the relays (RY1+RY2) go back to their home position. The circuits to the oven lamp, power transformer, fan motor and turntable motor are cut off.

5. When the door is opened during a cook cycle, the switches come to the following condition

CONDITION DURING DOOR OPEN

SWITCH CONTACT COOKING (NO COOKING) 1st. latch switches COM-NO Closed Open 2nd. interlock relay

control switch COM-NO Closed Open Monitor switch COM-NC Open Closed

The circuits to the power transformer, fan motor and turntable motor are cut off when the 1st. latch switch and 2nd. interlock relay control switch are made open. The oven lamp remains on even if the oven door is opened after the cooking cycle has been interrupted, because the relay (RY1) stays closed. Shown in the display is the remaining time.

6. MONITOR SWITCH CIRCUIT The monitor switch is mechanically controlled by oven door, and monitors the operation of the 1st. latch switch and 2nd. interlock relay.

6-1 When the oven door is opened during or after the cycle

of a cooking program, the 1st. latch switch and 2nd. interlock relay control switch must open their contacts first. After that the contacts (COM-NC) of the monitor switch can be closed.

6-2. When the oven door is closed, the contacts (COM-NC)

of the monitor switch must be opened. After that the contacts of the 1st. latch switch and 2nd. interlock relay control switch are closed.

6-3. When the oven door is opened and the contacts of the

1st. latch switch and 2nd. interlock relay remain closed. The fuse M8A will blow, because the monitor switch is closed and a short circuit is caused.

VARIABLE COOKING

When the microwave oven is preset for variable cooking power. Rated voltage is supplied to the power transformer intermittently within a 32-second time base through the relay contact which is coupled with the relay (RY2). The following levels of microwave power are given.

SETTING;

32 sec. ON

24 sec. ON

18 sec. ON

12 sec. ON

6 sec. ON

8 sec. OFF

14 sec. OFF

20 sec. OFF

26 sec. OFF

HIGH

MEDIUM HIGH

MEDIUM

MEDIUM LOW

LOW

Approx. 70%

Approx. 50%

Approx. 30%

Approx. 10%

NOTE: The ON/OFF time ratio does not exactly correspond

to the percentage of microwave power, because approx. 2 seconds are needed for heating up the magnetron filament.

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R-4A68

FUNCTION OF IMPORTANT COMPONENTS

DOOR OPEN MECHANISM

The door can be opened by pushing the door open button on the control panel. When the door open button is pushed, the latch lever is moved upward, operating the latch head. The latch head is moved upward, and released from the latch hook. Now, the door can be opened.

LATCH HEADS

LATCH HOOK

2ND. INTERLOCK RELAY CONTROL  SWITCH

MONITOR  SWITCH

SWITCH LEVER

1ST. LATCH  SWITCH

Figure D-1. Door Open Mechanism

1ST. LATCH SWITCH AND 2ND. INTERLOCK RELAY CONTROL SWITCH

1. When the oven door is closed, the contacts (COM - NO) must be closed.

2. When the oven door is opened, the contacts (COM - NO) must be opened.

MONITOR SWITCH

1. When the oven door is closed, the contacts (COM- NC) must be opened.

2. When the oven door is opened, the contacts (COM- NC) must be closed.

3. If the oven door is opened and the contacts (COM- NO) of the 1st. latch switch and 2nd. interlock relay fail to open, the fuse (M8A) blows simultaneously with closing the contacts (COM-NC) of the monitor switch.

CAUTION: BEFORE REPLACING A BLOWN FUSE (M8A)

TEST THE 1ST. LATCH SWITCH, 2ND. INTERLOCK RELAY, 2ND. INTERLOCK RELAY CONTROL SWITCH, MONITOR SWITCH AND MONITOR RESISTOR FOR PROPER OPERATION. (REFER TO CHAPTER “TEST PROCEDURE”.)

MONITOR RESISTOR (0.8Ω 20W)

The monitor resistor prevents the fuse (M8A) bursting when the fuse blows due to the operation of the monitor switch.

THERMAL CUT-OUT 145˚C (OVEN)

The thermal cut-out located on the top of the oven cavity is designed to prevent damage to the oven if the foods in the

oven catch fire due to over heating produced by improper setting of cook time or failure of control unit. Under normal operation, the oven thermal cut-out remains closed. However, when abnormally high temperatures are reached within the oven cavity, the oven thermal cut-out will open at 145˚C, causing the oven to shut down. The defective thermal cut-out must be replaced with new one.

