1.
Connect
an
oscilloscope to the
cue
playback output.
Re-
produce prerecorded
cue
tone
known
to
be
recorded
at
NAB
cue
tone
level.
Measure
the
peak
to
peak
amplitude of the
tone
on
the oscilloscope.
Record
this
measurement
for
future reference.
2.
Disconnect the
ac
power
and
mount
the Playback/Logic board
on
the
919-1504
extender card. Referring to the assembly
diagram, connect the signal generator to terminal 7 with
the generator shield to terminal 6.
(A
10
Ohm
load
is
provided,
so
install
a
560
Ohm
resistor
in
series
with the
generator
if
its
output
impedance
is
600
Ohms.)
Reconnect
the
ac
power.
Observing the oscilloscope
adjust
the gen-
erator
output to
yield
an
amplitude one-half
that
measured
in step
1.
3.
Do
not load a
cartridge
in the
unit,
but manually actuate
the microswitch
on
the
deck
and
operate the
controls.
Set
the
CUE
SENS
controls to
minimum
(extreme counter-clockwise).
Adjust the controls
until
the sensor
just
triggers.
5-12.
PROGRAM
RECORD
ADJUSTMENTS
5-13.
BIAS
TRAP
TUNING
Disconnect the
ac
power
and
mount
the Record/Amplifier Bias
printed
circuit
board
on
the
919-1504
extender card. Referring to the
assembly diagram connect
an
oscilloscope to
test
point
L.
Reconnect the
ac
power
and
place the
unit
in
the record
mode.
With
a non-metallic screw-
driver,
tune
L1
for
minimum
100
kHz
signal as observed
on
the oscilloscope.
In
stereo
units,
reconnect the oscilloscope to
test
point Rand tune
L2.
When
finished,
disconnect the
ac
power
remove
the extender board.
Remount
the
Record
Amplifier/Bias
Board
in the
unit,
and
replace the card cage cover.
5-14.
PROGRAM
BIAS
LEVEL
I
uon
l
THE
BIAS
SUPPLIED
TO
THE
RECORD
HEAD
IS
MOST
IMPORTANT
IN
PROVIDING
OPTIMUM
FREQUENCY
RESPONSE
AND
DISTORTION.
BIAS
REQUIREMENTS
VARY
BETWEEN
BRANDS
OF
TAPE
(AND
BETWEEN
SERIES
OF
ONE
BRAND).
IF
MORE
THAN
ONE
TYPE
OF
TAPE
IS
IN
USE,
CHECK
THE
PERFORMANCE
OF
EACH
TYPE
AT
ITS
OPTIMUM
BIAS
LEVEL
OF
OTHER
TYPES.
WHERE
OLDER
AND
NEWER
TYPES
ARE
BOTH
IN
USE
(SUCH
AS
3M154
AND
3M156),
BIAS
JUST
LESS
THAN
THE
OPTIMUM
FOR
THE
NEWER
TYPE
USUALLY
IS
AN
ACCEPTABLE
COMPROMISE.
26
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