THOMSON Proscan LaserDisc PSLD40 Installation guide

PRoScAN RCA
LASER si?
Technical Training
Manual
THOMSON CONSUMER ELECTRONICS INC. /TECHNICAL TRAINING
P.O. BOX 1976 INDIANAPOLIS IN 46206
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/D
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FOREWORD
e
'4 8.we
This technical training manual addresses the operation and troubleshooting of the
ProScan model PSLD40 and RCA model LDR300. The principles of operation and
troubleshooting techniques presented in this manual can be applied to all laser disc
players.
NOTE: This manual is intended to be used as a servicing aid and is not intended to
replace the service data. Servica data for these instruments contain specific informa-
tion on parts, safety, and alignment procedures. Service data should be consulted
before performing any service.
Safety Information Caution
Safety information is contained in the appropriate RCA or ProScan Service Data.
All product safety requirements and testing must be completed prior to returning the
instrument to the consumer. Servicers who defeat safety features or fail to perform
safety checks may be liable for any resulting damages, and may expose themselves
and others to possible injury.
CAUTION; The laser diode emits invisible infrared radiation, which is dangerous to
the eyes. When servicing the laser disc player do not look directly into the laser lens.
NOTE: All integrated circuits and many other semiconductors are electrostatically
sensitive and require special handling techniques.
Prepared by
Thomson Consumer Electronics, Inc.
Technical Training
600 N. Sherman Drive
Indianapolis. Indiana 46201
First Edition 9043 - First Printing
Copyright 1990 by Thomson Consumer Electronics, Inc.
Trademark(s) Registered Marca(s) Registrada(s)
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CONTENTS
Introduction 5
Features 5
Laser Disc Overview 6
Video Disc 7
Digital Audio 11
The Laser Disc Player 13
Overview LDR300 17
Mechanism 17
System Control 18
Servo 18
Signal Processing 21
Overview PSLD40 23
Mechanism 23
System Control 25
Servo 26
Signal circuits 27
Service Procedures 28
System Control 29
LDR300 29
PSLD40 30
Servo Section 34
Focus Servo 34
Height Servo 38
Tracking Servo 39
Slider Servo 41
Tilt Servo 43
Time Base Correction Servo 46
Signal Processing Section 50
Video Section 50
Digital Audio 52
Analog Audio 54
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Appendixes
Appendix A
Test Mode 56
Appendix B
Laser Power Confirmation 59
Appendix C
Laser Lens Cleaning 60
Appendix D
IC201 (Digital Audio Decoder) 61
Appendix E
ICI 1 (Mode Control Microprocessor) 63
Appendix F
IC801 (Mechanical Control Microprocessor) 64
Appendix G
IC601 (Servo Controller) 66
Appendix H
IC901 (Time Base Correction Servo) 67
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INTRODUCTION
The ProScan PSLD40 and the RCA LDR300 can be
grouped into a new category of laser disc player. This
category is called multi players, these players have the
ability of playing all available laser disc formats. The
advantage of a multi player is the elimination of separate
components to play video discs and compact audio
discs. This advantage alone saves space and greatly sim-
plifies connecting the laser disc player to the audio video
system.
Both the RCA and ProScan disc players implement new
features not previously found in laser disc players. One
of these features is a one bit digital to analog converter.
The new design generates less noise in the conversion
process when compared to multi-bit converters.
The PSLD40 has an additional feature of dual side play-
back. This enables the PLSD40 to play both sides of a
laser disc without having to remove the disc from the
player. This allows remote control selection of informa-
tion from either side of a laser disc.
Features
Some additional features of the PSLD40 and the
LDR300 are.
On-Screen Programming
Displays the operating status of the player on the televi-
sion screen, and on the front of the unit. Plus, video
prompts are used to assist the operator in programming
the players features.
Direct Access Play
Instantly accesses any point on a disc for playback. The
player searches for that point and resumes normal play-
back from that point forward.
Memory Repeat
On the operator's command, memorizes a location on a
disc. The player will then search for that point and
resume playback.
Still Frame
On CLV (Constant Linear Velocity) formatted discs the
laser disc player can still pause on one frame of video.
Because there is no physical contact between the pickup
of the player and the disc, this pause can be held
indefinitely.
Intro Scan
Plays the first 8 seconds of each chapter or track on a
disc. This gives a preview of all the material recorded on
the disc.
Random Playback
Plays chapters or tracks of a disc in a random order.
This allows familiar disc to be played back in a unfamil-
iar order.
