Pioneer PX-7 Service Manual page 119

SYNC
(b)
V SYNC
(c)
FH
•
External video and superimpose modes
The
gate array
internal
connections
in external
video
and superimpose modes
are outlined
in
Fig.
13-59.
The
vertical
and composite
synchroniz-
ing signals
separated
from
the
external video
signal
are applied to pins 13 and 14
(VSYNC
and
HSYNC),
and
the
same
negative
vertical
and
horizontal
synchronizing
signals
as in
computer
mode
are
passed
to
the
RGB
terminal by IC109 and
IC106.
These
synchronizing
signals are
thus synchronized
with the
external video
signal.
The
color
subcarrier
(4.
433618MHz)
synchronized
with
the
color
synchronizing
signal in
the
external video
signal
is
passed
from
the color
subcarrier oscillator to pin
17 (CKI1).
The
composite
synchronizing
signal
separated
from
the
external video
signal
is
passed
to pin
7
(EXSI).
Horizontal synchronizing
signal
noise
is
removed by
passing
the input
signal to G8,
a frequency
divider
(1/272),
and FF4.
Since the
pulse
width of the
G8
output
is
extremely narrow,
this
width
is
increased to
about
3.5/tsec
by
FF3.
In
external
video
and
superimpose modes, the
hori-
zontal synchronizing
signal
frequency
(pulse
width approximately
3.5/rsec)
is
obtained from
pin
3(EXHP1).
The
signal
synchronized with the pin 3 output
and
applied to pin
4
is
generated by
the horizontal
synchronizing
signal
processing
circuit.
This
signal
is
applied
to a
frequency
divider (1/4) in the gate
array
before being passed
to the phase comparator
as
a
3.906kHz
reference
signal.
When
the
external
signal
is
the standard
signal,
the
VCO
output
is
10.6785MHz and
is
applied to pin 29 (CKI2).
The CKI1
inverted
signal
passed
via the
counter,
and
the
HSYNC
obtained
from
EXSI
are applied
to
the
bur
st
gate pulse generator, resulting
in
output
of
BGP
from
pin
16,
BGP1
from
pin
21,
and
BGP2
from
pin 19.
The
LMUTE
signal
from
th e
gate
array (IC3)
is
passed to pin 22, the
CASON
signal
from PPI
(IC4)
is
passed to pin 31, and
the
RESET
signal
is
a
pplied to pin 27,
If
LMUTE
is
changed
to
H
when
CASON
and
RST
are
also at
H, an
L
outp
ut
is
obtained
from
pin
32
RMUTE.
And
if
RST
is
changed to L, the
RMUTE
output
is
chang-
ed to H. This
circuit
is
used to
control
muting
of
external
audio
signals.
Otherwise,
the
circuit
operates
in
the
same
way
as in
computer mode.
See
Fig.
Photo. 13-25
for relevant waveforms.
Photo 13-24 Relevant waveforms
in
computer
mode
119