Technics RS-646DS-D User manual

“ORDER NO. ARD-7706063C
Service Manual
Cassette Deck
RS-646DS-D
Portable High-Fidelity Stereo Cassette Deck with
Separate Bias/Equalizer and Mic Attenuator
RS-640U MECHANISM SERIES
Specifications (Catalog specifications for sales)
Power
requirement:
AC;
110/220V,
50/60
Hz
Input:
MIC;
sensitivity
0.25
mV/applicable
microphone
Power
consumption;
10
W
impedance
400Q~
10K
DC;
12V,
eight
R-20
size
dry
cell
batteries
INE;
sensitivity
60
mV/input
impedance
47
KQ
Motor:
1-DC
electronical
speed
control
motor
DIN;
sensitivity
16
mV/input
impedance
2.7
KQ
Track
system:
4-track
2-channel
stereo
recording
and
playback
Output:
LINE;
output
level
420
mV/load
impedance
50
K2
Tape
speed:
4.8cm/s
over
Battery
life:
Approx.
32
hours
with
alkaline
batteries
DIN;
output
level
420
mV/output
impedance
1
KQ
Wow
and
flutter:
0.1%
(WRMS),
£0.2%
(DIN)
HEADPHONE
;
output
level
65
mV/load
Frequency
response:
CrOz
tape;
50~14,000Hz
+3dB
impedance
82
45
~
14,000
Hz
(DIN)
Monitor
speaker;
output
power 0.8
W
(monaural)
Normal
tape;
50~14,000Hz
+3dB
Head:
2-head
system
45
~14,000Hz
(DIN)
1-super
permalloy
head
for
record/playback
Signal-to-noise
ratio:
Dalby
NR
in;
66dB
(above
5kHz)
1-doub!
gap
ferrite
head
for
erasure
Dolby
NR
out;
56 dB
Dimentions:
36.3cm(W)
X
10.6
cm(H)
X
28.0
cm(D)
(signal
level
max.
recording
level)
Weight:
5.0kg
(without
batteries)
Fast forward and
rewind time: Approx. 130 seconds with C-60 cassette tape
Specifications are subject to chang without notice.
gees 7 Matsushita Electric Trading Co., Ltd.
Technics
P.O.
Box
288,
Central
Osaka
Japan

LOCATION OF CONTROLS
AND COMPONENTS
DOAO@®D@OOOO@QOY Di
@ Eject button
@ Record button
@ Rewind button
@ Fast forward button
® Playback button
© Stop button
@® Cassette compartment cover
Pause button
Silent-stop button
Tape counter and reset button
Level meter
Level/battery check meter
Built-in speaker
Handle
Level controls lock button
Meter light button
Battery-check button
nput level controls
Tape-end indicator
Tone contro!
Speaker volume control
Equalization selector
Bias selector
Dolby noise-reduction switch
Limiter switch
Input selector
Microphone jacks
Headphones jack
Voltage selector switch
Car battery input jack
AC connection socket
Line output jacks
Record/playback DIN socket
Line input jacks
22 2) Q 19 48
SSSSSSSSSSSOSHSSSSsdQaGesoso@
32) 33) 34
Fig. 1

DISASSEMBLY
INSTRUCTIONS
—
(B)
Fig.
2
Fig.
3
Fig.
4
Fig.
5
—
Procedure
To remove — -.
Pes.
Shown in fig. ——.
1
Top
panel
(A),
(B),
(C),
(D),
4,2,2,2,3,4
2,3,4
a
Brent
natal
(G),
(H)
3,9
:
2,3
:
Mechaniern
(1)
.
:
neinlifier
i
),

MEASUREMENT & ADJUSTMENT
BEFORE ADJUSTMENTS OR REPAIRS ---.--
1. For electrically related adjustments only, each of the variable resistors and connection points for adjustment can be seen when the
bottom cover is removed as shown in fig. 7 below. Make adjustments by referring to each adjustment description.
—Connection
|
: :
-
;
woes
point
®
for
pele
a
ope
.
.
:
Connection
point
<B)
for
L-ch
playback
=
be
|
level
meter
adjustment.
frequency
.
response
adjustment.
2.
When
electrical
parts
of
printed
circuit
board
are
to
be
repaired,
rernove
the
mechanism,
amplifier
and
power
supply
printed
circuit
board
from the
case
as
shown
in fig.
8
below. When each section
is
reconnected
by
connectors,
the operation
of each
section
can
be
confirmed.
Note: 1. Secure the mechanism assembly to the jack angle.
2. Secure the power supply printed circuit board, in the same way, to the headphone jack angle.

