KD-A77 A
JVC KD-A77 A, KD-A77 B, KD-A77 C, KD-A77 U, KD-A77 E Service Manual
...
JVC
MODEL
KD-A77
A/B/C/E/J/U
STEREO
CASSETTE
DECK
No.
4186
September
1979
KD-A77A/8/C/E/J/U
r-
Contents
Specifications
.........................................................
2
Features
..................................................................
3
Controls and Connections
..........................................
3
Main Parts Location
...................................................
4
Maintenance
............................................................
4
New
Technique
......................................................
5
Removal
of
the Main Parts
..........................................
6
Main
Adjustments
...................................................
1 0
Block Diagram
......................................................
16
Integrant Circuit
......................................................
18
Standard Schematic Diagram
of
KD-A
77
Amplifier
circuit
................................................
1 9
Mecha. control
circuit
..........................................
20
Wiring
Connection
(1
)
of
KD-A 7 7
..............................
21
Specifications
Type
Track
system
Tape speed
Frequency response
OVU
Metal
tape
SA/Cr02
tape
-20VU
Metal
tape
SA/Cr02
tape
*
1
*2
SF/Normal tape
*
3
SIN ratio
Stereo cassette
deck
4-track,
2-channel
1-7/8
inch/sec
(4.8
cm/sec)
25-12500Hz
±3dB(Typical)
25
-
8000Hz
± 3dB(Typical)
15-20000Hz
25
-1
8000Hz
± 3dB(Typical)
15-20000Hz
25-
1
8000Hz
± 3dB(Typical)
15-19000Hz
25-17000Hz
±3dB(Typical)
Surpases DIN
45
500
60dB (from peak level, weighted,
Metal tape)
The SIN is improved by 5dB
at
1 kHz and by
10dB
above 5kHz
with
ANRS on.
(DIN
45
500
weighted)
Effect
of
Super ANRS : (normal tape)
Improvement
of
SIN : the same
as
with
ANRS
Improvement
of
frequency response
:
OVU
recording; 6dB
at
10kHz
+
5VU recording; 12dB at 10kHz
Improvement
of
distortion
Wow
and
flutter
Crosstalk
Hormonic
distortion
Bias
Erasure
Heads
No.4186
OVU
recording;
3 % or less
at
10kHz
+
5VU recoridng;
3 % or less at 10kHz
0.04%
(WRMS),
0.14%
(DIN
45
500)
65dB
(1
kHz)
K3;
0.4%,
THD:
1.0%
(metal tape, 1 kHz OVU)
AC bias
(85kHz)
AC erasure
(85kHz)
3 heads
SEN
ALLOY head
for
recording,
SEN
ALLOY X
cut
type
for
playback and
two-gap
SEN
ALLOY head
for
erasure
Wiring Connection (2)
of
KD-A77
..............................
22
Enclosure
Ass'y
and Electrical Parts
...........................
25
Enclosure
Ass'y
and Electrical Parts List
..................
23
Mechanical Components Parts
.................................
26
Mechanical
Components
Parts List
........................
28
Printed Wiring Board Parts
Main
Amp.
P.W. Board Parts
....................................
33
Power Supply P.W. Board Parts
.................................
34
Main
Amp.
P.
W.B
Parts List
.................................
30
Power
Supply P.W.B Parts List
..............................
35
Other
P.W.B Parts
...................................................
37
Other
P.
W.B
Parts List
.......................................
39
Packing
......................................................
Back cover
Accessories
................................................
Back cover
Motors
Fast
forward
time
Rewind
time
Semiconductors
Input terminals
Output
terminals
Power requirement
Power consumption
Dimensions
Weight
FG
type
DC
servo
motor
(for
Capstan)
DC
motor
(for
Reel)
85
sec.
with
C-60
cassette
85
sec.