Auto Program Editing
Automatically calculates the length of songs, or tracks
on a disc that will fit in order, on each side of a tape.
Stores the time into memory and uses this information
to place the laser disc player in pause mode, when one
side of the tape is full. This greatly simplifies dubbing
from laser disc to tape.
Compu Program Editing
Determines the length of the songs, or tracks on a disc.
Then resequences the songs or tracks to fit the maximum
amount of material on each side of a tape. The laser disc
player then plays them back in that order for recording
onto a tape. In this mode the laser disc player will auto-
matically go into pause mode when one side of the tape
is full.
Videoline"' Remote Compatibility
Permits RCA stereo monitor-receivers with Vid e olinkTM
remote control to command the laser disc player.
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LASER DISC OVERVIEW
In the reproduction of video and audio signals, the laser
disc format has definite advantages over the tape and LP
records. In video reproduction the laser disc can
reproduce up to 425 lines of horizontal resolution, out
performing broadcast, cable, and video tape formats.
Audio reproduction with the laser disc player provides
the clearest, and cleanest audio available for home use.
In the laser disc system a laser beam is focused on the
surface of a rotating disc. The disc has a series of bumps
(commonly called pits) etched spirally from the inside
edge to the outside edge of its surface. Information is
stored on the disc by varying the length of these pits. To
detect this information the laser disc player monitors the
level of light that is reflected from the discs surface back
into the optics of the laser disc player. For example, if
the laser beam strikes a flat surface on the disc, all of the
beam is reflected back into the optics of the player. In
comparison, if the beam strikes a bump (or pit) on the
disc surface some of the light is reflected away from the
optics reducing the amount of laser light entering the
1/4
WAVELENGTH
LASER
optics. The laser light that is not reflected away from the
optics is canceled by the laser light being transmitted by
the laser assembly. This cancellation is caused by the
height of the bump above the disc surface. This height is
1/4 wavelength, when the laser beam strikes the bump
it's phase is shifted by 180 degrees (See Fig 3). When the
phase shifted reflected signal strikes the transmitted
laser light the two signals cancel out, further reducing
the amount of laser light being reflected back into the
optics of the laser disc player.
The light that is reflected back into the optics of the
player varies in amplitude as the beam strikes the differ-
ent surfaces of the disc. This varying light is separated
from the transmitted light by the optics of the laser
assembly. Once separated the reflected light is applied to
a sensor that converts the varying levels into a electrical
signal. This electrical signal is called the RF signal. The
frequency of the RF signal is related to the length of the
pits (See Fig 4). The RF signal is then passed into the
signal processing stages where it is demodulated.
BEAM STRIKING PIT
Fig. 3 - Pit Detection
ttt
BEAM STRIKING
FLAT SURFACE
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Fig. 4 - RF Signal
The processing and demodulation of the RF signal
depends on the type of information recorded on the disc.
For example, to process an RF signal that carries video
information, the signal must be FM demodulated. A RF
signal that contains a digital audio signal must go
through processing to convert it back to a analog signal.
Video Disc
In the video disc format, the video information and the
analog audio information are independently FM modu-
lated and recorded on the disc. A digital audio signal
can also be added to some discs. This digital audio sig-
nal is optional, and is not included on all discs. When
included on a disc it is multiplexed with the FM modu-
lated signals for recording on the disc.
' quip ,
The frequency spectrum for the different signals rec-
orded on a video disc is shown in fig 5. The video infor-
mation is FM modulated with a center frequency of 8.5
MHz and a deviation of + /- 1.7 MHz. Unlike VCR for-
mat the video disc format does not separate the chroma
information from luminance information for recording.
This reduces the processing involved to play the signal
back and provides a clearer picture. The two analog
audio channels are FM modulated at 2.3 MHz for chan-
nel 1 and 2.8 MHz for channel 2. Both the analog audio
channels have a deviation of +/- 100 KHZ. The digital
audio information occupies the 0 to 2 MHz region of the
spectrum.
