Technics RS-676US User manual

TAPE RECOh.
Technics
Service Manual cee,
HI-Fl STEREO CASSETTE DECK WITH FRONT CONTROLS
AND DOLBY* NOISE REDUCTION SYSTEM
RS-676US MECHANISM SERIES
MODEL RS-676US
SPECIFICATIONS
Power Source: AC: 90~109, 110~125, 200~219, Frequency Response: Normal tape; 20~16,000 Hz
220~250 volts, 50/60 Hz 25~14,000 Hz (DIN)
Power Consumption: 25W. 30~13,000 Hz (+3 dB)
Motors: 2-motor system CrOz2 tape: 20~18,000 Hz
1-Electronic speed contro! motor for 25~15,000 Hz (DIN)
capstan drive 30~14,000 Hz (+3 dB)
1-DC motor for reel table drive Signal to Noise Ratio: Dolby NR out; 52 dB
Transistors: 28C1327 (6), 2SC644(2), (0 VU=250 PWb/mm)
28C828 (28), 2SC1318(3), 2SA719(1), Dolby NR in; 62 dB at 10 kHz
2SC1096Z (3), 2SC1384 (3), Harmonic Distortion: 2.0% (0 VU at 1,000 Hz)
2SD288 (1), 2SA666H(3), 2SC945(2), Inputs: MIC: sensitivity 0.3 mV/applicable
2S8C1407 (2), 2SK30(2) microphone impedance 600Q~
Head: HPF head for rec/playback head 20KQ
Diode & Rectifiers: 1$1211(8), OA90Z(20), OA91 (3), LINE: sensitivity 60 mV/110KQ
MA162(10), RD7A(2), FR202(6), TUNER: sensitivity 100 mV/190 KQ
M21C(2), EQA0119(1), 10DC1 (3), Outputs : LINE: output level 420 mV (max.)
1ODC1R(2) impedance 50 KQ over
Track System: 4-track 2-channel stereo recording HEADPHONE: output level 45 mV/8Q
and playback Rec/PB Connection: 5 P DIN type
Recording System: AC bias (90 kHz), AC erase Fast Forward and Approx. 80 second with C-60 cassette
Tape Speed: 4.8cm/s, (1-7/8 ips.) Rewind Time: tape
Program Time: 1 hour stereo recording with C-60 Dimensions: 410mm(W) x 140mm (H) x 360mm (D)
cassette tape 16-3/8” (W) x 5-1/2” (H) x 14-3/87 (D)
Wow and Flutter: 0.063% (WRMS) ,+0.15% (DIN) Weight: 10.5 Kg, (23-1/8 ips.) :
These specifications are subject to change in order to accommodate improvements in design.
Matsushita Electric Industrial Co.,Ltd. Baga |
MATSUSHITA ELECTRIC TRADING CO., LTD. begga <
P.O. Box 288 Central, Osaka, Japan

LOCATION OF PARTS
®
Q®@
@@OOO®
Q
@ Ejection button Dolby FM calibration controls
@ Cassette cover @ Recording level control
@ Fast forward button @ Tape selector
@ Tape counter and reset button Pause button
® Memory playback button @) Record button
© Dolby NR/MPX Filte @ Stop button
@ Dolby FM switch @ Playback button
Output level contro @ Rewind button
© VU meters @ Remote control jack
Peak-signal check button @) Dolby FM de-emphasis switch
@ Input source selector @) Tuner input jacks
@ Power switch @ Line input jacks
@ Headphones jack @ Record/playback connection socket
Microphone jacks @ Line output jacks
4) Recording balance control Voltage select switch
@) Ground terminal

DISASSEMBLY INSTRUCTIONS
HOW
TO
REMOVE
CASE
COVER,
BOTTOM
PANEL
AND
FRONT
PANEL
Procedure | How to remove-—— | Remove——. PCS.
1 Case cover (A) (4)
2 Bottom panel (B) (11)
3 | Front panel ©,©.© | ©.@, 2)
HOW TO REMOVE FRONT ANGLE AND CASSETTE COVER
Procedure | How to remove-—— -| Remove-—— Pcs. Remarks
1
|
Front
angle
©
(7)
In
this,
condition,
front
angle
car
be
tilted
2
Front
angle
(G)
(2)
in
this
condition,
front
angle
can
be
removed from chassis.
3 Cassette cover (H) (4) ;
NOTE:
Before
tilting
front
angle
(procedure
1),
remove
counter
belt
from
connection
pulley
and
hang
it
on
the
arrow position in
fig.
4.