ADJUSTMENTS
Before
measuring
and
adjusting
“Overall
frequency
response”,
“Overall
distortion”
and
“Overall
S/N
ratio”.
confirm
that
the
characteris-
tics
of
5
items
below
are
within
standard
which
have
much
relation
to
or
influence
on
electrical
performances
above.
1. Head azimuth adjustment. 2. Bias current. 3. Playback gain. 4, Overall gain.
5. Playback frequency response.
I. TEST INSTRUMENTS
1. Prepare test instruments which are equivalent in accuracy to those shown below.
2.
The
test
instruments
should
be
inspected
and
corrected
by
specialists
once
every
6
months,
because
a
long
period
of
use
without
maintenance
may
increase errors in
indication.
3.
Warm-up
the
test
instruments
for
30
minutes
and
the
set
to
be
measured
for
10
minutes
before
taking
the
measurements.
_
If
not,
there
may
arise
an
error
or
difference
between
the
initial
value
and
the
stabilized
value
measured
after
“aging”
4. Specifications of test instruments.
(1) Audio frequency oscillator
a. Oscillation frequency: 5Hz~ 500 kHz (5 ranges)
b. Frequency tolerance: +(3% +1Hz)
c. Sine wave
* Output voltage (at 25°C): 5Vrms £10% (without load)
2.5Vrms +10% (with 6002 load)
* Output frequency response: Within £0.2 dB, 20Hz~20kHz
Within £0.5dB, 5Hz~ 500 kHz
* Distortion factor: Not more than 0.05%, 200 Hz ~ 20kHz
Not more than 0.5%, 5Hz~ 500 kHz
* Output impedance: 6002 unbalanced, within + 15%
* Output attenuator: OdB, 20dB, error; within +0.2dB
d. Temperature in use of set: Temperature = 0 ~ 40°C, humidity = 90% or less
(2) Automatic-stop distortion meter (with vacuum tube voltmeter)
A. Distortion factor measurement
a. Frequency (fundamental wave): = 400Hz, 1kHz +10%
b. Measurement: 0.1~ 100% (6 ranges)
c. Input: 50mV~50V
d. Fundamental wave attenuation: 60 dB or more
B. Level measurement
a. Measurement: mV (—60 dB) ~ 30 V (30 dB) (9 ranges)
b. Frequency response (1kHz basis): 20Hz~100kHz £0.3¢dB
c. Input impedance: 1MQ2 +10%, less than 50 pF
d. Error in indicated value: Within £3% at 1kHz
C. Output terminal
a. Frequency response: OQHz~100kHz +1dB
100kH2~1MHz +3dB
b. Output voltage: 1Vrms + 10% (1kHz sine wave)

(3) Attenuator
a. Input impedance: 6002 unbalanced
b. Maximum attenuation: 121dB
c. Minimum attenuation: 0.1dB
(4) Oscilloscope
a. Cathode ray tube: Effective ranges 88cm
b. Vertical axis
* Input sensitivity : 30mV~30V/cm
* Frequency band: DC ~2MHz
* Transient time: 180ns.
* Input impedance: 1MQ, 35 pF
c. Horizontal axis
* Tuning range: 30 Hz ~ 2 MHz
* Sweep time: lus~ 100ms/cm
* External Sweep: 1Vp-p/cm or more
(5) Digital electronic counter
a. Number of figure: 4 (decimal system)
b. Input sensitivity; 100mVrms
c. Input impedance: 1MQ, 40 pF
d. Frequency measurement range: 10Hz~ 100 kHz
e. Counting time: 0.1s, Is, 10s
(6) Wow meter
a. Measured center frequency range: 3kHz +4%
b. Input level range: 30mV~3V
c. Input impedance: About 50 KQ unbalanced
d. Measurement: 0.01~3% (5 ranges)
e. Indicator error: Maximum error in indicated value +5%
in each range.
f. Frequency response: Contorming to weighting curve
characteristics (WRMS), JIS C5551.
Flat characteristics (RMS)
0.5~200Hz, within ~3 dB (4Hz basis)
g. Meter indication system: Effective value indication, conforming to
JIS C5551.
h. Meter response characteristic: About 5~ 7 sec.
i. Oscillation frequency: 3 frequencies (3kHz, 3kHz +3%)
j. Temperature range: 0~40°C

