Akai 1722W User manual

STEREO TAPE RECORDER
mopeEL 1722W
ALSO APPLICABLE TO MODEL 1722L
STEREO TAPE RECORDER
SECTION 1 SERVICE MANUAL ....... sig eteaternateis tentiefes, OS
SECTION 2 PARTS LIST ................... 0..-0.2--- 20
SECTION 3 SCHEMATIC DIAGRAM.................... 40
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SECTION 1
SERVICE
MANUAL
TABLE OF CONTENTS
L
SPECIFICATIONS:
«
2s.
caiccenigie
bebe
a
bes
det
ehh
Mobi
as
tases
Gees
tee
4
Il.
MEASURING
METHOD
.............-.0-
2202
e
eee
eee
ete
teens
6
1.
TAPE
SPEED
DEVIATION
...........
2...
eee
eee
ne
ete
6
2.
WOW
AND
FLUTTER
......
2...
eee
ee
teen
eee
6
3.
FREQUENCY
RESPONSE
.......-.
0
eee
eee
eee
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6
4.
SIGNAL
TO
NOISE:
RATIO
122.
dd
hie
Sioltal
tdacee
eb
eran
eR
eheee
eS
sk:
cng
BS
eee
Bas
6
5.
TOTAL
HARMONIC
DISTORTION
FACTOR
.......-....
0200
e
ee
eee
7
6.
CROSS
TALK
(Cross
talk
between
the
tracks)
...........0
02
e
ee
eee
eee
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7
7.
ERASE
RATIO
..
1...
ene
ene
ee
eee
tt
eee
7
8.
POWER
OUTPUT...
ee
eee
een
ees
7
Hl.
DISMANTLING
OF
UNIT
.............
02020
e
cee
eet
eae
8
IV.
MECHANISM
ADJUSTMENT
------
2-20-2000
c
eset
cere
c
treet
entrees
testes
9
I
PINCH
WHEEL
ADJUSTMENT
ig
aa
asa
ier
Pan
eee
Spb
ca
ate
Vain
he)
Griese
Ob
TS
eAD
eel
S
ec
R-Rh
One)
o.
wh
aleco Seine
aa
9
2.
SUPPLY
REEL
TABLE
TENSION
ADJUSTMENT
........-..---.5e
ee
eee
ee
eres
11
3.
TAKE
UP
REEL
TABLE
TENSION
ADJUSTMENT
...........-------+
eee
eeee
11
4.
FWD/REC
MODE
MECHANISM
CHANGE
AND
ADJUSTMENT
..........-.----
12
5.
DRIVE
BELT
POSITION
ADJUSTMENT
.........---.
eee
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eens
12
6.
FLYWHEEL
LOOSE
PLAY
ADJUSTMENT
..........-----5
ee
eee
renee
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12
7.
ADJUSTMENT
OF
IDLER
#2
POSITION
AT
FAST
FORWARD
MODE
bBo
Ral
aap
et
Batata
ea
Za
14
8.
AUTOMATIC
SHUT-OFF
OPERATING
POINT
ADJUSTMENT
............-..-.
14
V.
HEAD
HEIGHT
ADJUSTMENT
........-.....06.
0000
c
eee
te
tenes
15
1.
HEAD
HEIGHT
ADJUSTMENT
...........0-
2
ee
eee
eee
ee
eee
15
2.
HEAD
SLANT
ADJUSTMENT
.........-.-
2-22
cece
eee
eee
eee
15
3.
RECORDING/PLAYBACK
HEAD
AZIMUTH
ALIGNMENT
ADJUSTMENT
.......
16
Vi.
-AMPLIFIER.
(se
ieee
26
dag
hh
he
PIS
Oe
en
tee
gigas
See
eet
17
1.
RECORDING
BIAS
FREQUENCY
CHECK
...........-.-2
eee
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eee
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17
2.
FREQUENCY
RESPONSE
CHECK
......-..
00-2
cece
ee
eet
tent
eee
17
3.
RECORDING
BIAS
VOLTAGE
CHECK
..
«1...
eee
eee
17
4."BRASE°
VOETAGE:.
«0
cock
coed
pie
ee
Wie
a
od
Be
2
aa
eS
ese
aE dg
aE
SOS
2S
Ge
17
5.
HUM
ALLEVIATION
COIL
ADJUSTMENT
.........-....
0-2
e
eee
eee
17
VIL
D.C.
RESISTANCE
OF
VARIOUS
COILS
.............0-02
5-062
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18
VIII.
COMPOSITE
VIEWS
OF
COMPONENTS.
.............---2-0
0
cece
e
ree
eens
.
19
nett

