SHARP R305MR Service Manual

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R305MR

SERVICE MANUAL

S1701R305MPR/

MICROWAVE OVEN

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..)

CONTENTS

PRECAUTIONS TO BE OBSERVED BEFORE AND
DURING SERVICING TO AVOID POSSIBLE EXPO­SURE TO EXCESSIVE MICROWAVE ENERGY
CHAPTER 1. WARNING TO SERVICE PERSONNEL

CHAPTER 2. MICROWAVE MEASUREMENT PRO­CEDURE

CHAPTER 3. FOREWORD AND WARNING

MODEL

CHAPTER 8. TEST PROCEDURES

CHAPTER 9. TOUCH CONTROL PANEL ASSEMBLY

CHAPTER 10. PRECAUTIONS FOR USING LEAD­FREE SOLDER

CHAPTER 11. COMPONENT REPLACEMENT AND
ADJUSTMENT PROCEDURE

R-305MR

CHAPTER 4. PRODUCT DESCRIPTION

CHAPTER 5. GENERAL INFORMATION

CHAPTER 6. OPERATION

CHAPTER 7. TROUBLESHOOTING GUIDE

CHAPTER 12. CIRCUIT DIAGRAMS

Parts List

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

CONTENTS

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

CHAPTER 1. WARNING TO SERVICE PERSON­NEL

[1] Before Servicing.......................................... 1-1

[2] When the testing is completed,................... 1-1

[3] After repairing.............................................. 1-1

CHAPTER 2. MICROWAVE MEASUREMENT
PROCEDURE

[1] Requirements:............................................. 2-1

[2] Preparation for testing:................................ 2-1

[3] Leakage test: .............................................. 2-1

CHAPTER 3. FOREWORD AND WARNING

[1] FOREWORD............................................... 3-1

[2] WARNING................................................... 3-1

[3] DANGER..................................................... 3-1

CHAPTER 4. PRODUCT DESCRIPTION

[1] SPECIFICATIONS ...................................... 4-1

CHAPTER 5. GENERAL INFORMATION

[1] GROUNDING INSTRUCTIONS.................. 5-1

[2] OVEN DIAGRAM ........................................ 5-1

CHAPTER 6. OPERATION

[1] DESCRIPTION OF OPERATING SE-

QUENCE .................................................... 6-1

[2] OVEN SCHENATIC .................................... 6-2

[3] DESCRIPTION AND FUNCTION OF

COMPONENTS .......................................... 6-3

CHAPTER 7. TROUBLESHOOTING GUIDE

[1] TROUBLESHOOTING CHART ................. 7-1

CHAPTER 8. TEST PROCEDURES

[1] A: MAGNETRON ASSEMBLY TEST .......... 8-1

[2] B: POWER TRANSFORMER TEST ........... 8-1

[3] C: HIGH VOLTAGE RECTIFIER TEST....... 8-1

[4] D: HIGH VOLTAGE CAPACITOR TEST..... 8-2

[5] E: TEMPERATURE FUSE OR THER-

MAL CUT-OUT TEST ................................. 8-2

[6] F: SECONDARY INTERLOCK SWITCH

TEST........................................................... 8-2

[7] F: PRIMARY INTERLOCK SYSTEM

TEST........................................................... 8-2

[8] G: MONITOR SWITCH TEST ..................... 8-3

[9] H: BLOWN MINITOR FUSE TEST ............. 8-3

[10] I: NOISE FILTER TEST .............................. 8-4

[11] J: TOUCH CONTROL PANEL ASSEM-

BLY TEST ................................................... 8-4

[12] K: KEY UNIT TEST ..................................... 8-5

[13] L: RELAY TEST .......................................... 8-6

[14] M: DEFROST TEST.................................... 8-6

[15] N: FOIL PATTERN ON THE PRINTED

WIRING BOARD TEST............................... 8-6

CHAPTER 9. TOUCH CONTROL PANEL ASSEM­BLY

[1] OUTLINE OF TOUCH CONTROL PAN-

EL ............................................................... 9-1

[2] SERVICING FOR TOUCH CONTROL

PANEL ........................................................ 9-2

CHAPTER 10. PRECAUTIONS FOR USING LEAD­FREE SOLDER

CHAPTER 11. COMPONENT REPLACEMENT
AND ADJUSTMENT PROCEDURE

[1] WARNINGS ...............................................11-1

[2] OUTER CASE REMOVAL .........................11-2

[3] POWER TRANSFORMER REMOVAL ......11-2

[4] HIGH VOLTAGE COMPONENTS RE-