A block diagram of the laser disc record process is
shown in fig 6. The video and analog audio information
are independently FM modulated. Once modulated the
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DIGITAL
AUDIO
O
-10
-20
-30
2.3Mhz
CH1
ANALOG
AUDIO
2.8Mhz
CH2
ANALOG
AUDIO
8.1Mhz
9.3M 1 hz
7.6Mhz
FIJ
Ti I É
0 2 3 4 5 6 7 8 9 10 11 12 13 14
VIDEO
SIGNAL
VIDEO
MODULATOR
Fig. 5 - Frequency Spectrum of LD Player
L AUDIO J L CHANNEL I
MODULATOR
R AUDIO J R CHANNEL 1
MODULATOR
DIGITAL
RIGHT
CHANNEL
DIGITAL
LEFT
CHANNEL
DIGITAL
AUDIO
PROCESSING
MIXER 1
VIDEO
ANALOG AUDIO
MIXER 2
ANALOG
AUDIO. VIDEO)
DIGITAL
Fig. 6 - LD Record Process
UMITER
GLASS
DISC
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three FM signals (video, CH1 audio, CH2 audio) are
applied to mixer 1 where they are combined. The output
of mixer 1 is then applied to mixer 2. Mixer 2 is only
used on laser discs that include digital audio. The pur-
pose of mixer 2 is to combine the FM modulated analog
signals with digital audio. Before this occurs the digital
audio signal must be produced by converting an analog
audio signal to a digital signal. The process for doing
this is the same procedure used in the manufacturing of
compact discs and will be covered in the digital audio
section of this manual.
The output of mixer 2 is a composite signal that includes
the FM signals with digital audio. This composite signal
then is amplitude limited and applied to an optical mod-
ulator. The optical modulator takes the limited compos-
ite signal and uses it to control the on/off operation of a
laser.
This laser cuts the pits (or bumps) on a multi layer glass
disc. This glass disc is treated to have a layer of photo
resist on the surface of it. The laser beam strikes this
layer exposing it. The glass disc is rotated by a spindle
motor, while the laser is pulled from the center of the
disc to the outside edge. This creates a long track of
exposed portions of photo resist running from the center
to the outside edge of the disc. When exposing is com-
pleted the photoresist layer is developed to reveal the
pits caused by the laser exposure. The disc then has a
SPEED
1800 RPM
VERTICAL BLANKING
INTERVAL
VER11CAL BLANKING
INTERVAL
CAV
DISC
ROTATION
layer of nickel deposited on it to make the master disc.
The master disc is the mold from which the reproduced
disc are made.
In the exposing of the master disc, it is very important
that the manufacturing environment is free of dust. The
reason for this is due to the size of the information rec-
orded on the disc. With the average bump diameter of .4
micro meters and the spacing between the tracks of 1.67
micro meters, a speck of dust can cover large areas of
information. If a large number of dust particles are pres-
ent in the mastering process the disc could even be ren-
dered unplayable.
The speed in which the disc is rotated, and the rate the
laser is pulled across the disc surface, is determined by
the format of the disc. Video laser disc come in three for-
mats; CAV (Constant Angular Velocity), CLV (Con-
stant Linear Velocity), and CAA (Constant Angular
Acceleration). These three formats can be recorded on
either a 8" disc or a 12" disc.
In the CAV format the disc is rotated at a constant 1800
RPM. The video information is laid out so each rotation
of the disc consists of one frame, or two fields. In this
format the horizontal blanking and sync pulses are
aligned into two narrow strips radially across the disc
(See Fig 7).
INNER TRACK 1 FRAME OF VIDEO
OUTER TRACK 3 FRAMES OF VIDEO
LEAD INN
TRACKS
VERTICAL BLANKING _1 H
INTERVAL
Fig. 7 - LD Format
CLV
DISC
ROTATION
SPEED
INNER TRACK 1800 RPM
OUTER TRACK 600 RPM
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EQUALIZING
PULSES
HORIZONTAL
UNE 1
NUMBER
HORIZONTAL
UNE
NUMBER
VEFMCAL
SYNC
EQUALIZING
PULSES
MCA
CODE
r A-
PHILIPS
1 3 1 4 1 5 1 8
EQUAUZING
PULSES
VERTICAL
SYNC
CODE
i ll if \
1 7 1 8 1 9 110 111112 113 114 115 118 117
FIRST VERTICAL FIELD
EQUALIZING
PULSES
MCA
CODE
r A- \
18 r 19 1 20 1 21 1 22 1
PHIUPS
CODE
IIL I\ \1\
1 2841 285 12881 287 1 288 1 289 1 270
271 127212731274127512781277127812791280
2ND VERTICAL FIELD
Fig. 8 - Philips Code Location
In the CAV format each frame is assigned a number
from 1 to 54000, plus separate numbers called chapter
numbers can also be encoded on the disc. These num-
bers can be used to find a location on the disc, or to find
the start of a segment of video. In the CAV format the
maximum playing time is 30 minutes per side.
In the CLV format a constant velocity is maintained
between the data on the disc and the pickup assembly.