i
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“9
I. SPECIFICATIONS
An asterisk next to a figure indicates the minimum guaranteed performance.
TRACK SYSTEM 4-track 2-channel stereo/monaural system. —-- =a
REEL CAPACITY
TAPE SPEED
WOW AND FLUTTER
Up to 7” reel
7-1/2 and 3-3/4 ips. +2% (*4+3%)
Less than 0.14% (*0.15%) R.M.S. at 7-1/2 ips.
Less than 0.18% (*0.20%) R.M.S. at 3-3/4 ips.
TOTAL WOW AND FLUTTER
Less than 0.22% R.M.S. at 7-1/2 ips.
(Scotch #175 TAPE 3,000 Hz recording and playback)
FREQUENCY RESPONSE
WIDE RANGE TAPE
LOW NOISE TAPE
1,000 Hz -16VU Recording, measured at speaker output
30 to 21,000 Hz (*50 to 20,000 Hz)+3 dB at 7-1/2 ips.
40 to 15,000 Hz (*50 to 12,000 Hz)+3 dB at 3-3/4 ips.
30 to 18,000 Hz (*50 to 18,000 Hz)43 dB at 7-1/2 ips.
40 to 13,000 Hz (*50 to 10,000 Hz)+3 dB at 3-3/4 ips.
DISTORTION FACTOR
Less than 2% at 7-1/2 ips.
TOTAL DISTORTION FACTOR Less than 3% at 1,000 Hz “0’’VU recording at 4 mV mic Input,
Output 2W and Tone Control Max using Scotch #211
SIGNAL TO NOISE RATIO
Better than 50 dB (*47 dB) at 10 dBm output and
Tone Control Max (from Speaker Out)
TOTAL SIGNAL TO NOISE RATIO
Better than 43 dB at 10 dBm output and Tone Control Max.
(from Speaker Out)
CROSS TALK
Better than 60 dB (*55 dB) Monaural (Mic input 4 mV,
1,000 Hz +3 VU recording, measured at line output)
Better than 45 dB (*43 dB) Stereo (mic input 4 mV,
1,000 Hz +3 VU recording, measured at line output)
ERASE RATIO Better than 70 dB (*65 dB) 1,000 Hz +3 VU recording
INPUTS
MIC INPUT
LINE INPUT
DIN INPUT
OUTPUTS LINE OUTPUT
DIN OUTPUT
PHONE OUTPUT
SPEAKER OUTPUT
RECORDING BIAS FREQUENCY
Volume at maximum, 1,000 Hz “0” VU indication
More than 0.5 mV
More than 70 mV
More than 70 mV (High)
More than 5 mV (Low)
OV (volume min) to 2.3V (volume max) using a 250 Hz eel
“0” VU pre-recorded tape at 7-1/2 ips.
1V
100 mV at 82 each CH.
3W/82 each CH.
*More than (2W/2W) continuous power at 82
63 kHz+8%
BIAS LEAK
Less than -20 VU measured at line output
HIGH FREQUENCY DEVIATION
RECORDING CAPACITY
FAST FOWARD AND REWIND TIME
MOTOR
With 2 dB using an 8,000 Hz 3-3/4 ips. pre-recorded tape at
7-1/2 ips. Tone Control Max
2 hours stereo recording using a 1,200 ft. tape at 3-3/4 ips
80/100 sec. using a 1,200ft. tape at 60/50 Hz
2-4 pole induction 2-speed motor.
type: IC-16Y
Revolutions: 1,790/1,490 r.p.m. at 60/50 Hz (Low Speed)
3,580/2,980 r.p.m. at 60/50 Hz (High Speed)
HEADS RECORDING/PLAYBACK HEAD
ERASE HEAD
Type: P4-150 Gap: 2 microns
Impedance: 1,25022415% at 1,000 Hz
D.C. Resistance: 912
Type: E4-200 Gap: 0.6 mm
Impedance: 2002+5% at 100 kHz
D.C. Resistance: 22 :

