JVC CD-1740 User Manual

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

JVC CD-1740 Specifications

General

Brand	JVC
Model	CD-1740
Category	Cassette Player
Language	English