To keep the velocity constant the rotation speed of the
disc must decrease as the pickup moves outward. This
allows more information to be stored in the outer tracks
of the disc than can be stored in the inner tracks. In the
CLV format the center of the disc produces one frame of
video per revolution and has a rotation speed of 1800
RPM. The outside edge of the disc will have three
frames of video per rotation and has a rotation speed of
600 RPM. The advantage of the CLV format is that it
stores twice as much information as the CAV format.
CLV formatted discs can store up to 1 hour of video per
side. This allows complete films to be stored on one disc.
The disadvantage of CLV formatted discs is that special
effects cannot be easily done. This is because of the
varying amount of information stored in one revolution
of the disc.
y
281 282 28312841
CAA format disc addresses one problem that seriously
affected the quality of the picture of a CLV disc. This
problem was interference between adjacent tracks of
video. This interference appeared as a vertical line that
floats through the picture. The cause of the interference
is imperfections in the disc (disc warping, incorrect cen-
tering, or uneven track-to-track spacing). These imper-
fection can be great enough to allow the laser beam to
strike the horizontal sync pulse of the adjacent track,
resulting in the interference. To correct this problem the
CAA formatted disc is recorded in many sections, each
section is at one constant speed. As the information
moves away from the center of the disc the speed in
which the sections are recorded is reduced. When play-
ing a CAA disc the laser disc player plays a section of
the disc at one speed, then increments to the next lower
speed to play the next section. This is unlike CLV
formatted discs, in which the speed slows gradually as
the pickup moves away from the center of the disc. The
advantage of slowing the speed in increments is that the
video tracks of the same speed can be lined up to pre-
vent sync tip interference. CAA discs are often referred
to as CLV discs because of there 1 hour playing time.
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The laser disc player has the capability of identifying
locations of the information on a disc. There are three
methods for identifying the information on a disc. The
first method is to number the boundaries of the informa-
tion on a disc, similar to chapter numbers in a book.
These numbers are even referred to as chapter numbers,
and are usually indexed on the jacket of the disc. The
next method is to number each frame of video on a disc.
This number is called the frame number and is only used
on CAV discs. The last method is to indicate the elapsed
time from the start of the disc. This time is recorded on
the disc in the same fashion as frame numbers. This
method is used for identifying locations on the CLV disc
and CAA discs.
In all three methods of identifying the information on a
video disc, every field of video must have data giving the
location of that field on the disc. This information is
located in the Philips code of the vertical sync interval
(see fig 8). During playback, this information is read
from the disc and sent to the system control micropro-
cessor for display and special effect functions. Along
with the location data the Philips code also contains sta-
tus information. Status information is data recorded on
the disc to tell the laser disc player the size of the disc, if
digital audio is present on the disc, and if noise reduc-
tion is used on the analog audio.
RIGHT
CHANNEL
AUDIO
LEFT
CHANNEL
AUDIO
LPF
AID
CONVERTER
D
CONVERTER
MULTIPLEXER
STAGE
1
Digital Audio
In the video disc format, the digital audio is processed in
the same manor as the digital audio recorded on a com-
pact disc. This allows the same circuitry to be used in
both the laser disc player as in the compact disc player.
The block diagram for the record process of digital
audio is shown in fig 9.
In the record process, the first step is to convert the ana-
log audio signal to a digital signal. To do this a analog
signal is first applied to a low pass filter. This low pass
filter has a cutoff frequency of 20 KHz to keep higher
frequencies from causing interference in the digital con-
version stages. After Low Pass Filtering the analog sig-
nal is applied to the Analog to Digital converter.
