Marantz 2245 - Audio Adjustments; Main Amplifier DC Off-set Alignment; Idle-Current Adjustment; Main Amplifier ASO Adjustment

wk
14. Muting Circuit Alignment
1.
Connect
a
VTVM
across
the
resistor
RO22
and
adjust
the
resistor
RO22
until
the
meter
reads
0.75
V
DC
at no
signal.
2.
Set
the
FM
SG
to
provide
1KuV
at
98
MHz
and
tune
the
receiver
to
the
same
frequency
correctly.
3,
Turn
on
MUTING
pushswitch.
Shift
the
FM
signal
generator
frequency
to
plus
and
minus
and
note
both
plus
and
minus
shifted
frequencies
at
which
undesirable
audio
side
responses
are
muted
out.
Adjust
the
RO22
so
that
the
same
shifted
frequencies
mute
the
undesirable
side
response.
15. Audio Adjustment
1. Voltage adjustment
Connect
a
DC
voltmeter
between
pin
Tenia
J802
and
J803,
and
adjust
the
trimming
resistor R809 for 35V DC.
2. Main Amplifier DC off-set alignment
Connect
a
DC
voltmeter
with
0.5
or
1V
range
between
the
speaker
terminals
and
adjust
the
trimming
resistor
R762
for
‘‘zero’’
DC
output
on
the
meter.
Repeat
the
same
procedure
for
the
other
channel.
Note:
During
this
alignment
no
load
should
be
‘connected
to
the
speaker
terminals.
3. Idle-current adjustment
Connect
a
VTVM
between
pin
terminals
J753
and
J754.
Next,
rotate
the
trimming
resistor
R763
fully
counterclockwise,
then
rotate
it
clockwise
again
until
the
VTVM
reads
S5mV
DC.
Repeat
the
same
procedure
for
the
other
channel.
4.
Check
DC
off-set
voltage
aligned
in
the
procecure
2
and
if
any
DC
output
is
observed
onthe
DC
voltmeter,
adjust
the
R762
again
for
‘‘zero”
output.
5. Phono-amplifier adjustment
Connect-a
oscilloscope
to
the
TAPE
OUT
jacks
and
an
audio
signal
generator
to
the
PHONO
jacks.
Place
the
selector
switch
in
the
PHONO
position.
Increase
1KHz
audio
signal
gradual
ly
until
a
slight
clipping
on
top
of
the
sine-wave
is
observed
on
the
oscilloscope.
Adjust
the
trimming
resistor
R708
for
equal
clipping
level.
For the other channel adjust R709.
6. Main Amplifier ASO adjustment
For
this
alignment
two
DC
oscilloscopes
are
necessary.
6.1
First,
make
calibration
on
each
oscilloscope
gain
for;
7
Vertical
Sensitivity
0.2
V/cm
Horizontal
Sensitivity.10
V/cm
6.2
Connect
pin
J753
to
the
scope
vertical
input
terminal.
Connect
pin
J756
to
the
scope
horizontal
input
terminal.
Adjust
the
horizontal
and
vertical
position
knobs
so
that
a
‘spo
t”’
on
the
scope
is
placed
on
the
lower
right
corner.
6.3
Connect
pin
J760
to
the
scope
vertical
input
terminal.
Connect
pin
J761
to
the
scope
ground
terminal.
Connect
pin
J756
to
the
scope
horizontal
input
terminal.
Adjust
the
horizontal
amd
vertical
position
knobs
so
that
a
‘’spot’’
on
the
scope
is
placed
on
the
lower
left
corner.
6.4
Remove
two
jumper
plugs
connected
between
the
PRE
OUT
and
MAIN
IN
jacks
on
the
ear
panel.
Connect
a
low-loss
oil
paper
capacitor
of
6hF
(or
equivalent)
to
the
speaker
terminals
being
adjusted.
6.5
Connect
an
audio
signal
generator
to
the
MAIN
IN
jack.
Increase
the
audio
signal
(1K4z)
input
level
until
the
Lissajou
Figures
as
shown
below
are
obtained
on
the
scopes.
Adjustt
he
trimming
resistors
R782
and
R783
for
the
height
of
2.5cm.
6.6
Change
the
audio
input
Wegiae
from
1KHz
to
20Hz-and
check
whether
the
spedcer
we