SHARP R1750, R-1751, R-1752, R-1754 Service Manual

12 : 45

Minute

Plus +

T O U C H S C R E E N

MINUTE

STOP/

PLUS

CLEAR

6x6 NO GUESS COOKING

6 Categories + 36 Foods

Meats

Vegetables

Fish/

Frozen

Seafood

Food

Fan

Light

Options

R-1750 R-1751 R-1752 R-1754

SERVICE MANUAL

S8019R1750X//

OVER THE RANGE

MICROWAVE OVEN

ONE TOUCH

SENSOR

Reheat

Popcoon

Baked

Potatoes

Kitchen Timer

Beverage

Center

Keep Warm

START

Defrost

3+6

Poultry

MORE FROM YOUR MICROWAVE

Pasta

6 x 6

Grains

Turntable

Set Up

On/Off

MODELS

R-1750 R-1751 R-1752 R-1754

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

WARNING TO SERVICE PERSONNEL: Microwave ovens contain circuitry capable of producing very high voltage and current. Contact with the following parts may result in a severe, possibly fatal, electrical shock. (Inverter unit that includes High Voltage Capacitor, High Voltage Power Transformer, High Voltage Rectifier and Heat sink etc., and Magnetron, High Voltage Harness etc..)

TABLE OF CONTENTS

Page PRECAUTIONS TO BE OBSERVED BEFORE AND DURING SERVICING TO

AVOID POSSIBLE EXPOSURE TO EXCESSIVE MICROWAVE ENERGY...................INSIDE FRONT COVER

BEFORE SERVICING ......................................................................................................INSIDE FRONT COVER

WARNING TO SERVICE PERSONNEL................................................................................................................1

MICROWAVE MEASUREMENT PROCEDURE ...................................................................................................2

FOREWORD AND WARNING...............................................................................................................................3

PRODUCT SPECIFICATIONS ......................................................................................................... .....................4

GENERAL INFORMATION...................................................................................................................................4

OPERATION..........................................................................................................................................................6

TROUBLESHOOTING GUIDE ............................................................................................................................14

TEST PROCEDURE............................................................................................................................................ 16

TOUCH CONTROL PANEL ASSEMBLY ............................................................................................................27

COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE ................................................................33

PICTORIAL DIAGRAM ........................................................................................................................................41

POWER UNIT CIRCUIT ......................................................................................................................................42

LSI UNIT CIRCUIT...............................................................................................................................................43

PRINTED WIRING BOARD .................................................................................................................................44

PARTS LIST ........................................................................................................................................................45

PACKING AND ACCESSORIES .........................................................................................................................50

SHARP CORPORATION

This document has been published to be used for after sales service only. The contents are subject to change without notice.

R-1750 R-1751 R-1752 R-1754

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.

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, 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.

BEFORE SERVICING

Before servicing an operative unit, perform a microwave emission check as per the Microwave Measurement Procedure outlined in this service manual. If microwave emissions level is in excess of the specified limit, contact SHARP ELECTRONICS CORPORATION immediately @1-800-237-4277.

If the unit operates with the door open, service person should 1) tell the user not to operate the oven and

2) contact SHARP ELECTRONICS CORPORATION and Food and Drug Administration's Center for Devices and Radiological Health immediately.

Service personnel should inform SHARP ELECTRONICS CORPORATION of any certified unit found with emissions in excess of 4mW/cm2. The owner of the unit should be instructed not to use the unit until the oven has been brought into compliance.

DANGER CAUTION

HIGH VOLTAGE

Do not energize a microwave oven with the outer case cabinet removed, because a microwave oven generates High Voltage in the circuit.

If you intend to operate the oven employing the high frequency switching power converter circuit, you should take special precautions to avoid an electrical shock hazard.

The high voltage transformer, high voltage capacitor and high voltage diode have energized high voltage potential approx. 8 KV.

The aluminium heat sink is connected to the switching power transistor Collector pole, and has an energized high voltage potential approx. 650V peak.

DO NOT ACCESS THE HIGH VOLTAGE TRANSFORMER, HIGH VOLTAGE CAPACITOR, HIGH VOLTAGE DIODE AND HEAT SINK WHEN THE POWER SUPPLY IS CONNECTED TO AN ELECTRICAL OUTLET.

W ARNING TO SER VICE PERSONNEL

Microwave ovens contain circuitry capable of producing very high voltage and current, contact with following parts fatal, electrical shock.

(Example) Inverter unit that includes High Voltage Capacitor,

High Voltage Power Transformer, High Voltage Rectifier, Heat sink etc., and Magnetron, High Voltage Harness etc..

