JVC CD-1920 User manual

MODEL
CD-1920/A/B/C/E/U
STEREO CASSETTE DECK
No. 4142
February 1976

Contents
Specifications..........
Features .............-
Controls and Connections
Main Parts Location .....
New Technique ........
Main Parts Removing ....
Enclosure Assembly ...
Electrical Parts.......
Mechanical Parts
Adjustments...........
Electrical Adjustment
Mechanical Adjustment
Specifications
Type
Track system
Cassettes
Frequency response
S/N
Wow and flutter
Crosstalk
Harmonic distortion
Bias
Erasure
Heads
Motor
Tape speed
Recording time
Fast forward time
Rewind time
Semiconductors
CD-1920/A/B/C/E/U
No. 4142
Stereo cassette deck
4-track, 2-channel
C-30, C-60, C-90
20 — 18,000Hz
(30 — 16,000Hz +3dB)
with chrome tape
20 — 17,000Hz
(40 — 15,000Hz +3dB)
with normal tape
52dB (from peak level)
The S/N is improved by 5dB
at 1kHz and by 10dB above
5kHz with ANRS on.
0.09% (WRMS)
65dB
1.3% (normal tape)
AC bias (95kHz)
AC erasure
2 heads
Hard permalloy head for
recording/playback and
ferrite head for erasure
Electronically governed
DC motor
4.8cm/sec.
2 x 30 minutes with C-60
cassette
125 sec., with C-60 cassette
125 sec., with C-60 cassette
7 ICs,
26 transistors,
2 SCRs and
42 diodes
Input jacks
Output jacks
DIN connector (REC/PB) :
Power requirement
Power consumption
Dimensions
Weight
Page Page
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Mic jack x2
Max. sensitivity 0.2mV
matching impedance
6002 — 10k2
Input jack x2
Min. input level 80mV
Input impedance 100k2
Output jack x 2
Output level 0.3V
Output impedance 5kQ
Matching load impedance
50kQ or more
Headphone jack x 1
Output level 0.3mW
Matching impedance
82 — 1ka
Min. input level 15mV
Input impedance 10ka
Output level 0.5V
Output impedance 5ka
Matching impedance
50kQ or more
AC 120V, 60Hz (CD-1920/C)
AC 240V, 50Hz (CD-1920A/B)
AC 100V,120V,220V, 50Hz
(CD-1920E)
AC 100V,120V ,200V ,220V
50/60Hz (CD-1920U)
30W
Width; 15-3/8"" (390mm)
Height; 5-15/16” (151mm)
Depth; 12-5/8" (321mm)
15.8 Ibs. (7.2kg)
Design and specifications are subject to change without notice.

Features
“N/ertical-open-view”’ cassette deck
Multi-point peak level indicators
ANRS Integrated Circuit
ID (Independent Drive) mechanism
Full auto stop
Air-damped cassette door (Pat. pending)
Input select switch
Tape select switches
Controls and Connections
Oo ® 8 ®© G8 &©®D B® YD ®@ ®W ® ®
Fig. 1
WARNING
When oot in use ‘or
fomaving covers’ sh
from mains by withdrawing
wall plug.
Fig. 2
1 Headphone jack (PHONES) 16 REC-LEVEL controls
2 Right channel microphone jack (MIC-R) 17 Rewind button (REW)
3 Left channel microphone jack (MIC-L) 18 Record button (REC)
4 Left channel level meter 19 Play button (PLAY/REC)
5 PEAK level indicators 20 Fast forward button (FF)
6 Right channel level meter 21 STOP/Eject button (STOP/EJECT)
7 REC indicator 22 Pause button (PAUSE)
8 ANRS indicator 23 POWER switch
9 Cassette door 24 Left channel LINE IN terminal
10 Tape COUNTER 25 Right channel LINE IN terminal
11 Counter reset button 26 Left channel LINE OUT terminal
12 INPUT SELECT switch 27 Right channel LINE OUT terminal
13 ANRS switch 28 DIN socket (REC/PB)
14 TAPE SELECT EO switch 29 Power cord
15 TAPE SELECT BIAS switch
CD-1920/A/B/C/E/U
No. 4142

Main Parts Location
©
®
Fig. 3
New Technique
The multi-point peak level indicators let you know the
precise levels of the peak signal pulses that the mechanical
VU meters cannot follow. They are essential aids for
making good recordings, for they allow recording at
maximum levels without exceeding the magnetic saturation
level of the tape. During adjustment, sine waves are used
and the indication of the VU meters corresponds to that of
the peak level indicators. But, for ordinary musical signals,
the VU meters usually indicate lower values because of
their slower response.
oro na a = = =
O !