This converter samples the analog audio signal at 44
KHz rate (double the audio frequency) and assigns a 16
bit digital word for each sample. This processing is done
for each channel of audio. After conversion the 16 bit
codes for each channel are multiplexed together. The
output of the multiplexer is a string of 16 bit words
alternating from the left to right audio channel. This
string of alternating data is applied to the CIRC (Cross
Interleave Reed Solomon Code) stage. This stage is for
correcting data drop outs in the play mode. The CIRC is
a digital data correcting code that corrects for errors in
two ways:
CIRC
CONTROL
DATA
_01 MULTIPLDUNG
STAGE
2
Fig. 9 - CD Record Process
EIGHT
TO
FOURTEEN
MODULATION
GLASS
DISC
SYNC
DATA
I MULTIPLEXING
STAGE
3
OPTICAL
MODULATOR
SPINDLE
MOTOR
I 1
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TABLE OF CONTENTS
CrOC)
DATA UP TO
31 MILUON
FRAMES
(70) MINUTES
SYNCRONIZAT1ON DATA
CONTROL AND DISPLAY DATA
COMPACT DISC
DATA
‘' DISC
ROTATION
SPEED
INNER TRACK 500 RPM
OUTER MICK 200 RPM
\
BITS 24 14 14 14 14 14 /4
t t t t
/4
/4 /4
MERGING BITS (3)
14 14 14 14 14 14 14
FRAME
588 BITS
/4 14 14
14 14 14 /4 /4 14
/4
14
14 14 14 14
14 /4
Fig. 10 - CD Format
A. The first method corrects for random errors of miss-
ing bits of data. This type of error is usually a random
one or two bits of missing data. To correct for this extra
bits of data are inserted into data groups. These bits are
either l's or O's and called parity bits. Whether a 1 or a 0
is added to the data depends on the amount of l's or O's
in the data stream. For example if all the l's in a data
stream add up to a even number, the parity bit would be
a 0. If all the l's in a data stream add up to a odd
number, the parity bit would be a 1. In the playback
process the parity bits are read and compared to the
data stream to determine if data is missing.
B. The second method of error correction is for burst
errors. Bursts errors are groups of missing data, usually
caused by scratches or finger prints on the disc surface.
To prevent this type of error from making the disc
unplayable, adjoining bits of data are separated when
recorded on the disc. By recording adjoining symbols in
places remote from each other, the risk of losing consec-
utive bits of data can be reduced. This process is called
interleaving and is very similar to shuffling a deck of
cards in a predetermined order. Naturally, if the data is
shuffled in record, it must be unshuffled in the same
order when played back.
After interleaving, the CIRC stage divides the data into
groups of 8 bits. These 8 bit groupings (named symbols)
are then applied to a second multiplexer stage. This mul-
tiplexer takes the data and groups it into frames of 32
symbols. To separate the frames, an 8 bit control word is
added to the start of each frame. This control symbol (8
bits) is only one piece of a larger control word that is
spread out over 98 frames of data. The control word ini-
tially informs the system how many tracks are included
on the disc, and how long the disc can play. This infor-
mation is referred to as the table of contents, and must
be read before the disc will actually start playing.
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To read tile complete control word, the player must read
98 frames of information. Each frame of information is
read and stored into memory until the complete word is
stored. The time it takes for the laser disc player to read
the 98 frames is approximately 13.3 mSec. Once the con-
trol word is read and stored into memory the remaining
control words on the disc are used to keep the memory
updated.
Once the control word is added, the data is now sent to
an eight-to-fourteen bit modulator. The EFM (Eight-to-
Fourteen Modulator) breaks the frame into eight bit
symbols. The symbols are then assigned a fourteen bit
code to indicate their value. With eight bits of data there
are only 256 possible combinations. By using a 14 bit
code the number of possible combinations increases to
16,384. By having this many possible codes to chose
from, codes can be chosen to meet some specifications.
1. One of these specifications is that a code cannot have
more than 10 consecutive l's or O's. If there are more
than 10 consecutive bits of the same data, the laser
disc player will have problems tracking and decoding
the information.
2. The second specification is that the difference
between codes used must be great enough that if one
bit of data is missing, a different usable code could
not be created.
Once 14 bit codes are chosen they are assigned to an 8
bit code for the conversion process. After conversion, 3
bits are added to separate 14 bit codes from each other.
This is done to prevent 10 consecutive bits of data being
created when the 14 bit words are added together. These
bits are named merging bits.
The final stage of the encoding process is the addition of
the sync signal by the third a multiplexer. The sync sig-
nal is a 24 bit code added to the start of each frame of
data: The sync signal tell the player the start of each
frame of data. Once the sync signal is added to the com-
posite signal it is applied to a optical modulator, for
recording on a compact disc. When recording on a video
disc, the composite signal is added to the FM modulated
analog signals, and then recorded on the disc.
The CD composite signal is shown is fig 10. In the figure
one frame of information is made up of 588 bits, this
includes the sync and the control data. The disc shown
in fig 10 is a example of the format of a compact disc. In
the compact disc format the speed varies from 500 RPM
on the inside tracks, to 200 RPM on the outside tracks
of the disc. In the compact disc format, the frames of
data are recorded on the disc very similar to the CLV
format laser disc.
The Laser Disc Player
For a laser disc player to receive and decode the infor-
mation recorded on a disc it must be able to;
1. Keep the laser beam focus on the laser disc as it
rotates.