with
C-60
cassette
1 8 ICs,
49
transistors,
59
diodes,
14
LEDs
Mic jack x
2,
Max. sensitivity;
0.2mV
(-72dBs)
Matching impedance;
6000-10kO
Input jack x
2,
Min. input level;
80mV
(-20dBs)
Input impedance;
100kO
Output
jack x
2,
Output
level;
0-300mV
Output
impedance; 6kO
Matching impedance:
50kO or more
Phones jack x 1,
Output
level;
0-0.5mW/SO
Matching
impedance:
80-1
kO
AC
120V,
60Hz
(KD-AnCW
AC
240/220/120V,
50/60Z
(KD-A
n
A/B/E)
AC
240/220/120/1
OOV,
50/60Hz
(KD-A77U)
36W
17-3/4"
(450
mm) W
4-3/4"
(120
mm) H
12-7/16"
(316mm)D
18.3
Ibs
(8.3
kg)
Note:
*
1 ... SCOTCH MET AFINE or Equivalent
*
2 ... TDK SA or Equivalent
*
3 ... MAXELL
UD
or Equivalent
Design and specifications are subject
to
change
without
notice.
- 2 -
Features
1. 3
SA
(SEN-ALLOY) heads
Combined
SA
(SEN-ALLOY) record/play (X-cut type)
heads make possible record monitoring. The erase
head is a 2-gap head also made
from
SA
(SEN-ALLOY).
2.
Two-motor
ID (independent Drive) mechanism
This mechanism incorporates a
newly
developed Back
Tension
system
which
gives improved tape
contact
with
the
head.
3.
Self-illuminated
buttons
for
full logic mechanical
operation (excluding STOP or REC-MUTE modes.)
4.
Three position Metal-Tape-Compatible tape select
switch.
METAL - FeCr _
SA/Cr02
NORM
(Automatic
switching
between
SA/Cr02
and NORM)
5. The
REC
MUTE
button
is at
the
right side
of
the
mechanical operation
buttons.
KD-An
A/B/C/E/J/U
6.
ANRS
which
reduces tape hiss
to
an
inaudible level
and Super ANRS
which
improves linearity
at
high fre-
quencies are incorporated.
7.
MEMORY/AUTO
REW
switch
8. Recording equalizer
switch
9.
Timer
standby
capability
for
automatic
recording or
playback using an
AC
timer.
10.
Geared and oil-damped cassette holder.
11.
New
Metal-Tape-Compatible
multi-peak
level in-
dicators
(+
9dB,
+ 6dB, +
3dB,
-2dB, -7dB).
together
with
back-lit VU meters
with
the
expanded
coverage
from + 7VU
to -20VU,
make level observa-
tion
easier.
12.
OUTPUT volume (for LINE and HEADPHONES use)
13.
Remote control terminal (for
the
optional remote
con-
trol
unit
- R-30E).
Controls and Connections
2 3
4
5
6
10
11
12
14
15
16
17
18
19
20
21
==
==
==
==
==
==
==
==
==
==
r-
==
. .
==
'-
1.
VU
meters and
Multi-point
peak level indicators
2.
INPUT LEVEL control
3.
TAPE
indicators
4.
ANRS/Super ANRS indicators
5.
Cassette holder
6.
MEMORY/AUTO REW
switch
7.
Tape counter/counter reset
button
8.
EJECT
button
9.
TIMER STANDBY
switch
10.
PHONES
jack
11.
MIC jacks
12.
INPUT SELECT
switch
13.
ANRS
switch
14.
TAPE
SELECT
switch
15.
REC
EQ
switch
1
6.
OUTPUT LEVEL
control
n
LJ
•
22
23
24
[f]
r~:f
~1
r
-[
~
I
1 7. MONITOR
switch
1 8. Cassette Operation
buttons
~~
REW
(rewind)
button
~~
FF
(fast
forward)
button
~
PLA Y
button
• STOP
button
o
REC
(record)
button
11
PAUSE
button
REC
MUTE
button
19.
POWER
switch
20.
Power
cord
21.
Voltage select
switch
(KD-A
77
A/B/E/U)
22.
REMOTE CONTROL
socket
23.
LINE
IN
(REC)
terminals
24.
LINE OUT (PLAY) terminals
- 3 -
No.4186
KD-A77
A/B/C/E/J/U
Main Parts Location
2 3 4 5 6
7
9
"--------
8
1 1
1 2 1 3
(Mechanical parts)
1.