HOW
TO
REMOVE
JACK
BASE
PLATE
AND
PRINTED
CIRCUIT
BOARD
(AMP
&
CONTROL)
Procedure How to remove—— Remove——
| Pcs.
1 Jack base plate O.O.® | ©.0.@
2
Printed
circuit
board
(CONTROL)
(L)
eee
ee ee
3 Printed circuit board (AMP) — wm | © (6)
HOW TO REMOVE HEAD COVER
1.
Pushing
the
head
cover
as
shown
in
Tig.
7,
and
lift
it
up
as
shown
in
fig.
8.
2. Then head cover can be removed.

ADJUSTMENTS
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 stablized
value measured after “Warming up”. :
4. Specifications of Test Instruments.
(1) Audio Frequency Oscillator
a. Oscillation Frequency
5 Hz~500 kHz (5 ranges)
b. Frequency Tolerance
+(3% +1 Hz)
c. Sine Wave
* Output Voltage 5 Vrms+10% (open)
(at 25°C) 2.5 Vrms +10% (600Q load) f
* Output Frequency Response Within +0.2dB 20Hz~20 kHz
Within +0.5dB 5Hz~500 kHz
* Distortion Factor Not more than 0.05% 200 Hz~20 kHz
Not more than 0.5% 5Hz, 500 kHz
* Output Impedance 600Q Unbalanced Within +15%
* Output Attenuator 0,20dB Error: Within +0.2 cB
d. Temperature in Use of Set
Temperature=O0~40°C: Humidity=90% or less
(2) Automatic-spot Distortion Meter (with Vacuum Tube Voltmeter)

A. Distortion Factor Measurement
a. Frequency (Fundamental wave)
b. Measurement
c. Input
d. Fundamental Wave Attenuation
B. Level Measurement
a. Measurement
b. Frequency Response (1 kHz basis)
c. Input Impedance
d. Error in Indicated Value
C. Output Terminal
a. Frequency Response
b. Output Voltage
(3
Ww
Attenuator
400 Hz 1 kKHZz+10%
0.1~100% (6 range)
50mV~50V
— 60 dB or more
1 mV (—60 dB) ~30 V (30 cB) 9 range
20 Hz~100 kHz+0.3 dB
1MQ+10% Less than 50 pF
With in +3% at 1 kHz
10 Hz~100 kHz+1 dB
100 kHz~1 MHz+3 cB
1 Vrms+10 % (1 KHz Sine Wave)
a. Input Impedance
b. Maximum Attenuation
c. Minimum Attenuation
(4) Oscilloscope
Ba
600Q Unbalanced
“121 dB
0.1 dB

a.
Cathode
Ray
Tube
Effective
Range
8x
8cm
b. Vertical Axis
e
Input
Sensitivity:
30
mV~30
V/cm
e
Frequency
Band:
DC~2
MHz
e Transient Time: 180 ns
«
Input
Impedance:
TMQ,
35
pF
c. Horizontal Axis
«
Tuning
Range:
30
Hz~2
MHz
«
Sweep
Time:
lus~100
ms/cm
°
External
Sweep:
1
Vp-p/cm
or
more
(5) Digital Electronic Counter
a. Number of Figures: 4 (decimal system)
b. Inout Sensitivity: 100 mV rms
c. Input Impedance: 1 MQ, 40 pF
d. Frequency Measurement Range: 10 Hz~100 kHz
e. Counting Time: 0.1,1,10s
(6) Wow Meter