L-CH ! Power supply
Input H . | terminal
terminal I re Da404aP I Vcc=5V
R-ch
H
“
x
Light
Emitting
{
Input
I
Diode
(LED)
!
terminal Mecsas es Se es Se 4
Fig. 4
CD-1920/A/B/C/E/U
No. 4142
MIC jack circuit board
Main amp circuit board
Peak level circuit board
DIN jack
PIN jacks
ANRS circuit board
Power transformer
Power supply circuit board
Motor ass’y
Cds lamp
Flywheel ass’y
Head wire terminal circuit board
Air-damp pipe
Level meter (Right)
Indicator circuit board
Level meter (Left)
OONOoORWN =
The left and right channel inputs are individually rectified
and the capacitor C is charged by the higher of the left and
right channel signal levels. The variable resistor VR adjusts
the lighting level of the LED. When no input signal is
available, the transistor X is conducting because base
current is applied through the resistance. At this time the
output terminal of the IC TD3404AP is at a high level (5V),
providing no current to the LED, which does not light up.
When the base potential of the transistor X is reduced to
below 0.6V by the input signal, X becomes non-conducting,
the IC output is at a low level (OV) and current flows to the
LED and lights it up.
The multi-point peak level indicators consist of five of the
circuits encircled by the broken line, connected in parallel.
Each of the VRs is adjusted according to the signal level at
which the LED lights up to indicate.
A circuit which, with high level inputs, provides low level
outputs and vice versa, such as TD3404AP, is usually called
an inverter. This 1C TD3404AP, widely used in computers,
is a digital |C which includes six such inverter circuits, five
of which are used in this set.
For easy use, the peak level indicator circuit of this set is so
designed that the higher one of the right and left channel
signal levels is detected to light the LED. The attack time is
established at about 4msec, achieving both easy visibility
and indication accuracy.
For adjustment, see the section ‘“ADJUSTMENTS” on page
rp

Main Parts Removing
This cassette deck which features a compact design and high performance uses minuature-sized parts which are closely
arranged. Use special care when servicing it.
Enclosure Assembly
Steel cover
REC-LEVEL Bottom cover
knobs
Fig. 5
REC LEVEL Pull off the inner knob and the outer ring @)
control knobs to front side.
Cassette door 1. Press the EJECT button to open the GB)
cassette door.
Inner knob — for left channel
Outer ring — for right channel
e When the cassette door be
removed, can easy clean or
demagnetize the head.
e When replace the cassette door,
insert it that ball bearings be
full locked.
. Remove the cassette door by sliding it
upward.
Remove 2 screws and washers of both
sides (L & R).
Steel cover Almost all parts of circuit board
can be checked when only steel
cover is removed.
Bottom cover e 3¢ 8mm screws
e Almost all pattern side of circuit
board can be checked when only
bottom cover is removed.
Remove 6 screws and 6 washers fastening
the bottom cover.
Front panel . Remove 3 tapping screws fastening
up side of the F. panel.
. Remove 2 tapping screws fastening
under side of the F. panel.
Remove the front panel after
removing the steel cover and
bottom cover.
Remove meter escution after
removing the front panel.
Meter escution Remove 2 screws (L and R side of up-
ward) fastening the meter escution.
Rear cover . Remove 3 screws fastening the bottom
cover.
. Remove 2 screws (L and R side of
under side) fastening the rear cover.
@
®
®
©
@
©
Electrical Parts
Main amp C. board
Fig. 6
Main amp
circuit board
Remove the main amp circuit
board after removing the front pan
1. Remove 2 screws fastening the switch
ass’y.
. Remove rod of the recording lever.
. Remove 4 tapping screws fastening the
main amp circuit board.
REC volume Remove washer and nut of the V. Resistor
shaft fastening the front bracket.