FUSE (M8A)

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 the contacts (COM-NO) of the 1st. latch switch and 2nd. interlock relay remain closed with the oven door open and then the monitor switch closes.

TEMPERATURE FUSE 150˚C (MG)

This fuse protects the magnetron against overheating. If the temperature goes up higher than 150˚C because the fan motor is interrupted, the air inlet duct is blocked or the ventilation openings are obstructed, the fuse blows and puts the oven out of operation. The defective fuse must be replaced with new rated one.

FAN MOTOR

The fan motor drives a blade which draws external cool air. This cool air is directed through the air vanes surrounding the magnetron and cools the magnetron. This air is channelled through the oven cavity to remove steam and vapours given off from the heating foods. It is then exhausted through the exhausting air vents at the oven cavity.

TURNTABLE MOTOR

The turntable motor drives the turntable roller assembly to rotate the turntable.

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R-4A68

SERVICING

WARNING TO SERVICE PERSONNEL

Microwave ovens contain circuitry capable of producing very high voltage and current, contact with any part of the high voltage circuit will result in electrocution. High voltage capacitor, Power transformer, Magnetron, High voltage rectifier assembly, High voltage harness.

REMEMBER TO CHECK 3D

1) Disconnect the supply.

2) Door opened, and wedged open.

3) Discharge high voltage capacitor. WARNING: AGAINST THE CHARGE OF THE

HIGH-VOLTAGE CAPACITOR

The high-voltage capacitor remains charged about 60 seconds after the oven has been switched off. Wait for 60 seconds and then short-circuit the connection of the high-voltage capacitor (that is, of the connecting lead of the high-voltage rectifier) against the chassis with the use of an insulated screwdriver.

Sharp recommend that wherever possible fault-finding is carried out with the supply disconnected. It may in, some cases, be necessary to connect the supply after the outer case has been removed, in this event carry out 3D checks and then disconnect the leads to the primary of the power transformer. Ensure that these leads remain isolated from other components and the oven chassis. (Use insulation tape if necessary.) When the testing is completed carry out 3D checks and reconnect the leads to the primary of the power transformer.

REMEMBER TO CHECK 4R

1) Reconnect all leads removed from components during testing.

2) Replace the outer case (cabinet).

3) Reconnect the supply.

4) Run the oven. Check all functions.

Microwave ovens should not be run empty. To test for the presence of microwave energy within a cavity, place a cup of cold water on the oven turntable, close the door and set the microwave timer for two (2) minutes. Set the power level to HIGH and push the START button. When the two minutes has elapsed (timer at zero) carefully check that the water is now hot. If the water remains cold carry out 3D checks and re-examine the connections to the component being tested.

When all service work is completed, and the oven is fully assembled, the microwave power output should be checked and microwave leakage test carried out

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.

TROUBLESHOOTING GUIDE

IMPORTANT: If the oven becomes inoperative because of

a blown fuse M8A in the 1st. latch switch 2nd. interlock relay - monitor switch - monitor resistor circuit, check the 1st. latch switch, 2nd. interlock relay, 2nd. interlock relay control switch, monitor switch and monitor resistor before replacing the fuse M8A.

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R-4A68

MAGNETRON

POWER TRANSFORMER

H.V. RECTIFIER ASSEMBLY

HIGH VOLTAGE CAPACITOR

1ST. LATCH SWITCH

2ND. INTERLOCK RELAY

CONTROL SWITCH

MONITOR SWITCH

MONITOR RESISTOR

TEMPERATURE FUSE

THERMAL CUT-OUT

FAN MOTOR

TURNTABLE MOTOR

FUSE M8A

TOUCH CONTROL PANEL

RELAY (RY-1, RY-2)

FOIL PATTERN ON P.W.B.

POWER SUPPLY CORD

OVEN LAMP OR SOCKET

HIGH OLTAGE WIRE

SHORTED WIRE HARNESS

OPENED WIRE HARNESS

WALL OUTLET

HOME FUSE OR BREAKER

WRONG OPERATION

MISADJUSTMENT SWITCH

BLOCKED COOLING FAN

BLOCKED VENTILATION OPENING

Home fuse blows when power supply cord is plugged into wall outlet.