. Measured Center Frequency Range: 3 kHZz+4%
a
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:
Conforming
to
Weighting
Curve
Characteristic
(WRMS),
JIS
C5551.
Flat Characterstic (RMS)
0.5~200 Hz, Within —3 dB (4 Hz basis)
. Meter Indication System: Effective Value Indication, conforming to JIS C5551
g
h. Meter Response Characteristic: About 5~7 sec.
i. Oscillation Frequency: 3 Frequencies (3 kHz, 3 kHz+3%)
j. Temperatur Range: O~40°C ;
lH. MEASUREMENT CONDITIONS
1. Standard Measurement Conditions
* Ambient Temperature: 10°~30°C (50°~86°F)
* Ambient Humidity : 30~90% RH
* Power Voltage: Rated Voltage=120 V+5%
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 contro! knob for 1 V
(f=1 kHz) through the attenuator while keeping the attenuator at O aB.
* When supplying a signal to the tape recorder amplifier, adjust the input level using the attenuator.
Connection of Test Equipments.
Oscilloscope
é
ae
oo
.
a
‘
f
?
‘
Attenuator
=
#
Vacuum
Tube
Audio
Frequency
j
f
Voltmeter
~
Oscillator
.
é
f=1kHz Output Voltage=1 V (0 dB)

Il. TEST TAPE
«x 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
become
unreliable.
Even
in
such
a
case
where
a
tape
is
not
used,
but
stored,
for
a
Jong
period
of
time,
the
tape
shows
deterioration
in
performance
because
of
self
demagnet-
ization
due
to
storage
conditions,
etc.
Please
refer
to
the
tape
life
specification
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.
3% Test Tape
PARTS
NO.
PARTS
NAME
SPECIFICATIONS
REMARKS
5 TIMES REPETITIVE RECORDING
TAPE SPEED:
1-7/8 IPS (4.8CM/S),
FULL TRACK (10 MIN.)
STANDARD REC.
LEVEL & FREQ.
RESPONSE TAPE
0 dB: STANDARD REC ‘LEVEL (160 PWb/mm)
FULL TRACK (45 MIN.)
-10 dB
eee
pe
3
kHz
TAPE
SPEED:
1-7/8 IPS (4.8 CM/S).
0 dB: 250P Wb/mm)
em
FULL TRACK (15 MIN.)
AZIMUTH
TAPE
6.3
kH
TAPE
SPEED:
;
z
1-7/8
IPS
(4.8
CM/S).
0 dB: 250PWb/mm
REFERENCE BLANK
TAPE
NORMAL
UNRECORDED
TAPE
(20
MIN.)
REFERENCE BLANK
TAPE
CrOz
UNRECORDED
TAPE
(20
MIN.)

iV. MEASUREMENT & ADJUSTMENT METHOD
NOTE:
1. Make sure heads are clean.
2. Make sure capstan and pressure roller are clean.
3. Judgeable room temperature: 20+5°C (68+9°F)
4.
Source Selector:
ITEM
LINE IN 8. Dolby FM Switch: OUT
MEASUREMENT & ADJUSTMENT
5. Output Level Control: MAX.
6. Tape Select Switch: NORMAL
7. Dolby NR/MPX Filter Switch: OUT
REMARKS
Pressure of Pressure Roller
Equipment:
* Cassette Type Tension
Gauge (max. 500 gr)
\
Q
1. Place UNIT into playback mode.
2. Hook tension gauge to pressure roller shaft top (A), and
pull gauge in direction opposite to pressure of pressure
roller against capstan (See fig. 10).
3. Read pressure indicated on gauge immediately when pres-
sure roller moves away from capstan and stops rotating.
Standard Value: 400+50 gr
Adjustment method
Adjust by bending the (B) part of the pressure roller spring
(See fig. 10).
* Playback Mode
Takeup Tension
Equipment:
* Cassette Torque Meter
(RP-8063N)
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+15 gr-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. 11).
Plate Spring
Fig. 11
Head Azimuth Adjustment
Equipments:
* VTVM
* Oscilloscope -
* Test Tape (Azimuth)
.C-AA
«x Tape Path Viewer
. RT-8133
Record/playback head adjustment
1. Test equipments connection is shown below.
LINE OUT
(av)
(Test Tape) (Playback Mode)
Fig. 12
2. Play azimuth tape (C-AA 6.3 kHz).
3. Adjust record/playback head angle adjustment screw (C).
in fig. 13 so that output level at LINE OUT becomes maxi-
mum. ;
4. Measure both channels, and the level difference between
channels shoud be minimised by adjusting.
5. After adjustment lock head adjustment screw with lacquer.
(Oscilloscope)
Erase head adjustment
1. Test equipments connection is the same above but use the
tape path viewer (RT-8133) in stead of test tape (C-AA).
2. Play this tape.
3. Adjust screw (D) shown in fig. 14 so that the tape may
not get curled or malformed by tape guide of the erase
head.
4. After adjustment lock head adjust screw with lacquer.
* Playback Mode
Fig. 13
Erase Head