Peak level Remove 4 tapping screws fastening the
C. board peak level C. board.
Power supply Remove 4 tapping screws fastening the
C. board power supply C. board.
ANRS C. board Remove 4 tapping screws fastening the
power ANRS C. board.
Power transformer Remove 2 screws and washers fastening
the power transformer.
MIC jack ass’y Remove 2 screws fastening the MIC jack
ass’y.
Remove the V. Resistor after
removing the front panel.
The left side of front bracket.
CD-1920/A/B/C/E/U
No. 4142

Mechanical Parts
Cassette holder
Removing the cassette holder
Don’t remove this case
froin. mecha chassis Remove only the motor
Mecha
chassis
Cassette
Motor speed
adjustment holl
Flywheel holder
®
Front bracket
. @ Nylon washer
Fig. 7
CD-1920/A/B/C/E/U
No. 4142
Remarks
. Press the EJECT button, then the
cassette door be loaded
Remove the brake arm (1) from stud
of cassette holder.
. Remove a screw @ fastening the
recording arm.
. Remove 4 screws fastening the front
bracket.
. Pull off the mecha-ass’y to back side.
Cassette holder
. Remove a screw fastening the cassette
holder.
. Remove “E” ring holding the brake arm.
. Remove “E” ring holding the shaft.
. Pull off the shaft to right side.
. Remove the cassette holder by sliding
it upward on A position of panel
bracket.
Don’t remove the motor case from mecha
chassis and remove the motor only, you
can be easy replaced it.
1. Remove the take up belt.
2. Remove the capstan belt.
3. Disconnect 2 wires of motor.
4. Remove a screw fastening the bottom
plate of motor.
. Remove a screw fastening the transistor.
. Press the motor from upward (pully
side), then can be removed the motor.
Flywheel . Remove 2 screws fastening the muting
SW bracket.
. Remove the capstan belt.
. Remove 4 screws fastening the flywheel
holder.
. Pull off the flywheel.
Pinch roller
arm ass’y
. Remove “E” ring holding the pinch
roller arm ass’y.
. Remove spring on the arm ass’y.
. Remove 2 screws fastening the cassette
holder.
. Remove the counter belt.
. Remove “E” ring holding the take up
disc.
. Pull off the disc from the shaft.
Take up disc
. Remove the cassette holder.
. Remove “E” ring holding the supply disc.
. Pull off the disc from the shaft.
Supply disc
NOTE: 1. Don’t dirty, slippery and undue run-out the capstan belt and counter belt.
When the brake arm remove, be
carful not to stain the ‘‘O” ring
and don’t less grease.
When replace the cassette holder,
don’t forget 2 washers of the shaft.
Be carful not to stain the belt.
Be carful no to stain the belt.
When replace the flywheel, don’t
forget to insert a nylon washer
to it’s shaft.
2. Adjust height of the motor pulley, when the capstan belt connect to the flywheel from the motor, pulley,
so that it will be parallel to the chassis.

Adjustments
Electrical Adjustment
Equipment and measuring instruments used for adjustment.
1. V.T.V.M. (measuring AC in millivolt)
2. Audio-frequency oscillator
(range: 50—20kHz and output OdB with impedance
6002 )
3. Attenuator
4. Reference tapes for REC/PB
TS-1 (QP-12, C521V) — normal tape
TS-2 (TP-18, C401R) — chrome tape
5. Reference tapes for playback
VTT-664 (1kHz 16mM)
VTT-666 (400Hz 22mM)
6. Resistors
1002 (for measurement of the bias current)
AUDIO Freq. OSC
6002 (for attenuator matching) Fig. 8
. Set the deck in the record mode, and
set INPUT SELECT switch at LINE
IN.
2. Input 1kHz signals (about 10dBs)
from LINE IN jacks and adjust
volume control so that test points
and are -3dBs.
3. Adjust semi-fixed resistors VR103
and 203 in this condition it obtain
zero VU meter reading.
Peak level 1. Set as same mode at step(1) and (Peak level
adjust semi-fixed resistor VR703 so C. board
that the 0” indicator is lighting and TAA305306)
no lighting at -1dB from step(1) with VR703
attenuator.