FUSE M8A blows when power supply cord is plugged into wall outlet.

Display does not show anything when power supply cord is plugged into wall outlet.

Display does not operate properly when STOP / CLEAR pad is touched.

Oven lamp does not light at door opened. (Display appears.)

Oven does not start when the START pad is touched. (Display appears)

Oven lamp does not light (Display appears.)

Fan motor does not operate. (Display appears.)

Turntable motor assembly does not operate. (Display appears.)

Oven or any electrical parts does not stop when cooking time is 0 or TOP / CLEAR pad is touched.

Oven seems to be operating but little or no heat is produced in oven load. (Microwave power level is set at HIGH)

Oven does not seems to be operating properly when MEDIUM HIGH, MEDIUM, MEDIUM LOW or LOW is set. (Oven operates properly at HIGH and when the TOP / CLEAR pad is touched the oven stops.)

Oven goes into cook cycle but shuts down before end of cooking cycle.

OFF CONDITION

TEST PROCEDURE

CONDITION

CK = Check / RE = Replace

ABCDEEEFGG H H I JLMRERE CKCK CKCK CK CK CKCK CK

PROBLEM

CONDITION

POSSIBLE CAUSE

AND

DEFECTIVE PARTS

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R-4A68

TEST PROCEDURES

PROCEDURE

LETTER

CARRY OUT 3D CHECKS. 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 (IEC705)

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 can be measured by using water load how much it can be absorbed by the water load. To measure the microwave output power in the microwave oven, the relation of calorie and watt is used. When P(W) heating works for t(second), approximately P x t/4.187 calorie is generated. On the other hand, if the temperature of the water with V(ml) rises ∆T (°C) during this microwave heating period, the calorie of the water is V x ∆T.

NEVER TOUCH ANY PART IN THE CIRCUIT WITH YOUR HAND OR AN INSULATED TOOL WHILE THE OVEN IS IN OPERATION.

A MAGNETRON 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.........47 sec.

P = 90 x ∆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 5˚C.

5. Select stirring devices and measuring instruments in order to minimize addition or removal of heat.

6. The graduation of the thermometer must be scaled by 0.1°C at minimum and accurate thermometer.

7. The water load must be (1000±5) g.

8. “t” is measured while the microwave generator is operating at full power. Magnetron filament heatup time is not included.

NOTE:The operation time of the microwave oven is “t + 2” sec. 2 sec. is magnetron filament heat-up time.

Measuring method:

1. Measure the initial temperature of the water before the water is added to the vessel. (Example: The initial temperature T1 = 11°C)

2. Add the 1 litre water to the vessel.

3. Place the load on the centre of the shelf.

4. Operate the microwave oven at HIGH for the temperature of the water rises by a value ∆ T of (10 ± 2)˚C.

5. Stir the water to equalize temperature throughout the vessel.

COMPONENT TEST

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R-4A68

TEST PROCEDURES

PROCEDURE

LETTER

COMPONENT TEST

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.

Initial temperature .................................................................................................. T1 = 11°C

Temperature after (47 + 2) = 49sec. ...................................................................... T2 = 21°C

Temperature difference Cold-Warm.................................................................... ∆T1 = 10°C

Measured output power

The equation is “P = 90 x ∆T” ...................................................... P = 90 x 10°C = 900 Watts

JUDGMENT: The measured output power should be at least ± 15 % of the rated output power.

CAUTION: 1°C CORRESPONDS TO 90 WATTS REPEAT MEASUREMENT IF THE POWER IS

INSUFFICIENT.

1000g

T1˚C

T2˚C

Heat up for 49 sec.

B POWER TRANSFORMER TEST

WARNING: High voltages and large currents are present at the secondary winding and filament

winding of the power transformer. It is very dangerous to work near this part when the oven is on. NEVER make any voltage measurements of the high-voltage circuits, including the magnetron filament.

CARRY OUT 3D CHECKS. Disconnect the leads to the primary winding of the power transformer. Disconnect the filament and

secondary winding connections from the rest of the HV circuitry. Using an ohmmeter, set on a low range, it is possible to check the continuity of all three windings. The following readings should be obtained:

a. Primary winding ....................approx. 1.13 Ω

b. Secondary winding ...............approx. 104.4 Ω

c. Filament winding...................less than 1Ω

If the reading obtained are not stated as above, then the power transformer is probably faulty and should be replaced.