Read the Service Manual carefully and follow all instructions.

may result in a severe, possibly

Don't Touch ! Danger High Voltage

R-1750 R-1751 R-1752 R-1754

Before Servicing

1. Disconnect the power supply cord , and then remove outer case.

2. Open the door and block it open.

3. To discharge high voltage capacitor, wait for 60 seconds.

WARNING:RISK OF ELECTRIC SHOCK.

DISCHARGE THE HIGH-VOLTAGE CAPACITOR BEFORE SERVICING.

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 highvoltage capacitor (that is the connecting lead of the highvoltage rectifier) against the chassis with the use of an insulated screwdriver.

Whenever troubleshooting is performed the power supply must be disconnected. It may in, some cases, be necessary to connect the power supply after the outer case has been removed, in this event,

1. Disconnect the power supply cord, and then remove outer case.

2. Open the door and block it open.

3. To discharge high voltage capacitor, wait for 60 seconds.

4. Disconnect the leads to the primary of the inverter unit.

5. Ensure that these leads remain isolated from other components and oven chassis by using insulation tape.

6. After that procedure, reconnect the power supply cord.

1. Disconnect the power supply cord, and then remove outer case.

2. Open the door and block it open.

3. To discharge high voltage capacitor, wait for 60 seconds.

4. Reconnect the leads to the primary of the inverter unit.

5. Reinstall the outer case (cabinet).

6. Reconnect the power supply cord after the outer case is installed.

7. Run the oven and check all functions.

After repairing

1. Reconnect all leads removed from components during testing.

2. Reinstall the outer case (cabinet).

3. Reconnect the power supply cord after the outer case is installed.

4. Run the oven and 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 power to HIGH and set the microwave timer for two (2) minutes. When the two minutes has elapsed (timer at zero) carefully check that the water is now hot. If the water remains cold carry out Before Servicing procedure and reexamine 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 should be carried out.

When the testing is completed,

R-1750 R-1751 R-1752 R-1754

SERVICING FOR INVERTER UNIT

WARNING

This inverter unit contains circuitry capable of producing high voltage and high current. Contact with any part of the high voltage will result in electrocution.

DO NOT ACCESS ANY PARTS OF INVERTER UNIT WITH POWER SUPPLY CONNECTED. DO NOT OPERATE INVERTER UNIT ITSELF.

It is dangerous because this unit contains high voltage components.

MICROW A VE MEASUREMENT PROCEDURE

A. Requirements:

1) Microwave leakage limit (Power density limit): The power density of microwave radiation emitted by a microwave oven should not exceed 1mW/cm2 at any point 5cm or more from the external surface of the oven, measured prior to acquisition by a purchaser, and thereafter (through the useful life of the oven), 5 mW/cm2 at any point 5cm or more from the external surface of the oven.

2) Safety interlock switches Primary interlock relay and door sensing switch shall prevent microwave radiation emission in excess of the requirement as above mentioned, secondary interlock switch shall prevent microwave radiation emission in excess of 5 mW/cm2 at any point 5cm or more from the external surface of the oven.

B. Preparation for testing: Before beginning the actual measurement of leakage, proceed as follows:

1) Make sure that the actual instrument is operating normally as specified in its instruction booklet. Important:

Survey instruments that comply with the requirement for instrumentation as prescribed by the performance standard for microwave ovens, 21 CFR 1030.10(c)(3)(i), must be used for testing.

2) Place the oven tray in the oven cavity.

3) Place the load of 275±15 ml (9.8 oz) of tap water initially at 20±5˚C (68˚F) in the center of the oven cavity. The water container shall be a low form of 600 ml (20 oz) beaker with an inside diameter of approx. 8.5 cm (3-1/2 in.) and made of an electrically nonconductive material such as glass or plastic. The placing of this standard load in the oven is important not only to protect the oven, but also to insure that any leakage is measured accurately.

4) Set the cooking control on Full Power Cooking Mode

5) Close the door and select a cook cycle of several minutes. If the water begins to boil before the survey is completed, replace it with 275 ml of cool water.

C. Leakage test:

Closed-door leakage test (microwave measurement)

1) Grasp the probe of the survey instrument and hold it perpendicular to the gap between the door and the body of the oven.

2) Move the probe slowly, not faster than 1 in./sec. (2.5 cm/sec.) along the gap, watching for the maximum indication on the meter.

3) Check for leakage at the door screen, sheet metal seams and other accessible positions where the continuity of the metal has been breached (eg., around the switches, indicator, and vents). While testing for leakage around the door pull the door away from the front of the oven as far as is permitted by the closed latch assembly.

4) Measure carefully at the point of highest leakage and make sure that the highest leakage is no greater than 4mW/cm2, and that the secondary interlock switch does turn the oven OFF before any door movement.