2. Keep the laser centered on the row of pits as as it spi-
rals outward on the disc.
3. Maintain a constant rotational speed, that can be
varied with the different formats of laser discs.
A block diagram of a basic laser disc player is shown in
fig 11. The pickup assembly is responsible for retrieving
the reflected laser light. The reflected laser light is con-
verted to a RF signal and applied to the signal process-
ing stages. The pickup assembly also generates the error
signals. These error signals are applied to the different
servo loops to keep the laser focussed and tracking cor-
rectly throughout the disc.
Focus Servo
The focus error signal is the most important error signal
for the operation of the laser disc player. Without proper
focus of the laser beam on the disc surface data cannot
be retrieved. The focus error signal is applied to the
focus servo. The focus servo develops a drive signal for
pickup assembly. The drive signal is applied to the focus
coil which moves a lens in the optics of the pickup.
When this lens is moved up and down the focal point of
the laser beam is varied, allowing the pickup assembly to
keep the laser beam focused on the disc.
Tracking Servo
The tracking error signal is used to keep the laser beam
following the track of information on the disc as it spi-
rals outward. An error signal is generated in the pickup
assembly. This signal is applied to the tracking servo.
Like the focus servo, the tracking servo uses this error
signal to develope a correction signal. This correction
signal is then applied to the pickup assembly, where it is
used to drive the tracking coil. Unlike the focus coil the
tracking coil moves the lens side to side. This side to side
movement keeps the laser beam centered on the track of
information as it moves spirals outward.
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MOTOR
ORNE TWEBASE
FG SERVO
IN CO ERROR
VIDEO
OUT
VIDEO
PROCESSING
1
DISC
FG
SENSOR
PICKUP
ASSEMBLY
SPINDLE
MOTOR
ANALOG AUDIO
PROCESSING
DIGITAL AUDIO
PROCESSING re
ERROR
FOCUS
SERVO
FOCUS
SUM
TRACKING
TRACKING SERVO PICKUP
RETURN FOR REV
SUDER MOTOR
ORNE DRIVE
Fig. 11 - Laser Disc Player
Slider Servo
The slider servo can be thought of as a extension of the
tracking servo. Since the tracks of a laser disc continu-
ally spiral outward, there is some point at which the
tracking servo is at the end of its operating range. The
slider servo monitors the movement of the tracking lens,
then moves the complete pickup assembly to keep the
tracking lens within its operating range. The slider servo
monitors the DC level on the return line of the tracking
coil. When this level exceeds a threshold voltage the
complete pickup assembly is moved. By doing this the
tracking servo is operating in the center of its range,
allowing it to have more correction range. The slider
servo also moves the pickup assembly forward and back-
ward during the search and scan modes. This command
comes from the system control through the tracking
servo.
R IN
L IN
AUDIO
SWITCH
R IN
L IN
FOCUS
LOCK
CH
R CH
AUDIO
OUT
SYSTEM
CONTROL
D
A
Y
Time Base Servo
The time base servo has two functions in the laser disc
player. The first of these functions is to maintain the
spindle motor at the correct speed as it plays a disc. The
second function is to correct for errors in the timing of
the video signal. These timing errors can be seen on the
television screen as horizontal jitter.
To control the spindle motor speed on a video disc, the
TBS (Time Base Servo) compares a horizontal sync
pulse (supplied from the video section) with a master
clock. The phase difference between the 2 signals is then
used to develop an error signal. The error signal is used
in two areas of the laser disc player. First the error signal
is used to develop the spindle motor drive. To do this the
low frequency component of the signal is used. The error
signal is also sent to the video processing stage.
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The high frequency component of the error signal is
used to correct for horizontal jitter in the video signal.
When playing a audio compact disc the laser disc player
cannot use the horizontal sync signal from the video sec-
tion. In this case the laser disc player uses a error signal
generated in the digital audio processing section. This
error signal is developed from the sync signal that is rec-
orded at the start of each digital audio frame. This sync
signal is compared to a master clock in the digital pro-
cessing IC and a error voltage is generated from the dif-
ference of the 2 signals. This error signal is then sent to
the TBS section for generation of the spindle motor cor-
rection signal.
In order for the TBS to operate, it requires a input from
either the digital audio section, or the video processing
section. These signals are generated from the data rec-
orded on the laser disc. If the spindle motor is not rotat-
ing near the correct speed information cannot be read
from the disc. To get the spindle motor rotating close to
the correct speed, FG pulses are generated from a sensor
mounted on the spindle motor. The TBS section uses
these pulses to get the spindle motor running at a prede-
termined speed. At this speed the pickup assembly is
able to read the data from the laser disc. Once the data is
read from the disc the TBS section switches over to the
error signal generated in the signal processing sections.
