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3. Recording bias current
Readjust
following
the
produre
below
if the
head
is
replaced or the adjustment seems incorrect.
First adjust for chrome tape, then for normal tape.
Insert
a 1009
resistor into the ground side wiring of the
head as shown in Fig. 13.
Remember
that the ground side during recording becomes
live during play back.
Be sure to insert the resistor to the
recording ground side of the wiring after disconnecting the
wiring from the circuit board.
Connect the AC VTVM
across the resistor.
Adjust the bias control semi-fixed variable resistors VR501,
VR502 so that the currect becomes correct for both the L
and R channels setting of the CHROME
bias position.
Adjust the bias control semi-fixed variable resistor VR503
setting of NORMAL
bias position.
R/P HEAD
The standard currents are
NORMAL 400pA (40mV/1002 )
CHROME 600zA (60mV/1002 )
1000
V.T.V.M
4. Recording signal current
Fig: 13
If the recording signal currents are not adjusted correctly,
the recorded signal does not indicate the reference level on
VU meter.
More
over
the
Dolby
recording/playback
characteristics
may be so degraded that reproduction of the original sound
is impossible.
The
most
suitable
current
intersity
depends on the tape
used.
Fuji FM-C90
regular tape and Fuji FC-60 chrome
tape were used to adjust the currents in the factory.
Follow the procedure below for readjustment.
Level
meter
deflection,
bias
current
and _ playback
sensitivity must be adjusted in advance.
Adjustment for normal tape (e.g. FM-90)
1) Set the equalizer and bias switches to NORMAL.
2) Set the deck to the record
mode.
Input 1kHz signals
from
MIC
or LINE
IN jacks (with a level of —50dBs
approx.
for the MIC
input, or -10dBs
approx. for the
LINE
IN
input)
and
adjust
the
recording
volume
controls
so
that
the
level
of Line out terminals
are
-5.5dBs.
3) After
setting the signal level in this way, record the
signal on blank tape.
Playing
back
the
tape
just recorded,
adjust
VR104
(L-ch) and VR204 (R-ch) so that the level of LINE OUT
terminals
are
-5.5dBs.
Repeat
the
recording
and
playback adjustments if necessary.
5. Dolby NR circuit
(See Dolby NR circuit board = page 14)
1) Set the Dolby
NR
circuit in the record mode, and the
FET gate short to ground.
2) Adjust two semi-fixed
variable resistors VR301,401
so
that
the
voltage
of
it's
center
terminal
become
maximum.
3) Apply 5kHz sine wave signal to input terminal of Dolby
circuit.
Adjust the INPUT level so that the level of REC
MONI terminal is 17.5mV
(—33dBs).
4) Check
the level of NR
OUT
terminal, when
NR
SW
terminal shorts to ground.
CD-1740/A/B/E/U
No. 4133
5) When
NR
SW
terminal
opens,
adjust two
semi-fixed
variable resistor VR303,402 so that the level of NR OUT
terminal is +10dB +0.25dB rise at 4) step.
6) When
FET gate opens, adjust two semi-fixed variable
resistors VR301,401
so that NR
OUT
terminal level is
-2dB +0.25dB rise at 5) step.
7) Replace fet gate short and check that level at REC OUT
terminal
returns
exactly
to that observed
in step 6)
above.
8) Adjust the
INPUT
level so that
REC
MONI
terminal
level is -2.5dBs.
Check the NR OUT terminal level is not changed (0.5dB
is limit)
when
NR
SW
terminal
open
and
short
to
ground.
9) Set the playback mode.
Adjust the INPUT
level so that
REC
MONI
terminal
level is -2.5dBs.
Check
Line out terminal
level is not
changed (0.5dB is limit) when the NR SW terminal open
and short to ground.
Mechanism adjustment
1. Take-up torque
Standard torque: 40~60 gr-cm
If not as specified,
1) Replace the take-up lever arm (Fig. 14 @).
2) Replace the take-up lever arm pressure spring.
3) Clean or replace the capstan belt (Fig. 14 @).
4) Clean the right-side reel rubber outer surface, or replace
the reel rubber.
2. Fast forward torque
Standard torque: 70 gr-cm or more
If not as specified,
1) Clean the right-side reel rubber outer surface, or replace
the reel disc ass'y (Fig. 15@).
2) Clean the fast forward idler, or replace the fast forward
idler ass''y @).
3) Clean the flywheel outer surface and belt.
SPEED
ADJ
ct
th
s
Fig. 14
3. Rewinding torque
Standard torque: 70 gr-cm or more
If not as specified,
1) Clean the left-side reel © outer surface, or replace the
reel disc ass'y ©.
2) Clean the rewind idler ©.
3) Clean the flywheel outer surface and belt.
4. Tape speed
Standard
speed:
3000Hz
+2%
(at playing a 3000Hz test
tape)
If not as specified,
1) Insert your driver in hole with the motor
up side and
adjust a semi-VR for speed control in the motor case.
2) Replace the motor.
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