NOTE: After servicing, record data on service invoice and microwave leakage report.

SERVICE MANUAL

R-1750 R-1751 R-1752 R-1754

OVER THE RANGE

MICROWAVE OVEN

R-1750 / R-1751 / R-1752 / R-1754

FOREWORD

This Manual has been prepared to provide Sharp Electronics Corp. Service Personnel with Operation and Service Information for the SHARP OVER THE RANGE MICROWAVE OVEN, R-1750, R-1751, R-1752, R-1754.

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

Check the interlock switches and the door seal carefully. Special attention should be given to avoid electrical shock and microwave radiation hazard.

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 no other visible damage with the oven.

PRODUCT DESCRIPTION

GENERAL INFORMATION

OPERATION

TROUBLESHOOTING GUIDE AND TEST PROCEDURE

TOUCH CONTROL PANEL

COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE

WIRING DIAGRAM

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

DANGER

Certain initial parts are intentionally not grounded and present a risk of electrical shock only during servicing. Service personnel - Do not contact the following parts while the appliance is energized; Inverter unit that includes High Voltage Capacitor, High Voltage Power Transformer, High Voltage Rectifier, Heat sink, etc., and Magnetron, High Voltage Harness etc.; If provided, Vent Hood, Fan assembly, Cooling Fan Motor.

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

Removal of the outer wrapper gives access to voltage above 250V. All the parts marked “∆” on parts list may cause undue microwave

exposure, by themselves, or when they are damaged, loosened or removed.

SHARP ELECTRONICS CORPORATION

PARTS LIST

SHARP PLAZA, MAHWAH,

NEW JERSEY 07430-2135

R-1750 R-1751 R-1752 R-1754

PRODUCT SPECIFICA TION

ITEM DESCRIPTION

Power Requirements 120 Volts / 14 Amperes / 1600 W

60 Hertz Single phase, 3 wire grounded

Power Output 1100 watts (IEC TEST PROCEDURE)

Operating frequency of 2450MHz

Case Dimensions Width 29-15/16"

Height 16-3/8" Depth 16- 1/8" (Not including the door handle)

Cooking Cavity Dimensions Width 21"

Height 8-7/8"

1.6 Cubic Feet Depth 14-7/16" Hood lamp 2 bulbs, 20W x 2, Incandescent light bulbs Hood fan Approx. 300 C.F.M. Control Complement Touch Control System

Clock ( 1:00 - 12:59 ) Timer (0 - 99 min. 99 seconds)

Microwave Power for Variable Cooking Repetition Rate;

P-HI..................................................Full power throughout the cooking time

P-90 .................................................................... approx. 90% of Full Power

P-80 .................................................................... approx. 80% of Full Power

P-70 .................................................................... approx. 70% of Full Power

P-60 .................................................................... approx. 60% of Full Power

P-50 .................................................................... approx. 50% of Full Power

P-40 .................................................................... approx. 40% of Full Power

P-30 .................................................................... approx. 30% of Full Power

P-20 .................................................................... approx. 20% of Full Power

P-10 .................................................................... approx. 10% of Full Power

P-0 .................................................... No power throughout the cooking time

TOUCH SCREEN, ONE TOUCH SENSOR pads, Beverage Center pad Keep Warm pad, Defrost pad, MINUTE PLUS pad, STOP/CLEAR pad START pad, 6 x 6 NO GUESS COOKING pads MORE FROM YOUR MICROWAVE 6 x 6 pad, Fan Options pad Light Options pad, Turntable On/Off pad, Set Up pad

Oven Cavity Light 20W x 1 Incandescent light bulb Safety Standard UL Listed FCC Authorized

DHHS Rules, CFR, Title 21, Chapter 1, Subchapter J

Weight Approx. 46 lbs.

GENERAL INFORMATION

GROUNDING INSTRUCTIONS

This oven is equipped with a three prong grounding plug. It must be plugged into a wall receptacle that is properly installed and grounded in accordance with the National Electrical Code and local codes and ordinances. In the event of an electrical short circuit, grounding reduces the risk of electric shock by providing an escape wire for the electric current.

WARNING: Improper use of the grounding plug can result in a risk of electric shock.

R-1750 R-1751 R-1752 R-1754

Electrical Requirements The oven is equipped with a 3-prong grounding plug. DO NOT UNDER ANY CIRCUMSTANCES CUT OR REMOVE THE GROUNDING PIN FROM THE PLUG. The power supply cord and plug must be connected to a separate 120 Volt AC, 60 Hz, 15 Amp. or more dedicated line, using a grounded receptacle. The receptacle should be located inside the cabinet directly above the Microwave Oven/Hood system mounting location.