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TRANSISTORS
2SC458LG(B)
(C)...
4
2SCLOTSTSD)
.
4
2SC711
(D)
(E)...
4
28C1312
(F)
(G)...2
2SC968
(3)
(Red)...
2
DIODES
IN34A
...
2
10DC-1
(Blk)
...1
:
10DC-1
(Red)...
2
SPEAKERS
2
built
in
(S”
x
7’)
Oval
speakers
Impedance:
82
POWER
SUPPLY
100
to
240V
A.C.
50/60
Hz
120V A.C. 60 Hz for CSA/UL Models
220V A.C. 50 Hz for CEE Models
POWER CONSUMPTION SOW
DIMENSIONS
1722W
358(W)
x
360(H)
x
248
(D)mm_=
(14”
x
14.1”
x
9.8")
1722L
359(W)
x
366(H)
x
248
(D)mm__—((14.1""
x_
14.4"
x
9.8")
WEIGHT
1722W
13.2
kg
(29
tbs.)
1722L 14.0 kg (30.8 Ibs.)
NOTE: Specifications subject to change without notice.
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H. MEASURING METHOD
1. TAPE SPEED DEVIATION 3. FREQUENCY RESPONSE
a
Line
Audio
1722w
(Output
Input
Frequency
Frequency
Counter
Oscillator
Fig.
1
As shown in Figure 1, connect a Frequency Counter
to the Line Output of the recorder. Take a
frequency counter reading at the beginning, middle,
and end of tape winding during playback. The
maximum value of these respective readings will
represent tape speed deviation. Fig. 3
High Sensitivity
V.T.VM.
1) Connect the various instruments as shown in
2.WOW AND FLUTTER Fig. 3 and supply a 1,000 Hz sine wave signal to
the Line Input of the recorder from an Audio
Wow and Frequency Oscillator through an Attenuator. Set
Flutter Meter recorder to “REC” mode and turn recording
level control volume to obtain “O” VU meter
Fig. 2 reading.
2) Under conditions described in 1) above, readjust
Method A Attenuator so that the Line Input is -16 dB, and
As shown in Fig. 2, connect the Line Output of the record 50 to 18,000 Hz spot frequencies.
recorder to the Input of a Wow and Flutter Meter. 3) Rewind tape and playback from the beginning.
Use a 3,000 Hz pre-recorded test tape and take a Take V.T.V.M. spot frequency readings and plot
wow and flutter meter reading at the beginning, values on a graph. fogs
middle, and end of tape winding. The maximum ope,
value of these respective readings will represent the NOTE: When measuring frequency response, new
wow and flutter. tape should be used.
Method B
Supply a 3,000 Hz sine wave signal from an Audio 4. SIGNAL TO NOISE RATIO
Frequency Oscillator and make a recording on a Speaker
blank tape at the beginning, middle, and end of tape Output Input . rae
‘ >
pu
npu
winding.
Rewind
and
playback
tape.
Measure
wow
1722W
ee
eed
a
ae
and
flutter
with
a
Wow
and
Flutter
Meter.
(The
aches
Fig. 4
ad wow and flutter value of Method B will be close to
| 2 times of Method A)
Connect the various instruments as shown in Fig. 4
and playback a 250 Hz “0” VU pre-recorded test
tape and adjust volume control to obtain +10 dbm
V.T.V.M. reading. Then remove the tape and measure
the noise level under the same condition. Convert
each of the measured values into decibels.