MOVAL(HIGH VOLTAGE CAPACITOR
AND HIGH VOLTAGE RECTIFIER AS-

SEMBLY) ...................................................11-2

[5] MAGNETRON REMOVAL .........................11-2

[6] POSITIVE LOCK CONNECTOR (NO-

CASE TYPE) REMOVAL ...........................11-3

[7] CONTROL PANEL ASSEMBLY RE-

MOVAL.......................................................11-3

[8] GRAPHIC SHEET AND MEMBRANE

SWITCH REPLACEMENT .........................11-3

[9] TURNTABLE MOTOR REMOVAL .............11-4

[10] COOLING FAN MOTOR REMOVAL..........11-4

[11] POWER SUPPLY CORD REPLACE-

MENT.........................................................11-5

[12] DOOR SENSING SWITCH/SECOND-

ARY INTERLOCK SWITCH AND MONI-

TOR SWITCH REMOVAL..........................11-5

[13] DOOR SENSING SWITCH/SECOND-

ARY INTERLOCK SWITCH AND MONI-

TOR SWITCH ADJUSTMENT ...................11-6

[14] DOOR REPLACEMENT ............................11-6

CHAPTER 12. CIRCUIT DIAGRAMS

[1] Pictorial Diagram (Figure S-1) .................. 12-1

[2] Control Unit Circuit (Figure S-2)................ 12-2

[3] Printed Wiring Board of Power Unit (Fig-

ure S-3) ..................................................... 12-3

Parts List

R305MR

R305MR

PRECAUTIONS TO BE OBSERVED BEFORE AND DURING SERVICING TO AVOID

Service Manual

POSSIBLE EXPOSURE TO EXCESSIVE MICROWAVE ENERGY

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

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/cm . The owner of the unit should be instructed not to use the unit
until the oven has been brought into compliance.

2

i

R305MR

R305MR

CHAPTER 1. 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.

(Example)

High Voltage Capacitor, High Voltage Power Transformer, Magnetron, High Voltage Rectifier Assembly, High Voltage Harness etc..

Read the Service Manual carefully and follow all instructions.

Service Manual

Don't Touch !
Danger High Voltage

[1] 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 high-voltage capacitor
(that is the connecting lead of the high-voltage 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.

[2] 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.

[3] 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.

1 – 1

R305MR

R305MR

CHAPTER 2. MICROWAVE MEASUREMENT PROCEDURE

Service Manual

[1] Requirements:

1. Microwave leakage limit (Power density limit): The power density of microwave radiation emitted by a microwave oven should not exceed 1mW/

2

cm

at any point 5cm or more from the external surface of the oven, measured prior to acquisition by a purchaser, and thereafter (through the use-

ful life of the oven), 5 mW/cm

2. Safety interlock switches:

Primary interlock switch shall prevent microwave radiation emission in excess of the requirement as above mentioned. Secondary interlock relay
and door sensing switch shall prevent microwave radiation emission in excess of 5 mW/cm
the oven.

2

at any point 5cm or more from the external surface of the oven.

2

at any point 5cm or more from the external surface of

[2] 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±5 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.

[3] 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.

2

4. Measure carefully at the point of highest leakage and make sure that the highest leakage is no greater than 4mW/cm
interlock relay and the primary interlock switch do turn the oven OFF before any door movement.

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

, and that the secondary

2 – 1

R305MR

R305MR

CHAPTER 3. FOREWORD AND WARNING

Service Manual

[1] FOREWORD

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

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.

[2] WARNING

Never operate the oven until the following points are ensured.

(A) The door is tightly closed.

(B) The door brackets and hinges are not defective.