3-Pronged Plug

Grounded Receptacle Box

Grounding Pin

3-Pronged Receptacle

OVEN DIAGRAM

1. Oven door with see-through window.

2. Door hinges.

3. Stirrer cover.

4. Turntable motor shaft.

5. Oven lamp. It will light when oven is operating or door is open.

6. Door latches. The oven will not operate unless the door is securely closed.

7. Auto-Touch control panel.

8. Touch Screen.

9. Ventilation openings.

10.Light Cover.

11.Grease filters.

12.Removable turntable. The turntable will rotate clockwise or counterclockwise. Only remove for cleaning.

13.Removable turntable support.

14. Power supply cord

R-1750 R-1751 R-1752 R-1754

See note.

CONTROL PANEL

12 : 45 PM

Minute Plus +

T O U C H S C R E E N

MINUTE

PLUS

6x6 NO GUESS COOKING

6 Categories + 36 Foods

Meats

Fish/

Seafood

Vegetables

STOP/

CLEAR

Frozen

Food

Kitchen

Timer

START

Poultry

Pasta

Grains

ONE TOUCH

SENSOR

Reheat

Popcoon

Baked

Potatoes

Beverage

Center

Keep

Warm

Defrost

3+6

MORE FROM YOUR MICROWAVE

6 x 6

See note.

Fan

Options

Light

Options

Turntable

On/Off

Set Up

NOTE: The directed features are disabled after three minutes when the oven is not in use. These features are automatically enabled when the door is opened and closed or the STOP/ CLEAR pad is pressed.

OPERATION

DESCRIPTION OF OPERATING SEQUENCE

The following is a description of component functions during oven operation.

OFF CONDITION

Closing the door activates the stop switch, primary interlock switch and secondary interlock switch. (In this condition, the monitor switch contacts are opened.) When oven is plugged in, 120 volts A.C. is supplied to the control unit (Figure O-1).

1. "Set clock" key and "Video demo" key will be appeared on the touch screen.

2. Touch "Set clock" key and set the clock referring to the operation manual.

NOTE: If no keys are touched within 30 seconds, the touch

screen will go on to the Video Demo mode. To cancel the Video Demo mode, touch the STOP/ CLEAR pad. And then set the clock.

3. The touch screen will show the home page after setting the clock.

4. The following is an example of the Home page when the time of the day is set to 12:30 p.m..

12 : 30 PM

123 456 7809

Minute

Plus +

Kitchen

Timer

NOTE: Even if the clock is not set, the display will show the

Home page by touching the STOP/CLEAR pad within 30 seconds after being plugged in.

COOKING CONDITION

Program desired cooking time touching the NUMBER pads. When the START pad is touched, the following operations occur:

1. The contacts of relays are closed and components connected to the relays are turned on as follows. (For details, refer to Figure O-2)

RELAY CONNECTED COMPONENTS RY1 Oven lamp / Fan motor / Stirrer motor RY2 Turntable motor RY3, RY4 Hood fan motor

2. 120 volts A.C. is supplied to the inverter unit and is converted in order to power of the magnetron by the high frequency switching power circuit. The frequency is approx. 27 _ 40 KHz.

3. The filament winding voltage of H.V. transformer heats the magnetron filament and the H.V. winding gives a high voltage approx. 2 KV to activaite a voltage doubler circuit. Then approx. 4KV peak voltage power is supplied to the magnetron cathode terminal.

4. The microwave energy produced by the magnetron is channelled through the waveguide into the cavity feedbox, and then into the cavity where the food is placed to be cooked.

5. Upon completion of the cooking time, the inverter unit, oven lamp, etc. are turned off, and the generation of microwave energy is stopped. The oven will revert to the OFF condition.

When the door is opened during a cook cycle, the monitor switch, stop switch, secondary interlock switch and primary interlock switch are activated with the following results. The circuits to the stirrer motor, the cooling fan motor, the turntable motor, and the inverter unit are de-energized, and the touch screen displays the time still remaining in the cook cycle when the door was opened.

7. The monitor switch is electrically monitoring the operation of the secondary interlock switch and primary interlock switch and is mechanically associated with the door so that it will function in the following sequence. (1) When the door opens from a closed position, the

primary interlock switch and secondary interlock switch open their contacts, and then the monitor switch contacts close. And contacts of the relay (RY1) remain closed.

(2) When the door is closed from the open position, the

monitor switch contacts first open and the stop switch contacts open, and then the contacts of the secondary interlock switch and primary interlock

switch close. And contacts of the relay (RY1) open. If the secondary interlock switch and primary interlock switch fail with their contacts closed when the door is opened, the closing of the monitor switch contacts will form a short circuit through the monitor fuse, secondary interlock switch, primary interlock switch and relay (RY1) causing the monitor fuse to blow.

