LG LHT754 Service Manual

LHT754

Home Theater

In A Box

Troubleshooting

Home Theatre Troubleshooting - 2007

Overview of Topics to be

Discussed

•Features

•Power Supply

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•Front Display

•Loader

•Amplifier Section

•Main Control

Safety Rules

Home Theatre Overview

Safety & Handling Regulations

1. Approximately 10 minute pre-run time is required before any adjustments are performed.

2. Do not exceed Higher voltage than is required for the product.

3. Be cautious of electric shock from the PBC modules since the modules use high voltage, and it is
recommended that you should not touch the drive circuits for at least one minute because of residual
current stored.

4. Circuit drive has c-mos circuits which should be protected from static electricity.

5. Be careful of short circuits when measuring voltages.

6. Be cautious of screws and other metal objects to prevent a short in the circuitry.

Troubleshooting

Checking Point before Replacing PCB Modules

1. Check the appearance of Power Supply and PCB's

2. Check the model label. Verify model names and board model matches.

3. Check details of defective condition and history.
IE: Software Updates, Service Bulletins

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Model : LHT754

1000 WATT HOME THEATER SYSTEM

1000W TOTAL POWER

Powerful sound with 1000 watts of total output power.

MADE FOR iPOD

Connect, control and play directly from your iPod.

1080i UP-CONVERSION

Superior image quality and convenience with 1080i up conversion via
HDMI™ output.

USB MEDIA PLUS

Experience your digital music, photo and video library with USB Media Plus.

XM READY*

Enjoy hundreds of channels of XM Satellite Radio (subscription required)
with an optional XM Mini-Tuner Antenna.

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LG SIMPLELINK

Allows for convenient control of other LG SimpLink products using the
existing HDMI™ connection.

MSRP : $329.95

FEATURES

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DVD Specifications

The DVD specification supports the MPEG video information on a DVD disc in one of the two formats
required for incompatible television systems: the 525/60 NTSC or 6 25/50 PAL/SECAM video standard.
The program material recorded on a DVD disc can belong to only one of the two video standard s ,
not both. This restriction applies to only one side of the DVD. If a DVD disc is double-sided, the video
on one side can be recorded in 525/60 NTSC format, and the video on the other side can be 625/50 PAL.
This is because the contents on one side are unrelated to the contents on the opposite side. However,
such a disc is rare in production. In general, there are two types of DVD-Video discs commonly known
as NTSC DVDs and PAL DVDs.

There are three major differences between DVD discs designed for playback on different television
systems:

1: Picture Dimensions and pixel aspect ratio

(720x480 NTSC, 720x576 PAL),

2: Display frame rate (29.97 frames/sec NTSC, 25 frames/sec PAL),

3: The default audio options (Dolby Digital with NTSC video, MPEG audio with PAL video).
All PAL DVD players can play Dolby Digital audio tracks, but not all NTSC players can
play MPEG audio tracks. Even though PAL video format has a lower display frame rate,
because of its higher picture resolution, the video contents almost always takes more
storage space than what would require for the equivalent the NTSC version.

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Dolby Digital Audio

Dolby Digital soundtracks are very popular with many commercial DVD-Video releases. However, the
DVD specification does not require that the soundtrack have to be Dolby Digital. There are other formats
such as MPEG audio, PCM audio, and DTS. Dolby Digital, DTS, and MPEG audio record audio samples
in compressed format while PCM audio samples are uncompressed.

The full name of Dolby Digital or AC-3 is Dolby Di gital 5.1. The name describes the sound distribution
on six channels in space. All the six channels are compressed into one stereo file, which is unpacked
with a special decoder and divided into six audio columns. According to the AC-3 format the sound is
heard from five wide-band columns: left, right, rear left, rear right, central and from one narrow band,
which is used for low frequency effects (LFE) only. This LFE effect is better felt than heard in the movie
theatres. The number 5.1 indicates five general channels and one LFE channel. Dolby Digital is a great
step forward comparing to Dolby Surround, concerning perception of the spatial sound. The following
illustration shows an ideal setting to enjoy
Dolby Digital soundtracks.

The Dolby Digital format supports soundtracks
in a variety of formats such as mono, dual
mono, stereo, Dolby Surround stereo, Dolby
Surround 5.1 (also commonly known as AC-3).
DVDs with DTS audio soundtracks are required
to include a Dolby Digital audio track. Each DVD
disc can have up to 8 different soundtracks.
Commercial NTSC DVD-Video usually contains
the first soundtrack in Dolby Surround 5.1
and the secondary soundtrack in Dolby Digital Stereo.

