Technics SU-7300 Service Manual

@ NOTE
The
unit
is
provided
with
the
speaker
circuit
protection
fuses
at
the
right
and
left
channels
respectively.
The
fuse
is
to
prevent
the
power
transistor
from
destruction,
should
the
speaker
terminals
be
short-circuited.
Accordingly,
if
the
unit
fails
to
function
upon
completion
of
the
speaker
connections,
check
the
speaker
protection
fuses
first
of
all
for
possible
blowing.
w ALIGNMENT INSTRUCTIONS
e
When
the
power
transistor
is
replaced,
be
sure
to
apply
silicone
compound
(or
equivalent
thermal
diffusion
agent)
onto
the
mica
plate,
and
at
the
same
time
confirm
the
idling
current
of
the
power
transistor.
(measure
voltage
across
the
emitter
resistance)
For adjustment with DC voltmeter
. Turn the speaker switch “OFF”.
_
Connect
the
DC
voltmeter
as
in
Fig.
7
of
the
adjusting
spot
diagram.
_
If
the
reading
is
under
25mV
approximately
several
minutes
after
turning
ON
the
power
supply,
the
circuit
is
“OK”.
On
the
other
hand,
if
the
reading
is
over
25mV,
cut
off
the
lead
wire
for
L
inthe
case
of
left
channel
(The
lead
wire
for
R
in the
case
of
right
channel).
4.
Should
the
reading
not
fall
under
25mV
even
when
the
lead
wire
has
been
cut
off,
there
is
something
wrong
with
the
circuit,
and
therefore,
check
the
power
source
Circuit
or
main
amplifier
circuit.
Oon—-&
NOTE:
When
cutting
off
the
lead
wire,
cut
off
the
same
at
the
root.
®
Current
should
be
checked
only
when
adjustment
is
made
with
a
tester.
(measuring
instrument
incapable
of
measur-
ing
voltage
in
mV
unit).
. Turn OFF the power supply for the set.
. Connect the ammeter as shown in Fig. 9.
.
After
ensuring
that
the
ammeter
will
not
come
off,
turn
ON
the
power
supply.
.
If
the
reading
is
under
75mA
after
serveral
minutes
(But,
when
nothing
resistance
of
internal
resistor
by
ammeter)
the
circuit
is
"OK".
If
over
75mA,
cut
off
the
lead
wire
for
L
in
the
case
of
left
channel
(The
lead
wire
for
R
in
the
case
of
right
channel).
5.
If
the
reading
does
not
fall
under
75mA,
there
is
something
wrong
with
the
circuit.
BWOWN >
NOTE:
The
adjustment
may
be
made
either
by
@)
or
by
(B
method.
(We
recommend
the
method
‘®
where
possible).
Figs.
8
and
9
are
related
to
the
case
of
left
channel.
+B DC VOLTMETER +B DC AMMETER
TP204] [TP202
R ch.
Less than
OC 25 mv
L ch,
Less than
OC 25mvV
Voitage check method Current check method
(Stromspannung-priifmethode) (Stromstarke-Priifmethode)
Méthode de vérification Méthode de vérification
de tension de courant
Fig. 7 (Abb. 7) Fig. 8 (Abb. 8) Fig. 9 (Abb. 9)
[4] SU-7300

Technics SU-7300 Specifications

General

Damping Factor	30
Speaker Load Impedance	4Ω to 16Ω
Input Sensitivity	2.5mV (MM)
Signal to Noise Ratio	90dB (line)
Channel Separation	55dB (line)
Output	150mV (line)