VARIABLE COOKING

When Variable Cooking Power is programmed, the 120 volts A.C. is supplied to the inverter unit which is operated by the control unit. Microwave power operation is as follows: The oven can be set for any of 11 power levels: 0% to 100%(HIGH). The variable cooking power less than 40% is

programmed at the ratio of ON time and OFF time within 32 sec./ cycle time base.

CONNECTION BETWEEN POWER SETTING AND ON/ OFF TIME OF INVERTER UNIT.

OUTPUT POWER SETTING ON TIME OFF TIME

Power 100% Power 90% Power 80% Power 70% Continue operation Power 60% Power 50% Power 40% 26 sec. 6 sec. Power 30% 22 sec. 10 sec. Power 20% 16 sec. 16 sec. Power 10% 8 sec. 24 sec. Power 0% 0 sec. 32 sec.

Note: The ON/OFF time ratio does not correspond with

the percentage of microwave power, because approx. 3 seconds are needed for heating of the magnetron filament.

SENSOR COOKING CONDITION

Using the Sensor cooking function (See sensor cooking menus), the food is cooked without figuring time, power level or quantity. When the oven senses enough steam from the food, it relays the information to its microprocessor which will calculate the remaining cooking time and power level needed for best results. When the food is cooked, water vapor is developed. The sensor “senses” the vapor and its resistance increases gradually. When the resistance reaches the value set according to the menu, supplementary cooking is started. The time of supplementary cooking is determined by experiment with each food category and input into the LSI. An example of how sensor works: (BAKED POTATOES)

1. Potatoes at room temperature. Vapor is emitted very slowly.

2. Heat Potatoes. Moisture and humidity is emitted rapidly. You can smell the aroma as it cooks.

AH SENSOR

MICROWAVE

R-1750 R-1751 R-1752 R-1754

3. Sensor detects moisture and humidity and calculates cooking time and variable power.

Cooking Sequence.

1. Operate the oven in sensor cooking mode by referring to the operation manual.

NOTE: The oven should not be operated on SENSOR

immediately after plugging in the unit. Wait two minutes before cooking on SENSOR.

2. The coil of shut-off relay (RY-1) is energized, the turntable motor, oven lamp and cooling fan motor are turned on, but the inverter unit is not turned on.

3. After about 32 seconds, the cook relay (RY-2) is energized. The power transformer is turned on, microwave energy is produced and first stage is started. The 32 seconds is the cooling time required to remove any vapor from the oven cavity and sensor.

NOTE: During this first stage, do not open the door or touch

STOP/CLEAR pad.

4. When the sensor detects the vapor emitted from the food, the display switches over to the remaining cooking time and the timer counts down to zero. At this time, the door may be opened to stir, turn, or season food.

5. When the timer reaches zero, an audible signal sounds. The shut-off relay is de-energized and the inverter unit, oven lamp, etc. are turned off.

6. Opening the door or touching the STOP/CLEAR pad, the time of day will reappear on the display and the oven will revert to an OFF condition.

The following are the sensor cooking menus.

Reheat Popcorn Baked potatoes Vegetables Ground beef or Meat Boneless Chicken Breast, Bone-in Chicken Pieces and Ground Poultry of Poultry Fish / Seafood Vegetables, Entrees, Main Dishes and Snacks of Frozen food White Rice and Brown Rice of Pasta Grains Frozen breakfast food, Meal in cup, Hot dogs in buns, Soup, Frozen sandwich, Stuffed Acorn Squash, Ratatouille, Bacon, Microwave pizza of More From Your Microwave.

VENTILATION METHODS HOT AIR EXHAUST

1. VERTICAL VENTING For this venting method, hot air rising from the conventional range below is drawn in by the hood fan motor through the grease filters at the right and left sides of the base cover, up through the right and left sides of the oven cavity, then discharged vertically at rear center top of the oven, into the customer's vent system.

: AIR FLOW

TO DUCT

HOOD FAN MOTOR

HOOD INTAKE DUCT

GREASE FILTER

TO DUCT

2. HORIZONTAL VENTING The air handing is the same as VERTICAL VENTING except that the final air discharge is directed horizontally out from the top rear of the oven into the customer's vent system.

: AIR FLOW

HOOD FAN MOTOR

TO DUCT

HOOD INTAKE DUCT

GREASE FILTER

3. RE-CIRCULATION (INSIDE VENTING) The air handing is the same as VERTICAL VENTING except that the final air discharge is directed horizontally through the upper front of the oven into the kitchen. In this case, the accessory charcoal filter RK-230 must be provided to filter the air before it leaves the oven.

