Sharp MMD24B, MMD24S User Manual

SERVICE MANUAL

MICROWAVE DRAWER

MODELS

MMD24S
MMD24B

S38M289MMD24S

MMD24S

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

WARNING TO SERVICE PERSONNEL:

This service manual is intended for use by persons having electrical and mechanical training and a level of
knowledge of these subjects generally considered acceptable in the appliance repair trade. Sharp Electronics
Corporation cannot be responsible, nor assume any liability, for injury or damage of any kind arising from the
use of this manual.

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

MMD24B

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 .................................................................................................................3

MICROWAVE MEASUREMENT PROCEDURE .....................................................................................................4

FOREWORD AND WARNING ...............................................................................................................................5

PRODUCT SPECIFICATIONS ...............................................................................................................................6

SCHEMATICS ......................................................................................................................................................10

TEST PROCEDURES ..........................................................................................................................................11

TOUCH CONTROL PANEL ASSEMBLY ..............................................................................................................19

MICROWAVE DRAWER DISASSEMBLY .............................................................................................................27

WIRING DIAGRAMS ............................................................................................................................................33

PRINTED WIRING BOARDS ...............................................................................................................................34

PARTS LIST .........................................................................................................................................................38

PACKING AND ACCESSORIES ..........................................................................................................................43

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

1

MMD24S
MMD24B

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 compart-

ments, 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 DACOR immediately

1-800-793-0093.

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

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

Service personnel should inform DACOR of any certified unit found with emissions in excess of 4mW/

2

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

cm
compliance.

2

WARNING TO SERVICE PERSONNEL

Microwave Oven units contain circuitry capable of producing very high voltage and current,
contact with following parts

(Example)
High Voltage Capacitor, High Voltage Power Transformer, Magnetron, High Voltage Rectifier

Assembly, High Voltage Harness, Heating Elements, etc..
Read the Service Manual carefully and follow all instructions.

Before Servicing

1. Disconnect the power supply cord , and then
remove cabinet.

2. Open the drawer and keep it open.

3. Discharge high voltage capacitor.

WARNING: RISK OF ELECTRIC SHOCK.

DISCHARGE THE HIGH-VOLTAGE
CAPACITOR BEFORE SERVICING.

may result in a severe, possibly fatal, electrical shock.

MMD24S
MMD24B

When the testing is completed,

1. Disconnect the power supply cord, and then remove
covers.

2. Open the drawer and keep it open.

3. Discharge high voltage capacitor.

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

5. Reinstall the covers.

6. Reconnect the power supply cord.

7. Run the unit and check all functions.

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
neccessary covers.

2. Open the drawer and keep 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.

After repairing

1. Reconnect all leads removed from components during
testing.

2. Reinstall the covers.

3. Reconnect the power supply cord.

4. Run the oven and check all functions.

Microwave ovens should not be operated empty. To test for
the presence of microwave energy within a cavity, place a
cup of cold water on the oven tray, close the drawer 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 re-examine
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.

3

MMD24S
MMD24B

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 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/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.

Survey instruments that comply with the requirement for instrumentation as prescribed by CSA and NHW performance
standard for microwave ovens must be used for testing recommended instruments are , NARDA 8100 and NARDA

8200.

2) Place the load of 275±15 ml (9.8 oz) of tap water initially at 20±5

O

C (68OF) 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 non conductive 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.

3) Set the cooking control on Full Power Cooking Mode.

4) Close the drawer 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-drawer leakage test (microwave measurement):

1) Grasp the probe of the survey instrument and hold it perpendicular to the gap between the drawer 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 drawer 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 drawer, pull the drawer 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 primary interlock switch/secondary interlock relay does turn the oven OFF before any door
movement.

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

4

SERVICE MANUAL

MICROWAVE DRAWER

PRODUCT DESCRIPTION

MMD24S
MMD24B

MMD24S / MMD24B

FOREWORD

This Manual has been prepared to provide Dacor Service Personnel
with Operation and Service Information for the DACOR MICROWAVE
DRAWER.

