Sharp VC-780E

i
rere re
Problemes
The tape is not running (the tape is
not taken up at loading).
Probable causes end countermeasures
The reel idler is defective.
The reel brake is defective.
* Check if the reel idler is stained or defective.
The unit stops sometimes during
playback or recording.
The tape can’t be taken up when
tape unloading.
The tape is scratched when it is
wound.
Video search is impossible.
* Check if there are produced capstan motor
control singals at the system controller (servo
clack signal at pin 27 of C801, servo data signal
at pin 28 of C801, capstan motor pull up signal at
pin 29 of 1C801, capstan motor unloading signal
at pin 30 of 1C801, loading motor control forward
signal at pin 63 of IC801, cassette and loading
motors revers control signal at pin 62 of IC801),
1C701 is defective.
* Check if the mixed signal of drum PG and drum
FG is applied to pin 11 of !C701.
* The playback phase generator MM control | is
misadjusted (R751 for PAL/MESECAM signal,
R753 for NTSC signal).
Fine noises appear at the reproduced
picture.
* Check for capstan servo circuit (capstan
frequency generator’s signal at pin 41 of !1C701
and playback control signal at pin 40 of IC701).
Noises appear intermittently at the
reproduced picture.
The drum servo circuit is defective.
*
Check
if
the
mixed
signal
of
drum
PG
and
drum
FG
is
applied
to
pin
11
of
IC701.
* Check if the switching of 50Hz mode
(PAL/MESECAM) and 60Hz mode (NTSC) is done
properly.
The picture collapses in the
horizontal direcrion.
Noise
bar
appears
in
slow
mode,
Check
if
the
PB
CTL
signal
is
input
to
pin
1
of
!C801.
or
noise
bar
is
not
positioing
properly.
When
system
sw
is
in
auto
position,
the
selection
of
E-E
(REC)
mode
does
not
function
well.
*
Check
if
the
composit
sync
signal
from
pin
1
of
AC
connector
is,
after
being
removed
its
vertical
sync
signa!
at
Q801,
applied
to
pin
4
of
|C801.
*
Check
if
the
output
of
pin
54
of
IC801
is
sent
to
pin
15
of
1C802
(at
50Hz,
pin
54
is
“H”
level,
and
at
60Hz,
pin
54
is
“L”
level).
*
Check
if
the
voltages
of
pin
17
and
pin
18
of
iC802
are
appropriate
values
(at
EE
(REC)
mode,
both
pin
17
and
pin
18
of
IC802
are
approx.
5V).
*
Check
if
the
signal
applied
to
pin
15
of
IC802
is
output
from
pins
8,
9
and
10
of
1C802
(at
5OHz,
pins
8,9
and
10
are
approx.
5V).
IC801
and
IC802
are
defective.
37
VC-780E
VC-790ET