Sharp RT-1157H - Page 11

Oe o. Sree oh A Le
Cautions on Repairing
1) The following parts out of those which are used for
Dolby NR circuit should be at less than the error of
+ 5%,
R145, R245, R114, R214, R119, R219, C114, C214,
C115; C215, C116, C216, C119, €219
2)
The
following
parts
should
be
those
with
the
error
of
within
+
10%.
Cis
(Cols.
Gll2.e2l2
OUTPUT
(dB)
-?
7?
PRCEeT 2
Cie ePLAYBACK mode!
4
4 ‘
4
’
IN PUT (dB)
-20
INPUT LEVEL {dB}
Figure
15—1
Figure
15—2
APSS (Auto Program Search System)
APSS
is
an
abbreviation
of
Auto
Program
Search
System
uniquely
developed
by
SHARP,
which
can
automatically
detect
the
Starting
position
of
each
program.
With
the
APSS
system,
if
the
fast
forward
button
or
rewind
button
is
depressed
during
playback
mode,
the
tane
is
fast
forwarded
to
the
starting
position
of
the
next
program
{the
end
position
of
the
previous
program}
and
then
the
fast
forward
button
or
rewind
button
is
automatically
released
to
make
the
mechanism
be
put
in
playback
mode.
OUTLINE OF APSS
LIMITER
AMP.
This
amplifier
is
composed
of
0401
and
0402
and
serves
to
amplify
the
output’
of
pre-amplifier
to
the
level
where
the
APSS
starts
to
operation.
VOLTAGE DOUBLING RECTIFIER CIRCUIT
This
voltage
doubling
rectifier
circuit
is
composed
of
D401
and
D402.
TIME CONSTANT CIRCUIT
This time constant circuit is camposed of R409 and C404.
LEVEL COMPARISON CIRCUIT
This
level
comparison
circuit
is
composed
of
0403
and
Q404.
With
this
level
comparison
circuit
of
which
the
function
is
based
on
switching
characteristic
of
transistors,
the
rectifying
voltage,
which
has
been
produced
by
the
voltage
doubling
rectifier
circuit
and
time
constant
circuit,
is
used
to
be
input
to
the
base
of
Q403.
PLUNGER CONTROLLED CIRCUIT
This
plunger
controlled
circuit
is
composed
of
0405
and
Q406.
The
Q4085
is
a
differential
circuit
to
utilize
the
signal
coming
from
the
level
comparison
circuit
to
initiate
the
plunger
only
at
the
breaking
time.
The
Q406
uses
ihe
signal
coming
from
the
differential
circuit
to
cause
switching
of
ihe
plunger.
-~15—
ere ee re Seer
FUNCTION
OF
APSS
(Auto
Program
Search
System)
The
following
are
detailed
functions
of
the
system.
During
APSS
mode,
signals
amplified
by
the
integrated
circuit
(1C1,
1C2}
enter
the
limiter
amplifier
(Q401,
Q402)
and
fimited
by
the
transistors
(Q401,
Q402)
and
the
output
of
Q402
is
rectified
by
the
diodes
(D401
and
D402),
The
output
of
D402
is
compared
by
the
level
comparison
circuit
(0403
and
0404).
Next,
when
the
Q403
is
turned
on,
the
Q404
is
turned
off,
and
the
potential
of
Q404
collector
stabilizes
at
19.5
V.
Therefore
the
Q405
is
not
turned
on,
in
consequence,
neither
is
the
Q406.
As
a
result,
Q406
is
not
actuated.
In
other
words,
as
far
as
the
tape
carries
signals
the
plunger
does
not
work,
that
is,
the
tape
is
continuously
fast
for-
warded
according
to
the
mechanism
of
the
APSS.
Meanwhile,
when
there
is
no
signal
on
the
tape,
therefore
the
Q403
is
turned
off,
the
Q404
is
turned
on.
Therefore,
the
collector
potential
of
Q404
becomes
0
V,
and
con-
sequently,
the
19.5
V
voltage
passes
through
the
R415,
allowing
a
charge
current
to
flow
towards
the
C405,
By
this
charge
current
the
potential
of
the
O405
base
drops
momentarily,
and
the
Q405
is
turned
on,
the
current
runs
in
the
base
of
Q406.
At
this
time,
current
runs
in
the
solencid
to
make
it
be
attracted
and
the
mechanism
is
changed
to
playback
mode
from
APSS
mode.
PR
AM
“Mei ATi
ro “by
wetee,
WAH
|
2
{AtQ402
collector)
OOUBLING
OUTPUT ®
VOL TAGE a
1
1
F.F./ REWIND
PUSH Yy PUSH
PLAY
|-
aPSS
ON—»
-
PLAY
—
aps
on»
NO
SIGNAL
{At C404}
1
|
+
,
1
{At SOL401)
Figure 16—1
FUNCTION
OF
FULLY
AUTOMATIC
END-OF-TAPE
STOP
SYSTEM
The
automatic
end-of-tape
stop
system
of
this
set
has
a
design
that
a
mechanical
detection
of
the
end
of
tape
results
in
electrical
signal
to
activate
the
solenoid
(SOL
401).
When
the
tape
reaches
its
end
during
playback,
record,
fast
forward
or
rewind
mode,
the
automatic
end-of-
tape
stop
mechanism
begins
to
function
setting
the
automatic
end-of-tape
stop
switch
(SW10)
at
“charge”
position.
As
a
result,
a
charge
current
runs,
via
the
resistor
(R421),
in
the
capacitor
(C406)
to
be
charged
up.
Then
the
automatic
end-of-tape
stop
mechanism
begins
to
function
setting
the
automatic
end-of-tape
stop
switch
(SW10})
at
‘discharge’
position.
Accord-
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ees
ingly, the capacitor (C406) discharges so that the
resultant current is applied through the resistor (R419)
to the base of the transistor (Q407) where it is ampli-
fied. This amplified current is then supplied to the
base of the solenoid (SOL 401) driving transistor
{Q406), resulting in that the solenoid (SOL 401) is
attracted to make the mechanism be set at the stop
mode.
Speaking of APSS (Auto Program Search System) mode,
the APSS key is unlocked due to the first attraction
of solenoid and the play key is unlocked due to the
second attraction, which put the mechanism in the
stop mode.
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BaP orl OS4a7
H case Dh eae ere
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5 Boma FD one voiage 3 OEOS 2SC12(30
from)
Figure 16—2
—16—