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Some DVD packaging has small letters or icons under the Dolby Digital logo that indicates the channel configuration.
In many cases, there are often more than one Dolby Digital version of a soundtrack: a 5.1-channel track, and a track

remixed for stereo Dolby Surround. Your DVD player may indicate the playback of a Dolby Digital audio track while
your receiver indicates Dolby Surround. This simply means that the DVD disc contains a two-channel Dolby Surround
signal encoded in Dolby Digital format.

Each DVD disc contains many segments of video and audio contents organized as
chapters in separate video titles. The author of the disc may add optional
navigation commands to skip certain chapters or titles on the DVD. The author

can prohibit access to certain program material on the disc so that one or more
segments of the disc cannot be
seen or played back without
some means of human

intervention. In this case,

it is difficult oreven not possible

to access these hidden contents

from a stand-alone DVD player.

However, most DVD backup software
can display the entire contents of the
DVD so the user can select which
chapter or title to back up. The
hidden portions of the disc by
restricting access with DVD
navigation commands can then
be displayed on the computer
and backed up accordingly. The
navigation commands which skip
the display of these hidden contents
can be removed or modified so that
a standard DVD player may gain
access to these portions via the
menu or the remote control buttons.

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DIVX
DivX® is a technol ogy to compress and playback video files. DivXNetworks creates and distributes
this technology which is often referred to as the "MP3 of video". In a nutshell, DivX® has revolutionized
the creation, playback and distribution of high-quality digital video.

DivX® has become the most popular MPEG-4 compatible video compression technology on the
market due to its very high compression ratio which enables DVD-quality video and audio at typically
7-10 times smaller storage requirements than standard DVD/Mpeg2 compression technology.
A commercial DVD title which takes 4.7 gigabytes of storage can be converted to DivX® format with
no noticeable loss of video and audio quality within less than 700 megabytes of storage which can be
archived on cheap CD media. DivX® tech nology allows broadband users to encode and distribute
DVD-quality video at 500-700 Kbps. According to Viant Research, there are over half a million DivX®
video files traded daily on the Internet.

On the down side, DivX® movies are not compatible with DVD technology in the sense that all interactions
that require DVD commands are lost after the conversion. DVD menu presentation, title and chapter
selection, angle selection, etc. are not available with DivX® technology.

The following are some highlights of the DivX® video technology:
Video file format: Most common form as a Windows .avi file
Video Resolution: Variable, 640x480 is the most common or default PAL/NTSC resolution
Bit rate: Varies depending on the video resolution and the audio bit rate. 650 MB typically stores 80-90
minutes at 640x480

Video Quality: Varies depending upon compression parameters. Most common quality is

SVHS/DVD at 10-15% the storage requirements by DVD technology.

Audio Quality: Most common is CD Quality or better at 48 kHz or 96 kBits,

2-channel stereo.

Encoding time: 18-20 frames per second on a P3-1GHz.

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WMA
The Advanced Systems Format (ASF) is the file format used by Windows Media. Audio and/or Video content
compressed with a wide variety of codecs can be stored in an ASF file and played back with the Windows Media
Player (provided the appropriate codecs are installed), streamed with Windows Media Services or optionally
packaged with Windows Media Rights Manager.

ASF is an extensible file format designed to store synchronized multimedia data. It supports data delivery over
a wide variety of networks and protocols while still proving suitable for local playback. ASF supports advanced
multimedia capabilities including extensible media types, component download, scaleable media

(((XM))) READY
Of course, XM Connect & Play compatibility is only one of many reasons to choose a new LG receiver for your home

theater. The new XM-R ead y re cei vers incorporate LG's Digital TOP-ART circuit design concept for crystal-clear sonic

reproduction; a full complement of built-in surround decoders, augmented by LG's proprietary THS processing for

incredible cinematic realism; high-bandwidth component video pass-through for compatibility with 1080i and 720p
video sources; and a host of other advanced and proprietary technologies that make LG the perennial choice of true
home theater enthusiasts. When you think about it, it's a perfect fit: XM's superior, CD-quality broadcast fidelity and
mind-expanding variety is a great match for a high-end home entertainment system with one of these state-of-the-art
receivers at its center.