I. MEASUREMENT CONDITIONS
1, Standard measurement conditions
* Ambient temperature: 10~30°C (50~86°F)
* Ambient humidity: 30 ~90% RH
* Power voltage accuracy: 3%
2. Position of tape recorder
* When measuring, place the unit under test in a horizontal position.
3. Oscillator output voltage adjustment
* Connect the equipments as shown in the following and adjust the oscillator output control knob for 1 V (f=1kHz) through the
attenuator while keeping the attenuator at 0 dB.
* When supplying a signal to the tape recorder amplifier, adjust the input level using the attenuator.
Output control knob
Audio frequency oscillator } Attenuator : Vacuum tbe voltmeter Oscilloscope
f=1kHz
Testers
-
Output
voltage
1V
(OdB)
Il. TEST TAPE
Test tape life
The
more
frequently
the
test
tape
is
used,
the
more
the
tape
characteristics
will
deteriorate
(e.g.
lowering
of
recorded
level,
worsening
of
frequency
response
particularly
in
high-frequency
range,
and
an
increase
in
wow
due
to
tape
elongation)
until
measured
values
be-
come
unreliable.
Even
in
such
a
case
when
a
tape
is
not
used,
but
stored,
for
a
long
period
of
time,
tape
shows
deterioration
in
per-
formance because of self damagenetization due to storage conditions, etc.
Please
refer
to
the
tape
life
specitication
and
use
care
not
to
use
a
tape
longer
than
its
rated
life
when
servicing.
Frequence of use: Not more than 20 times for each tape length.
Storage period: Not more than 6 months.
Test tape
PARTS
NO.
PARTS
NAME
SPECIFICATIONS
REMARKS
Standard
recording
level
5
times
repetitive
recording
and
frequency
response
Tape
speed:
1-7/8ips.
(4.8cm/s)
tape
BS
x
Full
track
(10
min.)
OdB: STANDARD REC. LEVEL (160pWb/mm)
Ti d: 1-7/8ips. (4.
Wow
and
tape
speed
tepe
Tape
Speed:
1-7/8os,
(t.Bom/s
OdB: 250pWb/mm
Tape speed: 1-7/8ips. (4.8cm/s)
Azimuth
tape
6.3kHz
Full
track
(15
min)
OdB: 250pWb/mm
Reference blank tape
(Normal)
Unrecorded
tape
(20
min.)
Reference blank tape
(CrO2) Unrecorded tape (20 min.)

iV. MEASUREMENT & ADJUSTMENT METHOD
NOTE:
1.
. Make sure capstan and pressure roller are clean.
2
3. Judgeable room temperature: 20-+5°C (68+9°F)
4
Make sure heads are clean.
. Bias selector: Low
Pressure of pressure roller
Equipment:
* Tension gauge (max. 500 gr)
5. Dolby NR switch: OUT
7. Output level control: MAX
MEASUREMENT & ADJUSTMENT
Place UNIT into playback mode.
2. Hook the tension gauge to pressure roller lever and pull it in the direc-
tion of the arrow as shown in fig. 9.
. Measure the tension at the moment when the pressure roller moves
away from the capstan.
Standard value: 390+60 gr |
l
Adjustment method
Bend the part (A) of the pressure roller spring in either direction shown
by the arrow until the correct pressure is attained.
6. Equalizer selector: 120.8
REMARKS
* Playback mode
Pressure ~
roller spring
Fig. 9
Takeup tension
Equipment:
* Cassette torque meter
(SRK-CT or RP8063)
1. Mount cassette torque meter on UNIT.
2. Place UNIT into playback mode and read takeup torque.
3. Measure several times and determine the mean value.
Standard value: 55+15gr-cm |
If the measured value is not within standard, firstly clean the rotational
parts of the mechanism with alcohol, and if it still is not within standard,
make the following adjustment.
Adjustment method
Adjust by turning the plate spring attached in the takeup reel table (See
fig. 10).
* Playback mode
Plate spring
Fig. 10
Head azimuth adjustment
Equipment:
* VTVM
* Oscilloscope
* Test tape (azimuth) --- C-AA
Record/playback head adjustment
1. Test equipment connection is shown below.
VTVM
Fig. 11
Test tape Playback mode Oscilloscope
. Play azimuth tape (C-AA, 6.3 kHz).
. Adjust record/playback head angle adjustment screw (8) in fig. 12 so
that output level at LINE OUT becomes maximum.
. Measure both channels, and adjust levels for equal output.
. After adjustment lock head adjustment screw with lacquer.
* Playback mode
R/P Head