5.
TOTAL
HARMONIC
eh
Distortion
Meter
Fig. 5
1)
Connect
the
various
instruments
as
shown
in
Fig.
5.
Load
a
Scotch
#211
tape
and
set
Tone
control
to
“MAX”
position.
2)
Record
4
1,000
Hz
sine
wave
signal
at
“O”
VU.
Playback
the
resultant
signal
and
measure
the
overall
distortion
factor.
NOTE:
1)
At
this
time,
Distortion
factor
of
the
Audio
Frequency
Oscillator
must
be
suf-
ficiently
small.
2)
When
measuring
the
distortion
factor,
new
tape
should
be
used.
6.
CROSS
TALK
(Cross
talk
between
the
tracks)
— TAPE
DIRECTION
Fig. 6
As
shown
in
Fig.
6,
first
record
a
1,000
Hz
sine
wave
signal
on
Track
No.3
at
+3
VU
level.
Next,
record
under
a
non-input
condition.
Then,
playback
the
tape
on
Tracks
No.3
and
4
through
the
B.P.F.
(band
pass
filter
sensitivity
...
1
:
1)
and
obtain
a
ratio
between
the
two
from
the
following
formula:
Eo
C = 20 log
(dB)
2—7—"1
where,
= desired cross talk ratio (dB)
E, = 1,000 Hz signal output level (V)
E, = 1,000 Hz cross talk level (V) Wl
N
LA
E, = Non-input signal recorded level (V)
7. ERASE RATIO
As
shown
in
Fig:
4"8@Minect
a
High
Sensitivity
V.T.VM.
to
the
Line
Output
of
the
recorder.
Playback
a
virgin
tape
and
take
a
V.T.V.M.
reading
of
the
output
level.
Next,
record
a
1,000
Hz
sine
wave
signal
at
+3
dB,
then
playback
this
recorded
signal
and
take
a
V.T.V.M.
reading
of
the
output
level.
Next,
using
this
pre-recorded
tape,
record
under
a
non-input
condition
and
take
a
reading
of
the
noise
level
output
of
the
erased
signal
and
obtain
a
ratio
between
the
two
from
the
following
formula:
Er =20 log
(dB)
2— 1
where,
Er
=
Desired
erase
ratio
(dB)
Eo
=
1,000
Hz
signal
output
level
(V)
E,
=
Non-input
signal
recorded
level
(V)
E,
=
Virgin
tape
noise
output
level
(V)
. POWER OUTPUT
Speaker
High Sensitivity
V.T.VM.
Fig.
7a”
As
shown
in
Fig.
7,
connect
an
8Q
dummy
load
resistor
to
the
speaker
output
of
the
recorder
and
connect
this
terminal
to
a
High
Sensitivity
V.T.V.M.
Playback
a
250
Hz
“0”
VU
pre-recorded
test
tape
and
take
a
V.T.V.M.
reading
of
the
output
level.
The
resultant
output
can
be
obtained
from
the
results
of
the
above
measurement
by
using
the
following
formula:
E?
P=-—
= (W)
where,
P
=
Desired
power
output
(watts)
E
=
Measured
voltage
(V)
(R.MS.)
R = 8

I. DISMANTLING OF UNIT
In case of trouble, etc. necessitating disassembly, please disassemble in the order
in reverse order.
nal al guguguqugu glug gugugugugugTugTuqTug7g
a 1 :
»
PAUSE KNOB
sECHANISM: KNOBS
shows in photographs. Reassemble
—_—
SCREWS