: AIR FLOW

HOOD FAN MOTOR

HOOD EXHAUST LOUVER

HOOD INTAKE DUCT

CHARCOAL FILTER

BASIC OPERATION OF INVERTER CIRCUIT

Basic circuit diagram is shown Figure A-1. AC line voltage is rectified and converted to direct-current voltage (DC. Voltage). By switching the power transistor Q1 ON and OFF, High frequency current (about 27 - 40 KHz) is generated controlled by the IC of the inverter unit. OFF-time of the transistor Q1 is nearly constant. That is, on-time is varied. It is a kind of Pulse Width Modulation (PWM). Because off-time is constant, switching frequency is varied in response to the length of on-time and output power of magnetron is proportional to the length of on-time. Therefore, the frequency of inverter becomes low for high output and high for low output.

Wave-form of main parts are shown in Figure A-2. During off-time, flyback voltage appears on the primary winding of the high voltage transformer. The off-time depends on the inductance of the transformer and capacitance of the resonant capacitor C3. Synchronous circuit generates the timing signal by detecting the flyback voltage. The power transistor Q1 is periodically switched on when the collector voltage returns to zero (0) volt. High voltage (about 2 KV) appears on secondary winding of the transformer. The full-wave voltage doubler circuit increase to about 4 KV and is applied to the magnetron. The efficiency of the inverter unit itself is approx. 93%, and equal to that of current efficiency. Ferrite core is used for the high voltage transformer. It is superior to silicon steel core at high frequency, low magnetic loss. The power level is determined by the touch control board, and the PWM data corresponding to the level is set to the IC of the inverter unit through the control lines. The IC controls on-time of transistor Q1 by comparing the average value of the primary current with the magnitude of the power level data. The IC has the protection circuit which detects over-current of the main circuit and the high voltage circuit, over-voltage of the power transistor Q1 and AC power interruption. When abnormal phenomenon is detected, the IC pauses on the moment in order to protect the power transistor Q1 from

R-1750 R-1751 R-1752 R-1754

being destroyed. After approx. 60 millisecond, it starts generating the driving signal from the minimum pulse width and expands the length of on-time slowly until the current of the main circuit reaches the target level.

Driving signal

Collector current of Q1

Collector voltage of Q1

Secondary voltage of high voltage transformer

Synchronous signal

Figure A-2. Switching Wave-form

AC 120V / 60 Hz

+ V

Synchronous Signal for AC.

Output Control Signal

Bridge diode

Choke coil

Power transistor

Driving Circuit

Synchronous Circuit

Voltage Detector

Overcurrent and Overvoltage Detector

Average Current

High voltage transformer

D11

D12

C11 C12

102

Magnetron

103

Figure A-1. Basic Circuit

R-1750 R-1751 R-1752 R-1754

FUSE 20A

120 V AC. 60 Hz

BLKWHT

GRN

GND

HOOD FAN THERMAL CUT OUT

OVEN THERMAL CUT-OUT

B3 B1

HOOD MOTOR

MAGNETRON TEMPERATURE FUSE

CONTROL UNIT

RY3

RY4

High

N.C.

Low

HOOD CAPACITOR

A1 A3 B9 A5 A7 N.O.

HOOD LAMP

SSR

RY2 RY1

TTM

HL HL

TURNTABLE

MOTOR

FAN

MOTOR

COM.

OVEN LAMP

F1 F2

H1 H2 H3

STM

STIRRER

MOTOR

STOP SWITCH

PRIMARY INTERLOCK SWITCH

SCHEMATIC

NOTE: CONDITION OF OVEN

1. DOOR CLOSED

2. CLOCK APPEARS ON DISPLAY

AH SENSOR

A3 A1

AC3

INVERTER UNIT

MONITOR

SWITCH

FFA

MAGNETRON

FUSE 20A

120 V AC. 60 Hz

BLKWHT

GRN

GND

HOOD FAN THERMAL CUT OUT

OVEN THERMAL CUT-OUT

B3 B1

HOOD MOTOR

SECONDARY INTERLOCK SWITCH

Figure O-1. Oven Schematic-Off Condition

MAGNETRON TEMPERATURE FUSE

CONTROL UNIT

RY3

RY4

High

N.C.

Low

HOOD CAPACITOR

A1 A3 B9 A5 A7 N.O.

HOOD LAMP

HL HL

SSR

RY2 RY1

TTM

TURNTABLE

MOTOR

FAN

MOTOR

COM.

