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Fostex A-8 - Page 39

Fostex A-8
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if
the
voltage
is
1.1V
P-P.
If
it
is
off
spec,
check
frequency
(lOOKHz,
±0.5KHz)
of
the
bias/erase
master
oscillator
before
rotating
the
center
core
of
U108
to
adjust
bias
leakage.
6.4.5
Erase
current
adjustment
In
adjusting
the
erase
current,
put
the
track
to
be
adjusted
in
the
record
mode.
To
adjust
TRACK
1,
for
example,
hook
the
hot
side
of
the
oscilloscope
probe
to
TP-103
located
near
relay
K-101
and
the
ground
clip
of
the
probe
to
GND
pin
in
front
of
the
REP
EQ
pot,
R313.
Set
the
core
of
L-103
so
that
voltage
at
TP-103
is
1.7V
P-P.
The
test
point
for
TRACK
2
is
TP-203
located
near
relay
L-201.
The
GND
pin
to
be
used
is
located
left
of
the
REP
CAL
pot,
R324;
erase
current
is
adjusted
by
the
core
of
L-203.
6.4.6
Bias
current
adjustment
The
track
of
which
bias
current
is
to
be
adjusted
is
put
in
the
record
mode.
To
adjust
TRACK
1,
for
example,
hook
the
oscilloscope
probe
hot
side
to
TP-102
located
near
connector
J-101,
and
the
ground
clip
to
the
GND
pin.
Then,
set
the
BIAS
LVL
pot,
R317,
47KÍÍB
at
approximately
450mV
P-P.
For
an
accurate
adjustment,
load
a
blank
tape
(Ampex
#457,
Scotch
#227)
on
the
recorder,
record
a
test
signal,
set
the
NR
switch
to
INT,
and
trim
the
BIAS
LVL
pot
so
that
the
overall
frequency
response
is
within
3dB
between
250Hz
and
lOKHz,
or
within
5dB
when
the
higher
end
is
14KHz.
During
this
adjustment,
temporarily
set
the
screwdriver
adjusting
slot
of
REC
EQ,
R316,
1KÍÍB
so
that
this
slot
is
parallel
with
the
PCB
plane,
then
trim
it
for
a
more
flat
overall
frequency
response.
6.4.7
Recording
level
adjustment
1)
Proceed
to
the
following
adjustments
only
after
checks
and
adjustments
in
the
previous
Sections
6.4.1
n,
6.4.6
have
been
completed.
Set
the
front
panel
NR
INT/EXT
switch
to
EXT.
2)
Load
a
blank
tape
(Ampex
457
or
Scotch
227)
on
the
transport
and
apply
an
audio
oscillator
output
of
400Hz,
-lOdBV
(0.3V)
to
the
INPUT
jack
on
the
recorder
rear
panel.
Also,
plug
in
a
level
meter
to
the
OUTPUT
jack.
Taking
TRAC
K
1
as
an
example,
the
connector
number
is
"1"
for
both
INPUT
and
OUTPUT
jacks.
39

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