Sharp R-312AW, R-312AK User Manual

SER VICE MANU AL

S5707R312APK/

MICROWAVE OVEN

R-312AW
R-312AK

CHECK

INSTANT ACTION

To adjust quantity-touch pad again

POPCORN

BEVERAGE

DINNER

REHEAT

PLATE

CASSEROLE

BAKED

FRESH

POTATO

VEGETABLE

FRESH

FROZEN

ROLL / MUFFIN

ROLL / MUFFIN

1

Ground meat

2

Steaks / chops

COMPU

3

Chicken pieces

DEFROST

POWER

TIMER

LEVEL

CLOCK

STOP

START

CLEAR

MINUTE PLUS

R-312AW

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.

TABLE OF CONTENTS

PRECAUTIONS TO BE OBSERVED BEFORE AND DURING SERVICE TO

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

BEFORE SERVICING ...........................................................................................................................................1

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

FOREWORD.......................................................................................................................................................... 3

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

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

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

TROUBLESHOOTING GUIDE ..............................................................................................................................9

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

TOUCH CONTROL PANEL .................................................................................................................................15

COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE ................................................................19

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

POWER UNIT CIRCUIT ......................................................................................................................................26

CONTROL PANEL CIRCUIT ...............................................................................................................................27

PRINTED WIRING BOARD .................................................................................................................................28

PARTS LIST ........................................................................................................................................................29

PACKING AND ACCESSORIES .........................................................................................................................33

R-312AW
R-312AK

Page

ON

MODELS

DEF. LBS. QTY.

SHARP ELECTRONICS CORPORATION

Service Headquarters: Sharp Plaza, Mahwah, New Jersey 07430-2135

R-312AW
R-312AK

PRECAUTIONS TO BE OBSERVED BEFORE AND
DURING SERVICING TO AVOID POSSIBLE
EXPOSURE TO EXCESSIVE MICROWAVE
ENERGY

(a) Do not operate or allow the oven to be operated with the door open.
(b) Make the following safety checks on all ovens to be serviced before activating the magnetron or other

microwave source, and make repairs as necessary: (1) interlock operation, (2) proper door closing, (3)
seal and sealing surfaces (arcing, wear, and other damage), (4) damage to or loosening of hinges and
latches, (5) evidence of dropping or abuse.

(c) Before turning on microwave 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.

R-312AW
R-312AK

1

R-312AW
R-312AK

MICROWAVE 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

MICROWAVE OVEN

PRODUCT DESCRIPTION

R-312AW
R-312AK

R-312AW / R-312AK

FOREWORD

This Manual has been prepared to provide Sharp Electronics
Corp. Service Personnel with Operation and Service Informa­tion for the SHARP MICROWAVE OVENS, R-312AW, R­312AK.

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.

GENERAL INFORMATION

OPERATION

TROUBLESHOOTING GUIDE AND
TEST PROCEDURE

TOUCH CONTROL PANEL

COMPONENT REPLACEMENT
AND ADJUSTMENT PROCEDURE

WIRING DIAGRAM

SHARP ELECTRONICS CORPORATION

SHARP PLAZA, MAHWAH,

NEW JERSEY 07430-2135

PARTS LIST

3

R-312AW
R-312AK

SPECIFICATION

ITEM DESCRIPTION

Power Requirements 120 Volts / 13.0 Amperes

60 Hertz
Single phase, 3 wire grounded

Power Output 1000 watts (IEC-705 TEST PROCEDURE)

Operating frequency of 2450MHz

Case Dimensions Width 20-1/2"

Height 11-7/8"
Depth 15-7/8"

Cooking Cavity Dimensions Width 13-3/4"

Height 8-3/8"

0.9 Cubic Feet Depth 14-7/8"
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

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

Oven Cavity Light Yes
Safety Standard UL and C-UL Listed FCC Authorized

DHHS Rules, CFR, Title 21, Chapter 1, Subchapter J
Department of National Health and Welfare CANADA.

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.

4

R-312AW
R-312AK

Electrical Requirements
The electrical requirements are a 115 -120 volt 60 Hz, AC only,
15 or 20 amp. fused electrical supply. It is recommended that a separate

3-Pronged Plug

Grounded
Receptacle Box

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 contact a qualified

Grounding Pin

electrician and have it replaced with a properly grounded three-pronged
wall receptacle or have a grounding adapter properly grounded and
polarized. If an extension cord must be used, it should be a 3-wire, 15

3-Pronged Receptacle

amp. or more 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 REMOVE THE ROUND GROUNDING PRONG FROM

THIS PLUG.