Front
panel assembly
1.
Switch
holder (U
2.
DC solenoid
for
playback
2.
Supply
reel
ass'y
3.
Reel
motor
3.
Idler
ass'y
4.
Geared and oil-damped brake
ass'y
4.
Reel
motor
ass'y
5. Variable resistor (INPUT LEVEL control) 5. Take-up reel
ass'y
6.
Meter
cover
6.
Switch
holder
(R)
7.
LED P.W. Board
ass'y
7.
Connecting
wire
(for play solenoid)
8.
Hall
element
P.W. Board
ass'y
8.
Capstan
9.
Power
switch
9.
Slide base
ass'y
10.
Power
transformer
10.
Stad
with
pad (for
back
tension)
11.
Remote
control
socket
(DIN
socket)
11.
Erase head
12.
Pin
jacks
ass'y
12.
Combined
SA
(SEN-ALLOY) record/play heads
13.
Mecha.
control
P.W. Board
ass'y
13.
Pinch roller
ass'y
Other
mechanical parts are
the
same
as
location
of
model
KD-A6:
Please refer
to
the
service manual 0
KD-A6
A/B/C/E/J/U
(No.
4179
- page
4).
Maintenance
To
get
long, trouble-free service,
maintenance
is
important.
Do
not
forget
cleaning and
demagnetizing.
Cleaning
After
long,
the
heads and tape
part
- capstan,
pinch
roller,
etc. -will
become
dirty
with
dust
or
magnetize
particles.
Dirty
heads cause
imperfect
erasing
or
high
frequency
drop-off. A dirty
capstan and pinch roller
will
cause
unstable
tape speed, leading
to
increased
wow
and
flutter.
Always
keep
them
clean
by
following
the
procedure
below.
1.
Heads
1)
Push the EJECT
button
to
open
the
cassette
holder.
2)
Push
up
the
transparent
cover
to
remove
it.
3)
Use
the
head cleaning
stick
to
wipe
the
surface
where
the
tape
comes
into
contact
with
the
head.
(it
is
effective
to
moisten
the
cotton
with
alcohol.)
2.
Pinch roller and capstan
Close
the
cassette
holder
with
its
transparent
cover
remov-
ed. Press
the
tape
detection
pin inside
the
cassette
com-
partment
and
set
the
deck
in
the
playback
mode.
Insert
the
cleaning
stick
into
the
hole on
the
right
side
at
the
bottom
of
the
cassette
holder and clean
the
pinch roller and
oop"an.
~~:,"'h
"",,
~.~
Cleaning stick
No.
4186
- 4 -
3.
Cleaning the cabinet and panel
Wipe
the
cabinet
and panel clean
with a soft
cloth
dipped in
a neutral cleaner. Do
not
use thinner, benzine,
alcohol
or
other
strong
solvents,
as these
will
cause
damage
to
the
surface
finish
of
the
cabient
and panel.
Demagnetizing
The heads are made
from
a material resistant
to
magnetiza-
tion,
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 inceased,
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
of
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
30
cm
(1
2").
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
increase noise.
Oiling
Feed one or
two
drops
of
machine oil
to
pinch
roller
shaft
once
or
twice
a year
under
normal
conditions
of
use.
Avoid
oiling
them
excessively, or
rotation
may
become
ir-
regular because
of
oil splashes.
New
Technique
Combination
SA
heads
for
recording and
playback
(Fig.
Al
Due
to
its
high
recording
density,
Metal
Tape requires
recording and
playback
heads
that
are made
of
materials
having
a greater
maximum
magnetic
flux
density
than
con-
ventional
ferrite
or
permalloy.
The
combined
record/playback
heads,
newly
developed
for
the
KD-A
77,
both
employ
SA
(Sen-Alloy)
to
ensure high
performance.
The
SA head has
advantages
over
conventional
heads in
various fields
such
as
fewer
core loss, greater gap ac-
curacy,
better
wear
and corrosion resistance.
However,
its
biggest
feature
is its high
maximum
magnetic
flux
densi-
ty.
