NAD 4225 - FM ALIGNMENTS; NECESSARY INSTRUMENTATION; TUNING VOLTAGE (OSCILLATOR); RF ADJUSTMENT (TRACKING)

ALIGNMENT METHOD
FM ALIGNMENTS
NECESSARY INSTRUMENTATION
FM GENERATOR (less THAN 0.05% thd)
STEREO
GENERATOR
(less
than
0.05%
THD,
more
than
50
dB
separation
at
1
KHz.)
AUDIO
GENERATOR
(not
necessary
if
FM
generator
has
built
in
sweep;
i.e.
SOUND
TECHNOLOGY
ST
1000A
and
ST
1020A).
2 AC VIVM’s (or one with left/right channel switch)
THD ANALYZER (resolution better than 0.1%)
OSCILLOSCOPE
(5mV
or
better
sensitivity,
X
input
capability)
FREQUENCY COUNTER
VOM or DMM (high tapeaness must read in mV)
DIODE DETECTOR PROBE
COPPER/FERRITE INDUCTOR
IMPORTANT:
While
all
FM
generator
output
levels
hereafter
are
referred
to
the
300 ohm input, 75 ohm input can be used, but be aware of possible
equipment groundloops and divide the RF output level by 2. Before
alignments commence set input selector to tuner and release tape,
mono and FM NR. defeat switches (out) ALIGNMENT OF FRONTEND should
only be necessary afte: repair to frontend or drystal oscillator
circuits (pin 2 and 3 on Q911).
A TUNING VOLTAGE (OSCILLATOR)
Aes
Tune
to
108
MHz
and
adjust
L8
if
voltage
is
incorrect.
tal
ia
De
It
is
essential
to
check
tuning
voltage
before
aligning
the
rest
of
the
frontend.
Connect
DMM
between
shield
and
Pin
5
on
frontend.
SPECIFICATION 20.5V +0.5V
Tune
to
87.5
MHz
and
read
voltage,
repeat
step
2
and
3
if
incorrect.
SPECIFICATION 3V +0.5V
B RF ADJUSTMENT (TRACKING )
1
Lon]
.Connect.
RF
generator
to
antenna
input
and
detector
probe
to
pin
1,
Q104
(IF
DETECTOR)
.with
ground
to
detector
shield.
Adjust
sensitivity
of
oscilloscope
to
maximun
(5mV
or
better)
and
modulate
FM
generator
sweep
+300
KHz
or
more
with
modulating
(sweep)
signal
connected
to
X-input
of
oscilloscope.
“Set
tuner
to
90
MHz,
enter
into
preset
1,
and
tune
generator
so
that
curve
appears
on
oscilloscope.
Turn
down
RF
input
level
so
that
curve
covers
approximately
1/2
of
oscilloscope
display.
.Check
alignments
of
L2-L4-L5
by
inserting
copper/ferrite
inductor
close
to
them
while
watching
curve
on
oscilloscope.
Curve
should
decrease
in
height
with
either
ferrite
(same
as
increasing
inductance,i.e.
more
core)
or
with
copper
(same
as
decreasing
inductance,
i.e.
extend
size
of
coil).
If
curve
increases
in
size
more
than
10%,
adjust
only
the
coil
which
reacts
incorrectly.
Adjust
coils
by
gently
extend
or
contract
the
aircoil
with
a
non-metallic
and
non-static
tool(i.e.
plastic
knit-pin
or
a
wooden
stick).
Be
careful
not
to
deform
coil.
“Set
tuner
to
105
MHz,
enter
into
preset
2,
and
tune
generator
so
that
curve appears on osilloscope.
.Check
L2-L4-L5
again
with
the
ferrite/copper
inductor,
Curve.should
not
increase
more
than
10%
on
any
of
the
coils.