CARRY OUT 4R CHECKS.

C HIGH VOLTAGE RECTIFIER ASSEMBLY TEST

HIGH VOLTAGE RECTIFIER TEST CARRY OUT 3D CHECKS. Isolate the high voltage rectifier assembly from the HV circuit. The high voltage rectifier can be tested using an ohmmeter set to its highest range. Connect the ohmmeter across the terminal B+C of the high voltage rectifier and note the reading obtained. Reverse the meter leads and note this second reading. The normal resistance is infinite in one direction and more than 100 kΩ in the other direction.

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R-4A68

TEST PROCEDURES (CONT'D)

COMPONENT TEST

PROCEDURE

LETTER

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.

HIGH VOLTAGE RECTIFIER

D HIGH VOLTAGE CAPACITOR TEST

CARRY OUT 3D CHECKS. 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 CHECKS. Isolate the switch to be tested and using an ohmmeter check between the terminals as described in the

following table.

Table: Terminal Connection of Switch

Plunger Operation COM to NO COM to NC

Released O.C. S.C. Depressed S.C. O.C.

COM; Common terminal, NO; Normally open terminal NC; Normally close terminal S.C.; Short circuit O.C.; Open circuit

If incorrect readings are obtained, make the necessary switch adjustment or replace the switch. CARRY OUT

4R CHECKS.

F MONITOR RESISTOR TEST

CARRY OUT 3D CHECKS. Disconnect the leads from the monitor resist. Using an ohmmeter and set on a low range. Check between

the terminals of the monitor resistor.

The resistance of monitor resistor is approx. 0.8 ohms. If incorrect readings are obtained, replace the monitor resistor. CARRY OUT 4R CHECKS.

G TEMPERATURE FUSE OR THERMAL CUT-OUT TEST

CARRY OUT 3D CHECKS. Disconnect the leads from the terminals of the temperature fuse or thermal cut-out. Then using an

ohmmeter, make a continuity test across the two terminals as described in the table below. CARRY OUT 4R CHECKS.-

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R-4A68

TEST PROCEDURES (CONT'D)

PROCEDURE

LETTER

COMPONENT TEST

.Table: Thermal cut-out Test

Temperature of "ON" condition Temperature of "OFF" condition Indication ofohmmeter

Parts Name (closed circuit) (˚C) (open circuit) (˚C) (When room temperature

is approx. 20˚C) Thermal cut-out 145˚C This is not resetable type. Above 145˚C Closed circuit. Temperature fuse 150˚C This is not resetable type. Above 150˚C Closed circuit.

If incorrect readings are obtained, replace the temperature fuse or thermal cut-out. An open circuit temperature fuse 150˚C (MG) indicates that the magnetron has overheated, this may be

due to restricted ventilation, cooling fan failure or a fault condition within the magnetron or HV circuit. An open circuit thermal cut-out 145˚C (OVEN) indicates that the foods in the oven may catch fire, this

may be due to over heating produced by improper setting of the cooking time or failure of the control panel.

CARRY OUT 3D CHECKS. Disconnect the leads from the motor.

Using an ohmmeter, check the resistance between the two terminals as described in the table below.

H MOTOR WINDING TEST

Table: Resistance of Motor Motors Resistance Fan motor Approximately 295 Ω Turntable motor Approximately 12.2 kΩ

If incorrect readings are obtained, replace the motor. CARRY OUT 4R CHECKS.

I BLOWN FUSE M8A

CARRY OUT 3D CHECKS.

1. If the fuse M8A is blown, there could be shorts or ground in electrical parts or wire harness. Check them and replace the defective parts or repair the wire harness.

2. If the fuse M8A is blown when the door is opened, check the 1st. latch switch, 2nd. interlock relay control switch, 2nd. interlock relay, monitor switch and monitor resistor. If the fuse M8A is blown by incorrect door switching replace the defective switch(s) and the fuse M8A.

CARRY OUT 4R CHECKS. CAUTION: ONLY REPLACE FUSE M8A WITH THE CORRECT VALUE REPLACEMENT.

