Sharp R305dw Owner's Manual

SERVICE MANUAL

S3006R305DPW/

MICROWA VE OVEN

R-305DW

COOK

DEFOST

TO ADJUST QUANTITY TOUCH PAD AGAIN

CASSEROLE

BEVERAGE

BAKED

FRESH

POTATOES

VEGETABLES

1 GROUND MEAT
2 STEAKS/CHOPS
3 CHICKEN PIECES

1 2 3
4 5 6
7 8

POWER
LEVEL

0

STOP
CLEAR

NO.
LBS.
CUPS.

OZ.

MINUTE PLUS

POPCORN

ROLLS &
MUFFINS

COMPU DEFROST

9

TIMER
CLOCK

START

MODEL

R-305DW

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 following parts may result in a severe,
possibly fatal, electrical shock. (High Voltage Capacitor, High
Voltage Power Transformer, Magnetron, High Voltage Recti­fier Assembly, 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 ..............................................................................................................................9

TEST PROCEDURE............................................................................................................................................ 10

TOUCH CONTROL PANEL .................................................................................................................................18

COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE ................................................................22

PICTORIAL DIAGRAM ........................................................................................................................................28

POWER UNIT CIRCUIT ......................................................................................................................................29

CPU UNIT CIRCUIT ............................................................................................................................................30

PRINTED WIRING BOARD .................................................................................................................................31

PARTS LIST ........................................................................................................................................................32

PACKING AND ACCESSORIES .........................................................................................................................36

SHARP CORPORATION

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

R-3 05DW

PRECAUTIONS TO BE OBSER VED BEFORE AND
DURING SER VICING TO A VOID POSSIBLE
EXPOSURE TO EXCESSIVE MICROW A VE
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 power 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, 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.

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)
High Voltage Capacitor, High Voltage Power Trans-

former, Magnetron, High Voltage Rectifier Assem­bly, High Voltage Harness etc..

Read the Service Manual carefully and follow all
instructions.

may result in a severe, possibly

R-305DW

Don't Touch !
Danger High Voltage

Before Servicing

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

2. Open the door and block it open.

3. Discharge high voltage capacitor.

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. 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 the leads to the primary of the power
transformer.

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 a microwave leakage test should be carried out.

1

R-305DW

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.

2

SERVICE MANUAL

R-305DW

MICROWAVE OVEN

R-305DW

FOREWORD

This Manual has been prepared to provide Sharp Electronics Corp.
Service Personnel with Operation and Service Information for the
SHARP MICROWAVE OVEN, R-305DW.

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.

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;
High Voltage Capacitor, Power Transformer, Magnetron, High
Voltage Rectifier Assembly, High Voltage Harness;
If provided, Vent Hood, Fan assembly, Cooling Fan Motor.

PRODUCT DESCRIPTION

GENERAL INFORMATION

OPERATION

TROUBLESHOOTING GUIDE AND
TEST PROCEDURE

TOUCH CONTROL PANEL

COMPONENT REPLACEMENT
AND ADJUSTMENT PROCEDURE

WIRING DIAGRAM

PARTS LIST

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

Removal of the outer wrap 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

SHARP PLAZA, MAHWAH,

NEW JERSEY 07430-2135

3

R-305DW

SPECIFICATION

ITEM DESCRIPTION

Power Requirements 120 Volts / 13 Amperes

60 Hertz
Single phase, 3 wire grounded

Power Output 1100 watts (IEC TEST PROCEDURE)

Operating frequency of 2450MHz

Case Dimensions Width 20-1/2"

Height 11-7/8"
Depth 17-1/8"

Cooking Cavity Dimensions Width 14-3/4"

Height 8-3/4"

1.2 Cubic Feet Depth 15-3/4"
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

MINUTE PLUS pad, INSTANT START pads
COMPU DEFROST pads, Number selection pads
POWER LEVEL pad, TIMER/CLOCK pad
STOP/CLEAR pad, START pad

Oven Cavity Light Yes
Safety Standard UL Listed FCC Authorized

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

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.