Because
of
this,
the
SA
head can bring
the
most
out
of
the
superior
performance
of
Metal
Tape. This is especially
true
for
its
extended
frequency
response
at
high frequen-
cies;
something
that
has never been possible
to
realize
with
usual
cassette
tapes.
The
playback head
incorporates
a unique
X-cut
core
struc-
ture
to
improve
the
characteristics
of
the
low
frequency
range.
With
ordinary core
configurations,
playback
output
is
subject
to
peaks and dips in
the
low
frequency
range as
shown
in Fig.
B.
This is called
the
"contour
effect".
:this
effect
is caused
by
interference
between
the
length
of
the
tape-to-head
contact
area and
the
wavelength
of
the
recor-
ding
frequency.
With
the
X-cut
design
the
core is
cut
diagonally
to
enable
the
tape
to
leave
the
head,
not
abrupt-
ly,
but
with
a gradually lessening
contact
area.
The
result is, as
shown
in
the
diagram, reduction
of
the
contour
effect.
(Fig.
C)
Configuration
of
record/playback
combination
SA heads
CD
SA recording head
® 4/lm gaps
® 1/lm gaps
Fig.
A
®
X-cut
SA
playback
head
® SA chips
® Shield plate
rJ)
Zinc die-casting head base
- 5 -
KD-A77
A/B/C/E/J/U
Comparison
between
characteristics
of
conventional
cut
core and
X-cut
core
c
onventlona
I h d . h
ea
Wit
standard
core
constructi
on
in
~
-.
QJ
>
~
...
:J
B-
:J
0
-11
16
10
@~
I
:J
/
~
/
/,1./
Usign
standard
curre
/
I
I I I I
,
nt
recorded
tape
10
.0
70
100
100
.00
Frequence (Hz)
Fig. B
X
-cut
core
construction
in
:9
a;
>
~
...
:J
Cl.
...
:J
0
11
16
10
t--off----+
Using
standard
current
recorded
tape
I I I
10
.0
70
100
100
.00
Frequence (Hz)
Fig. C
Note:
SA
(Sen-Alloy) is a
trademark
of
JVC.
No.4186
KD-An
A/B/C/E/J/U
Removal of the Main Parts
This cassette deck
which
features a
compact
design and high performance uses miniature sized parts
which
are closely arranged.
Take special care
when
servicing it.
.11
Q
~
~--~.
~~~;;;;;:;;.;...f='.
Lever
knobs
Screws
(Top
view)
Screws
(Bottom
view)
Screw
Screws
Screw
l'
Enclosure assembly
1 . Cassette door
.....
Push
the
EJECT
button
to
open
the
cassette door. Slide
it
upwards
(approx. 5 mm)
to
unlock
its
pawls,
and
remove
it
to
frontward.
2.
Lever knobs (INPUT SELECT, ANRS, TAPE SELECT,
MONITOR) and level control knobs (INPUT LEVEL - L
and
R,
OUTPUT LEVEL and
REC
EQ)
Pull
them
to
frontward
3.
Top cover
.....
Remove 6
screws
fastening the
top
cover.
4.
Bottom
cover
Remove
7
screws
fastening the
bottom
cover.
5. Front plate assembly
1) Remove 5
screws
(3
screws
on upper side and 2
screws
on
bottom
side) fastening the
front
plate
assembly
2)
Remove TAPE & ANRS indicators wires
socket.
When adjusting or replacing REC/PB heads or Erase
head .....
1)
Remove
the
wires
of
the
control
switches
from
the
wire clamp and 2
wire
sockets
after
having removed
the top
cover.
2) Remove 2
screws
positioned
below
the
control
swit-
ches (on
the
bottom
of
the deck) and pull
the
control
section
forwards
- no need
of
removing
the
front
panel assembly.
Front
Caution
No.
4186
- 6 -
When
assembling
the
control
switch
assembly
to
the
front
panel,
do
in
the
order
of
the numbers as
below
as
not
to
damage
the
front
panel.
1 ) Wrap
the
sharp edges
of
the
front
panel
with
vinyl
tape, etc.
