Toshiba 14DL74, 20DL74 Schematic

FILE NO. 050-200414

SERVICE MANUAL

LCD TELEVISION

14DL74 / 20DL74

PUBLISHED IN TAIWAN, May 2004

Table of Contents

WARNINGS ...............................................................................................................................................................3

SERVICE SAFETY PRECAUTIONS .........................................................................................................................4

Examples of Marks................................................................................................................................................. 4

HANDLING THE LCD MODULE ................................................................................................................................5

Safety Precautions ................................................................................................................................................. 5

Precautions for Handling the LCD Module............................................................................................................. 5

LOCATION OF CONTROLS ......................................................................................................................................6

TV Front ................................................................................................................................................................. 6

TV Rear.................................................................................................................................................................. 6

Remote Control ..................................................................................................................................................... 7

LAYOUT OF MAJOR BOARDS ................................................................................................................................8

MECHANICAL DISASSEMBLY .................................................................................................................................9

PACKING DISASSEMBLY .......................................................................................................................................12

WIRING CONNECTION DIAGRAM .........................................................................................................................13

CIRCUIT BOARD DIAGRAMS .................................................................................................................................14

MAINBOARD ....................................................................................................................................................... 14

KEY/CONTROL BOARD...................................................................................................................................... 18

LIGHT-RECEIVING BOARD................................................................................................................................ 18

EARPHONE BOARD ........................................................................................................................................... 19

SCHEMATIC DIAGRAMS ........................................................................................................................................20

BLOCK DIAGRAM ............................................................................................................................................... 21

STANDARD MCU ................................................................................................................................................ 22

SCALER............................................................................................................................................................... 23

SCALER MEMORY.............................................................................................................................................. 24

VIDEO DECODER ............................................................................................................................................... 25

V-CHIP & CC ....................................................................................................................................................... 26

AUDIO PROCESSOR.......................................................................................................................................... 27

POWER AMPLIFIER............................................................................................................................................ 28

AV SWITCH ......................................................................................................................................................... 29

NTSC TUNER ...................................................................................................................................................... 30

USA MTS ............................................................................................................................................................. 31

PANEL CONNECTOR ......................................................................................................................................... 32

POWER SYSTEMS ............................................................................................................................................. 33

I/O CONNECTOR ................................................................................................................................................ 34

USA 480P ............................................................................................................................................................ 35

IR BOARD............................................................................................................................................................ 36

EARPHONE BOARD ........................................................................................................................................... 37

KEYPAD BOARD...................................................................................................................

.............................. 38

CHASSIS AND CABINET REPLACEMENT PARTS LIST ......................................................................................39

14DL74 ................................................................................................................................................................ 39

20DL74 ................................................................................................................................................................ 40

SPECIFICATIONS ....................................................................................................................................................41

14 / 20DL74 LCD TV Specifications ..................... ................................................... .............................................. 41

2

WARNINGS

Take care to heed the following warnings:

Always advise users to keep children away.

KEEP CHILDREN

AWAY

There is danger of injury to children from tools, disassembled products, etc.

Unplug

2

4

UNPLUG

H

SHOCK HAZARD

USE SPECIFIED

PARTS

CAUTION FOR

WIRING

Always disconnect the power plug before starting work whenever power is not
required.

Failure to disconnect the power plug before starting work can result in electrical
shock.

Depending on the model, use an insulation transformer or wear gloves when
servicing with the power on, and disconnect the power plug to avoid electrical
shock when replacing parts.

In some cases, alternating current is also impressed in the chassis, so electrical
shock is possible if the chassis is contacted with the power on.

Always use the replacement parts specified for the particular model when mak­ing repairs. The parts used in products have the necessary safety characteris­tics such as inflammability, voltage resistance, etc.; therefore, use only
replacement parts that have these same characteristics.

Use only the specified parts when the mark is included in a circuit diagram
or parts list.

Parts mounting and routing of the wiring should be the same as that used origi­nally.

For safety purposes, insulating materials such as tubing or tape is sometimes
used and printed circuit boards are sometimes mounted floating.

Also make sure that wiring is routed and clamped to avoid parts that generate
heat and which use high voltage. Always follow the original scheme.

CAUTION FOR

ASSEMBLY/WIRING

CHECK INSULA-

TION RESISTANCE

PROHIBIT REMOD-

ELLING

After a repair has been completed, reassemble all disassembled parts, and
route and reconnect the wiring, in accordance with the original scheme.

Do not allow internal wiring to be pinched by cabinets, panels, etc. Any error in
reassembly or wiring can result in electrical leakage, flame, etc., and may be
hazardous.

After completing the work, disconnect the power plug from the outlet, remove
the antenna, turn on the power switch. Then, use a 500V insulation resistance
meter to check the insulation resistance of the antenna terminal, other metallic
parts and between the prongs of the power plug to make sure that the insula­tion resistance is 1M Ω or more. The set will require inspection and repair if the
insulation resistance is below this value.

Never remodel the product in any way.
Remodelling can result in improper operation, malfunction, or electrical leakage

and flame,
which may be hazardous

3

SERVICE SAFETY PRECAUTIONS

The caution items shown here describe major safety issues and should always be observed.
The meanings of the various indications are as follows.

Indicates a hypothetical situation in which service personnel and nearby third parties,
or even end users due to a product defect after the service operation is completed,
could possibly be in danger of injury or even death in the event of operational error.

WARNING

Indicates a hypothetical situation in which service personnel and nearby third parties,
or even end users after the service operation is completed, could possibly be in dan­ger of injury, or where there could be physical damage in the event of operational

CAUTION

* Physical damage means major damage to a home, furnishings and other possessions.