OVEN LAMP

F1 F2

H1 H2 H3

STM

STIRRER

MOTOR

SCHEMATIC

NOTE: CONDITION OF OVEN

1. DOOR CLOSED

2. COOKING TIME PROGRAMMED

3. VARIABLE COOKING CONTROL "HIGH"

4. "START" PAD TOUCHED

AH SENSOR

A3 A1

STOP SWITCH

PRIMARY INTERLOCK SWITCH

INVERTER UNIT

AC3

FFA

MAGNETRON

MONITOR

SWITCH

SECONDARY INTERLOCK SWITCH

Figure O-2. Oven Schematic-Cooking Condition

AC3

PWM

MCK

(CN-A)

CN-A

OSC

INT

GND

Q50

AGND

VP0

VCC

OUT

VP2

4.7K

39K

VP1

223

MAGNETRON

Q70

D11

D16

D50

D12

0.3µ / 580V

0.03µ

2800V

C11

0.06µ

3100V

C12

1000p/ 50V

C21

VRS3

120M

(H.V.RESISTOR)

R11

100

R103

PD2

D17

ZD70

RBV-2506

39K

100µ / 35V

0.9µ / 200V

- +

C35

1000p / 50V

C61

(J2)

R101

2.2/ 1W

R102

D100

2.2/ 1W

VRS2

47K

1.2KF

4.7K

R20

R35

R62

1.8K

R44

36K

1/2W

R43

33K

1/2W

R42

R55

4.7K

CF1

8MHZ

1.3K/ 5W

1/ 2W 33K

R31

R73

(R72)

D22

D23

D32

D20

D21

VR1

330

0.01µ/16V

C20

0.01µ/50V

2.2KF

R54

5.6KF

C50

100p/50V

ZD33ZD32

R61

300F

R50

(ZD50)

ZD40

10K

R56

100K

R71

1.5K

R22

120K

R63

4.7K

R30

1.2K

1/2W

R34

4.7K

1.3KF

R51

10K

R40

R70

10K

R25 TH2

ZD30

ZD31

D30

PD1

PH1

BF20

IC1

LR38166

(IZA406DR)

10µ / 50V

- +

C62

39K

R24

1µ / 50V

- +

C24

C40

18K

R21

430

R45

220p / 50V

C41

100p / 50V

1µ / 50V

- +

C31

1000p / 50V

C30

0.1µ/ 25V

C70

Q51

PD3

R-1750 R-1751 R-1752 R-1754

Figure O-3. Inverter Unit Circuit

R-1750 R-1751 R-1752 R-1754

CN-A

C70

Q70

PD3

EARTH

ZD70

CMK-P3X

94V - 0

R71

R53

R70

PD1

C62

Q50

R56

C24

R22

D16

ZD30

J11

C50 R50

R35

ZD50

PD2

R61

C61

R21

D70

R63

R24

R103

R55

TH1

R30 C21

D100

R51

R54

D30

C30

R62

C41

ZD31

CF1

IC1

C50

R44

R45

R40

D50

Q51

C51

ZD40

C31

R25

R34

C35

D23

TH2

D22

CT1

ZD33

ZD32

R20

VR1

AC3

BLUE

RED

VRS2

D32

R31

FA930DR

D20

D21

0.006µF 0.003µF

C12

C11

J10

R101

R102

D11

R43

D12

HS2

SOLDER

R42

HS1

R11

PH1

VRS3

R72

VRS4

R73

DANGER H.V.

Figure O-4. Printed Wiring Board for Inverter Unit Circuit

DESCRIPTION AND FUNCTION OF COMPONENTS

R-1750 R-1751 R-1752 R-1754

DOOR OPEN MECHANISM

The door is opened by pulling the door handle, refer to the Figure D-1.

Latch Hook

Latch Heads

Door

Stop Switch

Primary Interlock Switch

Monitor Fuse

Monitor Switch

Secondary Interlock Switch

Figure D-1. Door Open Mechanism

STOP, PRIMARY INTERLOCK AND SECONDARY INTERLOCK SWITCHES

The secondary interlock switch is mounted in the lower position of the latch hook and the stop switch is mounted in the upper position of the latch hook. The primary interlock switch is also in the upper position of the latch hook. They are activated by the latch heads on the door. When the door is opened, the switches interrupt the circuit to all components. A cook cycle cannot take place until the door is firmly closed thereby activating both interlock switches.

MONITOR SWITCH

The monitor switch is activated (the contacts opened) by the latch head on the door while the door is closed. The switch is intended to render the oven inoperative by means of blowing the monitor fuse when the contacts of the primary interlock switch and secondary interlock switch fail to open when the door is opened.

Functions:

1. When the door is opened, the monitor switch contact close (to the ON condition) due to their being normally closed. At this time the primary interlock switch and secondary interlock switch are in the OFF condition (contacts open) due to their being normally open contact switches. And the contacts of relay (RY1) are in the ON condition (contacts close).