ITEM
MEASUREMENT & ADJUSTMENT.
REMARKS
Tape Speed
Equipment:
* Digital Electronic
Counter or Frequency
Counter (RP-8067)
* Test Tape...C-WAT
Tape speed accuracy
1. Test equipment connection is shown below.
R/P Head (Playback Mode) (Digital Electric Counter)
Fig. 15
. Play test tape (C-WAT 3,000Hz), and supply playback
signal to frequency counter.
. Measure this frequency.
. On the basis of 3,000Hz, determine value by following
formula:
Tape speed accuracy=(47 3.000 100%
where, f=measured value
. Take measurement at middle section of tape.
Standard Value: +1.5% |
Adjustment method
1. Play the test tape (middle).
2. Adjust the tape speed adjustment VR shown on page 19
so that frequency becomes 3,000 Hz.
Tape speed fluctuation
Make measurements in Same manner as above (beginning,
middie and end of tape), and determine difference between
maximum and minimum values and calculate as follows:
fi=fe x100]%
Tape speed fluctuation=[ 3.000
f1=maximum value
fz=minimum value
Standard Value: 0.5%
* Playback Mode
Wow and Flutter
Equipment:
* Wow Meter
* Test Tape...C-WAT
1. Test equipment connection is shown below.
Test Tape Playback Mode
Fig. 16
. Use wow test tape (3,000Hz) and measure its playback
signal on wow meter.
_ Wow & Flutter is expressed in percentage and that
measurement can be weighted by JIS Network. (WRMS)
. Measure at middie section of test tape.
Standard Value: 0.063% (WRMS)
* Playback Mode
10

ITEM
MEASUREMENT & ADJUSTMENT
REMARKS
Playback Frequency
Response
Equipments:
* VTVM
* Oscilloscope
* Test Tape...C-FH
Playback Gain
Equipments :
* VTVM
* Oscilloscope
* Test Tape...C-FH
. Test equipments connection is as same as “Head Azimuth
Adjustment” but use- the test tape (C-FH) in stead of
head azimuth tape (See fig. 12).
. Place UNIT into playback mode.
. Play frequency response test tape (C-FH).
. Measure output level at 10kHz, 8kHz, 4kHz, 1 kHz, 125
Hz and 63Hz and compare output level with standard
frequency 333 Hz, 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
+5 dB 333 Hr
0 dB
—14dB
63 Hz 125 Hz VkHz = 4 kHz 8 kHz
Fig. 17
. lf measured value is not in standard, adjust VR1 (L-CH),
VR2 (R-CH) (See fig. 30 on page 19).
. Test equipments connection is shown in fig. 12.
. 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: 0.42 V (— 7 dB)
Adjustment
Le
2
If measured value is not standard, adjust VR3 (L-CH), VR4
(R-CH) (See fig. 30 on page 19).
After adjustment, check ‘Playback Frequency Response”
again.
* Playback Mode
* Playback Mode
Playback S/N Ratio
Equipments:
* VTVM
+ Oscilloscope
* Test Tape...C-FH
* Empty Cassette
. Test equipments connection is shown in fig. 12.
2. Play standard recording level test tape (C-FH 333Hz) and
read output level on VTVM.
Refer to “Playback Gain Adjustment”.
. Place empty cassette (which has been cut) and play gain
without moving adjusted playback VR.
. Measure noise level at this time using VTVM, and deter-
mine ratio of this level to test tape output signal voltage
(333 Hz).
Standard Value: Greater than 45 dB
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 (—7 dB)
En=2.5 mV (—52dB)
S/N ratio= ES _.
S/N ratio=Es (dB) —En (dB) = —7— (-52) =45dB
*« Playback Mode

