NAD 7130 Service Manual page 6

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
1020 A)
2
AC VTVM'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
impedance, must
read
in
mV)
DIODE
DETECTOR
PROBE
COPPER
/
FERRITE INDUCTOR
IMPORTANT
While
ail
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 dynsep
defeat
switches
(out)
ALIGNMENT
OF
FRONTEND
should only be
necessary
after repair to frontend or
crystal oscillator
circuits (pin 2
and 3 on
1C7)
A
TUNING VOLTAGE
(OSCILLATOR)
It is
essential to
check
tuning
voltage before
aligning the
rest
of the frontend.
1.
Connect
DMM
between
shield
and
pin
6 on
frontend.
2.
Tune
to 108
MHz
and
adjust
L 707
if
voltage
Is
incorrect.
SPECIFICATION
20.5V ±0.5V
3.
Tune
to 87.5
M
Hz and
read
voltage, repeat step
2 and
3
if
incorrect.
SPECIFICATION 3V
± 0.5V
B.
READJUSTMENT
(TRACKING)
1.
Connect
RF
generator to antenna
input
and
detectorprobe to
pin 1,IC2
(IF
DETECTOR).
with
ground
to detectorshield. Adjust
sensitivity
of oscilloscope to
maximum (5mV
or better)
and modulate
FM
generator sweep ± 300 kHz
or
more
WITH
modulating
(sweep)
signal
connected
to
X-imput of
oscilloscope.
2.
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.
3.
Check alignments
of L
702
-
L
704
-
L705
by
inserting copper/ferrite Inductor
close to
them
while walching
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
ii
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
rot
to
deform
coil.
4.
Set tuner
to
105MHz,
enter into preset
2,
and tune
generator
so that
curve appears on
oscilloscope.
5.
Check L
702
—
L 704
—
L
705
again
with the
ferrite/copper inductor.
Curve should not
increase
mor^than
10% on
any
of the
coils.
6.
Repeat
step 2
+
3
+
4+
5if
curve height
is
outside of
telerances,
if
necessary distribute the
error
between 90
and
105 MHz. Check
tuning
voltage again
if
tolerances not possible to achieve.
C.
IF
ADJUSTMENT
1.
Set tuner
to approximately
98
MHz
(the tuner
must
be tuned
to an unoccupied frequency)
enter into p-^set
3,
and tune
FM
generator to display
a
curve
on
the
oscilloscope.
2.
Adjust L 709 (IFT
tuner frontend) to
maximum
and
symmetrical curve on
the
display, using
as
little
h put
signal as possible.
-
6
-