2)
Insert
the
control
switch
assembly in the
front
panel.
3)
Remove
the
vinyl
tape.
4) Fasten 2
screws
for
the
control
switch
assembly.
Gear frame
ass'y
,CD
P.W.B holder
® Push
Screws
Screws
(Bottom
view)
- 7 -
KD-A77
A/B/C/E/J/U
Door brake and its related parts
1.
Gear frame
ass'y
.....
Remove 2
screws
CD.
2. Brake arm and tire
.....
Remove
the
E-ring and
torsion
spring ®.
3.
Spur gear and brake
drum
.....
Remove
the
E-ring, and
spring
@.
4.
Rack plate
.....
Remove
the
screw
and
the
collar
@.
5. Brake lever
ass'y
.....
Remove the E-ring
@.
Electrical parts
1. Power supply P.W.B. parts assembly.
1)
Remove a
pawls
of
P.W.B. holder in
the
order
of
the
numbers in
the
illustration
arrow
mark.
2) Remove 3
screws
fastening
the
P.W. Board.
3)
Open
the
P.W.B
to
upper side.
2. Main amp P.W.B parts assembly
1) Remove 4
screws
fastening
the
main amp. P.W.
Board (on
the
bottom
side).
2) Remove 4
screws
fastening
the
lever
switches
on
the
front
bracket.
3)
Remove 5 washers and 5
nuts
fastening
the
PHONES, MIC-L, MIC-R jacks and
REC
EO,
OUTPUT
LEVEL control shafts.
No.4186
K D-A
77
A/B/C/EI J/U
~ckPlate
Screws
-----,rl-I~rv
I
(Top
view)
Screws
Power
switch
Screws
Screws
(for
door
brake
related parts)
tIP_--_Screw
(Right side)
No_4186
- 8 -
3.
Power
switch
1) Remove
the
lock
plate
CID
holding
the
remote
bar.
2) Remove a
screw
®
fastening
the
power
switch
bracket.
3) Remote 2
screws
(j)
fastening
the
power
switch.
4.
Power
transformer
Remove
the 2 screws
and 2
washers
fastening
the
power
transformer.
Removal of the mechanical assembly
1 . Remove a
screw
fastening
the
arm
of
gear-oil
damper
(Left side
of
the
cassette
holder), and Remove 2
screws
fastening
the
gear
frame
ass'y
to
Remove
door
brake
related parts.
2.
Remove 5
screws
fastening
the
mechanical
bracket
to
the
amp. chassis (Right - 2 p.c.S,
Left
- 3
p.c.s).
3.
Remove a
screw
fastening
the
counter
bracket
to
the
front
bracket.
(Top
view)
Screws
..
(Front
view)
(Rear
view)
- 9 -
KO-An
A!B!C!E!J!U
4.
Remove 2
screws
fastening
the
joint
bracket
to
the
front
panel (upper side) .
Removal
of
the mechanical parts
1 . REC/PB head
.....
Remove
the
screw
CD
for
head
adjustment.
Remove
the
screw
CV.
2.
Erase head
.....
Remove
the
screw
®.
Remove
the
screw
®
3.
Pinch roller arm
ass'y
: .... Remove
the
E-ring
@.
4.
Supply
reel
disc
.....
Pull
out
the
reel
stopper
@.
5. Take-up
disc
.....
Pull
out
the
reel
stopper
(j) .
Remove
the
counter
belt.
Note:
1) Remove
the
reel disc
stoppers
with
a piece
of
sheet
metal inserted
between
the
reel
disc
and
the
stopper.
2)
Be
careful
not
to
stain
the
counter
belt.
6. Reel
motor
.....
Remove
the 3 screws ® fastening
the
reel
motor.
7.
Capstan
motor
.....
1) Remove
the
screw ® fastening
the
rubber
stopper.
2) Remove
its
motor
belt.
3)
Turn
the
motor
counter
clockwise
and pull
it
for
removal.
Note:
When
replacing
the
motor,
check
the
following
items.
1 )
Is
the
motor
placed in
the
correct
position?
