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Replacement and Adjustment of the Head
If either of the record/playback
head and the erase head
shows
low performance
because
of wear, broken
wire or
excessive magnetization, it should be replaced.
1. Replacing the head
Remove
the top cover, and the heads will be exposed to
view as show Fig. 11.
The record/playback head can be removed by loosening the
Screws
@
and QQ, while the erase head by loosening the
screws () and @
After replacement, adjust the head for azimuth.
If necessary, adjust playback sensitivity.
2. Azimuth adjustment
Insert the cord plug into the LINE OUT jack (or REC/PB),
and
connect
the other
end of the cord to a V.T.V.M.
(vacuum tube voltmeter).
Then play the azimuth adjustment standard tape (e.g. JVC's
VTT-615
10kHz), and turn the adjustment screw 2) so that
the output will become maximum.
Adjustments
Principal adjustment of electical circuit
(See main circuit board = page 10)
This deck
has many
check points in the circuits so that
checking and correct adjustment is easy.
Adjust the circuits according to the procedures given below.
Adjustments;
1. Deflection of level meters
2. Playback sensitivity
3. Bias currents
4. Recording signal currents
5. Dolby NR circuit
Equipment and measuring instruments used for adjustment.
1) V.T.V.M. (measuring AC in milivolts)
2) CR oscillator
3) Attenuator
4) Test tape (VTT664)
5) Blank tapes
[Fuji FM-C90
(normal) and Fuki FC-60
(chrome) or equivalent]
6) 1002
resistor (for REC bias current)
6002
resistor (for attenuator matching)
1. Level meter deflection
They were correctly adjusted before being shipped from the
factory, but readjustment will be necessary
if the related
parts are replaced.
1) Set the deck in the record mode.
2) Input 1kHz signals from MIC or LINE IN jacks (with a
level
of
-50dBs
approx.
for MIC
input or -10dBs
approx. for LINE IN input).
Adjust
the
recording
volume
controls
so
that
the
voltages across
Line out or recording monitor Terminal
or Dolby NR circuit are —5.5dBs.
3} Adjust
two
semi-fixed variable resistors VR103
(L-ch)
and VR203 (R-ch) so that the level meters indicate OVU.
If the azimuth
adjustment
standard
tape is not available,
play
a
music
cassette.
When
treble
response
becomes
optimum, set the adjustment screw.
After this adjustment, the screw @ should be locked with a
bond.
2. Playback sensitivity
Playback sensitivity of the head may
not be correct after
the head is replaced: follow the procedure below to adjust
it.
Before
adjusting
the playback sensitivity, the level meter
deflection must be adjusted.
*
Using
VT T664
A ikHz
16mM/mm
standard signal is recorded on this
tape.
Adjust VR101
(L-ch) and VR201
(R-ch) so that
the level of Line out terminal -5.5dBs while play back
the tape.
The
equalizer
switch
must
be set to NORMAL
when
tape VTT664
is used & the noise reduction switch must
be set to OFF position.
CR OSILLATOR
lore
OUT PUT
LINE IN
ATTENUATOR
50004.
~ouT Put
PUT
Fig. 12
CD-1740/A/B/E/U
No. 4133
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