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;
Inverter unit that includes High Voltage Capacitor, High Volt­age Power Transformer, High Voltage Rectifier, Heat sink, etc.,
and Magnetron, High Voltage Harness etc.;
If provided, Vent Hood, Fan assembly, Cooling Fan Motor.

SCHEMATICS

TEST PROCEDURE

TOUCH CONTROL PANEL

MICROWAVE DRAWER
DISSASSEMBLY 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 wrapper gives access to voltage above
250V.

All the parts marked “∆” on parts list may cause undue microwave
exposure, by themselves, or when they are damaged, loosened
or removed.

1440 Bridge Gate Dr.

Diamond Bar, CA 91765

5

MMD24S
MMD24B

MICROWAVE DRAWER SPECIFICATION

ITEM DESCRIPTION

Power Requirements Canada - 117 Volts / 13.0 Amperes / 1500 Kw / 60 Hz (CUL)
U.S.A. - 120 Volts / 13.6 Amperes / 1500 Kw / 60 Hz (UL)

Single phase, 3 wire grounded

Power Output 950 watts (IEC TEST PROCEDURE)
Operating frequency of 2450MHz

Cooking Cavity Dimensions Width 17-11/32
Height 5-7/8"

1.0 Cubic Feet Depth 17-1/8"
Outside Dimensions Width 23-13/16"

Height 15-5/8"
(Including drawer handle) Depth 26-3/8"

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 ..................................................................... appro

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

x. 90% of Full Power

START/EASY MINUTE pad, Defrost pad, Number selection pad, Micro-warm
pad, Power Level pad, Timer/Clock pad, Stop/Clear pad, Sensor Reheat,
Sensor Popcorn, Sensor Cook, Open pad, Close pad, Setup/Help, Control Lock
On/Off, Reheat.

Oven Cavity Light Yes
Safety Standard Canadian Standards Association
Health Canada, Industry Canada
UL Listed FCC Authorized
DHHS Rules, CFR, Title 21, Chapter 1, Subchapter J

6

MMD24S

3-Pronged
Plug

Grounded
Receptacle Box

Grounding Pin

3-Pronged Receptacle

GENERAL INFORMATION

MMD24B

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 (U.S.A.), 117 volt 60 Hz (Canadian) 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.

Where a two-pronged wall-receptacle 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 an extension cord must be used, it should be a 3-wire, 15 amp. or higher rated
cord. Do not drape over a counter top 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.

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.

7

MMD24S
MMD24B

OPERATION

DESCRIPTION OF OPERATING SEQUENCE

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

OFF CONDITION

Closing the drawer 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. (Page 10).

1. The display will show flashing "Enjoy Your Drawer Touch
Clear and Touch Clock".

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 Page 10)

the secondary interlock switch and secondary interlock
relay and is mechanically associated with the drawer so
that it will function in the following sequence.

8. When the drawer 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.

9. When the drawer 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 drawer
is opened, the closing of the monitor switch contacts will
form a short circuit through the fuse, secondary interlock
switch, relay (RY1) and secondary interlock relay (RY2),
causing the 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/stir fan 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
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 drawer 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 stir
fan 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

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.

8

SENSOR COOKING CONDITION

MICROWAVE

MICROWAVE

AH SENSOR

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

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

MMD24S
MMD24B

2. The coil of shut-off relay (RY-1) is energized, but the
power transformer is not turned on.

3. A

fter about 16 seconds, the cook relay (RY-2) is
energized. The power transformer is turned on,
microwave energy is produced and first stage is started.
The 16 seconds is the cooling time required to remove
any vapor from the oven cavity and sensor.

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

touch STOP/CLEAR pad.

4. When the sensor detects the vapor emitted from the
food, the display switches over to the remaining cooking
time and the timer counts down to zero.

At this time, the drawer may be opened to stir, turn or

season food.

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

6. Opening the drawer or touching the STOP/CLEAR
pad, the time of the day will reappear on the display
and the oven will revert to an OFF condition. When the
timer reaches zero, an audible signal sounds.

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

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

Cooking Sequence.

1. Touch one of the SENSOR pads.
NOTE: The oven should not be operated on sensor

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

9

MMD24S

3. Only certain models use the absol

ute humidity sensor.