2. Adjust semi-fixed resistor VR704 so VR704
that the ‘’-5” indicator is lighting at
-5dB from step(1) with attenuator.
3. Adjust semi-fixed resistor VR705 so VR705
that the ‘’-10” indicator is lighting
at -10dB from step(1) with attenuator
and no lighting at -11dB from step(1)
with attenuator.
4. Adjust semi-fixed resistor VR702 so
that the “+3” indicator is lighting at
+3dB from step(1) and no lighting at
+2dB from step(1) with attenuator.
5. Adjust semi-fixed resistor VR701 so
that the +6” indicator is lighting at
+5dB from step(1) with attenuator.
1. Level meter
deflection
(Main amp
C. board
TAA305204)
The angle of meter deflec-
tion has been factory-
adjusted, but should be
adjusted when parts are
replaced.
VR103,203 When adjust the level meter,
don’t use a headphone.
Playback 1. Set equalizer switch at normal and (Main amp 1. Adjust playback sensi-
sensitivity playback reference tape VTT-664. C. board tivity when heads are
Adjust semi-fixed resistors VR101(L) VR101,201 replaced.
and VR201(R) so that test points
and are —3dBs, then level
meters indicate zero VU (about
0.3V at LINE OUT).
2. Playback reference tape VTT-666 and
check that the VU meter indicate
CAL.
2. Make this adjustment
after making sure level
meter deflection angle is
correct.
No. Item
4. | Bias
current
Recording
signal
current
ANRS
circuit
(DC bias)
. Set the deck in the record mode.
. Input the 1kHz signals to LINE IN
Procedure
. Insert a 1009 resistor into the ground
side wiring of the head and connect
the V.T.V.M. across the resistor, and
set the BIAS SW at chrome or normal.
Set the deck in record mode.
Input signals to LINE IN jacks and
adjust the recording level control so
that the test points and are
-13dBs.
First adjust for chrome tape, then for
normal tape.
. After the deck correct the head wires,
input the standard level of 1kHz sig-
nals to use reference tape, and measu-
re REC/PB frequency response at
10kHz.
. Adjust semi-fixed resistors VR502,504
(chrome) 501, 503(normal) so that
the 10kHz frequency response does
become +10dBs
Repeat the recording and playback so
that 10kHz signals become correct fre-
quency response.
Level over at 10kKHz compared
with 1kHz — bias current less
Level less at 1OkKHz compared
with 1kHz — bias current over
jacks and adjust the recording level
control so that the test points and
are -13dBs, make recording in
such a way.
. Adjust the semi-fixed resistors VR104,
204 (chrome), VR105,205(normal) so
that the test points are -13dBs.
. Disconnect +B of bias circuit so that
oscillator does not operate.
(Desolder the BIAS CUT in main amp
circuit board)
. Set the deck in the record mode.
. Apply signal of 1kHz to LINE IN and
adjust volume control so that test
points [12] and [62] (in main amp
circuit board) are OdBs.
. Then, connect the V.T.V.M. to test
points (h) G) in main amp circuit
board and adjust below steps.
. Apply signal of 1kKHz, —40dB to LINE
IN and adjust R401,401 so that LINE
OUT is -34.3dB with ANRS ON.
. Apply signal of 5kHz +40dBs to LINE
IN and adjust R302,402 so that LINE
OUT is -17.5dBs with ANRS ON.
. When apply signal of 1kHz to LINE
IN and output is OdB, adjust steps (5)
through (6) so that level does not
change when ANRS is turned on and
off (£5dB less).
. Playback reference tape VTT-664 and
check LINE OUT level so that it’s
compare are +1dB less with ANRS SW
on to off.
. Connect +B of bias circuit (Solder the
printed in main amp circuit board for
connect +B).
(re | Ree [Remar
1. Adjust bias current when
heads or other parts are
replaced.
2. Use the highclass V.T.V.M.
for high frequency re-
sponse.
3. After the bias current
adjustment, check the fre-
quency response at 10kHz
signals.
chrome
VR502,504
normal
VR501,503
(Main amp
C. board)
. This adjustment is necessa-
ry when heads are replaced.
2. Make this adjustment after
adjusting steps (1) through
(4).