Electrical Requirements
The electrical requirements are a 120 volt 60 Hz, AC only,
15 or 20 amp. fused electrical supply. It is recommended that a separate circuit serving only this appliance be provided. When
installing this appliance, observe all applicable codes and ordinances.
A short power-supply cord is provided to reduce risks of becoming entangled in or tripping over a longer cord.
Where a two-pronged wall-receptacle is encountered, it is the personal responsibility and obligation of the customer to

4

R-305DW

4

3

1

12

7

2

8

9

6

10

5

11

contact a qualified electrician and have it replaced with a properly
grounded three-pronged wall receptacle or have a grounding adapter
properly grounded and polarized. If the extension cord must be used, it
should be a 3-wire, 15 amp. or higher rated cord. Do not drape over a
countertop or table where it can be pulled on by children or tripped over
accidentally.

CAUTION: DO NOT UNDER ANY CIRCUMSTANCES CUT OR RE-

MOVE THE ROUND GROUNDING PRONG FROM THIS
PLUG.

OVEN DIAGRAM

1. Door open handle.
Pull to open door.

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

3. Removable turntable support.

4. Removable turntable.
The turntable will rotate clockwise or
counterclockwise.

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

6. Oven door with see-through window.

7. Ventilation openings. (Rear)

8. Auto-Touch control panel.

9. Time display: Digital display, 99 minutes 99 seconds.

10. Coupling.

3-Pronged Plug

Grounding Pin

3-Pronged Receptacle

Grounded
Receptacle Box

11. Wave guide cover.

12. Power supply cord

TOUCH CONTROL PANEL

NO.

LBS.

CUPS.

DEFOST

COOK

TO ADJUST QUANTITY - TOUCH PAD AGAIN

CASSEROLE

BAKED

POTATOES

1 GROUND MEAT
2 STEAKS/CHOPS
3 CHICKEN PIECES

BEVERAGE

FRESH

VEGETABLES

OZ.

MINUTE PLUS

POPCORN

ROLLS &

MUFFINS

COMPU DEFROST

See note.

See note.

1 2 3

NOTE:
The directed features are disabled after one minute 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.

5

4 5 6
7 8

POWER

LEVEL

STOP

CLEAR

0

START

9

TIMER

CLOCK

R-305DW

OPERATION

DESCRIPTION OF OPERATING SEQUENCE

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

OFF CONDITION

Closing the door activates the door sensing 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. The display will show flashing "88:88".
To set any program or set the clock, you must first touch
the STOP/CLEAR pad. The display will clear, and " : "
will appear.

COOKING CONDITION

Program desired cooking time by touching the NUMBER
pads. Program the power level by touching the POWER
LEVEL pad and then a Number pad.
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 and is mechanically associated with the door so
that it will function in the following sequence.

(1) When the door opens from the closed position, the

primary interlock relay (RY2) and secondary interlock
switch open their contacts. And contacts of the relay
(RY1) remains closed. Then the monitor switch contacts
close.

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

monitor switch contacts open first. Then the contacts of
the secondary interlock switch and door sensing switch

close. And contacts of the relay (RY1) open.
If the secondary interlock switch and primary interlock relay
(RY2) fail with the 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,
relay (RY1) and primary interlock relay (RY2), causing the
monitor fuse to blow.

POWER LEVEL P-0 TO P-90 COOKING

When Variable Cooking Power is programmed, the 120
volts A.C. is supplied to the power transformer intermittently
through the contacts of relay (RY-2) which is operated by the
control unit within a 32 second time base. Microwave power
operation is as follows:

RELAY CONNECTED COMPONENTS
RY-1 oven lamp/turntable motor/fan motor
RY-2 power transformer

2. 120 volts A.C. is supplied to the primary winding of the
power transformer and is converted to about 3.1 volts
A.C. output on the filament winding, and approximately
2370 volts A.C. on the high voltage winding.

3. The filament winding voltage heats the magnetron
filament and the H.V. winding voltage is sent to a voltage
doubler circuit.

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 power
transformer, oven lamp, etc. are turned off, and the
generation of microwave energy is stopped. The oven
will revert to the OFF condition.