2. Terminal that is located on the right side on lamp socket's back view

1. Circuits / Wire Colors subject to change without notice.

NOTES:

must be connected to neutral wire.

(DOOR CLOSED, COOK OFF CONDITTION)

4. Power Transformer (Finish Lead) terminal must be connected to Hot wire (RED)

MAGNETRON

N

L

RESISTOR 470 k

Ω

1/2W

LINE CROSS CAPACITOR 1.0 µF 275V

NOISE SUPRESSION COIL

0.0033 µF 250V

LINE BYPASS CAPACITOR

0.0033 µF 250V

LINE BYPASS CAPACITOR

FUSE
20A

CUT-OUT

THERMAL

THERMAL

OVEN

MAG

CUT-OUT

H

N

MICROWAVE DRAWER

GRN

NOISE FILTER

GND

GRY

WHT

ORG

RED

BLK

WHT

"TO SOURCE"

"TO LOAD"

"TO LOAD"

"TO SOURCE"

SWITCHING

SWITCH

DOOR

SENSING

SENSOR

FAN MOTOR

HUMDITY

F3

F2

F1

SM

FM

OL

A3

COM

N.O.

STIRRER MOTOR

OVEN LAMP

SECONDARY INTERLOCK SWITCH

RY3

RY1

RY2

CAPACITOR

xxx µF
AC 2300V

H.V. RECTIFIER

POWER TRANSFORMER

COM

PRIMARY INTERLOCK RELAY

N.O.

E1

E3

B1

TRANSFORMER

LOW VOLTAGE

A1

M4

POSITION

SWITCH

FRONT

M5

POSITION

DOOR

SWITCH

REAR

DOOR OPEN-CLOSE

MICROWAVE DRAWER

MOTOR

DM

DOOR

RY4

MONITOR SWITCH

N.C.

COM

N.O.

COM

A5

H9

RY5

A7

3

CN501

1

CN501

2

CN502

CN502

3

CN502

GRN

GRN

GRN

GRN*2

GRY

BLU

GRN

1

GRN

H11

N.O.

COM

THIRD DOOR

SWITCH

REGULATOR

CONTROL UNIT

ORG

RED

ORG

BRN

BLK

RED

RED or BLK

RED

RED or BLK

ORG

GRY

WHT

BLK *2

BRN

RED *2

BLK *2

RED *2

GRY

RED

BLK

GRY

WHT

WHT

GRY

BLK or YLW

BLU

WHT

GRY

WHT

WHT
WHT

ORG or YLW

BLK or YLW

BLK

RED

GRN

WHT

N4

N5

M3

M1

N3

RED

N1

N2

ORG

BLU

YLW

BLK

GRN

BLK

or

or

or

YLW

or

GRY

WHT

MMD24B

SCHEMATIC (OFF CONDITION)

10

MMD24S

TEST PROCEDURES

PROCEDURE
LETTER
A TOUCH CONTROL PANEL ASSEMBLY TEST

COMPONENT TEST

MMD24B

The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore,

unlike conventional microwave ovens, proper maintenance cannot be performed with only a voltmeter
and ohmmeter.
In this service manual, the touch control panel assembly is divided into three units, Control Unit,
Keyboard Unit and Power Unit, and troubleshooting by unit replacement is described according to the
symptoms indicated.

Before testing,

1) Disconnect the power supply cord, and then disassemble as per "MICROWAVE DRAWER
DISASSEMBLY" page 27.

2) Open the drawer and block it open.

3) Discharge high voltage capacitor.

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

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

1. Keyboard Unit.
NOTE ;

1) Check Keyboard unit connection before replacement.

2) Reconnect all leads removed from components during testing.

3) Re-install the covers.

4) Reconnect the power supply cord after the covers are installed.

5) Run the oven and check all functions.

The following symptoms indicate a defective keyboard unit.
a) When touching the pads, a certain pad produces no signal at all.
b) When touching a number pad, two figures or more are displayed.
c) When touching the pads, sometimes a pad produces no signal.

If the Keyboard unit is defective.

1) Disconnect the power supply cord, and then remove covers.

2) Open the drawer and block it open.

3) Discharge high voltage capacitor.

4) Replace the Keyboard unit.

