Specifications

CONSTRUCTION
served that frequently, the picture/
frames froze on the
CTV
screen and the
power to the
MPEG
converter card had to
be switched off and on again. This fault
was attributed to inability of 7805 regu-
lator to deliver the required current
(about 300 mA) to the
MPEG
card. The
regulator circuit was therefore modified
as shown in Fig. 7 to provide a bypass
path for current above 110 mA (approxi-
mately). A step-down transformer of 9V-
0-9V, 500mA is adequate if the modula-
tor has its own power supply arrange-
ment (refer paragraph 4 below).
4.
RF
modulator for
TV
channels
E
2
and
E
3 are available in the market com-
plete with step-down transformer, hence
there may not be any need to wire up a
12V regulator circuit of part II.
5. Apart from the facilities (available
in the
MPEG
decoder card
KD
680
RF
-3
SC
from
C-cube) as explained by the author, there
are other facilities such as
IR
remote con-
trol of the card functions (via Jack
J
5)
and realisation of change-over between
NTSC
and
PAL
modes (via jack
J
4no
connections means
PAL
mode). Similarly,
Jack
J
1 is meant for external audio and
video input from exchange and connec-
tion of audio and video outputs to
CTV
. The foregoing information is avail-
able on document accompanying the
MPEG
decoder card. However, the detailed
application/information is not provided
and as such we have not tested these
facilities.
6.
EFM
is a technique used for encod-
ing digital samples of audio signals into
series of pits and lands into the disc sur-
face. During playback these are decoded
into digital representation of audio sig-
nal and converted to analogue form us-
ing digital-to-analogue converter for even-
tual feeding to the loud speakers.
7. For those enthusiasts who wish to
rig-up their own video modulator, an ap-
plication circuit from National Semicon-
ductor Ltd, making use of
IC
LM
2889,
which is pin for pin compatible with
LM
1889 (
RF
section), is given in Fig 8.
Tech Editor
player part. The
DSP
chip, more often than
not, would be a multipin
SMT
device. In
the
AIWA
system we located two such chips
(
LA
9241
M
and
LC
78622
E
both from Sanyo).
Their data-sheets, picked up from the
Internet, revealed the former chip to be an
ASP
(analogue signal processor) and latter
one
(
LA
78622
E
) is the
CD
player
DSP
chip for
which
EFM
IN
is not found in Table I. For
this chip
EFM
IN pin
is pin 10 while pin 8 is
the nearest digital ground pinswhich we
used.
2. Of the two converter cards
(one displaying Sony Digital
Technology' and the other dis-
playing C-cube Technology
on the
CTV
screen), the latter
card's resolution and colour qual-
ity was found to be very good
when tested by us. The C-cube
card needs a single 5V
DC
supply
for its operation.
3. During testing it was ob-
Fig. 8: Two channel video modulator with FM sound
Fig. 7: Modified 5V regulator for enhancing current
capability
adding the following information which
we have been able to gather during the
practical testing of the project at
EFY
.
1. There may be more than one
PCB
used in an audio
CD
player (i.e additional
for
FM
radio and tape recorder functions)
and even the
DSP
chips referred in Table1,
may not figure on it. For example, we could
not find the subject
IC
used in
AIWA
audio
CD
player. The
PCB
, which is located clos-
est under the laser system, is related to
CD
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