IV.
MECHANISM
ADJUSTMENT
CAPSTAN
<x
eee
PINCH ROLLER
Fig. 8
& a
Fig. 9
1.
PINCH
WHEEL
PRESSURE
MEASURMENT
2)
In
case
@)
and
in
Fig.
9
is
not
parallel,
_
check
for
the
following.
(See
Fig.
8)
a. Rubber part of pinch wheel is worn. (Replace
pinch wheel)
Confirm
the
following
prior
to
pinch
wheel
pressure
b.
Capstan
or
pinch
wheel
shaft
is
bent.
(Adjust)
measurement: (See Fig. 9) ;
The
part
of
the
pinch
wheel
over
which
the
tape
:
ae
passes
is
parallel
with
the
capastan
shaft.
(represented
NOTE:
This
condition
may
also
be
caused
by
by
@)
and
@)
in
Fig.
9)
twisted
tape
or
wow
and
flutter.
1)
As
shown
in
Fig.
8,
measure
pinch
wheel
pressure
with
a
spring
gauge
by
pulling
the
pinch
wheel
away
from
the
capstan
and
then
returning.
Take
a
reading
of
the
spring
gauge
indication
at
the
time
the
pinch
wheel
contacts
the
capstan.
Correct
pinch
wheel
pressure
at
this
time
is
within
1,150
to
1,200
gr.

per
ST
eal
2
; ee
cM
ia
iss
taHaBe
pe
Fig.
10

TAKE UP REEL TENSION ©)!
i
" SUPPLY REEL-TENSJON
<= 60mm
2. SUPPLY REEL TABLE TENSION
ADJUSTMENT (See Fig. 10 at left)
Clutch felt (2) is used on the bottom part of
rewind pulley (3) and reel table base plate (1) to
protect the tape from excessive tension at rewind
mode.
For measuring the tension of each reel, it is ideal to
use on empty 5” reel on which a tape has been wound
to cover a 60 mm diameter as shown in Fig. 11.
Check and Adjustment (See Fig. 11- @) )
(a) At rewind mode, the tension of felt (2) part
shown in Fig. 10 should be from 400 to 500
grams when the tape is gently pulled upward
with a spring gauge. If adjustment is necessary,
this can be accomplished by increasing or decreas-
ing the number of washers used.
(b) Felt (5) is for the purpose of applying suitable
clutch (back tension) at Forward and Recording
modes. Measure in the same way as outlined
in item (a) and adjust by strengthening or
weakening the tension by increasing or decreas-
ing the number of washers respectively to obtain
80 to 100 grams of tension.
(c) At Fast Forward mode, the tension (free tension)
should be 15 to 20 grams. To adjust, strengthen
or weaken tension by increasing or decreasing
the number of washers and by moving Pulley
(9) up and down and tightening to fixed position
with screw.
Fig. 11
3. TAKE UP REEL TABLE TENSION
ADJUSTMENT (See Fig. 10 at right)
Clutch
felt
(2)
is
used
on
the
bottom
of
reel
table
base plate (1) for the purpose of preventing excessive
tension from being applied to the tape and tape
stretch from occuring at Fast Forward mode.
Check and Adjustment (See Fig. 11- )
(a) To measure the tension between felt (2) and
rewind roller A (10), load the tape and at
forward mode, gently pull end of tape upward
with a spring gauge (Fig. 11- ) Ideal tension
at this part is 400 to 500 gr.
To adjust, increase or decrease the number of
washers used. Also, if rotation is not smooth
when turned by hand, replace felt.
(b) Felt (11) on take up roller D (12) is for the
purpose of clutch between take up roller A
(10) and take up roller D. Measure the tension
at this part in the same way as outlined in
paragraph (a).
Ideal tension is 150 to 180 grams. Adjust by
increasing or decreasing the number of washers
used.
(c) At Rewind mode the tension (free tension)
should be 15 to 20 grams. Adjustment can be
made by increasing or decreasing the number of
washers used and by moving set sleeve B (14)
up and down and repositioning.