1. One touch door open button.
Push 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.

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.

11.Wave guide cover.

12.Power supply cord

OVEN DIAGRAM

10

11

2

TOUCH CONTROL PANEL

56

7

9

8

12

1

4

3

DEF. LBS. QTY.

ON

INSTANT ACTION

To adjust quantity-touch pad again

POPCORN

DINNER

PLATE

BAKED

POTATO

FRESH

ROLL / MUFFIN

Ground meat

1

Steaks / chops

2

Chicken pieces

3

POWER

LEVEL

STOP

CLEAR

BEVERAGE

REHEAT

CASSEROLE

FRESH

VEGETABLE

FROZEN

ROLL / MUFFIN

COMPU

DEFROST

START

MINUTE PLUS

CHECK

TIMER

CLOCK

Time display

Indicator

5

R-312AW
R-312AK

OPERATION

DESCRIPTION OF OPERATING SEQUENCE

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

OFF CONDITION

Closing the door activates door sensing switch, primary
interlock switch and the third door switch. (In this condition,
the monitor switch contacts are opened.)
When oven is plugged in, 120 volts A.C. is supplied to the
noise filter and 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
and program the power level by touching the POWER
LEVEL pad and 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 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 3.2 volts
A.C. output on the filament winding, and approximately
2150 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
channeled 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, monitor
switch, door sensing switch, primary interlock switch and
third door switch are activated with the following results.
The circuits to the turntable motor, the cooling fan motor,
and the high voltage components are de-energized, and
the digital readout 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 primary interlock switch and it 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 third

door switch, primary interlock switch and door sensing
switch open their contacts, and then the monitor switch
contacts close.

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

monitor switch contacts first open, and then the contacts
of the primary interlock switch, door sensing switch and

third door switch close.
If the primary interlock switch fails 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
and primary interlock switch 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 an interval second time base. Micro­wave power operation is as follows:

VARI-MODE ON TIME OFF TIME

Power 10(P-HI) 32 sec. 0 sec.

(100% power)

Power 9(P-90) 30 sec. 2 sec.

(approx. 90% power)

Power 8(P-80) 26 sec. 6 sec.

(approx. 80% power)

Power 7(P-70) 24 sec. 8 sec.

(approx. 70% power)

Power 6(P-60) 22 sec. 10 sec.

(approx. 60% power)

Power 5(P-50) 18 sec. 14 sec.

(approx. 50% power)

Power 4(P-40) 16 sec. 16 sec.

(approx. 40% power)

Power 3(P-30) 12 sec. 20 sec.

(approx. 30% power)

Power 2(P-20) 8 sec. 24 sec.

(approx. 20% power)

Power 1(P-10) 6 sec. 26 sec.

(approx. 10% power)

Power 0(P-0) 0 sec. 32 sec.

(0% power)

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

NOTE: CONDITION OF OVEN

1. DOOR CLOSED

2. CLOCK APPEARS ON DISPLAY

R-312AW
R-312AK

120V AC

60 Hz

OVEN

THERMAL 

CUT-OUT

HN

FUSE 20A

CAPACITOR

NOISE FILTER

NOISE SUPPRESSION COIL

0.22µF / AC 250V

LINE CROSS CAPACITOR

LINE BYPASS

0.0033µF / AC 125V

CAPACITOR

LINE BYPASS

0.0033µF / AC 125V

Figure O-1. Oven Schematic-Off Condition

SCHEMATIC

NOTE: CONDITION OF OVEN

1. DOOR CLOSED

2. COOKING TIME PROGRAMMED

3. VARIABLE COOKING CONTROL "HIGH"

4. "START" PAD TOUCHED

MAGNETRON

THERMAL 

CUT-OUT

OVEN

LAMP

A3

PRIMARY
INTERLOCK
SWITCH

OL

TURNTABLE

MOTOR

CONTROL UNIT

TTM

(RY-1)

FAN 

MOTOR

THIRD
DOOR
SWITCH

POWER 

SWITCH

TRANSFORMER

CAPACITOR

0.94µF

MAGNETRON

RECTIFIER

FM

DOOR
SENSING
SWITCH

A1

B1

COM.

(RY-2)

B2

SECONDARY

INTERLOCK

RELAY

N.O.