(C) The door packing is not damaged.

(D) The door is not deformed or warped.

(E) There is not any other visible damage with the oven.

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

[3] 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.

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.

3 – 1

R305MR

CHAPTER 4. PRODUCT DESCRIPTION

Service Manual

[1] SPECIFICATIONS

ITEM DESCRIPTION

Power Requirements

Power Consumption 1530W / Approx. 13 Amperes

Power Output

Case Dimensions

Cooking Cavity Dimensions
(1.0 Cubic feet)

Control Complement

Oven Cavity Light Yes

Safety Standard

120 Volts
60 Hertz
Single phase, 3 wire grounded

1100 W nominal of RF microwave energy (IEC Test procedure)
Operating frequency 2450 MHz

Width 20-1/2" (520mm)
Height 12-1/4" (310mm)
Depth 17" (431mm)

Width 14-3/4" (375mm) NOTE: Internal capacity is calculated by measuring maximum width, depth and height.
Height 8-1/8" (206mm) Actual capacity for holding food is less.
Depth 15-1/4" (387mm)

Touch Control System
Clock (1:00 - 12:59)
Timer (0 - 99 minutes 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. 30% of FULL Power
P-30 -------------------- approx. 40% 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
POPCORN pad
MINUTE PLUS pad
SHORT CUTS pads
REHEAT pad
COOK pad
DEFROST pad
Number selection pads
POWER LEVELK pad
TIMER / CLOCL pad
STOP/CLEAR pad
START pad

UL Listed.
FCC Authorized
DHHS Rules, CFR, Title 21, Chapter 1, Subchapter J

R305MR

4 – 1

R305MR

3-Pronged
Plug

Grounded
Receptacle Box

Grounding Pin

3-Pronged Receptacle

14

8

9

7

12

13

1

5

3

4

2

6

11 310

R305MR

CHAPTER 5. GENERAL INFORMATION

Service Manual

[1] 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:

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 wall­receptacle is encountered, it is the personal responsibility and obligation of the customer to 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 REMOVE THE ROUND

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

GROUNDING PRONG FROM THIS PLUG.

[2] OVEN DIAGRAM

1. OVEN

1. Door opening button

Push to open door.

2. Oven door with see-through win­dow

3. Safety door latches

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

4. Door hinges

5. Door seals and sealing surfaces

6. Turntable motor shaft

7. Removable turntable support

Carefully place the turntable sup­port in the center of the oven floor.

8. Removable turntable

Place the turntable securely on the turntable support securely. The turntable will rotate clockwise or counterclockwise. Only remove for cleaning.

9. Ventilation openings (Rear)

10.Oven light

It will light when oven is operating or when the door is open.

11.Waveguide cover: DO NOT REMOVE.

12.Auto-Touch control panel

13.Time display: 99 minutes, 99 seconds

14.Power supply cord

5 – 1

2. TOUCH CONTROL PANEL

R305MR

NOTE: Some one-touch cooking features such as “MINUTE PLUS” are disabled after three minutes when the oven is not in use. These fea-

tures are automatically enabled when the door is opened and closed or the STOP/ CLEAR pad is pressed.

5 – 2

R305MR

R305MR

CHAPTER 6. OPERATION

[1] DESCRIPTION OF OPERATING SEQUENCE

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

Service Manual

1. OFF CONDITION

Closing the door activates 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 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.

2. COOKING CONDITION

Program desired cooking time by touching the NUMBER pads. Pro­gram the power level by touching the POWER LEVEL 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 3.3 volts A.C. output on the fila­ment winding, and approximately 2360 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 feed-box, 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 relay and is mechani­cally associated with the door so that it will function in the following
sequence.

a) 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.

b) 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.

3. 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:

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 (0% power) 0 sec. 32 sec.

NOTE: The ON/OFF time ratio does not correspond with the per-

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

4. POWER OUTPUT REDUCTION

If the oven is set for more than 20 minutes at 80, 90 or 100% power
level, after the first 20 minutes the power level will automatically adjust
itself to 70% power to avoid overcooking.