J TOUCH CONTROL PANEL ASSEMBLY TEST

The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore, unlike conventional microwave ovens, proper maintenance cannot be performed with only a voltmeter and ohmmeter. In this service manual, the touch control panel assembly is divided into two units, Control Unit and Key Unit, and troubleshooting by replacement is described according to the symptoms indicated.

1. Key Unit Note : Check key unit ribbon connection before replacement. The following symptoms indicate a defective key unit. Replace the key unit. a) When touching the pads, a certain pad produces no signal at all. b) When touching a number pad, two figures or more are displayed. c) When touching the pads, sometimes a pad produces no signal.

2. Control Panel The following symptoms indicate a defective control unit. Before replacing the control unit,

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R-4A68

PROCEDURE

LETTER

COMPONENT TEST

TEST PROCEDURES (CONT'D)

perform the Key unit test (Procedure L) to determine if control unit is faulty.

2-1 In connection with pads.

a) When touching the pads, a certain group of pads do not produce a signal. b) When touching the pads, no pads produce a signal.

2-2 In connection with indicators

a) At a certain digit, all or some segments do not light up. b) At a certain digit, brightness is low. c) Only one indicator does not light. d) The corresponding segments of all digits do not light up; or they continue to light up. e) Wrong figure appears. f) A certain group of indicators do not light up. g) The figure of all digits flicker.

2-3 Other possible troubles caused by defective control unit.

a) Buzzer does not sound or continues to sound. b) Clock does not operate properly. c) Cooking is not possible.

K KEY UNIT TEST

If the display fails to clear when the STOP/CLEAR pad is depressed, first verify the flat ribbon is marking good contact, verify that the door sensing switch (stop switch) operates properly; that is the contacts are closed when the door is closed and open when the door is open. If the door sensing switch (stop switch) is good, disconnect the flat ribbon cable that connects the key unit to the control unit and make sure the door sensing switch is closed (either close the door or short the door sensing switch connecter). Use the Key unit matrix indicated on the control panel schematic and place a jumper wire between the pins that correspond to the STOP/CLEAR pad marking momentary contact. If the control unit responds by clearing with a beep the key unit is faulty and must be replaced. If the control unit does not respond, it is faulty and must be replaced. If a specific pad does not respond, the above method may be used (after clearing the control unit) to determine if the control unit or key pad is at fault.

G12

G11

G10

G 9

G 8 G 7 G 6 G 5 G 4 G 3 G 2 G 1

KEY UNIT

54321

09876

POWER

LEVEL

INSTANT

COOK



START

CLOCK

Pasta

Vegetable

STOP

CLEAR

Steaks

/Chops

Minced

Meat

Dinner

Plate

( FROZEN

FOOD)

AUTO

START

Chicken

Pieces

Beverage

Dinner

Plate

( SNACKS &

REHEAT)

Jacket Potato

Fresh

Veg.

Casseroles

Rice

L RELAY TEST

CARRY OUT

3D CHECKS.

Remove the outer case and check the voltage between Pin Nos. 3 and 5 of the 3 pin connector (A) on the control unit with an A.C. voltmeter. The meter should indicate 220 volts, if not check oven circuit.

RY1 and RY2 Relay Test

These relays are operated by D.C. voltage. Check voltage at the relay coil with a D.C. voltmeter during the microwave cooking operation.

DC. voltage indicated .............. Defective relay.

DC. voltage not indicated ........ Check diode which is connected to the relay coil. If diode is good, control

Page 15

R-4A68

TEST PROCEDURES (CONT'D)

PROCEDURE

LETTER

COMPONENT TEST

unit is defective.

RELAY SYMBOL OPERATIONAL VOLTAGE CONNECTED COMPONENTS

RY1 APPROX. 13.5V D.C. Oven lamp / Turntable motor / Cooling fan motor RY2 APPROX. 13.0V D.C. Power transformer

CARRY OUT 4R CHECKS.

M PROCEDURES TO BE TAKEN WHEN THE FOIL PATTERN ON THE PRINTED WIRING BOARD

(PWB) IS OPEN

RY1

VRS1

CN-A

(J4)

(J1)

To protect the electronic circuits, this model is provided with a fine foil pattern added to the primary on the PWB, this foil pattern acts as a fuse. If the foil pattern is open, follow the troubleshooting guide given below for repair.

Problem: POWER ON, indicator does not light up. CARRY OUT

3D CHECKS.