(Don't
deflect
the
motor
at
mounting
it.)
2) Does
the
capstan
belt
run in
the
center
of
the
motor
pulley?
3) Does
the
capstan
belt run in
the
center
of
the
flywheel?
No.4186
K
D-A
77
AIBICIEI
J/u
Main Adjustments
[I] Equipment and measuring instruments used for adjustment
1.
Electrical adjustment
1) Electronic
voltmeter
2)
Audio
frequency
oscillator
(range;
50 -20kHz
and
output
OdB
with
impedance
600fl)
3)
Attenuator
4)
Standard tapes
for
RECIPB
Maxell UD -
SF
tape
(for normal) }
TDK
SA -SA
tape
(for
Cr02)
or
equivalent
SCOTCH MET AFINE -
Metal
tape
5) Reference tapes
for
playback
(JVC
Test
Tape)
VTT-658
(for
head
azimuth
adj.)
VTT-656
(for
motor
speed,
wow
flutter
adj.)
VTT-664
(for Reference level 1 kHz)
TMT-6002N
(for
playback
frequency
response)
6) Resistors
1
oon
(for
measurement
of
the
bias current)
600n
(for
attenuator
matching)
2.
Mechanical adjustment
1) Gauge
for
checking
the
head position.
2)
Torque
gauge.
3) Blank tape
(C-120)
for
tape
running checker.
[11]
Mechanical adjustment
Head adjustment
KO-A77
Back-tension
pad
Pad
(attached
to
the
cassette)
Tape
Clearance (A)
1.
After
installing
the
specified parts in
the
appropriate
positions:
A.
Snug
screw
CD
gently,
then
back
off
about
two
turns.
This makes
the
heads nearly horizontal.
B.
Snug
screw @ gently,
then
back
off
about
one
turn.
This
will
roughly
position
the
tape in
the
center
of
the
tape
path.
For
tightening
screw
@"
use a
home
make
screwdriver,
filed
down
to
the
specifications
shown
below.
The same
screwdriver
can be used
to
tighten
screw
(1).
Screwdriver
Pinch roller
Combination
head
2.
Make
sure
that
the
moving
part
of
the
erase head
assembly
moves
smoothly
around
the
pivot
of
screw
@
and also
confirm
that
there
is
enough clearance (A) in
the
play mode.
3.
Next,
make an operational
adjustment.
Load a C-1
20
cassette
and
adjust
the
height
of
the
erase head
by
turn-
ing
screw
@.
Watching
that
the
tape does
not
curl
at
the
guides
of
both
the
combination
and erase heads is
indication
of
proper
adjustment.
Correct
-1
Tape guide
t -Tape
Incorrect
f
Tap€
guide
--,
Tape guide
Tape l
__
'
_~--
Tape
No.4186
-10
-
KD-A77
A/B/C/E/J/U
Item
Adjustment
Adjusting
Standard
Remarks
point
value
Adjusting
Connect
a speed
meter
to
the
LINE Semi-
3000Hz
If
the
speed
meter
functions
as a
wow
motor
speed
OUT
terminals.
Play
back
the
fixed
and
flutter
meter,
also,
connect
the
VTT-656
test
tape.
resistor
deck
to
the
INPUT
terminals
of
the
Adjust
the
semi-fixed
resistor
on
the
on
the
meter.
motor
P.W.
board until
the
reading
of
motor
the
speed
meter
is
3000Hz.
P.w.
board
Checking play-
Employ
a
torque
testing
cassette
40-70
If
the
standard
torque
is
not
obtained,
back
torque
tape
for
the
checking, or remove
the
gr-cm
replace
the
take-up
disc
assembly.
cassette
cover
and
use
a
torque
gauge.
Checking
fast
Measure
the
torque
in
the
fast
for-
More
If
the
standard
torque
is
not
obtained,
forward
torque
ward
mode
in
the
same manner as in
than
perform
the
following.
the
above.
70
gr-cm
1 . Clean
the
capstan
belt,
the
idler
cir-
cumference,
the
motor
pulley,
the
take-up
reel
disc
circumference,
the
flywheel
circumference,
etc.