6 – 1

[2] OVEN SCHENATIC

1. Off Condition

SCHEMATIC

NOTE: CONDITION OF OVEN

1. DOOR CLOSED

2. CLOCK APPEARS ON DISPLAY

R305MR

120V AC
60 Hz

GRN

NOISE FILTER

LN

FUSE
20A

0.22μF / AC 250V

LINE CROSS CAPACITOR

NOISE SUPPRESSION COIL

CAPACITOR

LINE BYPASS

0.0033μF / AC 125V

CAPACITOR

LINE BYPASS

0.0033μF / AC 125V

(MAGNETRON)

OR OR

(MAGNETRON)

OVEN LAMP
RELAY

(RY1)

OL

(OVEN)

CONTROL UNIT

OVEN
LAMP

SECONDARY
INTERLOCK
SWITCH

NOTE: " " indicates components with potentials above 250V.

TTM

TURN­TABLE
MOTOR

FM

FAN
MOTOR

Figure O-1. Oven Schematic-Off Condition

2. Cooking Condition

SCHEMATIC

NOTE: CONDITION OF OVEN

1. DOOR CLOSED.

2. COOKING TIME PROGRAMMED.

3. VARIABLE COOKING CONTROL “P-HI”.

4. START PAD TOUCHED.

B2

PRIMARY
INTERLOCK
RELAY

DOOR
SENSING
SWITCH

(RY2)

POWER
TRANSFORMER

CAPACITOR

0.19μF
AC 2100V

B1

MONITOR

SWITCH

MAGNETRON

RECTIFIER

120V AC
60 Hz

GRN

NOISE FILTER

LN

FUSE
20A

0.22μF / AC 250V

LINE CROSS CAPACITOR

NOISE SUPPRESSION COIL

CAPACITOR

LINE BYPASS

CAPACITOR

LINE BYPASS

0.0033μF / AC 125V

0.0033μF / AC 125V

(MAGNETRON)

OR OR

(MAGNETRON)

OVEN LAMP
RELAY

(RY1)

OL

(OVEN)

CONTROL UNIT

OVEN
LAMP

SECONDARY
INTERLOCK
SWITCH

TTM

TURN­TABLE
MOTOR

FM

FAN
MOTOR

B2

PRIMARY
INTERLOCK
RELAY

DOOR
SENSING
SWITCH

Figure O-2. Oven Schematic-Cooking Condition

6 – 2

(RY2)

POWER
TRANSFORMER

CAPACITOR

0.19μF
AC 2100V

B1

MONITOR

SWITCH

MAGNETRON

RECTIFIER

R305MR

[3] DESCRIPTION AND FUNCTION OF COMPONENTS

1. 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 latch head. The
latch heads are moved upward and released from latch hook. Now the
door will open.

Door

Latch
Heads

Switch Lever

Figure D-1. Door Open Mechanism.

Latch Hook

Door Sensing
Switch

Monitor Switch

Secondary
Interlock Switch

2. 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.

3. 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 contacts 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 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 and secondary
interlock switch contacts close.

3) If the door is opened, and the primary interlock relay (RY2) and the
secondary interlock switch contact 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), 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.

4. TURNTABLE MOTOR

The turntable motor rotates the turntable located on the bottom of the
oven cavity, so that the food on the turntable is cooked evenly. The
turntable may turn in either direction.

5. COOLING FAN MOTOR

The cooling fan motor drives a blade which draws external cool air.
This cool air is directed through the air vents 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.

6. MAGNETRON TEMPERATURE FUSE

The temperature fuse 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 temperature fuse
remains closed. However, when abnormally high temperatures are
reached within the magnetron, the temperature fuse will open at
302°F(150°C) causing the oven to shut down.

7. THERMAL CUT-OUT (OVEN)

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 cut­out 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
293°F(145°C), causing the oven to shut down.

8. MONITOR FUSE

1) The monitor fuse blows when the contacts (COM-NO) of the pri­mary interlock relay (RY2) and the 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 short-circuited,
this monitor fuse blows to prevent an electric shock or fire hazard.

9. NOISE FILER

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

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