Technics SU-Z65 Service Manual

M@
TECHNICAL
GUIDES
1. SPEAKER IMPEDANCE DETECTION CIRCUIT
This
circuit
detects
the
impedance
of
the
speaker
connected
to
the
speaker
terminal
and
serves
to
keep
the
operation
of
the
unit
in
best
conditions,
controlling
the
constant
voltage
power
supply
circuit.
It
consists
of
a
‘‘voltage
comparing
circuit’,
‘reset
circuit’,
‘detection
signal
generating
circuit’’
and
‘‘relay
drive
circuit’’.
®
®
Basic principles
The
built-in
reset
switch
is
short-circuited
only
for
a
moment
when
speaker
selector
is
operated.
(Fig.
1-A)
Simultaneously,
the
reset
circuit
operates
(Fig.
1-B)
to
turn
both
RLY
301
and
RLY
302
OFF.
Subsequently,
the
reset
switch
opens
at
the
end
of
operating
the
speaker
selector.
Then,
the
detection
signal
generating
circuit
keeps
RLY
301
OFF
for
0.5
second
more.
(Fig.
1-C)
Since
RLY
301
Is
OFF,
the
speaker
connected
to
speaker
terminal
contacts
with
the
voltage
comparing
circuit.
The
difference
from
the
reference
voltage,
that
is,
the
type
of
speaker
connected,
is
detected;
and
the
secondary
side
tap
voltage
of
the
power
transformer
is
switched
by
RLY
301
so that the voltage matches the connected speaker.
main
A (8Q)
remote
(i Switch by speaker selector
(4Q)
Reset circuit operates to turn RLY 301
and RLY 302 OFF.
B — v/s F
i“ Detection signal generating circuit
C keeps RLY 301 OFF for 0.5 sec.
lhe
Relay 302
A
\ High
AC Line
|
(Primary)
| Low
To rectifier |
(Secondary) !
High
|
0.5 sec
(Operation time of each circuit)
Fig. 1
Reset
circuit
and
detection
signal
generating
circuit
As
already
explained,
when
the
reset
switch
is
short-circuited,
Q305
in
the
reset
circuit
turns
ON.
Positive
voltage
is
generat-
ed
at
the
collector
of
Q305
as
shown
in
Fig.
3-A,
causing
Q302
in
the
relay
drive
circuit
[I]
to
turn
ON.
(But,
the
base
of
0302
is
usually
at
0 volt
and
OFF.)
When
Q302
turns
ON,
the
base
of
Q301
is
grounded
.and
turns
OFF,
causing
RLY
301
to
turn
OFF.
Also,
the
collector
voltage
of
Q301
becomes
positive,
causing
Q306
as
well
as
RLY
302
to
turn
OFF.
(Q301
emitter
is
connected
to
pin
®
of
{C401
and
the
voltage
of
this
pin
is
usually
zero
or
a
little
positive.)
In
other
words,
RLY
301
and
RLY
302
are
OFF
while
the
reset
switch
is
short-circuited.
Also,
at
the
moment
when
the
reset
switch
opens,
the
voltage
as
in
Fig,
3-B
is
applied
to
the
base
of
Q304
in
the
detection
signal
generating
circuit
which
uses
a
multi-vibrator
due
to
the
charge
and
discharge
of
C301,
thus
causing
this
tran-
sistor
to
turn
ON.
And
voltage
as
in
Fig.
3-C
is
generated
at
the
collector.
The,
voltage
in
Fig.
3-C
turns
Q302
ON,
and
Q3010FF,
therefore
both
RLY
301
and
RLY
302
turn
OFF.
RLY
301
and
RLY
302
are
OFF
for
0.5
second.
That
is,
RLY
301
and
RLY
302
are
turned
OFF
during
shortcircuit
of
the
reset
switch
and
for
0.5
sec.
more
after
opening
of
the
switch.
AC Line
Low (Primary)
ot
(Power transformer)
Fig. 2
Shortcircuit time of reset switch
Collector voltage of O305
Voltage applied to Q304 base
Collector voltage of Q304
0.5 sec
OFF-—time of relays (RLY301
and 302)
(Voltage generated at each terminal)
Fig. 3

Technics SU-Z65 Specifications

General

Brand	Technics
Model	SU-Z65
Category	Amplifier
Language	English