System Control
The system control section is responsible for the overall
operation of the laser disc player. It receives the front
panel commands from the operator, and relays that
information to the appropriate section. It also receives
the data from the disc to tell it the chapter number,
frame number, and the elapsed time. This data is then
used for the special effect functions, and the displayed
on the front of the laser disc player.
The most important function of the system control sec-
tion is to control the operation of the servo sections of
the laser disc player. In most laser disc players the focus
servo is the first servo that is energized. Once the focus
servo is focused it sends a focus lock command to the
system control. The system control then starts the spin-
dle motor rotating, and allows the tracking servo to lock
onto the track of data.
During the time the spindle motor is rotating FG pulses
are monitored. When the predetermined speed is
reached, the system control section switches the TBS
over to monitor horizontal sync or digital audio sync.
This order of operation is varied with the different laser
disc players, but every laser disc player must have a start
up sequence to operate.
Video Processing
The video processing section receives the RF signal from
the pickup assembly and demodulates it. Once demodu-
lated, horizontal sync pulses are sent to the TBS section
for spindle speed correction. The video processing sec-
tion also receives a input from the TBS section, to correct
for horizontal jitter that is too high of a frequency for
the spindle motor to correct for. The output from the
video processing section can be sent to either a RF mod-
ulator or to a character generator, depending on the
laser disc player.
Analog Audio Processing
The analog audio section receives the RF signal from the
pickup assembly. It then separates the two RF carriers
for the right and left channel and demodulates them sep-
arately. Once demodulated, the right and left audio sig-
nal is then applied to a audio switch. This switch is
controlled by the system control micro and determine if
digital audio or analog audio is sent to the audio output
jacks and the RF modulator.
Digital Audio Processing
The digital audio section receives the RF signal and
decodes it. Because this signal is not FM modulated it
must be processed differently than the analog signals.
One of the major differences is establishing the logic
levels of the signal being applied. After this is done the
signal is then sent through the error correction stages.
Following error correction the digital signal is converted
from a 14 bit word to a 8 bit word. Then the last process
is to convert it back to the original analog signal.
The digital audio section must also send a error signal to
the TBS section to keep the spindle motor operating at
the correct speed. This error signal is only used when the
player is playing a compact audio disc. If the digital
audio signal is from a video disc the TBS section uses
the horizontal sync from the video processing stages to
control the spindle motor speed.
15
WorldRadioHistory

h •••.,
a
POWER PVCKUP
SUPPLY ASSEMBLY
LDR300 Service Position
VIDEO
SERVO PROCESSOR
'% "•••• *"1 11
lllll
DIGITAL
AUDIO
Fig. 12 - LDR.300
ANALOG
AUDIO
FRONT
PANEL
16
WorldRadioHistory

OVERVIEW LDR300
The service position and board location for the LDR300
is shown is fig 12. To put the player into the service posi-
tion the top cover and the disc tray must be removed. At
this point the back cover of the player is loosened to
allow the RF modulator, audio, and video jacks to be
released. The screws holding the main circuit board can
now be removed allowing the circuit board to be stood
on end. This service position allows access to both sides
of the main circuit board while keeping the laser disc
player fully operational.
The block diagram of the LDR300 is shown in fig 13.
The circuits of the LDR300 can be divided into 4 circuit
areas, mechanism, system control, servo, and signal
processing.
SPINDLE 0,
MOTOR
SENSOR
MSLDER
POSIT1ON
F ERROR
FOCUS
LASER cod.
ASSEMBLY
T ERROR
TRACKING
COIL
Mechanism
The mechanism of the LDR300 uses one motor to per-
form 3 functions. These functions are:
I. Move the disc tray in and out to let the operator a
place a disc onto the tray.
2. Once the tray is moved back into the machine, the
tray is lowered and the disc is clamped onto the spin-
dle motor.
3. After the loading sequence is completed, the loading
motor is then used to drive the tilt mechanism.