3. Check the frequency re-
chrome sponse at 10kHz after this
VR104,204 adjustment.
normal 4. Set EO and BIAS switches
VR105,205 according to type of tape
used,
1. See figure of ANRS
circuit.
2. Repeat steps (5) through
(6).
Step (5) is 5.7dB up.
Step (6) is 2.5dB up.
CD-1920/A/B/C/E/U
No. 4142

Mechanical Adjustment
1. Replacement and adjustment of the head
2.
(See @ ®@ © O in Fig. 7 of page 6)
If either of the record/playback head and the erase head
shown low performance because of wear, broken wire or
excessive magnetization, it should be replaced.
Screws to be removed
REC/PB head
E head
REC/PB head
After replacement, adjust the head for azimuth.
1. 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).
2. Play the azimuth adjustment test tape (e.g. JVC’s
VTT-653, 10kHz).
3. Turn the azimuth screw so that the output will
become maximum.
If the azimuth adjustment test tape is not available,
play a music cassette.
When treble response becomes optimum, set the
adjustment screw (@).
4. After this adjustment, the screw @) should be locked
with a bond.
If necessary, adjust playback sensitivity,
current, REC signal current and bias trap.
REC _ bias
Erasing head
After replacement, adjust the head for height position.
1. Play the test tape (C-120).
2. Turn the adjustment screw © so that the test tape
move running to no touch the tape guide tip (up or
under side).
If checking is difficult, cut front upper side of the
cassette of C-120 by a cutter knife, etc., then can easy
check it.
REC/PB HEAD
Adjusting the motor speed
1) Play back reference tape (3000Hz), and adjust the
semi-VR in the motor that it’s speed in 3000Hz+2%
(2970Hz~ 3060Hz).
2) CD-1920 need not to change cycle, whether the
commercial frequency in your area is 50 or 60Hz.
CD-1920/A/B/C/E/U
No. 4142
Trouble Shooting Guide
[ELECTRICAL CIRCUIT]
1. Playback tone quality is poor.
1. Check the record/playback head for dust.
2. Check the record/playback head for wear.
If worn excessively, the loss of treble response will
result.
3. Check wiring for a short-circuit.
Check each transistor for condition.
2. Recording tone quality is poor.
The playback tone quality of a recorded tape such as the
audition tape is good, but the recording by this unit
produces poor tone quality. In this case, the unit should
be checked in the following manner. ‘
1. By monitoring a music while recording, check the
tone quality. |
2. If found poor, check the wiring of the recording
system for a broken wire and short-circuit.
3. If no irregularity is found, check the recording bias
current. Also check the oscillation circuit.
3. For other failures, check the unit in the same manner as
other amplifiers.
a a
3. Standard torque
70 gr-cm or more
70 gr-cm or more
35~ 70 gr-cm
Fast forward torque
Rewinding torque
Take-up torque
4. Door opening speed adjustment
(See in Fig. 7 of page 6)
Door opening is opened slowly by screw E is loosened
and move the bracket position to back side. (The spring
tension varies strong)
[MECHANISM SECTION] (wow and flutter)
If wow and flutter increase, check the following points.
If there is defect in revolving parts, the wow and flutter
generated will increase in proportion to the number of
revolutions.
es
Capstan and
flywheel
Pinch roller
Take-up idler arm
[MECHANICAL REPAIRS]
Take-up idler arm Standard take-up torque not available.
Play a 3000Hz test tape, and defective part can be detected
from the sound.
Capstan shaft has excessive run-out.
Flywheel turns heavily.
(shaft seisure, thrust play, etc.)
Replace flywheel.
Adjust plastic screw with flywheel holder.
Clean the capstan shaft and the groove in the
flywheel.
Apply oil to the metal position.
Replace the capstan assembly.
Rough rotation (Deformation
scratches, or dust).
The angular position of the pinch
roller is not correct.
The pinch roller pressure is not correct.
Replace pinch roller.
Clean the pinch roller or apply oil to the rotary
shaft.
Adjust the pinch roller so that it-is parallel with
the capstan shaft.
Adjust the pinch roller spring.
Clean the belt or remove the distortion.
Replace the belt.
Belt has undue run-out. ;
Belt is dirty or slippery.
Back tension is irregular, or back
tension is too strong.
Replace supply disc.
Replace back tension spring (under supply disc),
or apply silicon grease.