5) Reconnect all leads removed from components during testing.

6) Re-install the covers.

7) Reconnect the power supply cord after the covers are installed.

8) Run the oven and check all functions.

2. Control Unit
The following symptoms indicate a defective control unit. Before replacing the control unit, perform

the Keyboard unit test (Procedure B) to determine if control unit is faulty.

2-1 In connection with indicators

a) At a certain digit, all or some segments do not light up.
b) At a certain digit, brightness is low.
c) Only one indicator does not light.
d) The corresponding segments of all digits do not light up; or they continue to light up.
e) Wrong figure appears.
f) A certain group of indicators do not light up.
g) The figure of all digits flicker.

2-2 Other possible problems caused by defective control unit.

a) Buzzer does not sound or continues to sound.
b) Clock does not operate properly.
c) Cooking is not possible.

3. Power Unit or Touch Control Transformer
a) Fan motor, stirrer motor, oven lamp or electrical parts do not turn on or do not turn off.
b) Digital display on the control unit does not show anything.

When testing is completed,

1) Disconnect the power supply cord, and then disassemble as per "MICROWAVE DRAWER

DISASSEMBLY" page 27.

2) Open the drawer and block it open.

3) Discharge high voltage capacitor.

11

MMD24S

STOP/
CLEAR

REHEAT

6

START/
EASY
MINUTE

1

2

7

SENSOR

COOK

SENSOR
REHEAT

DEFROST

9

8

3

4

OPEN

SENSOR

POPCORN

MICRO
WARM

TIMER

CLOCK

CLOSE

0

5

POWER
LEVEL

SET UP/

HELP

CONTROL

LOCK

ON/OFF

MMD24B

TEST PROCEDURES

PROCEDURE
LETTER

4) Reconnect all leads removed from components during testing.

5) Re-install the covers.

6) Reconnect the power supply cord after the covers are installed.

7) Run the oven and check all functions.

B KEY UNIT TEST

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

2. Open the drawer and block it open.

3. Discharge high voltage capacitor.

4. If the display fails to clear when the STOP/CLEAR pad is depressed,
first verify the flat ribbon cable is making good contact, verify that
the door sensing switch (stop switch) operates properly; that is the
contacts are closed when the drawer is closed and open when the
drawer is open. If the door sensing switch (stop switch) is good,
disconnect the flat ribbon cable that connects the key unit to the
control unit and make sure the drawer sensing switch is closed
(either close the drawer or short the door sensing switch connecter).
Use the Key unit matrix indicated on the control panel schematic
and place a jumper wire between the pins that correspond to the
STOP/CLEAR pad making momentary contact. If the control unit
responds by clearing with a beep the key unit is faulty and must be
replaced. If the control unit does not respond, it is faulty and must be
replaced. If a specific pad does not respond, the above method may
be used (after clearing the control unit) to determine if the control
unit or key pad is at fault.

5. Reconnect all leads removed from components during testing.

6. Re-install the outer case (cabinet).

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

8. Run the oven and check all functions.

COMPONENT TEST

C RELAY 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.

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

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

6. After that procedure, re-connect the power supply cord.

7. Remove the outer case and check voltage between Pin Nos. 5 and 7 of the 4 pin connector (CN-A)
The meter should indicate 120 volts, if not check oven circuit.

RY1, RY2, RY3 and RY4 Relay Test
These relays are operated by D.C. voltage
Check voltage at the relay coil with a D.C. voltmeter during the microwave cooking operation.

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

9. Open the door and block it open.

10. Discharge high voltage capacitor.

tape.

on the power unit with an A.C. voltmeter.

DC. voltage indicated Defective relay.
DC. voltage not indicated Check diode which is connected to the relay coil. If diode is good,

control unit is defective.

RELAY SYMBOL OPERATIONAL VOLTAGE CONNECTED COMPONENTS

RY1 Approx. 26V D.C. Oven lamp / Common
RY2 Approx. 25V D.C. Power transformer
RY3 Approx. 26V D.C. Stirrer motor
RY4 Approx. 26V D.C. Fan motor
RY5 Approx. 26V D.C. Switching regurator for drawer motor

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