Sharp R312aw Owner's Manual

SERVICE MANUAL

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

1

Ground meat

2

Steaks / chops

3

Chicken pieces

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 