MEASUREMENT & ADJUSTMENT
REMARKS
Bias Leak
Equipments:
* VTVM
* Oscilloscope
Bias Current
Equipments:
+ VTVM
* Oscilloscope
1. Test equipments connection is shown below (See AMP
circuit board on page 24).
R25(L-CH)
R26 (R-CH)
(VIVM) (Oscilloscope)
Fig. 18
2. Place UNIT into record mode.
3. Adjust trap coils L5 (L-CH), L6 (R-CH), so that measured
value become minimum (See adjustment parts location on
page 19).
4, Make adjustment for both channels.
1. Test equipments connection is shown below.
(VTVM) (Oscilloscope)
Fig. 19
. Place UNIT into record mode.
. Read voltage on VTVM and calculate bias current by follow-
ing formula.
Value read on VTVM (V)
Bias current (A) = 10 (OQ)
Standard Value: 0.17+0.05mA
. Adjust trimmer capacitors of VC301 (L-CH), and VC302
(R-CH) (See adjustment part location on page 19).
* Record Mode
* Record Level Control
«MAX.
* Record Mode
* Be sure the ground end of
the meter is connected
to the ground end of the
resistor.
* When bias current is
adjusted on one channel
only, note that bias
current on the other
channel may vary.
12

13
ITEM
MEASUREMENT & ADJUSTMENT
REMARKS
Erase Current
Equipments:
* VTVM
* Oscilloscope
* Resistor (1Q)
Balance
(for recording level)
Equipments :
* VTVM
* Oscilloscope
* AF Oscillator
* ATT
1. Connect 1Q resistor between ground side terminal of
erase head ground lead wire remove (See fig. 21).
2. Connect VTVM to both ends of 1Q resistor.
Erase Head
Fig. 20
3. Place UNIT into record mode and, measure voltage across
the 1Q resistor.
4. Determine erase current with the following formula.
Voltage across both ends of 1 (Q)
Erase current (A) = T (a)
Standard Value: 140+35mA
1. Test equipments connection is shown below.
LINE IN LINE OUT) -——~
(AF Oscillator) (ATT) (Record Mode) (VTVM) (Oscilloscope)
Fig. 22
. Place UNIT into record mode, and set the record level
control VR to minimum.
. Supply 1kHz signal (—7dB) from AF oscillator, through
ATT, to LINE IN (L-CH).
. Set the balance control VR to L-CH maximum.
. Adjust record level contro! VR so that the output level at
LINE OUT on VTVM becomes —7 cB.
. At this time, connect test equipment to R-CH, and supply
1 KHz (—7 dB) to LINE IN (R-CH) (record VR should not be
moved).
. Set the balance volume to R-CH maximum.
. Measure the output level at LINE OUT (R-CH).
. Adjust VR20 so that measured value at LINE OUT (R-CH)
becomes —7 dB (See adjustment parts location on page ~
19).
* Record Mode
Erase Head
* Record Mode

