Sharp VC-780E

| VC-790ET
TROUBLESHOOTING GUIDE
TROUBLES
OF
CONTROL
SYSTEM
(SERVO,
SYSTEM
CONTROLLER
CIRCUIT)
Problems
No power is supplied.
No operation is available.
After tape loading, the unit is
stopped with the tape kept wound
over the drum, or the cassette can't
be ejected.
The unit will stop immediately after it
is set in playback or record mode.
The
unit
will
stop
a
few
seconds
after
it
has
been
set
in
playback
or
record
mode.
36
Probable
causes
and
countermeasures
The
fuse
is
blown
out:
Check
if
there
occurs
a
short-circuit
in
the
internal
circuit...
Check
if
there
are
produced
AT6.5V,
AT12V
and
AT9V
in
the
power
circuit:
If
not,
this
means
that
the
power
circuit
is
defective.
Check
if
the
system
controller
(1C801)
is
normally
functioning:
Check
if
there
are
produced
reset
signals
functioning:
Check
if
there
are
prod
uiced
reset
signals
(ACL)
at
pin
45
of
1C801
and
clock
signal
at
pins
46
and
47
of
1C801.
Check
if
the
power
control
signal
ve
level}
goes
out
of
pin
19
of
(C801.
Check
if
the
end
sensor
signal
(cassette
housing
side)
and
start
sensor
signal
are
applied
to
pins
56
and 57 of {C801 respectively.
Check if the unit is in timer mode.
Check
if
the
unit
is
in
sensor
stop
mode
(DEW
display).
The
cam
switch
is
poorly
adjusted
for
its
positioning.
Check
if
the
unit
is
not
in
the
child
lock
mode.
Check
if
the
read-in
of
operation
key
is
done
well.
The
cam
switch
is
poorly
adjusted
for
its
positioning.
IC803 is defective.
Check if AT 12V is supplied.
Check
if
the
head
switching
pulse
is
applied
to
pin
3
(for
the
drum
sensor)
of
IC801.
Check if the drum motor is rotating.
Check
if
the
mixed
signal
of
drum
FG
and
drum
PG
is
applied
to
pin
14
of
1C701
of
servo
circuit.
-
Check
if
the
reel
sensor
pulse
is
applied
to
pin
58
(for
the
ree!
sensor)
of
1C801.
Check if the reel disk is rotating.
Check
if
the
capstan
motor
is
rotating.
Check
if
the
reel
idier
is
stained
or
defective.