Philips N4307 - Interconnection Diagram; Recording Bias Current; Modulation Level Indicator Calibration

connecting
leads,
taking
care
not
to
bend
or
deform
the
switch
blades
of
54(b).
When
refitting
the
printed
panel
frame,
ensure
that
the
switch
operating
levers
are
correctly
engaged
with
the
switch
sliders
and
that
S4(a)
and
S4(b)
operate
properly.
Recording
Bias
Current:
The
recording
bias
current
should
be
18mV,
measured
as
a
voltage,
but
may
be
set
within
the
limits
10-25mV.
Switch
to
“Record”,
set
the
track
selector
switch
to
“1-4”
and
adjust
R441
so
that
a
voltage
of
18mV,
measured
with
an
A.C,
millivoltmeter,
is
obtained
at
MPr.
Similarly,
in
track
position
“2-3”,
the
same
reading
should
be
obtained
at
MP2
by
adjusting
R442.
Check
the
overall
frequency
response
and
if
neces-
sary
make
further
adjustments
to
the
bias
current
to
obtain
the
response
required.
Reducing
the
bias
current
will
increase
the
treble
response;
conversely,
increasing
the
bias
current
will
reduce
the
treble
response.
Should
the
value
of
bias
current
be
below
the
lower
limit
specified,
it
will
cause
dis-
tortion
at
high
modulation
levels;
if
above
the
upper
limit,
it
will
result
in
poor
treble
response.
If
after
adjustment,
the
level
of
bias
current
is
outside
the
range
specified
above,
a
defect
in
the
record/playback
head
or
in
the
ampli-
fier
circuitry
should
be
suspected.
Mod. fevel
Indicator
NOTES:
All sockels viewed on solder tags.
Add 200 to all contact numbers on SZ
Add 300 to all contact numbers on S3.
WIRING CODING
——e
On
unit
A,
lead
marked
@
ts
connected
to
unit E and there marked (4). Simltarly, on
unit D, tead marked is connected to unit
A and there marked
(W257) CoMPONENT LayvouT AND
INTERCONNECTION DIAGRAM —
W257d
Modulation
Level
Indicator
Calibration:
Set the
track
selector
switch
S2
to
track
“1-4”
(or
“‘2-3”’),
turn
Radio/Phono
record
level
control
R444
to
maximum
and
depress
the
“Record”
key
only.
Apply
a
1
kHz
signal
to
pin
3,
Sktr,
adjusting
the
level
so
that
a
voltage
of
3mV,
measured
with
an
A.C.
millivoltmeter,
is
present
at
MP1
(or
MP2).
The
pointer
of
the
modulation