Motor shaft has undue run-out.
Motor pulley is oily and dusty.
Replace motor.
Clean motor pulley.
Pulley has deflection.
Pulley is stuck.
Replace take-up idler arm.
Replace take-up idler arm.
Replace take-up idler arm pressure spring.
Clean or replace capstan belt.
Clean rubber rim of the right reel.
Reel disc and idler Fast-forward torque not available. Clean rubber rim of the right reel or replace reel
disc assembly.
Clean or replace fast-forward idler.
Clean rubber rim of the left reel or repalce reel
disc assembly.
Clean rewind idler tire.
Door brake Door does not open fully. Apply a small quantity of silicon grease to the
inside surface of the brake pipe.
(SHIN ETSU KAGAKU KS-64 or equivalent)
Braking not sufficient. Replace brake pipe or rubber O-ring.
Check slide lever and solenoid iron core for
smooth movement.
Check if the locking and sliding parts of the
operation button cam are well coated with
molybdenum.
Auto-stop
mechanism
Auto-stop not operating.

Maintenance
To
get
long,
trouble-free
service,
maintenance
is
important.
2.
Pinch
roller
and
capstan
Do
not
forget
cleaning
and
demagnetizing.
1)
Press
the
EJECT
button
with
the
POWER
switch
ON
to
open
the
cassette
door.
Cleaning
2)
Press
the
PLAY
button,
and
the
pinch
roller
will
After
long
use,
the
heads
and
tape
part
—
capstan,
pinch
move
out
and
rotate.
roller,
etc.
—
will
become
dirty
with
dust
or
magnetic
3)
Apply
a
soft
cloth
(soaked
in
alcohol,
it
will
be
more
particles.
Dirty
heads
cause
imperfect
erasing
or
high
effective)
to
the
rotating
pinch
roller
and
capstan.
frequency
drop-off.
A
dirty
capstan
and
pinch
roller
will
Be
careful
not
to
let
the
cloth
get
caught!
cause
unstable
tape
speed,
leading
to
increased
wow
and
*
Do
not
use
any
cleaner
besides
alcohol
or
a
flutter.
specifically
prepared
tape
head
cleaning
solution.
Always
keep
them
clean
by
following
the
procedure
below.
1.
Heads
1)
Press
the
EJECT
button
with
the
POWER
switch
OFF
to
open
the
cassette
door.
a
2)
Remove
the
cassette
door
by
sliding
it
upward.
a
fo
—~ ra
Soft cloth —- a
Direction of rotation
Nj f pinch roll
Pinch roller N ih ile
Capstan i
oy,
d
Fig. 10 Fig. 12
3. Cabinet
When
the
cabinet
becomes
dirty,
wipe
it
with.
a
soft
3)
Press
the
PLAY
button
to
move
the
heads
out.
cloth
soaked
with
a
neutral
cleaning
solution
of
a
4) Use the head cleaning stick provided to wipe the polishing cloth.
surface where the tape comes into contact with the * Do not use thinner or benzine.
head.
(It
is
effective
to
moisten
the
cotton
with
alcohol.)
Demagnetizing
The heads are made from a material resistant to
magnetization, but after long use they may become
magnetized. A magnet brought into their vicinity can
magnetize the heads, causing excess noise. If noise seems to
have increased, demagnetize the heads with a head
demagnetizer through the following procedure.
1. Turn the POWER switch OFF.
2. Wrap the tip of the demagnetizer with vinyl tape or soft
cloth so as not to damage the head surface. Switch on
the demagnetizer and bring it close to the head.
3. Move the tip of the demagnetizer slowly first to the left
and right, then up and down in front of the head.
Gradually move it away from the head and switch it off
at a distance of more than 30cm. (12’’)
4. The erase head need not be demagnetized. The capstan
shaft and tape guide should be demagnetized in the same
way as the record/playback head.
* Do not bring a magnetized metallic object (a
.
screwdriver,
for
example)
near
the
head
as
this
will
Fig.
11
increase
noise.
CD-1920/A/B/C/E/U
No. 4142

Wiring
CD-1920A/B
CD-1920E
Select switch
CD-1920U
Fig. 13
CD-1920/A/B/C/E/U
No.
4142
-