6. When the door is opened during a cook cycle, the
monitor switch, door sensing switch, secondary interlock
switch, relay (RY1) and primary interlock relay are
activated with the following results. The circuits to the
turntable motor, the cooling fan motor, and the high
voltage components are de-energized, the oven lamp
remains on, and the digital read-out displays the time still
remaining in the cook cycle when the door was opened.

7. The monitor switch electrically monitors the operation of
the secondary interlock switch and primary interlock

VARI-MODE ON TIME OFF TIME
P-HI (100% power) 32 sec. 0 sec.
P-90 (approx. 90% power) 30 sec. 2 sec.
P-80 (approx. 80% power) 26 sec. 6 sec.
P-70 (approx. 70% power) 24 sec. 8 sec.
P-60 (approx. 60% power) 22 sec. 10 sec.
P-50 (approx. 50% power) 18 sec. 14 sec.
P-40 (approx. 40% power) 16 sec. 16 sec.
P-30 (approx. 30% power) 12 sec. 20 sec.
P-20 (approx. 20% power) 8 sec. 24 sec.
P-10 (approx. 10% power) 6 sec. 26 sec.

P-0 (approx. 0% power) 0 sec. 32 sec.

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

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

6

SCHEMATIC

120V AC
60 Hz

OVEN
LAMP

TURN­TABLE
MOTOR

FAN
MOTOR

POWER
TRANSFORMER

CAPACITOR 0.94µF

AC 2200V

MONITOR
SWITCH

RECTIFIER

MAGNETRON

SECONDARY
INTERLOCK
SWITCH

TTM

OL FM

MONITOR
FUSE 20A

A1

A2

N.O.

COM.COM.

N.O.

DOOR
SENSING
SWITCH

(RY-1)

(RY-2)

CONTROL UNIT

PRIMARY
INTERLOCK
RELAY

THERMAL
CUT-OUT (OVEN)

THERMAL
CUT-OUT (MG.)

SH-B SH-A

GRN

OVEN
LAMP

TURN­TABLE
MOTOR

FAN
MOTOR

POWER
TRANSFORMER

MONITOR
SWITCH

RECTIFIER

SECONDARY
INTERLOCK
SWITCH

TTM

OL FM

N.O.

N.O.

DOOR
SENSING
SWITCH

SH-B SH-A

(RY-1)

(RY-2)

CONTROL UNIT

PRIMARY
INTERLOCK
RELAY

120V AC
60 Hz

GRN

MONITOR
FUSE 20A

THERMAL
CUT-OUT (OVEN)

THERMAL
CUT-OUT (MG.)

COM.

CAPACITOR 0.94µF

AC 2200V

A1

A2

COM

RECTIFIER

MAGNETRON

NOTE: CONDITION OF OVEN

1. DOOR CLOSED

2. CLOCK APPEARS ON DISPLAY

R-305DW

NOTE: Indicates components with potential above 250 V.

SCHEMATIC

NOTE: CONDITION OF OVEN

1. DOOR CLOSED

2. COOKING TIME PROGRAMMED

3. VARIABLE COOKING CONTROL "P-HI"

4. "START" PAD TOUCHED

Figure O-1. Oven Schematic-Off Condition

Figure O-2. Oven Schematic-Cooking Condition

7

R-305DW

DESCRIPTION AND FUNCTION OF COMPONENTS

DOOR OPEN MECHANISM

The door is opened by pulling the door. Refer to the Figure
D-1.

Door

Latch
Heads

Latch Hook

Door Sensing
Switch

Monitor Switch
Secondary

Interlock Switch

Figure D-1. Door Open Mechanis

DOOR SENSING AND SECONDARY INTERLOCK
SWITCHES

The secondary interlock switch is mounted in the lower
position of the latch hook and the door sensing switch in the
primary interlock system is mounted 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
power to all high voltage components. A cook cycle cannot
take place until the door is firmly closed thereby activating
both interlock switches. The primary interlock system con­sists of the door sensing switch and primary interlock relay
located on the control circuit board.