2. Replace
the
belt and idler.
Checking re-
Measure
the
torque
in
the
rewind
More
If
the
standard
torque
is
not
obtained,
wind
torque
mode
in
the
same manner
as
in
the
than
clean
the
capstan
belt, idler,
motor
above.
70
gr-cm
pulley,
flywheel
circumference,
rewin-
ding idler
circumference,
left
reel
disc
circumference,
etc.
Checking
wow
Connect a wow
and
flutter
meter
to
If
the
reading becomes
moving
value
and
flutter
the
LINE
OUT
terminals.
even
if
conforming
to
the
standard,
a
Play
back
the
VTT-656
test
tape. re-claim
may
be raised. Repairs are
Check
to
see
if
the
reading
of
the
necessary.
meter
is
within
0.04%
(WRMS).
[Ill] Repair of
wow
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.
Play a
3000Hz
test
tape, and
defective
part
can
be
detected
from
the
sound.
Section
Trouble
Repair
Capstan and
flywheel
Capstan
shaft
has excessive
run-out
Replace
flywheel.
Flywheel
turns
heavily. Clean
the
capstan
shaft
and
the
groove
in
the
(shaft
seisure,
thrust
play,
etc.)
flywheel.
Apply
oil
to
the
metal
position.
Replace
the
capstan assembly.
Pinch roller
Rough
rotation
(Deformation
scrat-
Replace pinch roller, or pinch roller spring.
ches, or dust)
Clean
the
pinch roller
or
apply oil
to
the
rotary
The
angular
position
of
the
pinch
roller shaft.
is
not
correct.
Adjust
the
pinch roller so
that
it
is
parallel
with
The pinch roller pressure is
not
correct.
the
capstan shaft.
Replace
the
pinch roller spring.
Belt
Belt has undue run-out. Clean
the
belt.
Belt is
dirty
or slippery. Replace
the
belt.
Back tension
Back tension
is
irregular, or back ten- Replace back tension spring (under supply disc).
sion
is
too
strong.
Motor
Motor
shaft
has undue run-out. Replace motor.
Motor
pulley
is
oily and
dusty.
Clean
motor
pulley.
Damping gear
oil
Oil
employed - Torque grease specified
by
JVC
(KANTO KASEI GP-608)
Applying method -
Apply
in both concaved sections
as
shown
in
the
figure.
-11-
K
D-A
77
A/B/C/E/
J/U
[IV]
Adjustment
Location
of
Electrical
Circuit
No.4186
Power
Supply P.W. Board
Front
l]-R
'~'
_ 1
.,,'
'"
m
...
om"'''''"
',,""'m,m
_
U L
(Turning
in
the
direction
of
the
arrow
Increases
the
deflection
angles.)
t
VR302
VR801
(3-R
VR701
For
playback
level
adjustment.
\G-L
(Turning
In
the
direction
of
the
arrow
increases
the
playback
levels.)
VR803
11
_____
L _
For
playback
frequency
response
adjustment
,,~
(Turning
In
the
direction
of
the
arrow
Increases
the
signal
current)
VR703Rtl
Q-
L For
ANRS
adjustment
at
playback
mode
_
__#
'-----------.J
(Turning
In
the
direction
of
the
arrow
Increases
the
ANRS
gains.)
Main
P.
W Board
VRAOl
VR501
T.;-L
VR601 G L
For
recoridng
level
adjustment.
·0
~
Rl
T.P-R
(Turning
in
the
direction
of
the
arrow
in-
creases
the
recording
levels.)
1
Front
L ] For
ANAS
adjustment
at
recording
mode.
(Turning
in
the
direction
of
the
arrow
increases
the
ANRS
gains.)
VRBOl
(eR
VR504
VR502
VR503
((~((~G-
L J ero, t -For bias CUrrent
adjustment.
(Turning
in
the
direction
of
the
arrOw
in-
Q Q
G-
v
:
creases
the
bias
current
value.1
VR604
VR602
603
r
I
LL'::=~==rNORM~
I R I I J
L I
METAL
R---~
In
nl
n
n
~12~
Loading...