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Marantz SM-8 - Page 6

Marantz SM-8
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4.
TEST
EQUIPMENT
REQUIRED
FOR
SERVICING
This
table
lists
the
test
equipment
required
for
servicing
the
Model
Sm-8
Stereo
Power
Amplifier.
Distortion
Analyzer
Distortion
measurements
Audio
Oscillator
AC
VTVM
Oscilloscope
Sinewave
and
squarewave
signal
source
Voltage
measurements
(AC)
Waveform
analysis
and
trouble
shooting
and
ASO
alignment
|
Circuit
Tester
DC
VTVM
Trouble
shooting
Voltage
measurements
(DC)
AC
Wattmeter
Line
Voltmeter
Variable
Autotransformer
(0
~
140V
AC,
10A)
Monitors
primary
power
to
amplifier
Monitors
potential
of
primary
power
to
amplifier
Adjust
level
of
primery
power
to
amplifier
Shorting
Plug
5.
ADJUSTMENT
PROCEDURES
1.
Class
B
idting
adjustment
a)
Apply
a
sine
wave
signal
of
1
to
2
VRMS
to
JL14
from
an
audio
oscillator
in
order
to
forcibly
make
it
Operate
as
a
class
B
amplifier.
b)
Adjust
RL43
and
RL44
so
as
to
give
DC
voltage
of
7
mV
at
the
JJO1-02
and
JJ03-04
test
points.
NOTE:
Carry
out
the
adjustment
one
minute
after
the
switch
is
turned
on.
After
the
set
is
stabilized,
the
voltage
should
be
27
mV
(50
mA).
2.
Class
A
idling
adjustment
a)
Disconnect
the
input
to
JL14.
b)
Adjust
RL39
and
RL40
so
as
to
give
DC
voltage
of
440
mV
at
the
JJO1-02
and
JJ03-04
test
points.
NOTE:
Carry
out
the
adjustment
one
minute
after
the
input
to
JL14
is
disconnected.
The
class
B
ad-
justment
must
be
done
first.
After
the
unit
is
stabilized,
the
voltage
should
be
370
mV
(655
mA).
3.
Comparator
balance
adjustment
a)
Connect
a
trigger
oscilloscope
to
JL14.
b)
Set
the
load
of
the
device
to
OPEN,
apply
a
signal
with
a
frequency
of
1
kHz
and
increase
it
gradually.
c)
While
observing
the
output
waveform
of
the
unit
and
pulses
at
JL14,
adjust
RL31
so
as
to
generate
two
pulses
per
output
waveform
period.
Shorts
amplifier
input
to
eliminate
noise
pickup
rae
acs
Output
waveform
+5V
|
|
JL14
T.P
Ov
4.
Switching
level
adjustment
a)
Connect
a
trigger
oscilloscope
to
JL14.
b)
Set
the
load
of
the
unit
to
OPEN
and
apply
a
signal
having
a
frequency
of
1
kHz
to
the
L
channel.
c)
With
the
output
set
to
15.5V,
adjust
RLOQ
so
as
to
generate
pulses
at
JL14.
d)
Apply
a
signal
to
the
R
channel
and,
similarly,
adjust
RL10.
5.
Power
meter
adjustment
a)
Set
the
load
of
the
unit
to
8Q,
apply
a
signal
having
a
frequency
of
1
kHz
and
increase
the
input
signal
to
30.9V.
b)
Adjust
the
following
so
as
to
give
a
reading
of
120V
on
the
meter.
For
the
L
channel,
adjust
R
X05.
For
the
R
channel,
adjust
RX06.

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