MADE FOR IPOD
The LHT754 iPOD Dock lets you connect your iPod to this receiver. You can listen to your iPod music and watch iPod

images and movies on your monitor via the receiver. You can also operate your iPod via the receiver’s remote unit with

the On-Screen Display and charge your iPod. Works with iPod nano, iPod mini and iPod .

PLAYS WINDOWS MEDIA
Consumer Electronic Devices (Including but not limited to: digital audio players, car stereos, home stereos, and
consumer Internet appliances)
All consumer electronic devices must meet the criteria below to qualify for the Logo:

Product utilizes a Microsoft Windows Media codec (i.e., Windows Media Audio, Windows Media Video) pursuant to a
Microsoft OEM License Agreement for Embedded Windows Media (or subsequent Windows Media license agreement
from Microsoft).

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PLAYS WINDOWS MEDIA (continued)

Criteria specific to CD Players

CD Players must support playback of .WMA files at bit rates between 64k and 160k inclusive.
CD Players must ignore any files that they cannot play, they should be skipped.
CD Players must support CD-ROM, CD-R and CD-RW.
CD Players must support at least ISO 9660 level 2 file names (31 character names including separator).
CD Players must locate files in subdirectories nested up to eight levels deep.
CD Players must be capable of handling CDs with at least 200 media files with maximum length file names stored in 16

or more subdirectories.
CD Players must display at least the first 32 characters of WMA metatags including at a minimum Title and Artist.
CD Players should not require that discs be closed (finalized)
CD Players should play multi-session discs. Players should support at least five sessions on a disc.
CD Players should support discs containing 400 or more media files.
CD Players should support playback of Variable Bit Rate (VBR) .WMA files with a peak bit rate up to 160Kbps and support

at least a 1.5 second buffer.

CD Players may support Joliet extensions (64 character Unicode file names).

Criteria specific to DVD Players

In addition to supporting all of the requirements for CD players listed above, DVD players
that are capable of playing .WMA files on DVD media have the following requirements:
DVD Players must support discs containing at least 2000 media files with maximum length file names.
DVD Players must support discs that have not been closed (finalized).
DVD Players must support multi session discs.
DVD Players should support discs containing 4000 or more media files.
DVD Players should support playback of Variable Bit Rate (VBR) .WMA files with a peak bit rate up to 160Kbps and

support at least a 1.5 second buffer.

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JPEG
One of the hottest topics in image compression technology today is JPEG. The acronym JPEG stands for the
Joint Photographic Experts Group, a standards committee that had its origins within the International Standard
Organization (ISO). In 1982, the ISO formed the Photographic Experts Group (PEG) to research methods of
transmitting video, still images, and text over ISDN (Integrated Services Digital Network) lines. PEG's goal was
to produce a set of industry standards for the transmission of graphics and image data over digital communications
networks.

In 1986, a subgroup of the CCITT began to research methods of compressing color and gray-scale data for facsimile
transmission. The compression methods needed for color facsimile systems were very similar to those being
researched by PEG. It was therefore agreed that the two groups should combine their resources and work together
toward a single standard

GIF, for example, can store only images with a maximum pixel depth of eight bits, for a maximum of 256 colors. And its
LZW compression algorithm does not work very well on typical scanned image data. The low-level noise commonly
found in such data defeats LZW's ability to recognize repeated patterns. Both TIFF and BMP are capable of storing
24-bit data, but in their pre-JPEG versions are capable of using only encoding schemes (LZW and RLE, respectively)
that do not compress this type of image data very well. JPEG provides a compression method that is capable of
compressing continuous-tone image data with a pixel depth of 6 to 24 bits with reasonable speed and efficiency.
And although JPEG itself does not define a standard image file format, several have been invented or modified to
fill the needs of JPEG data storage.

Glossary
.asf - A file name extension for a file in Advanced Systems Format (ASF).
.asx - The file name extension of a metafile that references audio files, audio playlist files, video files, or video playlist files.
.avi - The file name extension for a video file in Audio Video Interleaved (AVI) format.
.midi - The file name extension of a Musical Instrument Digital Interface (MI DI) file.
.mp3 - The file name extension of an audio file in MPEG format.
.mpeg - The file name extension of a video and audio or audio-only file in MPEG format.
.smi - The file name extension of a digital media companion file containing captions in Synchronized Accessible Media Interchange (SAMI) format.
.wav - The file name ex tension for a sound file in WAV format.
.wma - The file name extension of an audio file in Windows Media Format.
.wmv - The file name extension of a video file in Windows Media Format.
.wmz - The file name extension of a compressed Windows Media Player skin or border file.