REC, LEVER2
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|
pS
eat
M1T,2 LEVER !
RECémprwo. {7 \T
CLILETESSSSSLLETLLEETED ESSE
4, FWD/REC MODE MECHANISM CHANGE
AND ADJUSTMENT
OPERATION
(1) Set REC/PLAY Lever from FWD to REC
position.
(2) Cam @) pushes Cam Roller ©) and Arm ® as
illustrated by the dotted lines in Fig. 12.
(3) Arm pulls Lever Spring shaft @) as
indicated by the arrow mark.
(4) Then, Recording Levers 1 and 2 (@ and ©)
a
set
Slide
Switches
SW-1
and
SW-2
to
recording
| condition.
In the event that the Recording Levers (REC
LEVER 1 @) , REC LEVER 2 () ) do not
push the Slide Switches perfectly, too much
loose play exists.
* Vibration or the inability to record is sometimes
caused by imperfect slide switch operation.
Adjustment: Adjust position of Recording Levers
1 and 2 while checking to confirm
that the levers are pushing the Slide
Switches perfectly.
Fix at adjusted position with screws
@® and @
LEVER SPRING
)
CC
2 6)
“~~ CAM ROLLER A
Fig. 12
5. DRIVE BELT POSITION ADJUSTMENT
If drive belt position adjustment is necessary, with
the powe turned ON, insert a U shaped washer in
the place indicated in the figure so that the drive
belt come to the center of the motor pulley as
shown in Fig. 13.
6. FLYWHEEL LOOSE PLAY ADJUSTMENT
With a minus driver, turn bearing and adjust gap to
obtain a 0.3 mm loose play between the Steel Ball
and Bearing when the flywheel is moved as indicated
by the arrow mark (<=) in Fig. 14.
Fix at ideal position by turning nut to right (see
figure).
oe
ww.
—_

—
=>) U-TYPE WASHER
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TrID
DLT
I
IO
LILLE
APTI
ZT
ZAI
LP
A NUT
Yd} Von
Neat
FLYWHEEL
a
= Cerra
Fig. 13
Fig. 14

7.
TAKE UP ROLLER A
IDLER WHEEL #2
KNURLING PULLEY
MECH. KNOB
INDICATES F. FWD.
—-——-- INDICATES STOP
A LEVER SHAFT
ADJUSTMENT OF IDLER #2 POSITION
AT FAST FORWARD MODE
Move Cam © shown in Fig. 15 up and down as
indicated by the arrow mark (~>) in the figure and
adjust Lever ©) height so that Idler #2 contact
between Take Up Roller A and the knurling Pulley
is uniform when the F.FWD/RWD Lever is set to
F.FWD position. Fix at adjusted position with
Adjustment Screw ()
During operation, confirm that the rotating position
of Idler #2 is ideal.
LEVER |
RA ASAAS SG
CAM C ADJUSTING SCREW ©
Fig. 15
PINCH ROLLER
MICRO SW,
CUT POINT
Fig. 16
8. AUTOMATIC SHUT-OFF OPERATING
POINT ADJUSTMENT
Move Micro Switch as indicated by the arrow mark
(~=) in the figure and fix Screws (a) and ©) so
that when the Automatic Shut-off Switch is at ON
position, the Micro Switch is perfectly turn off at
position at which the gap between A lever shaft
and AS lever Stopper is about 5 mm as shown in
Fig. 16.
AO,

V.
HEAD
HEIGHT
ADJUSTMENT
oo _
(HEIGHT ADJUSTMENT
LANT ADJUSTMENT
©,@
HEIGHT ADJUSTMENT
SLANT ADJUSTMENT.
@,®
ERASE REC./P.B.
HEAD HEAD
Fig. 17
As
head
adjustment
is
of
utmost
importance
to
the
2.
HEAD
SLANT
ADJUSTMENT
(See
Fig.
17)
operation
of
a
tape
recorder,
please
be
especially
careful
in
making
these
adjustments.
Also
please
Adjust
Adjustment
Screws
@)
,
)
,
©),
and
(@)so
check
the
tape
travel
system.
that
the
erase
and
recording/playback
heads
contact
If
the
tape
travel
system
is
faulty,
because.
this
the
tape
at
the
proper
angle
in
relation
to
tape
causes
the
tape
to
twist,
etc.,
be
sure
that
reel
travel.
height adjustment is precise.
1. HEAD HEIGHT ADJUSTMENT
1) Erase Head
Loosen
Screws
(a)
and
©)
and
adjust
the
erase
head
height.
Tighten
screws.
At
position
at
which
the
upper
edge
of
the
tape
is
0.15
mm
lower
than
the
upper
edge
of
the
erase
head
core.
2)Recording/Playback Head
Adjust
with
Head
Height
Adjustment
Screws
©)
and
@)
so
that
the
upper
edge
of
the
tape
and
the
upper
edge
of
channel
1
head
core
are
the
same height.
a
3 watt.