ITEM
MEASUREMENT & ADJUSTMENT
REMARKS
Overall Gain
Equipments:
* AF Oscillator
* VTVM
* ATT
* Oscilloscope
* Test Tape (Reference
Blank Tape)...C-RA
1. Test equipments connection is shown in fig. 23.
R/P Head
Oscilloscope)
(Test Tape) (Playback Mode) (VTVM)
Fig. 23
. Place UNIT into record mode.
. Supply 1kHz signal (—24dB) from AF oscillator, through
ATT, to LINE IN.
. Adjust ATT until monitor level at LINE OUT becomes 0.42V
(—7 dB).
. Make recording.
. Playback recorded tape, and make sure the value at LINE
OUT on VTVM becomes 0.42 V.
. lf measured value is not 0.42V, adjust VR9 (L-CH), VR10
(R-CH) (See fig. 30 on page 19).
8. Repeat fromstep (2).
How To Check Recording Current
LINE IN
R/P Head
Fig. 24
. Test equipments connection is shown in fig. 24.
. Stop bias oscillation by unsoldering a wire (C) shown in
adjustment parts location on page 19.
. Supply 1kHz signal (—24dB) again and adjust ATT until
monitor level at LINE OUT becomes 0.42 V.
. Measure voltage and then calculate recording current by
formura given below.
Value read on VTVM (V)
Recording current= 10 (0)
| Standard Value: 40”A |
. At this time, set the tape selector switch to CrOz position
and confirm variation of recording current.
| Standard Value: 602A-+1dB |
«x Record/Playback Mode
* Record Level Control
MAX.
* Standard Input Level:
+3 dB
—244+3 dB
—36+43dB
—20+3dB
R25, R26 are shown in
AMP circuit board on page
24.
14

15
ITEM MEASUREMENT & ADJUSTMENT REMARKS
Level Meter 1. Test equipments connection is shown in fig. 22. * Record Mode
Equipments: 2. Supply 1kHz signal (-7dB) from AF oscillator, through | * Balance Control
* VTVM ATT, to LINE IN jack. ...Center
* Oscilloscope 3. Adjust record level control VR so that monitor level at
* AF Oscillator LINE OUT becomes 0.42 V.
* ATT 4. Adjust VR15 (L-CH), VR16 (R-CH) so that VU meter indi-
cates 0 VU (See adjustment parts location on page 19).
Overall Distortion 1. Test equipments connection is shown in fig. 25. * Record Level Control
Equipments: 2. Supply 1 kHz signal to LINE IN and adjust ATT so that out- «MAX.
* Distortion Meter put level at LINE OUT indicates 0.42 V (—7 dB). -
* AF Oscillator 3. Make recording.
*
ATT
4.
Play
back,
and
measure
distortion
factor
of
output
signal.
5. When the distortion factor does not satisfy the standard,
* Oscilloscope
* Test Tape (Reference
Blank Tape)...C-RA
check the bias current. When the bias current is lower
than standard, distortion will increase.
Care should be exercised in the adjustment because the
bias current also has an influence on the overall frequency
response. Refer to ‘The Overall Frequency Response” and
“The Bias Current Adjustment”.
Fig. 25
Standard Value:
less than 2%...... Normal
less than 3.2%...CrO2