2. As the door goes to a closed position, the monitor switch contacts are first opened and the stop switch contacts close, and then the primary interlock switch and the secondary interlock switch contacts close. (On opening the door, each of these switches operate inversely.)

3. If the door is opened, and the primary interlock switch and secondary interlock switch contacts fail to open, the monitor fuse blows simultaneously with closing of the monitor switch contacts.

CAUTION: BEFORE REPLACING A BLOWN MONITOR

FUSE TEST THE STOP SWITCH, PRIMARY INTERLOCK SWITCH, SECONDARY INTER-

LOCK SWITCH AND MONITOR SWITCH FOR PROPER OPERATION. (REFER TO CHAPTER "TEST PROCEDURE").

NOTE: MONITOR FUSE AND SWITCH ARE REPLACED

AS AN ASSEMBLY

TEMPERATURE FUSE (MG)

The temperature fuse located near the waveguide is designed to prevent damage to the magnetron if an over heated condition develops in the tube due to cooling fan failure, obstructed air guide, dirty or blocked air intake, etc. Under normal operation, the temperature fuse remains closed. However, the temperature fuse will open at 302˚F (150˚C) causing the oven to shut down.

THERMAL CUT-OUT (HOOD )

This thermal cut-out located on the right base plate. It is designed to automatically turn on the hood fan motor whenever the hot air rising from the conventional range below causes the temperature at the thermal cut-out to rise to 140˚F (60˚C) or higher, thus removing this hot air from around microwave oven. When the temperature around the thermal cut-out drops to 113˚F (45˚C) or lower, the thermal cut-out shuts off the hood fan motor.

THERMAL CUT-OUT (OVEN )

This thermal cut-out is located on the top of the oven cavity. It is designed to prevent damage to the oven unit if the food in the oven catches fire due to overheating produced by improper setting of cooking time or failure of control unit. Under normal operation, the thermal cut-out remains closed. However, the thermal cut-out will open at 293˚F (145˚C) causing the oven to shut down.

TURNTABLE MOTOR

The turntable motor rotates the turntable located on the bottom of the oven cavity, so that the foods on the turntable cook evenly during cooking. Turntable will turn in either direction. The turntable motor can be turned off by touching TURNTABLE ON/OFF pad.

COOLING FAN MOTOR

The cooling 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 vapors given off from the heating foods. It is then exhausted through the exhausting air vents at the oven cavity.

HOOD FAN MOTOR

The hood fan motor is a two-speed, single-phase, double pole induction type, requiring a hood fan capacitor. It is located outside the upper rear part of the oven cavity, is to remove, from around the oven, hot air rising from the conventional electric or gas range over which it is installed. This air is then expelled either vertically or horizontally through the customer supplied duct system, or discharged back into the kitchen.

R-1750 R-1751 R-1752 R-1754

STIRRER MOTOR

The stirrer motor drives the stirrer fan to stir the microwave radiation from the waveguide.

HOOD LAMP

The hood lamps are mounted at the hood lamp angle on the base cover. The hood lamps can be turned off and on by touching the Light Options pad. And also the brightness can be varied to high or low by touching the Light Options pad.

TROUBLESHOOTING GUIDE

Never touch any part in the circuit with your hand or an uninsulated tool while the power supply is connected.

When troubleshooting the microwave oven, it is helpful to follow the Sequence of Operation in performing the checks. Many of the possible causes of trouble will require that a specific test be performed. These tests are given a procedure letter which will be found in the "Test Procedure "section.

IMPORTANT: If the oven becomes inoperative because of a blown monitor fuse, check the monitor switch, relay (RY1)

primary interlock switch and secondary interlock switch before replacing the monitor fuse. If monitor fuse is replaced, the monitor switch must also be replaced. Use part FFS-BA016/KIT as an assembly.

IMPORTANT: Whenever troubleshooting is performed with the power supply cord disconnected. It may in, some cases,

be necessary to connect the power supply cord after the outer case has been removed, in this event,

1. Disconnect the power supply cord, and then remove outer case.

2. Open the door and block it open.

3. Discharge high voltage capacitor.

4. Disconnect the leads to the primary of the power transformer.

5. Ensure that the leads remain isolated from other components and oven chassis by using insulation tape.

6. After that procedure, reconnect the power supply cord.

When the testing is completed

1. Disconnect the power supply cord, and then remove outer case.

2. Open the door and block it open.

3. Discharge high voltage capacitor.

4. Reconnect all leads removed from components during testing.

5. Reinstall the outer case (cabinet).

6. Reconnect the power supply cord after the outer case is installed.

7. Run the oven and check all functions.

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