Examples of Marks

H

SHOCK HAZARD

error.

The U indicates caution (including danger and warning).
The actual meaning of this caution is indicated inside the > or nearby illustra-

tions or text.
The example shown to the left indicates the danger of “electrical shock”.



PROHIBIT

DISASSEMBLY

Unplug

2

4

UNPLUG

The : indicates a forbidden action.
The actual meaning of this caution is indicated inside the or nearby illustrations

or text.
The example shown to the left indicates that disassembly is forbidden.

The c indicates a forced action (an action that must be performed).
The actual meaning of this forced action is indicated by c or nearby illustra-

tions or text.
The example shown to the left indicates that the power plug must be discon-

nected.

4

HANDLING THE LCD MODULE

Safety Precautions

In the event that the screen is damaged or the liq­uid crystal (fluid) leaks, do not breathe in or drink
this fluid. Also, never touch this fluid.

Such actions could cause toxicity or skin irritation.
If this fluid should enter the mouth, rinse the mouth
thoroughly with water. If the fluid should contact the
skin or clothing, wipe off with alcohol, etc., and
rinse thoroughly with water. If the fluid should enter
the eyes, immediately rinse the eyes thoroughly
with running water.

Precautions for Handling the LCD
Module

The LCD module can easily be damaged during
disassembly or reassembly; therefore, always
observe the following precautions when handling
the module.

1. When attaching the LCD
module to the LCD cover,
position it appropriately
and fasten at the position
where the display can be
viewed most conve­niently.

2. Carefully align the holes at all four corners of the LCD
module with the corresponding holes in the LCD cover
and fasten with screws. Do not strongly push on the
module because any impact can adversely affect the
performance. Also use caution when handling the

polarized screen because it can easily be damaged.

4. Leaving water or other fluids on
the panel screen for an extended
period of time can result in discol­oration or stripes. Immediately
remove any type of fluid from the
screen.

5. Glass is used in the panel, so do not
drop or strike with hard objects.
Such actions can damage the panel.

6. CMOS-LSI circuitry is used in the
LCD module, so avoid damage due
to static electricity. When handling
the module, use a wrist ground or
anchor ground.

7. Do not expose the LCD
module to direct sun­light or strong ultravio­let rays for an extended
period of time.

8. Do not store the LCD
module below the tem­perature conditions described in the specifications.
Failure to do so could result in freezing of the liquid
crystal due to cold air or loss of resilience or other
damage.

The metal edges of the LCD
module are sharp, so use cau­tion to avoid injury.

CAUTION

3. If the panel surface becomes
soiled, wipe with cotton or a
soft cloth. If this does not
remove the soiling, breathe
on the surface and then wipe
again. If the panel surface is
extremely soiled, use a CRT
cleaner as a cleaner. Wipe off the panel surface by
drop the cleaner on the cloth. Do not drop the cleaner
on the panel. Pay attention not to scratch the panel sur­face.

9. Do not disassemble the
LCD module. Such
actions could result in
improper operation.

10.When transporting the
LCD module, do not use
packing containing
epoxy resin (amine) or silicon resin (alcohol or oxim).
The gas generated by these materials can cause loss of
polarity.

5

LOCATION OF CONTROLS

TV Front

VOLUME –/+ Channel /

TV/VIDEO

Power button

Blue LED Indicator
(Power On)

Headphones Jack

TV Rear

AV 1

Audio (R)

Audio (L)

Video

S-Video

P

P

Power Jack

Red LED Indicator
(Stand by)

Audio Output (R)

Audio Output (L)

Audio (R)

Audio (L)

R

B

Y

Video

S-Video

ANT In

AV 2

6

Remote Control

The illustration shown displays the Remote Control Buttons.

POWER turns the TV on and off.
MUTE turns the sound on and off.
TV selects TV antenna as the input signal.
AV1/AV2 selects the AV input signal from one of these connectors.
Number Buttons allow direct access to channel positions.
VOL +/– Press + to raise the volume; press – to lower it.
CH S/T Press S to advance one channel number. Press T to go back

one channel number.

RECALL Press to go back to the last channel viewed.
MENU allows access to the menu display.
PICTURE Press to toggle between picture modes: USER, DYNAMIC,

MILD, and THEATER.

SOUND Press to toggle between sound modes: USER, THEATER,

NEWS, and HALL.

BRIGHT Press to toggle the brightness level between NORMAL,

BRIGHT, and DARK.

DISPLAY Press to toggle the display information on and off.
SKIP ON/OFF Press to delete a channel; the channel is skipped when

channel surfing. Press again to add the channel.

CLOSED CAPTION Press to enable closed captioning.
MTS Press to set the MTS mode.
SLEEP Press to set the sleep timer.

7

LAYOUT OF MAJOR BOARDS

Key/control board

Main board

Inverter board

Light receiving board

8

MECHANICAL DISASSEMBLY

B214

B215

A104

B211

A106

A108

B210

A102

B211

A107

9

B204

B209

B207

B208

B205

B214
B212
B203
B202

U004

B209

B210

A101
U003

W601

10

U902

B211

B206

U001

B201

E901

U002

A105

B208

11

PACKING DISASSEMBLY

K901

A702

Y150

Y151

Battery

Accessory Box

LCD TV Set

A703

Y101

A701

12

WIRING CONNECTION DIAGRAM

Key/control board

Inverter board

Main board

Light receiving board

Right speaker Left speaker

13

CIRCUIT BOARD DIAGRAMS

MAINBOARD

0171-4

14

15

0171-5

16

17