I_ASERDISC REPAIR:
PART 2: THEORY AND SAFETY
"My intent with this 6-part series on
laserdisc repair is to get a lot of useful
information into the hands of working
technicians as painlessly as possible.
Therefore, I will skip over some of the more
technical matters. This approach is
necessary, I have found, because the
alternative is to require technicians to study
for months before they have the proper
background for disc player repair. Even
without all that theory, there is a lot of good
that can be done, and that's my intent with
this series: to get the information where it
will do the most good." - Bill Turner
BY BILL TURNER, ~USTOMER SERVICE MANAGER, ELECTRO-SPORT, INC., COSTA MESA, CA
GETTING STARTED IN
LASERDISC SERVICE
Laserdiscs encoded in the
Phillips format are used in many
laser games. These discs use the
CAV, Constant Angular Velocity,
format, to enable the use of trick
functions and random access. In
the CAV format, the disc rotates
at 1800 RPM throughout the
playing time. On the disc, at
certain angles and lights, you can
see the vertical sync areas. CAV
discs can hold up to 30 minutes
continuous video, or 54,000 still
frames, on either side. See
Figure 1.
Our 6-part series continues with
"Theory and Safety". Part 1,
entitled "Short of Actual Repair",
covered the most frequent
problems with disc players, and
gave maintenance information
applicable to all laser games.
Part 1 appeared in our April
issue.
Part 2 will cover how the disc
player works, how the Pioneer
PR-821 O type disc players work,
and general safety information for
working with laser and high-
voltage equipment.
Next month and the remaining
3 months are outlined as follows:
JUNE - PART 3: VOIDING
YOUR WARRANTY
(OPENING THE DISC
PLAYER) - Disassembly of
the Pioneer PR-8210 type
disc players. Inspection of
mechanical components.
Inspection of fuses. General
troubleshooting.
JULY- PART 4: ALIGNMENT
AND REPAIR-The most
frequent alignment
procedures for the Pioneer
PR-8210 type disc players.
The most frequent problems
and their solutions.
AUGUST- PART 5: SOLID
STATE LASERDISC
PLAYERS- General
information on the new
generation of disc players.
Special maintenance and
alignment considerations for
solid state laser head
systems.
SEPTEMBER - PART 6:
COM PUTER·CONTROLLED
LASERDISC PLAYERS -
Covers the Pioneer PR-7820
type disc players. Explains
test and maintenance
considerations, and RS232
conventions.
The pits on the disc are the result
of video and sound channels
modulated by an FM carrier,
mixed, limited, and sampled.
Thus, the pits are strictly an
analog signal. The information
encoding and frequency
spectrum for the video disc are
shown in Figure 2. Laserdisc
players can be likened to
television in some parameters;
modulated FM video carriers,
audio in two separate carriers,
color phase circuitry and NTSC
phase decoding, etc., but disc
players add the eccentricities of
the disc medium to the signal
processing complications.
The CAV discs are organized into
a single spiral of pits, with one
revolution of the disc containing
two video fields (or one video
frame - remember, the display is
interlaced). Because the vertical
intervals are in the same place
throughout the disc, it is relatively
easy for the disc player to identify
the end of a frame, and jump
back to the beginning of a frame,
or locate different points along
the spiral of pits. Further, by
encoding frame and machine
data on some of the spare
horizontal lines, a great deal of
sophisticated application can be
realized. As in laser games.
advantage ·of lots of LSI and VLSI
technology; thus service persons
who could not ordinarily work on
such complex systems can take
advantage of the small physical
size and low parts count of the
disc players, and perform much
useful service work. With LSI and
VLSI, a technician need only
identify a circuit as faulty, then
replace the entire single-chip
circuit.
Although sophisticated, laserdisc
players offer the service
The optical conversion to an RF
video and audio signals, and the
response of the focus and
tracking circuitry, is
accomplished by bouncing three
laser beams off the disc surface.
In most laser players the main
and two first order beams are