ITEM
MEASUREMENT & ADJUSTMENT
REMARKS
Overall - Frequency Response
Equipments:
* VTVM
* AF Oscillator
* ATT
* Test Tape
(Reference Blank Tape)
...C-RA for Normal
...C-RF for CrO2
Note:
Before measuring and adjusting, make sure of the playback
frequency response (For the method of measurement, please
refer to the playback frequency response).
1.
2.
3:
Test equipments connection is shown in fig. 23.
Load reference blank test tape and place UNIT into record
mode.
Supply 1 kHz signal from AF oscillator, through ATT to LINE
IN.
. Adjust ATT so that input level is —20dB below standard
recording level (standard recording !evel=O VU).
. At this time, LINE OUT level indicates 0.42 V.
. Record each frequency 40Hz, 100Hz, 7O00Hz, 1 kHz,
2kHz, 7 kHz, 10kHz and 12kHz (13kHz for CrOz) at the
same level.
. Play back and express in dB the difference between play-
back output level of each frequency based on playback
output level of 1 kHz.
. Make sure that the measured value is within the range
specified in the overall frequency response chart.
Overall Frequency Response Chart (Normal)
+2 0B +24B
0 0 dB
—2
0B
—3
4B
—5 B Lite 2.4 7 kHz | 12 KHz
10
40 He kHz
Fig. 26
. Set the tape selector switch to CrOz position.
. Measure as Same as manner above.
. Make sure that the measured value is within the range
specified in the overall frequency response chart for CrOz2
tape below.
Overall Frequency Response Chart (Croz)
+2 0B
0dB
TkHz 2 kHz
Fig. 27
MPX Filter out position, normal tape
In case the line output deviation is not within the standard on
the basis of 1 KHz=O dB after measuring the overall frequency
response:
a
\f the frequency response varies from about 4~6kHz in
the middle-frequency range and becomes out of standard
in the high-frequency range, adjust it using the bias cur-
rent.
. If the frequency response is flat in the middle-frequency
range and varies excessively in the high-frequency range,
adjust it using the peaking coil for recording equalization.
Adjustment 1—Using bias current
4kHz 6kHz 8 kHz 12kHz
—$—$———
Fig. 28
* Record/Playback Mode
* Record Level Control
..MAX.
16

17
ITEM
MEASUREMENT & ADJUSTMENT
REMARKS
Overall Frequency Response
(AS a Standard for
Adjustment)
1.
When the frequency response between the middle- and
high-frequency range becomes higher than the standard
value, as shown by the solid line in the above diagram,
increase the bias current (by turning VC301 or VC302
clockwise).
. When it becomes lower, as shown by dotted line, reduce
the bias current (by turning VC301 or VC 302 counter-
clockwise).
Note:
ais
For adjustment when the bias current is lower than the
standard value 0.12mA, use the procedure indicated in
adjustment 2, because reducing the bias current beyond
this point may worsen the distortion factor.
. For the method of bias current measurement. refer to
“Bias Current Adjustment” on page 12.
Adjustment 2—Using the peaking coil for recording equaliza-
tio n
4 kHz 6 kHz 8kHz 12 kHz
fe
Fig. 29
. When the frequency response is flat in the middle-fre-
quency range and makes a sharp rise in the high-fre-
quency range, as shown by the solid line above, reduce
the inductance of the peaking coil (L3 or L4: for record-
ing equalization), thereby reducing the amount of record-
ing equalization (by turning L3 or L4 in the direction
opposite to that of the adjustment arrow marked on the
Unit).
. When it shows a sharp drop in only the high-frequency
Ad
range, as shown by the dotted line, increase the induct-
ance of the peaking coil, thereby increasing the amount
of recording equalization (by turning L3 or L4 in the same
direction as the adjustment arrow attatched on the Unit).
justment of the overall frequency response by using CrO2
tape.
NO
1
2.
3.
4.
5.
Ad
1.
TE:
. Dolby NR/MPX Filter switch is set to both OUT position.
Tape selector switch is set to CrOz position.
Overall frequency response for CrOz must measured after
confirmation of overall gain using normal tape.
Never adjust the bias current.
Must use technics CrOz tape.
justment method
In case the overall! frequency response in the high-fre-
quency rangé 10~14kHz is higher than the standard
value, increase the resistance of VR11 or VR12 (record-
ing equalization curve controls for CrOz frequency re-
sponse), which is done by turning in the direction opposite
to that indicated on the adjustment label attatched on the
Unit.
. Overall frequency response in the high-frequency range,
10~14 kHz, is lower than the standard value, decrease the
resistance of VR11 or VR12, which is done by turning in
the same direction as indicated on the adjustment label.