Tape speed
Equipment:
* Digital electronic counter or
frequency counter (RP8067)
* Test tape--- C-WAT
MEASUREMENT & ADJUSTMENT
Tape speed accuracy
1. Test equipment connection is shown below.
LINE OUT
Test tape Playback mode Digital electric counter
Fig. 13
2. Play test tape (C-WAT 3,000Hz), and supply playback signal to fre-
quency counter.
3. Measure this frequency.
4. On the basis of 3,000Hz, determine value by following formula:
f—3,000 5
3.000 x 100 (%)
where, f=measured value
5. Take measurement at middle section of tape.
Tape speed accuracy =
Standard value: +1.5% |
Adjustment method
1. Play the test tape (middle).
2. Adjust the tape speed adjustment VR shown on page 18 so that fre
quency becomes 3,000 Hz.
Tape speed fluctuation
Make measurements in same manner as above (beginning, middle and end
of tape), and determine difference between maximum and minimum values
and calculate as follows:
_ fi—fe 6
Tape speed fluctuation = 3.000 x 100 (%)
fi1=maximum value
f2=minimum value
Standard value: 1.5%
REMARKS
* Playback mode
Wow and flutter
Equipment:
+ Wow meter
* Test tape --- C-WAT
1. Test equipment connection is shown below.
LINE OUT
/
Test tape Playback mode Wow meter
Fig. 14
. Use wow test tape (3,000Hz) and measure its playback signal on
wow meter.
.
Wow
and
flutter
is
expressed
in
percentage
and
that
measurement
can
be
weighted
by
JIS
network
(WRMS).
. Measure at middie section of test tape.
I
| Standard value: 0.10% (WRMS)
+ Playback mode

Playback frequency
response
Equipment:
* VTVM
* Oscilloscope
* Test tape --- C-FH
Playback gain
Equipment:
*VTVM
* Oscilloscope
* Test tape--- C-FH
MEASUREMENT & ADJUSTMENT
. Test equipment connection is as same as “Head azimuth adjustment” |
but use the test tape (C-FH) instead of head azimuth tape (See fig.
11).
. Place UNIT into playback mode.
. Play frequency response test tape (C-FH).
. Measure output level at 1OkHz, 8kHz, 4kHz, 1kHz, 125Hz and 63Hz
and compare output level with standard frequency 333Hz, at LINE
OUT.
. Make measurement for both channels.
. Make sure that the measured value is within the range specified in the
frequency response chart.
Playback frequency response chart
150Hz 250Hz 333H2 sobez L ski
Fig. 15
. If measured value is not within standard, adjust the following points:
Change the “Connection points’ of the amplifier pattern, and then
adjust the playback frequency response.
@lf the high range (8~10kHz) decreases about —1~ —1.5aB,
short circuit connection points (@) as shown in fig. 7.
@lf the high range (8~10kHz) decreases about —1.5~ —2qB,
also short circuit connection points (B) as shown in fig. 7.
. Test equipment connection is shown in fig. 11.
Play standard recording level portion on test tape (C-FH 333Hz), and
using VTVM measure the output level at LINE OUT jack.
. Make measurement for both channels.
Standard value: 0.42V (—7dB)
Adjustment method
1. If measured value is not standard, adjust VR1 (L-CH), VR2 (R-CH)
(See fig. 28 on page 17).
2. After adjustment, check “Playback frequency response” again.
REMARKS
* Playback mode
; * Playback mode
Playback S/N ratio
Equipment:
* VTVM
* Oscilloscope
* Test tape---C-FH
* Empty cassette
. Test equipment connection is shown in fig. 11.
put level on VTVM.
Refer to "Playback gain adjustment”.
. Place empty cassette (which has been cut) and play again.
. Measure noise level at this time using VTVM, and determine ratio of
this level to test tape output signal voltage (333 Hz).
Standard value: Greater than 43dB |
An example calculation is shown below.
A: Es=playback output signal voltage of test tape (333 Hz)
B: En=playback output noise level
Es=0.42V (—7dB)
En=0.003 V (—50dB)
S/N ratio= Es _ _0.42V — 140
En 0.003 V
20 log:: 140=43dB
S/N ratio = Es(dB) — En(dB) = —7 —(—50) = 43dB
! * Playback mode
. Play standard recording level test tape (C-FH 333Hz) and read out- :