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 relay (RY2) 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 relay (RY2) and
secondary interlock switch are in the OFF condition
(contacts open) due to their being normally open contact
switches.

2. As the door goes to a closed position, the monitor switch
contacts are first opened and then the door sensing
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 relay
(RY2) 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 DOOR SENSING SWITCH,
PRIMARY INTERLOCK RELAY (RY2), RELAY
(RY1), SECONDARY INTERLOCK SWITCH
AND MONITOR SWITCH FOR PROPER OP­ERATION. (REFER TO CHAPTER "TEST PRO­CEDURE").

NOTE: MONITOR FUSE AND MONITOR SWITCH ARE

REPLACED AS AN ASSEMBLY.

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. The turntable may turn in either
direction.

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.

MONITOR FUSE

1. The monitor fuse blows when the contacts (COM-NO) of
the primary interlock relay (RY2) and secondary interlock
switch remain closed with the oven door open and when
the monitor switch closes.

2. If the wire harness or electrical components are short­circuited, this monitor fuse blows to prevent an electric
shock or fire hazard.

OVEN THERMAL CUT-OUT

The thermal cut-out, located on the top of the oven cavity, is
designed to prevent damage to the oven by fire. If the food
load is overcooked, by either error in cook time or defect in
the control unit, the thermal cut-out will open.
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 257˚F(125˚C), causing the oven to shut down.

MAGNETRON THERMAL CUT-OUT

The thermal cut-out located near the magnetron 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 thermal cut-out remains closed.
However, when abnormally high temperatures are reached
within the magnetron, the thermal cut-out will open at
293˚F(145˚C) causing the oven to shut down.

8

R-305DW

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 relay (RY2), door sensing switch and secondary interlock switch before replacing the
monitor fuse. If the monitor fuse is replaced, the monitor switch must also be replaced. Use part FFS­BA021WRK0 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.

9

R-305DW

CK = Check / RE = Replace

CONDITION

OFF
CONDITION

COOKING
CONDITION

TEST PROCEDURE

AND

POSSIBLE CAUSE

DEFECTIVE PARTS

PROBLEM

Home fuse or circuit breaker blows
when power cord is plugged into wall
receptacle

Monitor fuse blows when power cord
is plugged into wall receptacle.

All letters and indicators do not ap­pear in display when power cord is
first plugged into wall outlet.

Display does not operate properly
when STOP/CLEAR key is touched.
(Buzzer should sound and ":" or time
of day should appear in display.)

Oven lamp does not light when door
is opened.

Oven lamp does not go out when
door is closed.

Oven lamp lights but fan motor and
turntable motor do not operate.

Oven does not go into cook cycle
when START pad is touched

Oven seems to be operating but little
or no heat is produced in oven load.
(Food incompletely cooked or not
cooked at all at end of cook cycle.)

Oven goes into a cook cycle but
extremely uneven heating is pro­duced in oven load (food).

Oven does not cook properly when
programmed for Cooking Power P­50 mode. (Operates properly on
Cooking Power P-HI (100%) mode.)

Oven goes into COMPU DEFROST
but food is not defrosted well.

RE RE

ABCDEFFGH

SHORT IN POWER CORD

SHORT OR OPENED WIRING

MAGNETRON

POWER TRANSFORMER

H.V. RECTIFIER ASSEMBLY

RERE

HIGH VOLTAGE CAPACITOR

THERMAL CUT-OUT

PRIMARY INTERLOCK SYSTEM

SECONDARY INTERLOCK SWITCH

MONITOR SWITCH

MONITOR FUSE

OVEN LAMP OR SOCKET

CKICK CKCK

COOLING FAN MOTOR

TURNTABLE MOTOR

TOUCH CONTROL PANEL

WRONG OPERATION

LOW VOLTAGE

DIRTY OVEN CAVITY

JKLM

KEY UNIT

RELAY (RY1)

COMPU DEFROST

FOIL PATTERN ON PWB.

PROCEDURE

LETTER

A MAGNETRON ASSEMBLY TEST

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

2. Open the door and block it open.

3. Discharge high voltage capacitor.

TEST PROCEDURES

COMPONENT TEST

10