MEASUREMENT & ADJUSTMENT
REMARKS
Overall S/N Ratio
Equipments:
* VTVM
* AF Oscillator:
* ATT
* Oscilloscope
* Test Tape (Reference
Blank Tape)...C-RA
. Test equipments connection is shown in fig. 23. :
2. Supply 1kHz signal (—14 dB), and adjust record level
contro! so that VU meter indicates 0 VU.
. Further adjusting ATT, increase input signal by 4 dB. (Line
output level: 0.42 V (—7 dB) +4 dB=0.7 V (—3 aB))
. Make recording.
. Make another recording without supplying signal (discon-
nect input plug from LINE IN).
. Rewind to recorded part and playback.
. Measure output signa! level and no signal level (noise),
and determine the ratio in decibels (dB).
. The value is difference between “playback S/N and overall
S/N”, but for decibel calculation refer to “Playback S/N
measurement” on page 11.
Standard Value: Greater than 47 dB
(without NAB filter)
* Record/Playback Mode
* Record Level Control
.-MAX
* Erase the tape with a bulk
tape eraser.
Dolby NR Circuit
Equipments:
* VTVM
* AF Oscillator
* ATT
* Oscilloscope
Dolby FM
Equipments:
* VTVM
* AF Oscillator
* ATT
* Oscilloscope
. Place UNIT into record mode, set the Dolby NR switch to
OUT position and supply to LINE IN to obtain —34.5 dB at
TP3 (L-CH), TP4.(R-CH) (frequency 5 kHz).
. Confirm that the value at IN position is 8dB greater than
the value at OUT position of Dolby NR switch.
. When it is not in condition above, adjust as follows.
. Set VR401. (L-CH), VR402 (R-CH) to maximum.
. Set the Dolby NR switch to IN position.
. At this time adjust VR403 (L-CH), VR404 (R-CH) so that
the reading of VTVM become 10dB greater than the value
in step (1) above.
. Adjusting VR401 (L-CH), VR402 (R-CH), make the reading
of VTVM become 2dB smaller than the value obtained
through the adjustment in step (6) above.
. Test equipments connection is shown in fig. 22.
. Place UNIT into record mode:
. Set the Dolby FM switch to IN position and FM CAL VR,
VR21 (L-CH), VR22 (R-CH) to maximum.
. Supply 5kHz signal, and adjust ATT so that output level
at LINE OUT becomes 580 mv.
. Supply 5kHz signal (22dB smaller than the input level
above) to tuner input jack (selector switch: tuner).
. Confirm that the value at IN position is 8dB greater than
OUT position of Dolby NR switch.
+ Record Mode *%
* Record Level Control
..MAX.
* Stop the bias oscillation
by unsoldering a wire (C)
shown in adjustment
parts location on page
19.
* Record Mode
* Dolby FM Switch...IN
* De-Emphasis Switch
...Conventional Position
De-Emphasis Charactaristic
Equipments:
* VTVM
* AF Oscillator
* ATT
* Oscilloscope
. Test equipments connection is as same as above.
. Place UNIT into record mode.
. Set the Dolby FM switch to IN position and FM CAL VR21
(L-CH), VR22 (R-CH) to maximum.
. Set De- Emphasis switch to 75s position.
. Supply 100 Hz signal, to TUNER IN and adjust ATT so that
output level at LINE OUT becomes 58 mV. (selector switch:
TUNER)
. Change De-Emphasis switch to 25us position and confirm
that the value at LINE OUT is 3dB+1 greater than the
value for 75us position.
* Record Mode
* Source Selector... Tuner

ADJUSTMENT
PARTS
LOCATION
Tape Speed VC301 VC302 L4 VRI2 VR1O VR16
Adjustment VR
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ey rm :
cn ny 7 amg aa | ont om re “poet eet
: iy Bil a
/ 1 \
j 138 VR9_-VRI1-VRI5. VR20|
/
/
/
/
/
-—-—-——+—-—-—-4
I
OSC Coil |
r-----------
NOTE: VR11 can be adjusted
from back side.
bi
%
Dolby
is
the
trade
mark
of
Dolby
Laboratories
Inc.