JVC CA-C55BK - Electrical Adjustments; Playback Level, Frequency Response, and Bias Adjustments

DX-C55BK
3.
Electrical
Adjustments
(Make
the
following
adjustments
after
adjusting
the
head
azimuth.)
In principle, the adjustments should be made in the following sequence.
Set the NR switch to OFF and the BEAT CUT switch to 71”.
Adjustments
marked
with
an
asterisk
(*)
should
always
be
made
after
the
head
is
replaced
OdBs
=
0.775V.
Adjustment
|
Standard
;
Location
Value
Remarks
1) Adjust the normal speed first,
and perform the high speed
adjustment.
Adjustment Method
1. Connect a frequency counter to the DOLBY
TP(figure 3) and play back VTT-712.
2. Normal speed Adjustment
1) Mechanism B
Play back deck B to adjust the semi-fixed
resistor R400 on ENB- 180-2.
2) Mechanism A
Play back deck A to confirm that the
difference between deck A and deck B is
within +51Hz.
3,000 Hz
+10Hz
6,000Hz
. High- d check >
igh-speed chec vipa
1) Mechanism B
Play back deck B check 6,000Hz + 600Hz.
. Connect an electronic voltmeter to the DOLBY
TP (figure 3) .
Play back VTT-724 (1 kHz: -4dBs) to adjust
the semi - fixed resistors.
Standard level
(Playback
Level)
1) The playback level varies when
the head is replaced so should
be adjusted.
Use an electronic voltmeter
with an impedance of 100 kQ
or more.
Playback . Connect an electronic voltmeter to the DOLBY
Frequency TP (figure 3). ode
- s
Response
=
|2_
Play
VTT-703L
(10kHz:
-10dBs)
and
adjust
(245mV)
semi-fixed resistors to obtain the standard
values.
(
Recording
.
Connect
a
frequency
counter
to
the
BIAS 1331
100
kHz
{Set
the
BEAT
CUT
SWITCH
to
“1”.
Bias
TP(figure
3),and
perform
a
recording to
adjust
+6
kHz
Frequency
bias
frequency
.
Record/Play
|1.
Supply
1kHz
and
12.5kHz
with
30mV
signals
0+2dB
|Refer
to
figure
2
below.
Frequency
to
VCR/PHONO
terminals
respectively
to
record
ei
kHz
|!)
The
recording
and
playback
Response
them.
aati
iplas-
current)
with
1
kHz
frequency
response
of
a
2.
Connect
an
electronic
voltmeter
to
the
DOLBY
as
the
cassette
deck
are
adjusted
by
TP
(figure
3)
to
confirm
the
recorded
values
.
standard.
adjusting the bias.
2) Perform the adjustment with
normal tape and confirm that
the values are within the
range formetal tape.
3. If the values are not satisfied , adjust the
semi-fixed resistors and record the signal again
to confirm the recorded values.
Response With a small bias current
(dB)
Optimum level
R355(L)
R356(R)
Decreasing a
oO
in high frequency
With a large bias current
Increasing
in high frequency
Figure 2
100Hz
1kHz
12.5kHz
Frequency
{No.20474) 2-13
1