1722W/L LINE OUT
HIGH SENSITIVITY V.T.V.M.
Fig. 18
3. RECORDING/PLAYBACK HEAD
AZIMUTH ALIGNMENT ADJUSTMENT
(See Figs. 17 and 18)
1) Playback an Ampex Alignment Test Tape (8,000
Hz, 3-3/4 ips recorded) at 7-1/2 ips.
2) Connect a High Sensitivity V.T.V.M. to the line
output =iput as shown in Fig. 18 and adjust Screw (€) to
obtain maximum V.T.V.M. indication at -10 dBm
range.
3) Repeat Items 1 through 3 two or three times
for optimum performance.

VI. AMPLIFIER
REC/P.B. reo]
ERASE HEAD |
Z HIGH SENSITIVITY
V.T.V.M.
Fig. 19
REC./P.B. HEAD
Fig. 20
Connect the various measuring instruments as shown
inFig. 19. . =r"
1. RECORDING BIAS FREQUENCY CHECK
(See Fig. 19)
1) Set recorder to recording mode.
2) Connect a Frequency Counter to point @ of
the Recording/Playback Head as shown in Fig. 19
and read indication.
* Specified recording bias frequency is 63 kHz+8%.
. FREQUENCY RESPONSE CHECK
1) For measuring instrument connections, see Fig. 3.
Set recorder to recording mode and supply a
1,000 Hz sine wave signal to the line input from
an Audio Frequency Oscillator. Record at 1,000
Hz -16 VU and then switch the Oscillation
frequency of the Audio Frequency Oscillator
to 10,000 Hz and record.
2) The Volume Controls must be set to. obtain a
VU meter indication of -16VU at 1,000 Hz.
The Tone Controls should be set to maximum for
3-3/4 ips. tape speed and to about 4 or 5
position for 7-1/2 ips. tape speed.
3) The V.T.V.M. indication should display equally=* ~~
flat frequency response at the two frequencies
in items 1) and 2) (both channels).
.
RECORDING
BIAS
VOLTAGE
CHECK
Check
the
voltage
at
points
©
and
@
shown
in
Fig.
19.
Correct
recording
bias
voltage
is
about
13V
A.C.
_ ERASE VOLTAGE
Correct erase voltage is about 43.5V A.C.
.
HUM
ALLEVIATOR
COIL
ADJUSTMENT
(Refer
to
Fig.
4
of
Measuring
Method)
Connect
a
High
Sensitivity
V.T.V.M.
to
the
Speaker
output
Terminal
through
an
8
dummy
load
resistor,
Lead.a-250
Hz
“0”
VII
recorded.
test
tape
and
set
Tone
Controls
to
Maximum.
_Playback
the
Set
Deck
to
P.B.
mode
testtape
and
move
hum
alleviator
coils
as
indicated
by
the
arrow
marks
in
Fig.
20
while
observing
V.T.VM.
indication
and
position
at
place
where
V.T.V.M.
indication
is
minimum.
(Must
be
better
than
47
dB).
;

Vil.
D.C. RESISTANCE OF VARIOUS COILS
D.C. resistance value is average value.
- — —— -
Designation D.C. Resistance
Between Red-Vit
Between Gry-Vlt
Main Motor
Between Wht-BIk 14002
Between Ylw-Bik
Primary 150Q
Secondary 700
Driver Transformer N24-6847 AT
-
Between 1-3 0.32
Between 4-6 0.72
Between 7-9 8.20
Oscillation Coil
_ Erase- Head 22
Recording/Playback Head
Hum Alleviator Coil 20T 0.522
Power Transfomer LST-1
5 240V_BLU
(Refer to diagram shown below)
Chart 1