In the LDR300 the drive to the tilt loading motor is sup-
plied from a motor drive IC. This drive IC receives 3
DRIVE CD H BURST
OUT MRCP srpc vps
FC SERVO
TB ERROR
IBC
TP
e
FOCUS
SERVO encle
LOCK
TRACKING
RETURN
SUDER
MOTOR
MMHG
wise TRAC:KING
SERVO
DRIVE
TILT
SENSOR
I' RETURN su DER
PINE SERVO
MECHANISM
STATE
SWITCH
TILT/LOADING 0,
MOTOR
TILT ERROR
I BURST H STNC
VPS
TB ERROR
VIDEO
BF P4 PROCESSING
VIDEO
cw
MOTOR cc ,
DRIVE sw ,„
FOCUS LOCK
DIGITAL
ANALOG
TILT
ERROR
MECH
CONTROL
PD0071A
RF IN CD :MGR
norm
a4TA AUDIO
_,
I
RF ANALOG
e4 AUDIO
A
U
O
S
H
r CW CCW SI_OW
Fig. 13 - LDR300 Block Diagram
MODE
CONTROL
MICRO
P09017
FUNCTION
KEYS
VIDEO
e.
OUT
CHANNEL
CHANNEL
S
A
Y
17
WorldRadioHistory

inputs from the system control microprocessor. The
these inputs are CW, CCW, and slow. The CW and
CCW inputs control the rotation direction of the spindle
motor. The slow input is a high logic level during load-
ing and unloading to increase the speed of the motor.
The logic level is then pulled low to slow the speed of the
motor. This is done when the loading motor is used to
operate the tilt mechanism.
The position of the mechanism is monitored by the
mechanism state switch. This switch sends different
logic levels to the mechanical control micro as the load-
ing motor moves the mechanism through its different
positions.
System Control
The system control section consists of a mode control
microprocessor, and a mechanical control microproces-
sor. The mode control microprocessor performs the fol-
lowing functions;
1. Decodes the function input keys and the remote con-
trol input signal, then sends commands to the
mechanical control micro.
2. Controls the information displayed on the front
panel, and the television on-screen display.
3. Monitors the communications of the mechanical con-
trol micro. If a communication problem occurs, the
mode control microprocessor initializes a system
reset.
The mechanical control microprocessor receives com-
mands from the mode control micro, and sends control
signals to the appropriate sections. The mechanical
micro also receives data from the different circuit areas
to determine the status of the player.
After a disc is completely loaded the mechanical control
micro tells the focus servo to search for focus. If focus is
not achieved, the mechanical control micro then moves
the laser assembly inward to a position determined by
the slider position switch, and once again looks for a
focus condition. The position of the laser assembly when
focus lock is achieved, tells the mechanical microproces-
sor whether a compact audio disc, or a laser disc is in the
machine.
The mechanical control microprocessor then communi-
cates the type of disc to the different sections of the disc
player. This must be done to properly process the RF
signal read from the disc. After this information is pro-
18
cessed the mechanical control microprocessor then starts
the spindle motor rotating to its predetermined speed.
This speed is monitored by the FG pulses sent to the
mechanical control microprocessor. The micro not only
monitors the frequency of the pulses but also monitors
the amount of time it takes the spindle motor to reach its
predetermined speed. The microprocessor uses the time
information to determine what size of video disc is being
played (8" or 12"). During spindle rotation the tracking
servo is enabled, and the laser assembly is moved to the
inside tracks of the disc. Once the laser disc player as
gone through this sequence of events it enters the play
mode. This sequence is done every time a disc is loaded
into the machine. If a problem occurs somewhere in this
sequence, the mechanical control micro processor will
place the player in the stop mode.
Note; The system control section of the LDR300 has a
built in test mode. This test mode allows the servicer to
manually step through the different operations to get the
player to the play mode. This greatly simplifies the trou-
bleshooting of the laser disc player. See appendix A of
this manual for the operation of the test mode.
Servo
The LDR300 laser disc player uses 5 servo sections to
provide the correct control of the focus, tracking, and
spindle rotation.
The focus servo is the first servo in operation after a disc
is loaded into the laser disc player. The first step the
focus servo must takes is to find the initial focus point.
A search action is started by the mechanical control
microprocessor when the laser diode is turned on. When
searching, the focus servo generates a ramp voltage that
is used to drive the focus coil in the laser assembly. The
focus coil moves a lens in the laser assembly up and
down with the ramp voltage. This varies the focal point
of the laser beam throughout its range of movement. An
error signal is then generated by monitoring the reflected
laser light as it strikes the opto electrical converter.
The opto electrical converters main sensor section is
divided into four sections (see fig 14). These 4 sections
are paired together and the output of the 2 pairs is
applied to a comparator. If the distance from the disc to
the laser assembly is too far, the error voltage is positive.
If the distance is too close the error voltage is negative,
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