MONITOR 

120V AC

60 Hz

HN

FUSE 20A

NOISE FILTER

NOISE SUPPRESSION COIL

CAPACITOR

LINE BYPASS

0.0033µF / AC 125V

0.22µF / AC 250V

LINE CROSS CAPACITOR

CAPACITOR

LINE BYPASS

0.0033µF / AC 125V

Figure O-2. Oven Schematic-Cooking Condition

OVEN

THERMAL 

CUT-OUT

MAGNETRON

THERMAL 

CUT-OUT

OVEN

LAMP

A3

PRIMARY
INTERLOCK
SWITCH

OL

TURNTABLE

MOTOR

CONTROL UNIT

7

TTM

(RY-1)

FAN 

MOTOR

THIRD
DOOR
SWITCH

POWER 

SWITCH

TRANSFORMER

CAPACITOR

0.94µF

MAGNETRON

RECTIFIER

FM

DOOR
SENSING
SWITCH

A1

B1

COM.

(RY-2)

B2

SECONDARY

INTERLOCK

RELAY

N.O.

MONITOR 

R-312AW
R-312AK

DESCRIPTION AND FUNCTION OF COMPONENTS

DOOR OPEN MECHANISM

The door is opened by pushing the open button on the
control panel, refer to the Figure D-1.
When the open button is pushed, the open button pushes up
the switch lever, and then the switch lever pushes up the the
latch head. The latch heads are moved upward and re­leased from latch hook. Now the door will open.

LATCH HOOK

DOOR SENSING
SWITCH

LATCH
HEADS

MONITOR 
SWITCH

SWITCH
LEVER

THIRD DOOR 
SWITCH

PRIMARY INTERLOCK 
SWITCH

Figure D-1. Door Open Mechanism

DOOR SENSING, THIRD DOOR AND PRIMARY
INTERLOCK SWITCHES

The primary interlock switch is mounted in the lower position
of the latch hook and the door sensing switch in the
secondary interlock system is mounted in the upper position
of the latch hook. The third door switch is mounted in the
lower position at the back 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
except the oven lamp and the noise filter. A cook cycle
cannot take place until the door is firmly closed thereby
activating both interlock switches. The secondary interlock
system consists of the door sensing switch and secondary
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
blowning the monitor fuse when the contacts of the primary
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 is in the
OFF condition (contacts open) due to its 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, the primary interlock switch and third door switch
contacts close. (On opening the door, each of these
switches operate inversely.)

3. If the door is opened, and primary 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 PRIMARY INTERLOCK
SWITCH AND MONITOR SWITCH FOR
PROPER OPERATION. (REFER TO CHAP­TER “TEST PROCEDURE”).

NOTE: MONITOR FUSE AND 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 vapours given off from the heating foods. It is then
exhausted through the exhausting air vents at the oven
cavity.

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 foods
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
203˚F(95˚C) causing the oven to shut down, when the
magnetron has cooled to 167˚F (75˚C), the thermal cut-out
closes and cook cycle will resume.

NOISE FILTER

The noise filter prevents the redio frequency interference
that might flow back in the power circuit.

8

R-312AW
R-312AK

TROUBLESHOOTING GUIDE

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 in the monitor switch and primary interlock

switch circuit, check the monitor switch and primary interlock switch before replacing the monitor fuse. If
monitor fuse is replaced, the mintor switch should be replaced at the same time.

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 does not light in cook­ing cycle. (Lights when door is
opened.)

Oven lamp does not light at all.
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 5 mode. (Operates prop­erly on Cooking Power 10 (HIGH)
mode.)

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

RERE A B C D E F F G H RERECK J CKCKCK L K M N I

SHORT IN POWER CORD

SHORT OR OPENED WIRING

MAGNETRON

POWER TRANSFORMER

H.V. RECTIFIER ASSEMBLY

HIGH VOLTAGE CAPACITOR

THERMAL CUT-OUT

SECONDARY INTERLOCK SYSTEM

PRIMARY INTERLOCK SWITCH

MONITOR SWITCH

MONITOR FUSE

OVEN LAMP OR SOCKET

COOLING FAN MOTOR

TURNTABLE MOTOR

TOUCH CONTROL PANEL

WRONG OPERATION

LOW VOLTAGE

DIRTY OVEN CAVITY

RELAY (RY1)

KEY UNIT

COMPU DEFROST

FOIL PATTERN ON PWB.

NOISE FILTER

9