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SYSTEM INFORMATION MENU

System Information menu can be accessed by performing
the following remote key sequence
SETUP > TV Aspect > 16:9 > 1,3,9,7,1,3,9,ENTER

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DIVX Registration

http://www.vod.divx.com

DivX VOD is a digital video delivery service that lets you rent or purchase DivX movies from any of our licensed VOD
partners. These movies are encoded in the DivX format to offer you superior quality video and the fastest download
times.
In fact, DivX VOD is so fast you can even start watching the movie as it’s downloading! In addition, you can
transfer your DivX movies from your computer to your TV, your portable media player, your mobile phone or almost any
place else you can imagine

* all you need is a DivX
certified device, a computer
and a love for movies!

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Unit Layout

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Power Supply

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Power Supply

CN902
1~4 : 35V
5~9 : GND
10 : 3.5V
11 : P-CTRL
12 : +12V
13 : P-SENSE
14 : WIRELESS

CN901
1 : VKK
2 : FL+
3 : FL­4 : GND
5 : +12V
6 : -12V
7~8 : 3.5V
9~11 : GND
12 : 5.6V .XM
13 : 5VDC
14 : MOTOR 5V
15 : GND

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Power Supply

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Block Diagram

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Vacuum Tube

Fluorescent

display

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A vacuum fluorescent display (VFD) is a type of display used commonly on consumer-electronics
equipment such as video cassette recorders

liquid crystal displays

, a VFD emits a very bright light with clear contrast and can easily support
display elements of various colors. The technology is related to both the cathode ray tube
the nixie tube
The device consists of a hot cathode

.

(filaments), anodes (phosphor) and grids encased in a glass

, car radios, and microwave ovens. Unlike

and

envelope under a high vacuum condition. The cathode is made up of fine tungsten wires, coated
by alkaline
electrons are controlled and diffused
impinge on the phosphor-coated plates, they fluoresce

earth metal oxides, which emit electrons when heated by an electric current. These

by the grids, which are made up of thin metal. If electrons

, emitting light.

The principle of operation is identical to that of a vacuum tube triode

. Electrons can only reach
(and "illuminate") a given plate element if both the grid and the plate are at a positive potential
with respect to the cathode. This allows the displays to be organized as multiplexed displays

where the multiple grids and plates form a matrix, minimizing the number of signal pins required.

In the example of the VCR display shown to the right, the grids are arranged so that only one

digit is illuminated at a time. All of the similar plates in all of the digits (for example, all of the
lower-left plates in all of the digits) are connected in parallel. One by one, the microprocessor
driving the display enables a digit by placing a positive voltag e on that digit's grid and then
placing a positive voltage on the appropriate plates. Electrons flow through that digit's grid and
strike those plates that are at a positive potential. The microprocessor cycles through illuminating
the digits in this way at a rate high enough to create the illusion of all digits glowing at once.
The extra indicators (in our example, "VCR

", "Hi-Fi", "STEREO", "SAP", etc.) are arranged as if
they were segments of an additional digit or two or extra segments of existing digits and are
scanned using the same multiplexed strategy as the real digits. Some of these extra indicators
may use a phosphor that produces a different color of light, for example, orange.
The light produced by most VFDs contains many colors and can often be filtered to produce
a more-pure (saturated) color such as a deep green or deep blue, depending on the whims
of the product's designers.

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DIS301
FL DISPLAY

IC301

PT6315

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The picture below is the VFD used in the LHT754 Home Theatre System.
This is a 14 segment Alpha-Numeric display device

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LOADER

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Sled Motor

Laser Assy

Spindle Motor

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Tray Motor

AMPLIFIER

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AM / FM Tuner

Digital
Optical

Surround Sound Audio

Speaker Outputs

MICOM

EEPROM

7VDC Output Jack

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DSP IC

MOS Audio Amplifier

Heat Sink

Main Control

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Component/Composite
Outputs

Servo Control IC

MPEG Decoder

USB
Interface
Control IC

XM
Satellite
Antenna
input

iPOD
Link

HDMI
Output

HDMI
Transmitter

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Flash Rom

Ram Memory

The END!

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