STEPS OCCURANCE CAUSE OR CORRECTION

1 The rated AC voltage is not present at Check supply voltage and oven power cord.

POWER terminal of CPU connector (CN-A).

2 The rated AC voltage is present at primary Low voltage transformer or secondary circuit defective.

side of low voltage transformer. Check and repair.

3 Only pattern at "a" is broken. *Insert jumper wire J1 and solder.

(CARRY OUT

3D CHECKS BEFORE REPAIR)

4 Pattern at "a" and "b" are broken. *Insert the coil RCILF2003YAZZ between "c" and "d".

(CARRY OUT 3D CHECKS BEFORE REPAIR)

NOTE: *At the time of making these repairs, make

a visual inspection of the varistor. check for burned damage and examine the transformer with a tester for the presence of layer short-circuit (check primary coil resistance). If any abnormal condition is detected, replace the defective parts.

CARRY OUT

4R CHECKS.

Page 16

R-4A68

The touch control section consists of the following units as shown in the touch control panel circuit.

(1) Key Unit (2) Control Unit

The principal functions of these units and the signals communicated among them are explained below.

Key Unit

The key unit is composed of a matrix, signals generated in the LSI are sent to the key unit through R51, R52, R53, R60, R61, R62 and R63. When a key pad is touched, a signal is completed through the key unit and passed back to the LSI through R81, R82, R83 and R90 to perform the function that was requested.

Control Unit

Control unit consists of LSI, power source circuit, synchronizing signal circuit, ACL circuit, buzzer circuit and indicator circuit.

1) LSI

This LSI controls the key strobe signal, relay driving signal for oven function and indicator signal.

2) Power Source Circuit

This circuit generates voltages necessary in the control unit.

Symbol Voltage Application

VC -5V LSI(IC1)

TOUCH CONTROL PANEL ASSEMBLY

OUTLINE OF TOUCH CONTROL PANEL

3) Synchronizing Signal Circuit

The power source synchronizing signal is available in order to compose a basic standard time in the clock circuit. It accompanies a very small error because it works on commercial frequency.

4) ACL Circuit

A circuit to generate a signals which resets the LSI to the initial state when power is supplied.

5) Buzzer Circuit

The buzzer is responsive to signals from the LSI to emit audible sounds (key touch sound and completion sound).

6) Door Sensing Switch

A switch to “tell” the LSI if the door is open or closed.

7) Relay Circuit

To drive the magnetron, fan motor, turntable motor and light the oven lamp.

8) Indicator Circuit

Indicator element is a Light-emitting diode. Basically, a Light-emitting diode is triode having a cathode and an anode. The Light-emitting diode has 4-digits, 9-segments are used for displaying figures.

Page 17

R-4A68

DESCRIPTION OF LSI

LSI(IZA690DR)

The I/O signal of the LSI(IZA690DR) are detailed in the following table.

Pin No. Signal I/O Description

1 XOUT OUT

Internal clock oscillation frequency control output.

Output to control oscillation input of XOUT.

2 XIN IN

Internal clock oscillation frequency input setting.

The internal clock frequency is set by inserting the ceramic filter oscillation circuit with respect to XIN terminal.

3 RESET IN

Auto clear terminal.

Signal is input to reset the LSI to the initial state when power is supplied. Temporarily set to “L” level the moment power is supplied, at this time the LSI is set. Thereafter set at “H” level.

4 R70 OUT

Segment data signal.

Refer to the touch control panel circuit for the relationship between signals and indicators. Normally, one pulse is output in every synchronized signal period, and input to the anode of the light-emitting diode.

5 PULSE OUT

Signal to sound buzzer.

A: key touch sound(0.12sec.). B: Completion sound(2.4sec.).

6 R72 OUT

Digit selection signal.

Refer to the touch control panel circuit about the relation between signals and digits. Normally, one pulse is output in every synchronized signal period, and input to the lightemitting diode.

7-9 R40-R42 OUT

Digit selection signal.

Refer to the touch control panel circuit about the relation between signals and digits. Normally, one pulse is output in every synchronized signal period, and input to the light-

emitting diode. 10 AIN3 IN Terminal to change cooking constant. 11 R50 OUT

Segment data signal.

Signal similar to R70. 12 R51 OUT

Segment data signal.

Signal similar to R70.

Key strobe signal.